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Looking for help for a crankset and possibly bottom bracket for 1990 trek 4500

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Looking for help for a crankset and possibly bottom bracket for 1990 trek 4500

Old 04-27-23, 05:37 PM
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Looking for help for a crankset and possibly bottom bracket for 1990 trek 4500

Hi All,

New member looking for help. I have 5 kids and so I upgrade old bikes to save $$. I picked up a cheap 1990 Trek 4500. It had a stripped out drive side pedal. It has a Shimano BB-CT92 bottom bracket (square), An Atlus front derailleur that mounts on a bracket behind the bottom bracket and a Shimano 24/34/42 Dual SIS crank set. The previous owner ground up the rear side of the cranks where the pedals were, so I couldn't find a number but looking online it seems to be a C90 Atlus set.

I was hoping to just replace the crank set with a shimano atlus same tooth count set but found it was spaced too close and interfered with the derailleur mount. When I search for the C90 crank set and bottom bearing they are no longer available. I thought the crank set replacement would be the quickest and easiest, but not so sure now. Any advice on selecting an inexpensive crankset and bottom bearing that would work or is it just easiest/cheaper to helicoil the cranks?

Hopefully this is descriptive enough, if not let me know and I can add details if needed.

Thanks in advance for any help!!
Mike
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Old 04-27-23, 07:53 PM
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Originally Posted by kabonk
I have 5 kids and so I upgrade old bikes to save $$.
I'll be honest, the questions you are asking gives me an idea of your skillset and the time you'll be spending on bikes will equate to about 50-cents an hour.

This may be compared to digging out a swimming pool with hand shovels. It'll be faster collecting pay at a Starbucks, and then use that money to pay the contractor.

I'm always finding newish big box store bikes between free to $100, depending on who the seller is, and what their situation is. Unless your 5 kids are training for the olympics and need to watch their power watts, such bikes are fine.
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Old 04-27-23, 08:32 PM
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Helicoil repair of the current crank arm is likely similar or less in cost than complete crank replacement, and ensures that no chainline/bottom bracket issues will appear.
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Old 04-27-23, 08:43 PM
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You need to check the specs on the crankset and find out what length BB is required for it. Different generations of cranks, even of the same model, may require different spindle lengths. You're compounding it with the fact that you're looking for an e-type BB, these have a slightly wider shell to compensate for the space the der uses. You might be able to get away with a 68/73 compatible BB and careful use of spacers but it will require you to have a small range of spares since you'll be using it as an e-type.
Alternative is just buy whatever BB and front der is specced for the crank you have.

Edit, the 4500 is probably a 3x8? It isn't from 1990, that wasn't a model available in 1990. If a 3x8 you might want to simplify and go with a whole group to have everything running smoothly. They sell 130.00 with buy it now on ebay or you can bid on sets like this one
link

Last edited by Russ Roth; 04-27-23 at 08:56 PM.
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Old 04-27-23, 09:16 PM
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Originally Posted by JohnDThompson
Helicoil repair of the current crank arm is likely similar or less in cost than complete crank replacement, and ensures that no chainline/bottom bracket issues will appear.
i guess you missed the part about the crank being ground on by the previous owner.....
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Old 04-27-23, 09:37 PM
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Stock 4500 , 2010 model, ran this crankset.

https://www.ebay.com/itm/11488697147...4aa15e2c5f0eb3

this is the front derailleur that a 4500, 2010 model, runs.. https://www.amazon.com/SHIMANO-FD-M3...92623687&psc=1

and i have NEVER seen a BB mounted derailleur on a 4000 series Trek.. and i've worked on quite a few... all have been seat tube, clamp mount type ders.... someone played mix and match on that bike, i suspect.... BB plate mount Derailleurs are used on Suspension bikes to get around issues created by the rear suspension pivot location and/or no seat tube to mount to.

the 4000 series has been the same basic frame for it's entire life... they added disc brake mounts and the shape changed as the rider fit size changes, but they have remained basically the same bikes for a couple decades.
Try looking "trek 4500" up on the web and match the paintjob in the "images ", find a similar pic with a Year attached... then search add the word "Trek 4500 (place year here) specifications".

Last edited by maddog34; 04-27-23 at 09:48 PM.
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Old 04-28-23, 06:30 AM
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Originally Posted by Russ Roth
Edit, the 4500 is probably a 3x8? It isn't from 1990, that wasn't a model available in 1990. If a 3x8 you might want to simplify and go with a whole group to have everything running smoothly. They sell 130.00 with buy it now on ebay or you can bid on sets like this one
It is a 3x8 setup now. I mistyped the title, the frame is a 2000

Last edited by kabonk; 04-28-23 at 07:03 AM.
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