# Anybody able to ID this Schwinn frameset?



## terminaut (Dec 19, 2003)

I'm just cleaning through some stuff in the garage and realized I didn't have any idea what model this Schwinn is nor from what era. It looks like it could be an early MTB because of the straight forks? It's a NOS frame/fork and a sticker on the seat tube says "Made In Japan for Schwinn", but I'd appreciate any further insight offered. Thanks!


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## jjvw (Jul 2, 2007)

I'm digging up this 3 year dead thread because I have what appears to be the same frame as the OP. It's identical except mine is fully lugged and the fork is different. Here is what I know about it:

Forged no-name dropouts and fork tips
"Made in Japan" sticker on seat tube near BB
Ishiwata tubing
Serial # CS472494 on BB shell
Red Schwinn cross logo decal on seat tube near seat lug
Tang Falcon threaded headset
Tang BB
120 rear spacing
21.1mm steerer tube (requires Schwinn/BMX quill stem)

There are absolutely no remains of a model name on the top tube or the big SCHWINN decals on the down tube, assuming they were ever there to begin with.

I've scoured the old Schwinn catalogs going back to the late 70's and can't find anything acurately describing this frame. The best matches are the 84-85 Sierra and High Sierra, except every single one I have seen was made in Taiwan, was fillet brazed, and the braze-ons are in different locations. The OP's frame is the first I've located with identical braze-ons and what appears to be the same paint.

This is the third forum I've posted this to and no one can figure it out. Can you?


















-edit- I'm seeing that I have cable guides on mine.


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## 82Sidewinder (Jun 28, 2006)

Schwinn did import framesets in the early 80's which did not have model names. I recall seeing one offered in the 1983 catalog. In '83, Schwinn's only complete mountain bikes were the Sierra and the Sidewinder, both of which had heavy Varsity-type frames. In '84, they introduced their first "real" mountain bikes, the High Sierra and Sierra. They were made in Taiwan by Giant and were tig'd. I'll dig out the catalogs when I get home.

Craig


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## jjvw (Jul 2, 2007)

http://www.trfindley.com/flschwinn_1980_1990/1983Ltwt13.html

Here is the 1983 catalog page with the bare frames. All three are road bikes. There is the Voyager with cantis, but that is definitely not the same as mine.


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## mechagouki (Nov 30, 2007)

jjvw said:


> It's identical except mine is fully lugged and the fork is different.


So actually totally different then.............

Not strictly speaking "identical"......................

Not two items one would liken to 'peas in a pod'..........


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## pinguwin (Aug 20, 2004)

I had a similar-colored 1984 High Sierra and that color appears to be what they called "smoked pearl", which would put it vintage 84-85, IIRC.
I can't exactly remember what the seatstay bridges and the like were, so can't identify it more precisely.


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## jjvw (Jul 2, 2007)

Maybe I've spent too much time looking at pictures. Compared to what shows up in the official catalogs these two frames, aside from the obvious, have more in common with each other in the small details than anything I've found so far.

Where did the early 80's, Japanese built, Schwinn mountain bikes come from? Why can't I find any mention of them anywhere in Schwinn literature? Yet here are two.


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## CS2 (Jul 24, 2007)

Are those cantilever or U-brake mounts? The rear looks more like a U-brake.

Tim


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## jjvw (Jul 2, 2007)

Cantis. Both the front and rear mounts are the same.


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## ChattyMatty (May 15, 2014)

*Holy dead thread revival Batman...*

I'm assuming you have long since moved on from this frame (as much as I'm drooling over it lol) but just in case someone stumbles across this, here is where it is listed, in the 1983 Schwinn BMX catalog:









The Schwinns made by Giant in those days the serials began with a G, and I have seen where Bridgestone was making frames for Schwinn in Japan in those days, but can't say what the W means other than it likely does identify the builder in some way.


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## Scoutergtg (Feb 20, 2014)

That was awesome! I was hoping someone would solve this mystery! Good job Chatty Matty.


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## ChattyMatty (May 15, 2014)

A little more digging and I think I'll let my self be convinced this is a Bridgestone built frame. Looking at the lugs and tube angles looks like it's based on the MB-1, and the bars look identical.

Here's an 85 MB-1.


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## Silver King (Mar 5, 2013)

HA! I have that frame (not lugged) collecting spiders in my shop. I worked in a Schwinn shop in college (owners also had the Corte Madera Schwinn) and was told that it was a prototype MTB from early 80's.


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## laffeaux (Jan 4, 2004)

From the "cold case files"....


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## one less (Nov 17, 2014)

Terminaut,
If your are still out there, I have a frame the same as yous with forks the same as jjvw and continued the search on for dating these frames on forum page
ID-Lugged, Schwinn mtb frame - Page 3
I do not know if you still have your frame and forks, particularly the forks, but I would like to know the stamping on the steerer tube. Another pair of forks have come to light that are same as mine and jjvw`s with Tange 8.C stamped on them. 
Regards
one less


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## jeff (Jan 13, 2004)

He hasn't been around in over 10 years. Too bad. He was a great contributor to MTBR.


one less said:


> Terminaut,
> If your are still out there, I have a frame the same as yous with forks the same as jjvw and continued the search on for dating these frames on forum page
> ID-Lugged, Schwinn mtb frame - Page 3
> I do not know if you still have your frame and forks, particularly the forks, but I would like to know the stamping on the steerer tube. Another pair of forks have come to light that are same as mine and jjvw`s with Tange 8.C stamped on them.
> ...


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## one less (Nov 17, 2014)

jeff
Thanks. It is a pity but does any body know where the frame and forks are. My line of thought is the frame ffvw and I have have a replacement fork that could have been a replacement to the BMX type and checking the one that Terminaut has may indicate an original manufacture date. 
I anybody else has a lead it would be greatly appreciated.
one less


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## jeff (Jan 13, 2004)

Send him a PM. You never know.


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## dihummer (Jun 26, 2011)

For Terminaut and anyone else who may care after all this time.

I was reviewing some of my data on Schwinn serial numbers and came accross this thread again. I had read this before, several years ago.

I now recognize the format of the serial number for Terminaut's Schwinn.
The last character is difficult to recognize, but it is not a number. It is the letter "T" or "J".

The serial number is WAK23207T. This is a Danish VIN.

https://en.wikipedia.org/wiki/Danish_bicycle_VIN-system

The "W" is for Import into Denmark.
The "AK" is for the importer Age Kroll, later to mean Centurion of Europe (not Western States Imports).

The "T" at the end is for the year 1980.

The decals on the frame are consistent with 1980-81 Schwinn bicycles.

So this gives the year the frame was manufactured (or imported into Denmark).

I have no information as to the model.

You are all laughing now and asking: How does a Schwinn frame get a Danish VIN for a serial number?

All I can suggest is that the Japanese frame supplier had some surplus frame that had been destin for Centurion and Denmark. Schwinn was quick to respond to the Mountain Bike thing started by Specialized and Univega. Surplus frames may have been the fasted way to respond.

The fork for Terminaut's Schwinn is similar to the fork used on the Schwinn Sidewinder,
which was also an early response to supply "Mountain bikes" by Schwinn.


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## ChattyMatty (May 15, 2014)

Interesting info, dig it 

The forks in the OP are oddballs. The tapered legs look more like King Sting than Sidewinder, but the drops are different- looks like the same outer profile but where the KS/Sidewinder drops (which are shared) have a couple simple holes, this one has that elegant triangle cut out. And obviously neither had canti mounts.

Passed on one of these a year or so ago, and am still kicking myself. Someday.


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## one less (Nov 17, 2014)

I received a PM from haaki who I had sent a PM regarding his comments in respect to these frames. 

"Re: ID Schwinn frame set
Sorry for the late reply. Been offline on this forum for a long time. The earliest Schwann MTBs were Silver with Blue Logos. They were only available as frame sets
One of the early models (v1) is on Page 2 with the BMX Style fork. Just like the one I broke at the head tube. The Silver Lugged version halfway down looks to be second or 3rd Generation. 2nd Generation had same color as 1st (Silver with blue labels) 3rd Gen went to a darker Blue/grey Silver. Hope this helps (better late than never)"

He is basically saying the frame with the BMX style head was the first followed by the conventional style fork crow. It is just a matter of the dates. I have had reference to this frame being the same as the Takara Highlander, including the serial number. It is commonly stated the the Takara frames where made by Kuwahara. I have contacted Kuwahara who told me these frames where not made by them for Takara or Schwinn as they had stopped making frames at the end of the 1970`s for export for either. As Schwinn were selling these frames in 1983 did Takara buy them and sell them as Highlander. 
Oneless


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## ChattyMatty (May 15, 2014)

Interesting. Hadn't noticed that the lugged frame was a roadie HT and the OP was the BMX sized tube. There's always the possibility I suppose that one or the other is a Tange made frame as Schwinn did have an oddball 'Predator Aero' BMX available S/O in late 83-84 made by them. Tange also made the 1st-gen Sting forks, but by the time the KS forks were made they were all domestically sourced, so far as we know.

In the time that this thread has slumbered I picked up an '84 replacement frames price list, and three entries are listed as "Mountain Bike": 28374 (21" Smokey Pearl), 28375 (19" Smokey pearl) and 28538 (19" Smokey Black) each @ $122. That looks like our 1st/2nd gen- 3rd gen break perhaps. Given that both silver frame numbers are sequential, and the last one is the very last entry on the list, maybe the difference between the BMX style and the lugged style is the frame size difference- hard to tell from the pics but you wouldn't have to try to hard to convince me that the frame in the OP is a 21" and the lugged is a 19". Maybe these two frames were sold at the same time, and you got the one sized for you, with the black variant added later.

The only other bikes in the list with these paint codes are the Japanese road bikes like the Voyager, which I think were Panasonic sourced but I'm not 100% on that. Some models were, to be sure, but which ones in which years I'm not an expert on. The frame I passed on was black, which I assumed it to be a repaint, might not have been after all. If it was a 19", good thing


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## one less (Nov 17, 2014)

ChattyMatty
The lugged frame is made of Ishiwata MTB tubing not Tange, with a BMX 21,5 steerer tube. I believe the Ishiwata tubing was made in the late 70`s but cannot confirm the Ishiwata dating system that I believe was to the Japanese Showa dating system,
one less


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## ChattyMatty (May 15, 2014)

The bearing cups on the lugged frame are 32.5mm? Pic looks looks like they'd be the 30.2mm of road bikes. I know the mid/late 80's (imported) High Sierra used the smaller road cups rather than the larger BMX/beach cruiser size (which stuck me as odd when recently parting one out). Is yours a 19" frame?

Thanks for the all the info, not much out there obviously. Now to find someone who knows anything about my Akisu-made Predator lol.


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## one less (Nov 17, 2014)

ChattyMatty 
My frame is a 19" and the bearing caps are 1.37 x 24T 
This is the link to the Ishiwata MTB tubing catalogue
Ishiwata Tubing catalog circa late 1970's


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## one less (Nov 17, 2014)

ChattyMatty
Along with what you are saying, when I first started this research I came across this,
On Pg 147 of Schwinn Bicycles by Jay Pridmore, Jim Hurd
"The Schwinn Parts Division brought in some lugged mountain bike frames from Japan."
I have tried to locate Pridmore and Hurd but to no avail to confirm their statement origin. I do not know what their book holds in supplying what happened.
Further information on this would be good to receive as it would be of interest to know who the Japanese building company it was and how many of the frames where imported and sold. Given the date of my frame this action by Schwinn could have been earlier in 1980 given time and delivery. As I see, at the time in history, I am sure the Schwinn organisation would have been in some turmoil and certainty of supply could have been in doubt. There appears there could also some lack of a coordinated management plan on the view taken on the mountain bike future. In 1981 and 1983 Schwinn where not referring to a Mountain Bike at all in there catalogues, referring to the King Sting 5 in the Cruisers and Middleweights category.

I feel much of the supply of these frames is tied into the BMX part of Schwinn and possibly what happened was not of management approval. A BMX supplier could have made these frames as an experiment. Your contacts may know what happened, certainly Schwinn has the answer but is not about to confirm it. Hey, as a piece of history what ever happened it is relevant to MTB history, but not necessarily to Schwinn. There is the recorded King Sting etc bikes and the later High Sierra but other development could have been going on within Schwinn. These frames and bikes do indicate something was.
one less


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## Slow86gn (Feb 4, 2013)

Another 2 cents. In 1980 around September-October Mr G walk into Northridge Cyclery and flipped his Schwinn REP catalog open. Pointed his finger at a page. My friend who worked there said cool a mountain bike frame set. I laughed because it was a drawing of a frame set. It didn't give a size or what its made of nothing, just said Schwinn mountain frame set. I ordered around October of 1980, did not receive the frame until December of 1981. Mr G hoped I would be in the first order, March of 1981 or CS in the serial numbers. My serial number is a KS meaning October. The OP's bike I say is a1983 out of the Schwinn BMX catalog, UNI crown fork with a odd looking dropout like the picture. My bike came in all silver, with a red cross Schwinn sticker like the second poster. Also a made in Japan sticker near the BB.   The pink decals were put on for a friend of mine, who I gave the bike to. 25 years later became the Misses, still owns the bike.


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## ChattyMatty (May 15, 2014)

One more random thing to toss out here, recently a tube fork popped up on ebay with with the same elegant dropout shape which led me over to Fuji Bicycles - Indentification by Serial Number, Catalog, Model and History 1971-1991 and though not listed until 1983, their 26" cruiser did in fact have that fork (though chrome and no canti mounts). Dunno if the fork was made by Fuji or just something they sourced for another supplier though. And their Mt. Fiji MTB, though slightly different, were lugged frames with Ishiwata tubes


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## one less (Nov 17, 2014)

Slow96gn
I like your explanation but I would appreciated some clarification,
Mr G, did he purchase this frame and is he yourself or was he the Schwinn REP or the Horthridge shop owner or somebody else ?
It would be useful to see one of this REP catalog. I have seen the regularly Schwinn catalogs but not one expressed a REP catalog, I am sure they could have existed as a Schwinn in house to shops item, particularly for upcoming product and parts. 
Your Friend, who worked at the Northridge Cyclery, must have shown this listing to you and you made the order?
Where was the Northridge Cyclery located. 

I agree the Unicrown fork is a different frame and fork item, not to be confused with the Lugged frame.

ChattyMatty
I have looked at the Fuji format for serial numbers. The only part I can see that corresponds with this Schwinn serial number is the location on the bottom bracket. 
The K could be a Manufacturing Facility, S does not appear in the Month of Bicycle Frame Manufacture. In comparing the examples of FUJI Bicycle Serial Number Examples 1980-1989 KS314155 does not indicate a FUJI serial number, K could indicate a Facility, S does not exist in the FUJI identification for the month, 3 could be the year 1983. Overall it does not indicate a frame made by FUJI.

In respect to other frame in this discussion, particularly my frame BS3--- B does not exist as a Fuji Facilities, S is not a month listed by FUJI, and 3 could be the year. Overall it does not indicate a frame made by FUJI. Similarly for the Schwinn frames with serial numbers CS4----- and a Takara frame JS390868
The cast fork crown does appear on a few different manufactured frames, Trek, Takara, Pegasus MTB to name some. Most indicate 1982-3 and the frame tubing used is either Ishiwata or Tange tubing. I have not located a manufacturer of this fork crown but the Ishwata MTB tubing appears to be pre 1980 by the Ishwata catalog.

one less


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## ChattyMatty (May 15, 2014)

Funny how once you get looking at things they turn up. This bike's popped up on epay- looks like the 19" in the later darker blue color mention in earlier posts, yet another fork, and assuming he's referring to the headbadge stamp as the serial of 3482 put's it in December of '82.









And yeah, I noticed the Fuji serials didn't line up to the Schwinn format, it was the dropouts which caught my eye


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## one less (Nov 17, 2014)

ChattyMatty
It goes look like a 19" frame. I presume the s/n is MT3482, if so it looks likely to be a Schwinn number. Does it confirm the earlier numbers BS, CS etc to be 1981? The number 3482 does seem a little low for a December build or Schwinn`s production had dropped to that low in 1982. For a change of years the colours could have changed. There is a hole in the fork crown for a brake fixing. 
There does seem to be a number of manufacturers using that fork crown between Isiwata and Tange tubing which makes me think it was an independant supplier. The measurements for Ishiwata and Tange fork blades for the period say they are a different size but still oval.
one less


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## ChattyMatty (May 15, 2014)

I assumed he pulled it off a headbadge stamping using the normal 4-digit Julian date. The lister looks like a semi-pro parter-puter of Schwinn frames from his other listings so I didn't bug him. 

I tossed up a query over on the CABE since the guys over there are likely to have the dealer catalogs and monthly bulletins and such to see if maybe someone is bored enough to flip through their collections and see if maybe there was a mention of them there


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## one less (Nov 17, 2014)

one less said:


> ChattyMatty
> It goes look like a 19" frame. I presume the s/n is MT3482, if so it looks likely to be a Schwinn number. Does it confirm the earlier numbers BS, CS etc to be 1981? The number 3482 does seem a little low for a December build or Schwinn`s production had dropped to that low in 1982. For a change of years the colours could have changed. There is a hole in the fork crown for a brake fixing.
> There does seem to be a number of manufacturers using that fork crown between Isiwata and Tange tubing which makes me think it was an independant supplier. The measurements for Ishiwata and Tange fork blades for the period say they are a different size but still oval.
> one less


ChattyMatty
On a close look at this frame it is not as my frame and others in question.
It it 18.5" size.
The fork crown is not the same at all.
The serial number is only 3482 ie 348th day of 1982, yes December 1882.
The rear brake hangers are quite different.
From the add the frame is USA- Chicago made.
I have located the Ebay listing. 1980's old school schwinn MTB frame USA Chicago made | eBay
It would be good to see a REPs catalog
one less


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## ChattyMatty (May 15, 2014)

Yeah, but I didn't trust him when he said "Chicago made". My Akisu-made Predator has the same "Schiwnn Chicago" headbadge used on Stings even though it is undoubtedly a Taiwan frame. I hit him up and see if he's willing to check for any other numbers.

Looking back that the OP's pics again and now I need one of these tig'd frames even more... picked up a 21" King Sting over the holiday to which someone added canti mounts way back when, and that fork in the OP looks like it has the tapered legs of the KS forks with the canti mounts. Why do my little nerdy information hunts always end up costing me money?


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## one less (Nov 17, 2014)

ChattyMatty
If you can find Terminaut it would be an advantage, but he has not been seen for a long time. Try a personal message.
I have seen a Ritchey 1984 Montare that was made by Toyo in Japan that has the same fork crown. I have sent a query to them hoping for some information.
one less


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## one less (Nov 17, 2014)

one less said:


> I received a PM from haaki who I had sent a PM regarding his comments in respect to these frames.
> 
> "Re: ID Schwinn frame set
> Sorry for the late reply. Been offline on this forum for a long time. The earliest Schwann MTBs were Silver with Blue Logos. They were only available as frame sets
> ...


ChattyMatty
Back to this posting I did last year after I was replied to by Haaki. Interesting his 3rd generation Schwinn MTB description sound a bit like the latest you have found. It does look like the s/n stamping 3482 does indicate 1982 albeit late. Thus the 2 other style frames are earlier than December 1982. This does rule out 1983.
one less


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## one less (Nov 17, 2014)

*Anybody able to ID this Schwinn frameset*



ChattyMatty said:


> Yeah, but I didn't trust him when he said "Chicago made". My Akisu-made Predator has the same "Schiwnn Chicago" headbadge used on Stings even though it is undoubtedly a Taiwan frame. I hit him up and see if he's willing to check for any other numbers.
> 
> Looking back that the OP's pics again and now I need one of these tig'd frames even more... picked up a 21" King Sting over the holiday to which someone added canti mounts way back when, and that fork in the OP looks like it has the tapered legs of the KS forks with the canti mounts. Why do my little nerdy information hunts always end up costing me money?


ChattyMatty I hope this explains a bit, please add the image of the 1984 advertising if you can.

To all others who are interested, 
I have come back to this forum page after a very long absences and with the recommended approach of collection and analysing the records that exist. 
Not until recently I had seen a Specialised Stump Jumper of 1982 at a local Specialised dealer and I see considerable similarities to the Schwinn MTB frame, so much I consider a refreshed search for the Lugged frame history is required, so of again I go. 
This research is only for the Schwinn MTB with a serial numbers MSnnnnnn and whatever formats recognise that SN.
I consider all that is a record of these frames and approached the record and meanings of known appropriate formats and what is accepted as a historical Schwinn record and their good company policy at the time. 
During my time away I have continued to search, often running up against a blank wall and look for other ways. Persistent you might say. I have been on other Forums using different names for myself due to my seeing that some forum rules do not allow transfer of other information into their forum. This has not been done to mislead anybody by myself. The restriction on not being able to bring in information does make it difficult to bring together all in one place so comparisons what can be easy seen. Anything I bring into this forum I hope will not cause difficulties but is done to clarify what I consider needs to be included. I have been banned from one forum for what I see has no explanation, not my name given here and nor was I given a chance to discuss the reasons. Oh well, so it be.
What I am to explain on this page I have started placing on another forum but I cannot go back to the discussion or add to as my server will not allow me to do as there appears to be a warning of hackers on that site and I cannot access that forum at all from my computer. 
For the Schwinn Lugged MTB frames and forks of the 1980s I have concluded there are 2 Serial Number formats that can be followed, one is the Schwinn Chicago format of MYnnnnnn established in 1965 and used until 1983 and the ASNG (Asian Serial Number Guide) Japan (S1) MSYnnnnn using Bianchi as a supply of serial numbers using that format. These formats are not the same in their description and do not give the same result when compared in the others SNs meaning. The only aspect of both is that the written visual appearance is the same. There are definable differences which are 100% clear when they occur or not. There are comparisons that can be made in viewing years of SNs that define the meanings. I have always felt there was a difference that I had found but that will be discussed further on. 
A full description of the Schwinn format is easily available from a number is sources but the 1981 Schwinn Bulletin 23 is appropriate for the early 1980s.
The Bianchi format is only explained in the ASNG and appears to cover all years of the 1980s decade that most of the SNs are concluded to be exist in. Bianchi gives no explanation of the format used nor manufacturers, nor the country they exist in. Bianchi does not seem to indicate they have made bikes in any Asian country that I have seen. In all the cycle manufacturing is carried out in a number of different countries within Asia.

A KNOWN FORMATS TO CONSIDER WITH S
Schwinn Formats
Chicago Schwinn SN format MYnnnnnnn 
Schwinn Letour format SYnnnnnn
Other Formats
ASNG format Japan S(1) MSYnnnnn
ASNG format Japan S(3) SYnnnnnn

CONCLUSION OF KNOWN FORMATS WITH S

Chicago Schwinn SN format MYnnnnnnn Possible for 1981 
Schwinn Letour format SYnnnnnn Not possible as S in wrong location although it is recognised as a Japan built Schwinn Letour but can also be 1981 Chicago built Letour. 
Others 
ASNG format Japan S(1) MSYnnnnn Possible for any year but the decade is not defined.
ASNG format Japan S(3) SYnnnnnn Not possible as S in wrong location.

Only the Schwinn MYnnnnnnn and the ASNG MSYnnnnnn can be considered to analyse in detail all SNs that can the identified by each format and to the meaning of the format in the early 1980s. All the SN that are known will fit into both formats except for definable differences.

The Schwinn format MYnnnnnn Y= S=1981 so to help select the correct format I have tried to identify the differences between it and the ASNG S1 format. The Schwinn Lookup Tool can be used for both the Schwinn MTB SNs and most of the ASNG SNs that will give a positive Schwinn identification but knowing the Bianchi name exists on the frame they are not a Schwinn of any type. The SN with a particular letter gives a negative result and one letter used by Schwinn will never appear in the ASNG numbers. Should this not be retrospective, having Schwinn badging does not make the Schwinn MTB SN a Schwinn Format or an ASNG SN format without further investigation.

B ANY Difference between the ASNG SN Japan (S1) and the Schwinn sn MYNNNN in 1981.

I have referred to Bianchi formats as being one format that has many postings although other brands are referred to use this format. I consider using two cycle brand names provides another variation that my not resolve. The ASNG format has not been directly confirmed by Bianchi as Bianchi has never provided a statement of their formats. They appear to have a number of formats used with differing format arrangement used by Bianchi that are again not explained.

Also in respect to the ASNG Japan S(1) format I must point out as it is said by ASNG that they have no knowledge of what USA manufacturers as to the Serial Number formats they use and don't want to know therefore do not know about similar based formats. Therefore they will not be aware of Schwinn`s format that I am to explain. I will try to explain as clearly as I can as the differences are minor but different and detectable.
The Asian Guide I feel is a guide only and is stated not to be not 100% correct and the S means to be Asian made and does not identify the country although Japan is noted. 
The ASNG has been development as a Guide based on a data collection, looking for similarities and distinguishing features thus I have approached my search in the same manner.

The Schwinn is a manufacturer's identifiable format of MYnnnnnn. The SN`s of my Schwinn MTB frame, where S as a year 1981, can also be confirmed used within the ASNG S (1) format as a year 1983 or 1984 by the first number.

The Schwinn is an identifiable format from 1965 of MYnnnnnn. The SN`s of my Schwinn MTB frame, where S as a year, can be confirmed as 1981. This applied to the Schwinn Mass Produced Chicago cycles where up to c900,000 where built depending on the year (c600000 for 1981).

Firstly I confirm the ASNG Japan S(1) MSynnnnn appears to be correct for Bianchi SN`s. I have seen that other formats do exist. These formats are not confirmed by Bianchi and ASNG but should be. 
Most of the Asian made Bianchi SN`s of the 1980s can be identified as a 1981 Schwinn by the Schwinn Lookup Tool. The Bianchi S appears to only apply within the total 1980 decade.
During my initial search for the origin of my Schwinn lugged MTB SN I had always felt the ASNG Japan S(1) MSynnnnn could be used for its application of the Schwinn SN BS3nnnnn, YES as one number, but COULD IT BE for a similar group of others numbers that are also variation of MYnnnnnn, the month/year/ number application. I at one point gave into the fact it was the ASNG format therefore February 1983. 
Between BS4nnnnn, CS4nnnnn and KS3nnnnn I have RESERVATIONS on the year application and have continued to search for clarification. In that I have located a difference but needed additional information to confirm 100%.

Schwinn produced many thousands of product with the same SN format over 19 years from A to U that do not include I or O as a year. They stopped at U in 1983.
Most of the ASNG SN`s Japan (S1) MSynnnnn do qualify as by the Schwinn Lookup Tool as well, bar a few as a Schwinn 1981 production. I consider the Schwinn Look Up Tool seems only to refer to the SN date letters being the Month and Year letters, and not the numbers. The numbers in the Schwinn SN have their own meaning an individual sequential product Serial Number that has legal ramifications.
The Schwinn SN format MYnnnnnn do qualify as ASNG Japan (S1) MSynnnnn but for the MTB`s they are only recognised as February 1983 to March 1984.
I have compared a number`s of both the Schwinn Chicago SN from 1974 to 1984 and the ASNG format (Bianchi in particular). I have broken both formats looking at the detail of the actual letters and numbers, positions and their relationships within each other in the same format and across both formats. I have treated both formats as being within the same year and also different years hypothetically.
Bianchi include I as a month, a letter Schwinn never used as it confuses with 1. That even applied when they used earlier Asian manufacturing.
Thus Bianchi months are A to L and Schwinn are A to M, not including the letter I and Bianchi do not include a M.
This is a DEFINABLE DIFFERENCE between the two SN formats as they are visually read.
Furthermore the FIRST number for Schwinn SN over previous years to 1981 show a close relationship to the M and that the 1[SUP]st[/SUP] number that is increasing reasonably constant PRODUCTION RATE given there will be fluctuations in the PRODUCTION NUMBERS.
This is another DEFINABLE DIFFERENCE between the two SN formats as read visually.
These are a definable differenceS between the two SNs. I have seen ISYnnnnnn in the Bianchi SN but not a MSYnnnnnn . I have not seen on any of our Schwinn MTB frames ISYnnnnnn but one could exist if the format is ASNG. There is evidence that although Schwinn did manufacture to December (month M) each year and the production number did reach 900000 over the normal years, and in 1981 I have seen an MTB frame as KS3nnnnn,. The highest month letter for 1981seen is L then S then 5nnnnn for the production number indicating November 1981, 500000 as a possible production number. Higher numbers could exist in December MS?nnnnnn. There is reference to Schwinn Chicago being down 30% in 1981 thus an MS6nnnnn is likely to be as high as it could be.

There is definable differences between the two formats that cannot be ignored as all SN will fit, a different result is determined and neither can be confirmed nor excluded.

C A RANDOM LIST OF SCHWINN SERIAL NUMBERS AS CONFORMING TO THE SCHWINN CHICAGO FORMAT IN ORDER OF MONTHS FOR YEARS 1974 T0 1984 (YEARS OUT OF ORDER) BUT THE MONTHS ARE IN VERTICAL ORDER.

Schwinn SNs first letter fit as corresponding with a series of individual frame SN below organised vertically by month A to M. The first number progressively increases, 1 to 8 as the month letter reference dependent upon the production rate per month. The first number by the Schwinn description is not a year number for the Schwinn format.

The second letter is for the Year. Letters follow the letter for the year as per the Schwinn 
A=1965 to U=1984 format excluding I and O, S=1981

Frame Serial Number Date Month/Year 
These are Schwinn confirmed SN and dates 
AK10736 Jan 1974 
AR53355 Jan 1980 
BR553085 on BB u/s Feb 1980 
BS367823 Feb 1981 Lugged MTB SN position along with others 
BU510679 Feb 1983 
CU52824? Mar 1983 
CG669707 Mar 1971 
CR525040 Mar 1980 
CM559963 Mar 1976 
DR509170 Apr 1980 
DS5071927 on BB u/s Apr 1981 Schwinn Predator 
EF015984 May 1970 
FT520791 June 1982 
FU50293 June 1983 
FJ583293 Jun 1975 
GR733640 on BB u/s July 1980 Schwinn Predator 
HR561039 Aug 1980
KQ503804 Oct 1979
KR80055 Nov 1980 
KR800514 Dec 1980 King Sting MTB at Mombat Museum 
KS314155 Oct 1981 Last Lugged MTB known
LJ554886 Nov 1973
LS527689 Nov 1981 
MH520056 Dec 1972 
MR551380 Dec 1980 
MR654499 Dec 1980
MR826184 Dec 1980
MR826498 Dec 1980
Months are generally seen to align with the 1st number that is increasing at a reasonably constant amount give variations in a production rate of each year.
The S year (1981) production only reaches to around LS527689 for November, low as in respect to most other years previous.

D THE ASNG FORMAT JAPAN S(1) COMPARISON
The ASNG format presented in a manner of order by month that can be read below.
Serial Numbers been observed. Unless stated they are on the underside of the BB.

AS718273 1987 January On the seat tube, not the BB 
BS14121 1981 Feb T-Mar
BS581982 1982? LHS side of downtube T-Mar 
BS801036 1988 T-Mar
CS304982. 1982 T-Mar
CS474608 1984 T-Mar
CS480940 Sounds like a 1984/1985 model T-Mar
DS484284 made in Japan in 1984, but could be a 1985 model. No picture
IS513786 confirmed as 86 (not a Schwinn as M=I)
IS761045 1988 (not a Schwinn as M=I) T-Mar
JS682194 1994 on seat tube
JS763084 1987 Oct T-Mar
JS19084 84 Japanese Bianchi reply by owner not confirmed
KS548867 1984 T-Mar
LS326173 1984 T-Mar
LS285470 No explanation
LS25480 It's definitely a 1983 model manufactured in Japan during very late 1982, based on the serial number 
LS285709 1982 T-Mar
LS206786 No reply

For the letter S in the ASNG format it was placed and aligned in the same visual location as with the Schwinn list to be seen above. The months were aligned A to L vertically so the month letter and first number appeared opposite each other to be compared with the same positon as the Schwinn format MYnnnnnn below. 
Whichever with both formats referred to there is a clear indication to which month is being questioned.
Firstly if I for month appears as in a ASNG Japan (S1) MSynnnn it indicates September but as Schwinn did not use I then to be sure the SN is a ASNG format. If M appears the format is Schwinn as ASNG Japan (S1) MSynnnn cannot include an M. 
There could be minor variations but it does confirm the ASNG Japan S (1) and the Schwinn MYnnnnnn format are SIMILAR BUT NOT THE SAME MEANING, and have a different meanings but must be read giving thought to the formats used. Refer above to the Schwinn comparable listing.

The first Bianchi number presented in the Bianchi SN is not a similar increase to the Month code letter, so there is a definable difference that can be detected. The first number in the ASNG format is the year ranging from 0 to 9. The Schwinn format could reach a number 9 but generally is an 8 at least. There could be 0 but I have not seen so the first Schwinn number may be a 1nnnnn. 
By ordering the two SN formats as I have done, it can be seen that two different patterns form of increasing numbers in the Schwinn format but differing up and down greatly for the ASNG format. The Schwinn format provides an obvious increase in the production figure over a year, which varies a little due the fluctuation in monthly production. In 1980 and 1981 saw a 21% and 30% respectively for each year for the annual production. 
The ASNG Japan S(1) format has the first number will always be the same for that one year but the months alphabetically increase A to L. The formats as visually presented look the same, but have different distinction in meanings. 
For the Schwinn format I month will not appear and for the ASNG format M month will not appear. The ASNG format S appears to extend over a decade at least whereas the Schwinn S is for one year only, 1981. 
The serial numbers need to be judged using a few observations.
Understanding what the ASNG format means its interpretation can be calculated. Understanding the Schwinn format also means the same, but the result is different.
This does not mean we can simply rule out one in favour of the other or say only one format applies for the Letter/S/nnnnnn SN.

The result to this point is the all SN we know fit both formats and the Year determined are from 1981 (Schwinn) or 1983 and 1984 (ASNG).

The ASNG Months have I and M does not exist. I have found examples of the IS but no MS for ASNG. Unfortunately for the Schwinn format of 1981 no IS has appeared nor has MS in our MTB serial numbers. To simply say the Schwinn MTB SNs are either formats or the other cannot be said without conformation of what the SN format is or to consider any of the minor variations and other alignments that exist. There is total proof the Schwinn did use MYnnnnnn where Y=S for 1981 and approximately 600000 frames where fabricated but not completed as a bike which is totally common with Schwinn production over many years.

E THE SCHWINN LUGGED MTB FRAMES SN ANALYSED AS SCHWINN FORMAT MYnnnnnnn

These are the 8 MTB SNs known.
No consideration is given to the meaning of the numbers or order except they could be a sequential production order for the frames as compare with normal yearly Schwinn PRODUCTION numbers. In 1981 there appears to be a total production of approximately 600,000 bikes in the USA by Schwinn

BS357553 B=February 1981 The 1st to last numbers form a consecutive 
BS367578 B=February 1981 order for 1981 ie 57553 to 476244 
BS367823 B=February 1981 
BS367845 B=February 1981
BS440296 B=February 1981 
CS472494 C=March 1981 
CS476244 C=March 1981
KS314155 K=October 1981 If 314155 as a consecutive number for 1983
is completely out of order being aligned to K
for 1981 considered as a consecutive number that would align to a month. As it does not. I have read somewhere for Schwinn that if a cycle part that the SN was placed on was not used in manufacturing the SN being 314155 would have been reallocated to the most recent part containing the SN to keep the SN sequence in order. If the numbers 314155 was reused from a deleted SN BS314155 it would fit as the first MTB in the production order.
I do not know if this is true.

From the above list is a Schwinn Predator with an SN DS5071927 on BB u/s this dates as April 1981 and is clearly a Schwinn Chicago format as the Schwinn MTBs in question. Everything about the SN fits the Schwinn Format and the ASNG format, so it could be either again. DS comes after the CS and the 5 corresponds to the Schwinn production number series for 1981. If it is concluded as 1985 by the ASNG this puts the Schwinn actions way beyond the closure of the Chicago factory. I have viewed other Schwinn Predator SN for 1985 and they appear to be Giant made ie G0285/504501. This is a positive indication the Schwinn SN MYnnnnnn Y=S=1981 on the BB u/s is the SN used on the Schwinn MTBs. The 1985 Schwinn Predator clearly used the Giant production for Asian made product.

Refer to a similar analyse of the same numbers for ASNG format MSYNNNNN below.

F THE SCHWINN LUGGED MTB FRAMES SN ANALYSED AS AN ASNG FORMAT JAPAN S (1) MSYnnnnnn

These are the 8 MTB SN known.
No consideration is given to the meaning of the numbers or order except they could be a consecutive production order for the frames as nothing has been stated by ASNG.

BS357553 B=February 1983 The 2nd to last numbers form a consecutive 
BS367578 B=February 1983 production order for 1983 ie 57553 to 67825. 
BS367823 B=February 1983 
BS367845 B=February 1983

KS314155 K=October 1983 If 14155 as a consecutive production order 
number for 1983 is completely out of order being aligned to K if 3 is considered as a year number that would not align to a month K.
14155 as a sequential production number is completely out of order for 1983 as the ASNG format.

BS440296 B=February 1984 The 2nd to last numbers form a consecutive
CS472494 C=March 1984 order for 1984 ie 40296 to 476244 
CS476244 C=March 1984

From the above list is a Schwinn Predator with an SN DS5071927 on BB u/s, this dates as April 1985 by the ASNG and could be so but it is also clear Schwinn used Giant made product in 1985 ie G0285/504501. Thus this is a positive indication the ASNG MSYnnnnn on the BB u/s is not the SN used on the Schwinn Predator in 1985.

For E and F sections at this point I still have variation with both formats with no conclusion.

G THE SCHWINN FORMAT AND THE ASNG FORMAT JAPAN S(1) COMBINED FOR COMPARISON OF YEARS 1983 AND 1984
The both formats presented in a manner of order by month that can be read below. The numbers following the 1[SUP]st[/SUP] number 3 or 4 indicating the year 1983 and 1984. The following 5 numbers in the Schwinn SN are in a comparable order not including KS14155. The ASNG numbers serial numbers are for years 1983 and 1984 years only. 
BS357553 B=February 1981 Can be a Schwinn SN
BS367578 B=February 1981 Can be a Schwinn SN
BS367823 B=February 1981 Can be a Schwinn SN 
BS367845 B=February 1981 Can be a Schwinn SN
*CS304982. 1982 ASNG CS304982 out of order for all Schwinn SN fitting as 1983 ASNG due to C=March 1983 *
*LS326173 1984 ASNG LS326173 is not acceptable for defining all SNs as **ASNG 1983 as L= December 1983*

BS440296 B=February 1981 Can be a Schwinn SN

CS472494 C=March 1981 Can be a Schwinn SN Schwinn 
*CS474608 1984 ASNG is acceptable for defining all SN are ASNG 1984*
CS476244 C=March 1981 Can be a Schwinn SN

*CS480940 1984/1985 model **ASNG CS480940 1984 ASNG is acceptable for defining all SN are ASNG 1984*
*DS484284 1984, ASNG CS484284 is not acceptable for defining all SN are ASNG 1984 as there are DSnnnnnn to compare to*
*DS5071927 D=April 1981 Schwinn Predator In order for Schwinn but defines 1985 for ASNG that does not fit with Schwinn. *

KS314155 K=October 1981 If 314155 as a consecutive number for 1983
is completely out of order being aligned to K
for 1983 considered as a consecutive number that would align to a month. As it is out of sequence with the K and 3 its question of how that happened is not known.
 This can be a Schwinn SN

CS304982 ASNG is completely out of order for Schwinn as CS3 does not exist in the Schwinn SNs (only CS4nnnnn) and 304982 as a number would precede all the Schwinn BS3 SNs, and also KS314155. CS474608 can fit the order but CS480940, DS484284 are beyond the Schwinn SN but could fit. LS326173 is out of order but much like Schwinn KS314155On comparison some of the Schwinn can fit within the order set by the ASNG but others cannot fit. But there appears to be 2 defined groups

Conclusion from what I have from the above is the Serial Numbers from what is on the frames for both ASNG S(1) serial numbers MSYnnnnn and Schwinn MYnnnnnn format serial numbers. Both of these formats can be applied to the serial numbers that are known. There are few SN on frames to be found as most owners appear not to provide serial numbers. Even just the letters MY and the following next 2 numbers. The only Manufacturer approved SN is the Schwinn, from as early as 1965 to 1983.
DS5071927 D=April 1981 Schwinn Predator In order for Schwinn but defines 1985 for ASNG that does not fit with Schwinn history. 
This gives a strong indication the Format of the SN`s is Schwinn Chicago.

H ISHIWATA DATE STAMPING
My recent discussions with T-Mar and he wrote it was Gregorian dates but I asked for confirmation for the Ishiwata tubing date practice that they followed and he has not replied. I may have solved it myself, having seen only one that looks like Gregorian and relating to a Gregorian SN on a Bianchi close to the ASNG format for a similar year much as happens with the Schwinn MTBs.
This is not a confirmation but I consider it does not matter any way as I also take what he said as well, the date on the forks indicate the forks manufacture date not necessarily the frame. The Schwinn forks could have been replaced at a later date as stated by owners at the time they were first sold. This is a view held by others in reference to these frames.
I have seen one of the Schwinn MTB with an Ishiwata MTB double butted tubing decal affixed.
By measurement the frame does appear to be of Ishiwata MTB tubing, 32mm for the down tube. 
It is stated the original Unicrown forks where replaced and would be interesting to see one of the original forks and the date stamp.

There is still no confirmation of the Ishiwata SN calendar format but there is evidence the original forks had been replaced with a new date. The frames could be Ishiwata tubing by tubing size and Ishiwata MTB decal.
This still gives no date confirmation for either of the frame SN formats.

I SERIAL NUMBER LOCATION
One query I had with being Japanese made is that they are generally regarded they are u/s of the BB as mine is and to accepting it being a Schwinn SN searched to find a similar situation on a Schwinn stamped as per my frame. 
The ASNG comment is that if the SN is on the u/s of the BB the number is Japanese therefore ASNG Japan S (1). There is history of the u/s of the BB being a location for the SN on Schwinn bicycles, so I searched for an example within the 1980`s.
I recently came across a Schwinn BMX Predator being stamped GR733640 to the u/s of the BB. Clearly by the GR7nnnnn it was by the Schwinn Lookup Tool identified as a July 1980 as recognition of the Schwinn format MYnnnnnn. This was confirmed as such on the forum but a later identification stated it was 1987 because of the 7 as it looked like a 1987 model Predator. & does fit the month/production number alignment. There was no head badge SN which would indicate how many years passed. Regarding the location of the SN, I asked for that to be explained as a possibility within the Schwinn manufacturing and how it occurred as it did, with no reply. I also questioned the use of the 7 as a date, for which the Schwinn SN is clearly indicated by GR a MYnnnnn format of 1980. Is the location on the BB stamping (possibly indicating Japanese made) and of the 7 could be a hangover from the ASNG MSynnnnn without giving thought to the GR, July 1980. Of course nothing exists for a format GR in the ASNG. 
To me the location of the stamped SN indicated that Schwinn was somehow stamping to the u/s of the BB early 1980`s with the Schwinn MYnnnnnn format as with my MTB. 
This to me could be just another confirmation it is a Schwinn SN MYnnnnn, the Year being S, 1981. 
In a later search I did find another SN stamped to the underside of the BB a Schwinn SN MYnnnnnn. DS5071927 on BB u/s, Apr 1981 also being again a Schwinn Predator and that SN is entered into the sections above comparing SNs.

For the Schwinn format there is evidence it was placed on the u/s of the BB, a reason why and more examples are necessary to completely identify the reason or who did the stamping.

J CONCLUSION OF THE COMPARISON BETWEEN THE SCHWINN MYnnnnn FORMAT AND THE ASNG FORMAT
I consider the Month/first number of each to be critical for comparing for a yearly bases of each to select what format the SN is, ie either Schwinn or ASNG Japan (S1) MSynnnn. 
Visually the SN`s for Schwinn appear as the ASNG, Japan (S1) MSynnnn but as the SN of a Schwinn indicates 1981, both are similar but the meaning isnot the same. Also if M appears in a SN it is not definitely not an ASNG Japan (S1) MSynnnn, that SN is a Schwinn. If I appears the number is an ASNG Japan (S1) but not a Schwinn SN MYnnnnn.
If IS appears in this search and if one does it will confirm the ASNG format applies and as we have a K one could. If a MS appears we have Schwinn format.
I have all ways thought there was a difference but not until I arranged comparative results the MINOR difference became obvious.
Essentially the ASNG Japan (S1) format is MSynnnnn where the S means Japanese, or whatever built but the Schwinn format is MYnnnnnn where Y is S for the year 1981, in respect to a Schwinn format from A=1965 to U=1984 when Schwinn ceased using the format. 
The SN is confirmed by Schwinn as a 1981 and was to be from 1965.
My Schwinn SN BS3nnnnn can fit with the ASNG Japan (S1) MSynnnnn where the 3 could be 1983. Similarly one of the CS4nnnn Schwinn SN`s can fit the ASNG Japan (S1) but when the comparison of the Month letter to the first number of all Schwinn SN MYnnnnn for all production between 1965 and 1984 where the for all months A to M have a relationship with the first digit that is reasonably similar. The Schwinn months do not include I for the same reason
Whereas the ASNG the Month to the first number has no similar relationship as the first number is not within the same year as the Schwinn is but indicates a year.
*The SN DS5071927 DS=April 1981 for the Schwinn Predator does indicate to me Very Strongly the Serial Number format is Schwinn Chicago and separate of the Schwinn MTBs *

K THE FRAME CONSTRUCTION AND GEOMETRY
Can these frames be considered as an early MTB. 
I have measured and weighed the Schwinn frame. Angles are seat 67.5 degree and steering head 68.5 degree. The wheel base is 44". The tubing, by size appears by the Ishiwata MTB catalogue to be Ishiwata MTB tubing and I have seen a photo of one of a Schwinn MTB that has an Ishiwata decal on the frame. I have also seen decaled as Cro-Mo 4130 and made in Japan. I had also consider the original tubing is Ishiwata considering the forks had been replaced by Ishiwata.
By measurement the frame does appear to be of Ishiwata MTB tubing, 32mm for the down tube. 
The Schwinn frame weighs 5.4 lb and the forks 2.2lb (heavy) The weight of a Specialized Stumpjumper frame only would help. The only weight I have seen is 29lb as a complete MTB.
Apart from the weight there are direct comparisons to be made with the Trek 1982 as well. 
There is also comparison to the Tom Ritchey 1980s MTB frames for angles but not construction. I have read somewhere in the last 6 years Tom Richey was not in favour of the Unicrown fork head in the early 80s and did not recommend them. His own Japanese made lugged1983 Canadian MTB had the same fork crown that replaced the failed original Schwinn MTB Unicrown.
There is also close comparison to be made with Breezer 1 1977 for angles and tube sizing although the tube layout is quite different. 
The Schwinn MTB 1981 can be considered as an MTB geometry of the period of early MTB development pre 1981.

L SERIAL NUMBERS
The reason for a serial number is to create an individually identifiable number for a particular item manufactured eg Cycle, Motor car, a piece of mechanical plant, home appliances etc. Now any particular item can be required to be identified for repair and parts to be supplied, insurance and theft identification etc. It is a criminal offence to alter Serial Numbers particularly of motor vehicles. Thus it would seem unlikely that a manufacturer would issue the same number twice.
Serial numbers can include a production date as these have with the MY followed by a series of individual numbers. Schwinn do state the procedures they followed in establishing SN formats.
For Schwinn by their use of the MYnnnnnn format in 1981 for 600,000 individual items viewed as AS1nnnnnnn to LSnnnnnn including BS3nnnnnn, BS4nnnnnn, CS4nnnnnn and KS3nnnnnn it is expected that in 1983 and 1984 they would not produce item produce and sell another 10 items plus with the same Serial Numbers without knowing and checking in 1983 and 1984 that it was happening.
There would have been steps taken to change the SN stamping. There is reference in the 1981 Bulletin of such variation to a SN to include an extra T in BMX frames Tri-oval frame. 
Thus as this did not happen and there is evidence of the Predator frames with similar SN in 1980 and 1981 can we be satisfied the SN format is Schwinn for 1981.

M THE 1983 AND 1984 SCHWINN ADVERTISING OF THESE FRAME FORK SETS
The advertising of the frame/fork lugged frames were advertised in 1983 and then in 1984 with additional components for a complete MTB cycle. These advertisements are regarded as the earliest advertising and taken to confirm the ASNG date of 1983/84.
In 1983 the advertisements show a lugged frame in the BMX catalogue, two sizes and in the general Schwinn catalogue as one size only shown. The 1984 advertising is the same lugged frame as in the BMX catalogue with more componentry. 
The frames photographed are referred to by the same 2 parts catalogue numbers for either the 19" and 21" frames but the forks photographed in each catalogue are different, the lugged forks in the BMX and the unicrown forks in the general catalogue. The frame in the BMX catalogued is clearly the Lugged construction and given part number 21" 29 265 and 19" 29266
The general Schwinn catalogue is vague in quality and could be welded construction but is given a part number 29 265 only.
With the reference to the forks being replaced from Unicrown to Lugged, this is the reference to original forks. Essentially there is only one lugged frame in 2 sizes with replacement forks after arrival, one version supplied from 2 orders. 
Now to the advertising process as undertaken by Schwinn that would have been in 1983. I have contacted Gene2 at the BMX catalogue and he told me the advertising for any particular year ie 1983 would have been commissioned in the previous year ie 1982 for the supply of the catalogue to be sent out in around September (1982) to the dealers for the pre-Christmas 1982 sales. Thus the frames and whatever forks they had, existed in October 1982 at least. 
The SN number as applied to the frames existed in 1982 thus the ASNG number indicating 1983 is in doubt and also is 1984 if the frames are the same as per photographs.

N SCHWINN INTEREST IN MOUNTAIN BIKES 
It is commonly stated Schwinn did not have an interest in the MTB but in reality never used Mountain Bike wording due to a company called Mountainbikes. 
In 1979 Gary Fisher and Charlie Kelly set up Mountainbikes as a business. This had an effect on sales advertising of other suppliers. Schwinn, Specialised, Tom Ritchey and others could not use the words "Mountain Bikes" for fear of breaching copyrights owned by Gary Fisher and Charlie Kelly so Schwinn chose to use ATB, All Terrain Bikes. This applied to Schwinn King Sting and Sidewinder also.
This publication date would also satisfy Schwinn to regard the use of the "Mountainbike" word as not being a restricted item in 1983.
Schwinn would have feared legal ramifications so used the term All Terrain Bikes, ATB. They also followed their long term philosophy of bicycle for the aging BMX riders. I see Specialised and Tom Richey did not use the words Mountain Bikes in advertising at that time either.
When these Schwinn MTBs were being sold in 1981 they were not advertised on paper, at least no evidence exists but it has been spoken about that it happened at a more personal level, word of mouth.

From Disreli Documents , Schwinn All Terrain Bikes
Schwinn All Terrain Bicycles
This is a good article regarding the 1979 to 1983 ATB and the restrictions imposed on the use of Mountain Bike wording and its implications.
It does include a good copy of the Schwinn ATB Owners Operating & Maintenance Manual that again indicates Schwinn interest in the ATB cycling and their application of Schwinn cycle manufacturing expansion from BMX.

O OLD REFERENCES
Pridmore, Hurd and haaki . 
In 1996 Jay Pridmore and Jim Hurd wrote in the Schwinn book of the Schwinn Parts department importing MTB frames and sell them as frame/fork sets. 
Haaki earlier on this forum, also wrote of these frames and the forks breaking and being replaced by Schwinn.
Jim Hurd was the Curator of the Schwinn Family Collection before and after the Schwinn bankruptcy. He was also at the Bicycle Museum of America at Chicago`s North Pier Terminal that after 1996 most of the collection was sold and it became the 'Bicycle Museum of America" in New Breman Ohio
The comments about the 1981 Schwinn Parts Department importing MTB frames selling them as frame /fork sets cannot be confirmed. Jim Hurd appears to be well regarded in Schwinn affairs and cycling thus it is a great pity he cannot be asked. I have read this book is rubbish but also Jim Hurd is a respected Schwinn historian.

FINALLY
From all the above I am sure a final acknowledgement for which year for the Serial Numbers can be clarified.
This has been a long posting and even longer to prepare. Fortunately for most of it I have been in an enforced, complete national isolating lock down with only digital contact allowed for most of the time to put this together. 
Any comments and additions are welcome,
Keep well and safe.
I`m one less


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