# Yet another 20" Hotrock build thread...



## Roaming50 (Apr 30, 2009)

I've stripped down this wreck of a 2003 Hotrock that I picked up cheap.









My priorities is to get the bike up and running for as cheap as possible. Upgrades may come down the road after I have weighed everything and made a weight to cost analysis.

This bike is for my son who is 6. I picked up one of those ING Marins cheap so he has that for when he is bigger in about 18-24 months hence I don't want to spend too much.

I have a SRAM X3 shifter and a X4 rear mech to go on the bike. I also plan to change out the 6-speed freewheel for a 7-speed mega range which I already have. I have new grips as well and a old Easton XC90 carbon flat bar to put on. I have a new PC890 chain as well.

I would like to find a better saddle but seat post and stem works for now.

The bottom bracket needs replacing. I plan to get a Shimano UN73 bb but I am not sure the axle length I need. If I stick with the existing cranks is it right that I need a 128mm length? If I go for a Sinz crank then I'll need a 113mm ?

The axles on the wheels probably need replacing as well but I'll look into that another day.

As I strip the bike I am weighing every part. For now I have:

Frame + headset cups 2611g
Headset bearings 30g
Fork + crown race 978g
Stem 209g
Headset spacers 13g
Stem cap 17g
Crank bolts 33g
Crankset 613g
Pedals 331g
Saddle 349g
Seat post (cut to 240mm) 289g

Rear wheel 1000g
Tire 540g
Tube 130g

Front wheel 910g
Tire 520g
Tube with thorn protection. 180g

Off
Bottom bracket 299g
Chain keeper 255g
Shimano 14-28 cassette 440g
Handlebar 404g
Bike stand 254g
Shimano SIS rear mech 311g
Bottle cage 52g
Rear mech protector 119g
Front reflector 45g
Shimano Revo shifter 114g

New
Shimano UN-73 68x113 264g
Shimano 14-34 mega range 483g
Easton CT2 carbon handlebar 125g
Shimano shifters ?
Shimano TX75 rear dérailleur ?

Yes that frame is a tank. This is the steel version of the Hotrock and the frame weighs more than my FS 26er. Oh well...


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## mhkang (Nov 1, 2008)

Are you gonna rebuild the wheels? Wondering what rims you were gonna use? I'm rebuilding a 20 and 24 inch bike. Can't find the light Alex ace 20s


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## stom_m3 (Jun 28, 2011)

mhkang said:


> Are you gonna rebuild the wheels? Wondering what rims you were gonna use? I'm rebuilding a 20 and 24 inch bike. Can't find the light Alex ace 20s


I don't know if you have a preference for Alex rims but they are not that light @ 570g per rim. I used Sun Envy Lite @ 330g/ per rim. That's a savings of 1.1lbs on the rims alone. I used Sapin dbl btd spokes with XT hubs. The wheels came out looking really nice, at least I think they did.


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## Roaming50 (Apr 30, 2009)

I'm not planning to rebuild the wheel. Well not yet anyway. The rims seem to be in pretty good condition for what they are and they hold air running ghetto tubeless okay. 

I ran into a problem today. While my new 7-speed mega range freewheel fits okay on the wheel and in the frame I am having issues with the SRAM X4 rear mech. The issue is that even with the limit screw all the way out the mech stops before the outer sprocket (14). The furthest it goes is midway between the two outer sprockets. I also think the cage is a bit long for a 20" wheel. 

Now my son has the 24" Marin Bayview - brand new doing nothing. I'm looking at that bike thinking I can cannibalize it for its Shimano Altus and Easyfire shifter instead. It looks like that mech may work better. May try that in the morning. 

I've updated my weights on the first thread but I'll continue to update it as I work it.


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## Roaming50 (Apr 30, 2009)

Oh in the end I ordered a 68x113mm UN-73 bottom bracket. After some measuring I figure the existing cranks (152mm) will still work as they are quite outboard right now. 

I would like to pick up a 135mm or 140mm Sinz crank as I have a nice 34T Middleburn 110bcd middle ring in my parts bin complete with Ti crank and chainring bolts. Unfortunately there's no deals right now so I'll keep an eye open and wait.


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## mhkang (Nov 1, 2008)

Not sure about the cog/ derailleur issue. I stuck an old ultegra and it handles the stock 28. Was gonna use an old XT if she needed more than the 28. Wonder if the mega freewheel is spaced differently or sits higher or further away from the hub. 

I thought the Ace 20s were 310 gm for the 20" and 385gm for 24". Also able to use only 32 spokes. But LBS can't order them and the eBay seller someone else on the forum listed is not responding about availability. May have to use the envy lites.


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## TwoTone (Jul 5, 2011)

kerryn said:


> I'm not planning to rebuild the wheel. Well not yet anyway. The rims seem to be in pretty good condition for what they are and they hold air running ghetto tubeless okay.
> 
> I ran into a problem today. While my new 7-speed mega range freewheel fits okay on the wheel and in the frame I am having issues with the SRAM X4 rear mech. The issue is that even with the limit screw all the way out the mech stops before the outer sprocket (14). The furthest it goes is midway between the two outer sprockets. I also think the cage is a bit long for a 20" wheel.
> 
> ...


You need a rear derailleur that can handle the 34 tooth rear, I bought a derailleur, freewheel and shifter for around $45 on amazon.

This is a link to the 3 pieces I bought and are working great on my daughters 20inch.
http://forums.mtbr.com/9296622-post12.html


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## alex_sdca (Apr 6, 2009)

The set of Alex Ace 20 24" rims I have weigh 408 and 409 grams respectively with no rim strips.


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## Roaming50 (Apr 30, 2009)

I think I may have fixed my issue with the X4 mech. I disassembled the rear axle today and placed a spring washer on the drive side to shim out the axle width.









I was expecting to have to pry the chain stays apart but the wheel slipped right in as if it should have been like this from the beginning. Perhaps it was missing a shim?

Anyway it now looks like the X4 mech will drop down to the tallest gear now.


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## Roaming50 (Apr 30, 2009)

Oh yeah, I forgot. I have to redish the wheel a smidgen now. 

I've still got concerns with the X4 mech. Though it clears the 34 ring just fine at its lowest point (granny gear, cage vertical) it clears the ground by only a 1 1/2 inch. That seams too small....


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## Roaming50 (Apr 30, 2009)

TwoTone said:


> You need a rear derailleur that can handle the 34 tooth rear, I bought a derailleur, freewheel and shifter for around $45 on amazon.
> 
> This is a link to the 3 pieces I bought and are working great on my daughters 20inch.
> http://forums.mtbr.com/9296622-post12.html


What is the clearance to the ground with the rear mech?


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## TwoTone (Jul 5, 2011)

kerryn said:


> What is the clearance to the ground with the rear mech?


I'll try to get pics tomorrow for you


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## Roaming50 (Apr 30, 2009)

stom_m3 said:


> stom_m3, do you happen to know the weight of the Siren tires you have? On the DansComp site they list the 20x2.125 as being 434g (15.3oz) but IRC list it as 550g. Hoping you can confirm more real world measurements.


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## stom_m3 (Jun 28, 2011)

Interesting. I think it's a typo on IRC's website. It's probably 450g. My 20 x 1.75 Sirens weighed 403.2 on my scale vs the website @ 410. I would believe Dan Comp's #. Also, my build thread has weight of most of the components I used if interested.


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## Roaming50 (Apr 30, 2009)

Thanks for that Stom.

I think I will order some Sirens to replace the worn Specialized rubber I have now even though they seem to be holding up well to tubeless - still i want the grip. Are you running the Sirens tubeless?

I have decided to replace the SRAM rear mech and put the X3/X4 trigger/mech on my daughters' 24"Hotrock where it will fit better. For the 20" I am proceeding with the Shimano Acera trigger shifter/derailleur mainly due to the cage length of the derailleur.


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## TwoTone (Jul 5, 2011)

Here are the pictures with the linked parts installed







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## Roaming50 (Apr 30, 2009)

Good confirmation Two Tone :thumbsup:

While I did not order the same derailleur I did order the Acera. Which has similar dimensions.










The current X4 drops below the rim. Not good.


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## mhkang (Nov 1, 2008)

alex_sdca said:


> The set of Alex Ace 20 24" rims I have weigh 408 and 409 grams respectively with no rim strips.


ouch, that's a bit off their claimed mark. was gonna pull the trigger on the envy lites from the LBS when I got a response back from the ebay seller.

Stom_m3 did you weigh your rims? Was 330 the actual weight vs claimed


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## TwoTone (Jul 5, 2011)

kerryn said:


> Good confirmation Two Tone :thumbsup:
> 
> While I did not order the same derailleur I did order the Acera. Which has similar dimensions.
> 
> ...


Should work fine, part of the determining factor for me was getting all the parts from same place to save on shipping and handling.


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## stom_m3 (Jun 28, 2011)

mhkang said:


> ouch, that's a bit off their claimed mark. was gonna pull the trigger on the envy lites from the LBS when I got a response back from the ebay seller.
> 
> Stom_m3 did you weigh your rims? Was 330 the actual weight vs claimed


The numbers I quoted were the manufacturer's. Possibly I'm seeing the wrong numbers from Alex rims. I couldn't find the Ace on their website so I assumed you were talking about the light versions. The Alex Supra EX claims 440 which is their current lightest rim. Dan's comp has the Sun Envy Lites at 11.8oz or 335g. Sun has them listed @ 330g.


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## stom_m3 (Jun 28, 2011)

stom_m3 said:


> The numbers I quoted were the manufacturer's. Possibly I'm seeing the wrong numbers from Alex rims. I couldn't find the Ace on their website so I assumed you were talking about the light versions. The Alex Supra EX claims 440 which is their current lightest rim. Dan's comp has the Sun Envy Lites at 11.8oz or 335g. Sun has them listed @ 330g.


Surfing the Alex rims website a little more, I finally found the Ace 20 wheels. They are quoted at 310g's. The only thing to take note is the width. They are slightly narrower than the Envy Lites which will have a slight effect on tire profile.


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## Roaming50 (Apr 30, 2009)

*Tire choice?*

My boy will mostly be riding pavement and dry dirt single-track but we also have a number of multi-use trails around here which are the kind where we have hard limestone bed with a loose and dusty top 1/8 to 3/8 inch of gravel.

My challenge is to fine a decent lightweight tire that won't break the bank that is fast rolling on the pavement and hard baked dirt single track but can also provide grip on the looser multi-use trails.

Based on this (thanks Stom) I thinking:

IRS Siren 20 x 2.125 at 550g and $17.99 
or
Tioga Comp III 20 x 2.1 at 460g and $15.99.

I'm skipping the Small Block 8s for now as I plan to run tubeless and there is a question mark on how the Kendas perform in this aspect.

Based on weight and cost the Tioga seems like the tire of choice but I can't help thinking that for most of my boy's riding the Tioga Comp X 20 x 2.1 at 500g and $14.99 may actually be better still. My only concern is if this tire will hook up on the loose multi-use limestone trails.

Thoughts?

EDIT: I forgot that in another thread I had a discussion with Stom_m3 on the weight of the Siren 20x2.125. This assumption is that 550g on the IRC site is wrong and that this is more likely around 440-460g. I may still go for them.


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## Roaming50 (Apr 30, 2009)

Arrgggg!

I got my shifter and mech from Amazon but I was shipped a different Acera mech than what was displayed. It will work but it was not quite what I was after. I think I will send it back.

I may just do the Tourney TX75 as TwoTone did. Ideally I want an X3 medium cage but I can't find one online. They're all long cage.... Humf.


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## IAmHolland (Jul 8, 2010)

Medium cage starts at x5, IIRC. Short cage starts with x7. The tourney should be medium cage.

I have the 20" SB8 wire bead, may try to go ghetto tubeless with it. Aside from it possibly reacting with Stan's, I'm not keen on having to keep pumping it up and having to reseal or reseat.


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## Roaming50 (Apr 30, 2009)

According to SRAM you can get the X3 in medium cage but the only place I find it for sale is in some former eastern block country.

I looked into X7 short, It would be perfect but I'm not sure I want to spend $54 (how well will it hold up to 6-year old abuse?). The X5 mid cage is doable but that is still $38 and I don't get free shipping on that one so call that $44. 

I think tourney TX75 is what it will be... unless I decide to put my 1995 XTR mid cage on there and upgrade my bike to something more modern


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## mhkang (Nov 1, 2008)

Tried ordering the sun envy lites through my LBS on the isle. Not available. Finally got a response from the ebay vendor, ACE 20s are in short supply, may need to wait til July. 
Sheesh. Guess we'll just keep riding til then.


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## Roaming50 (Apr 30, 2009)

I ended up ordering the Tourney; I should get it Saturday. 

I noticed tonight that my test of going tubeless failed. The rear tire that I was testing this on deflated and the tire popped its bead lock. I'll try again when I get the Sirens but I'll probably just stick with tubes. 

I fitted the BB tonight. For what it's worth the 68x113 fits just fine with the original cranks. The 68 shell width is actually a couple of mm too large without the chain retention device but that allows some wiggle room in chain line. I was aiming for a 41mm chain line and I ended up with about 38-39mm. Close enough for me. A 68x118 may be better still but if you think you may change out cranks later then 68x118 is probably your best bet. Btw the UN-73 was only $16 and weights 264g. Bargain!


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## Roaming50 (Apr 30, 2009)

I got the Tourney mech and that thing weighs a ton. Also I don't like the look of it on the bike so it's going back. 

I ripped the Altus from the Marin and stuck that on and it is perfect. I should have just done that in the beginning. I may put an SLX back on the Marin. 

Also got the IRC Siren SX tires. Weight came in at 535g for the 20x2.125. Higher than I was hoping for. For now I will run them with tubes to get the bead used to the wheel. Later I'll try tubeless but the sidewall feels thin so I'm not sure how that'll work. 

I have all the bits to complete the build now so I'll do that later today.


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## Roaming50 (Apr 30, 2009)

Damn I hit a new snag with my build. I was reassembling the brake levers when I noticed that the right is different than the left. The right is designed to fit around the twist shifter. 








Trouble is that I have the Shimano trigger that is thumb forward, index back. This brake does not work with this Shimano trigger. I can see it working with the X3 trigger but the cheapest short cage X mech is the X7 at $54.

So I guess I'm looking for new brake levers. Any recommendation to levers that fit a 6 year old?


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## IAmHolland (Jul 8, 2010)

put the brake inboard.


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## mountaingoatepics (Jan 30, 2004)

kerryn said:


> Damn I hit a new snag with my build. I was reassembling the brake levers when I noticed that the right is different than the left. The right is designed to fit around the twist shifter.
> View attachment 699612
> 
> 
> ...


I know ur worried about the long cage on the bike but the 09 Scott Scale 20 I bought my daughter had a long cage on it originally and now has the X3 long cage rear derailleur and its working ok.

Also some links to Sram Medium cage rear derailleurs

New SRAM X4 7/8-speed MTB Rear Derailleur medium cage | eBay

SRAM X.5 X5 8/9 SPEED REAR DERAILLEUR MEDIUM CAGE NEW | eBay


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## Roaming50 (Apr 30, 2009)

IAmHolland said:


> put the brake inboard.


That won't work because there is a gear display on the shifter.


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## stom_m3 (Jun 28, 2011)

kerryn said:


> Damn I hit a new snag with my build. I was reassembling the brake levers when I noticed that the right is different than the left. The right is designed to fit around the twist shifter.
> View attachment 699612
> 
> 
> ...


Kerryn - couple things, bummer about the tire weight. I don't know why the 2.25's are that much heavier than the 1.75's.

As for the brakes, Avid has 5's for $11 and 7's for $20 @ Jenson's. You will need to turn the screw reach adjusters in all the way. That's probably going to be your cheapest quality solution outside of buying used.


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## IAmHolland (Jul 8, 2010)

kerryn said:


> That won't work because there is a gear display on the shifter.


Hmm, I guess that's why I use SRAM Attack or X.5 for the roller indicator.

Any brake levers would work for a kid, just adjust it. I'm not sure what's local to you, but assuming you want it this weekend, performance bike is having a sale now and you can pick up some levers there.

I tend to use Tektro brakes, because they are cheaper and they take a beating from mishandling and crashes. When they get older they can get Avid SD7.

I also use short brakes, Tektro BMX brakes, 930AL. Shorter arms for less pull, allowing closer adjustment of the lever to the handlebar.


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## Roaming50 (Apr 30, 2009)

I got my son's bike finally built last night - I'll take photos over the weekend. The weight the bike came in at was 24lbs 7oz. Not exactly lightweight but better than what it was and the shifting and gear range is much improved.

One thing I can't figure out is that I am off by some 430g between the final bike weight and the individual components. That is not just brake cables. What am I missing?

Finally weights are:


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## Roaming50 (Apr 30, 2009)

Ah, I got it!

I forgot the chain weight. I guess that is about 300g with the rest being the brake cables and index cable housing.

I'm still toying with the idea of putting SRAM X3 with a X7 short cage on the back but I will probably just leave it how it is now.

I may change out the pedals for something smaller and lighter as the Avenir ATB are pretty large for my son's small feet. I'm still on the lookout for a better saddle as well.

This bike will never be "light weight" with its steel frame and fork but I was riding it last night while testing it and it felt good so I am, for the most part pleased with the changes. The biggest disappointment was the weight of the tires and that one of the tires is not "round". Having already spent the money I am not going to change out the tires but if I were to do this again I would get the Kenda Small Block 8s.


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## cmg (Mar 13, 2012)

kerryn said:


> One thing I can't figure out is that I am off by some 430g between the final bike weight and the individual components.


air in the tyres


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## Roaming50 (Apr 30, 2009)

Here are some pictures of the updated bike focusing on the changes.


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## Roaming50 (Apr 30, 2009)

For those interested in chain line and converting a 6-speed to 7-speed this is with the original cranks on a Shimano 68x113 bottom bracket. I think a 118mm would be perfect but as my kids stay mostly on the lowest gears this actually works out quite well.

The rear axle is "shimmed" using a spring washer which takes the width from 130mm to 132.5 which is actually what the chain stay spacing appears to be.


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## alex_sdca (Apr 6, 2009)

Great thread and nice finished bike!
I'm sure people following the same path in the future will appreciate this info you have shared. 

Good work.


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## stom_m3 (Jun 28, 2011)

Kerryn - Did you try going tubeless on your Siren's yet? I may try the SB8's.


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## Roaming50 (Apr 30, 2009)

No not yet. I got busy with other things.

I will have to look at them soon as the rear tire is rubbing on the crosswire at the top of the V-brakes as it rotate - it's oval in shape not round. Perhaps it is a fitting issue but until I look at it I can't be sure.


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## pascale27 (Aug 26, 2011)

if the chain is coming off the chainring, this is a chaep good fix. I have one on my 1x10 works great. And is about $10.

N-Gear: What Is A Jump Stop?


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## chuckactor (Apr 11, 2013)

Thanks for the inspiration. I found the same bike at a local thrift shop and copied most of your upgrades.

I used the Altus shifter and derailleur with the 14-34 Tourney freewheel. Added a KMC X8 chain and the Avid levers. I added a set of Maxxis Holy Roller tires (1.95 front, 1.75 rear, a Bontrager bar, new seat, some ODI grips from the BMX parts box and a set of Time Atac pedals.

My 7 y/o loves it.


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## Vxc961 (Apr 20, 2013)

chuckactor said:


> Thanks for the inspiration. I found the same bike at a local thrift shop and copied most of your upgrades.


 Chuckactor-do you mind sharing the initial cost and that of the upgrades! I've had more fun tinkering with my 6yo's Hidden Canyon, and my 5yo Hotrock than I ever thought I could, but I don't want to break the bank!


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## chuckactor (Apr 11, 2013)

I paid $20 for the bike at a thrift store. It needed a little tune up to get going. The usual brake adjustments and repacking the wheel bearings. The upgrades were all pretty cheap.

Seatpost (? nice micro adjust) - $5 swap meet
Handlebar (Bontrager Race) - $5 swap meet
Time Atac Pedals - $10 BMX meet
ODI Ruffian lock-on Grips - $0 parts box

All below from Niagra Cycle 

Altus RD-M310 Derailleur - $16.61
Altus SL-M310 Shifters - $12.95
Tourney MF-TZ31 14-34 Freewheel - $9.87
KMC X8.93 Chain - $9.80
Avid FR-5 Levers - $19.00
Velo Scion S1 Seat - $14.88
Maxxis HR 20x1.75 tire - $16.52

Looks like I have about $120 bucks in it. My son wants a suspension fork. Which is a bummer since I sold a Trek MT60 because it had a suspension fork on it. I didn't want to hassle with him dragging around the weight of a fork that didn't work. I did find a Manitou 4 fork at the local bike Co-op. I'm going to see if I can get it for 10 or 20 bucks and shorten it to work on the 20".

Chuck


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## Xtatic77 (Sep 23, 2015)

This is a great thread. Just got my son an mt60. Looks like I've got some more reading and a parts list to get it good to go.


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## Xtatic77 (Sep 23, 2015)

So, Followed this thread and a couple others with info for my 6yo's Trek MT60.

Here is my amazon buy list..Just posting here since this thread has been revived from the dead, and if anyone will post.


-Shimano UN55 BB Square Taper Bottom Bracket (68x118mm)
-I did the 118mm because someone mention chainline issue with the 113mm.
-KMC X8.93 Bicycle Chain 7.3mm 6, 7, 8 Speed
-Avid FR-5 Bicycle Brake Lever Set (Silver)
-Shimano MF-TZ31 Tourney Freewheel (14-34T Mega 7 Speed)
-Shimano Acera SL-M310 Rapid Fire Shifter, Right (Black, 7-Speed)

Sound about right to you guys?


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## jochribs (Nov 12, 2009)

Xtatic, what's your plan? What are you going for, in terms of an end result? Are you wanting to customize it, or are you replacing those parts because the bike's in bad shape and you want to get it running?


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## Xtatic77 (Sep 23, 2015)

Bad shape getting it running.


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## jochribs (Nov 12, 2009)

Sounds good. If those parts are in bad shape then make sure you get yourself new brake cables, brake housing, housing ferrules and cable crimps. I don't think levers are going to come with it. You should be getting derailleur cable and housing with your shifter, but check to be sure. If it does come with it, it will most certainly be 4mm housing. If it doesn't, just get yourself some 5mm derailleur housing as well. (Brake and derailleur are different housings.) Need brake pads too?? Depending on state of wear on current ones, you can file them to freshen them up, but I'd just get a new set if it were me. How are the tires?

Anyway, post a few pics if you can. It'll be easier for us to tell you what you may/may not need if we can see what things look like.


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## Xtatic77 (Sep 23, 2015)

Well, I did order all that I listed above. Here are some pics of how it looks as it sits now.


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## Xtatic77 (Sep 23, 2015)

Forks look gross. Im sure the hubs are gross just like everything else. It needs a good cleaning and lube job inside and out. Wheels looks straight. Tires aren't cracked but middles are pretty flat of tread. Brakes look good and operate good but will still upgrade the pads on them. The boy rode it for a little bit and he loves it compared to his bmx hot wheels bike, lol. Hes like, Dad I can go shred on trails with you now..just about fell over. lol.


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