ret3

Likely due in parts to abuse from going over bumps wrong at high speed, my large mass, extra belt tension to prevent slippage, and neglect from an inexperienced cyclist, the right crank arm on my GT Aerostream is holding on by two of its four bolts. The other two bolts are still present, but the metal on the crank arm's mounting holes has broken away from them. Clearly, it needs replacing.

I'm pretty sure I can manage to remove the current crank arms and put on new ones if I knew what to look for in a replacement arm or set. For example, how do crank arm sizes work? Are there standard bolt-hole patterns? How about inboard-outboard clearance?

CACycling

A little better explaination of exactly what is broken would be helpful and pics would be even better. You have a belt-driven bike. The spider is part of the right crank arm. The belt ring bolts to the spider and the crank arm is attached to the bottom bracket spindle. If the broken metal is on the belt ring, you don't need a new crank arm. If the crank arm itself is damaged, you can either try to figure out that brand and model of the crankset (should be stamped or molded into it somewhere) to get a replacement or just replace the whole thing (which may entail a new BB if the spacing is different.

As for crank arms, there are different crank lengths (usually 165mm to 175mm in 2.5mm or 5mm increments), different bolt circle diameters as well as different number of bolts and they often sit in different locations relative to the BB so that needs to be taken into acount as well. Not sure how widely available belt drive parts are. You may be better off going to an LBS that sells GT to get parts.

jezmellors

Is this it?



I think the way to do it is to find out exactly what the fitted one is and just replace like for like. It should have the model number on it if it's Shimano.

ret3

Ah! I don't have a pic handy, but using the right terminology may help: two of the bolt holes in the spider are broken. The belt ring and the bolts themselves seem fine. I have the shop trying to contact GT presently, but it's been a few days and I was wondering if a compatible, non-OEM replacement part might be easier to find.

ret3

The very same, except I have the step-over style with much less pink. The metal forming the outside edge of the two upper (as pictured here) bolt holes on the spider has cracked. On one, an entire corner is gone; on the other, the corner is hanging on by a thread of metal.

fietsbob

GT doesn't make the cranks , they just have something they bought in bulk fitted, ..
sounds like you broke the right side , buy a whole crankset.

your LBS should help you find something suitable..