dm-tm

My Trek 7300 is about 2 months old, and has around 130-140 miles on it.

Tonight coming home from work I noticed a noise in the cranks, and I stopped as soon as I could (in a well-lit area), and I noticed the non-drive side crank arm bolt was very loose, I could move it with my finger, so I walked the bike the rest of the way.

Once I got home, I removed the nut, took the crank arm off, but I didn't see any damage, and the square taper looked still square, on both the crank arm, and the BB. These are Bontrager Select cranks, and some Bontrager(?) BB.

Since I stopped riding right away, and the square-ness of the crank arms and the BB seem still square, everything should be alright...right? When I put the crank arm back on, I made sure to really tighten down the allen bolt.

Bill Kapaun

You might ride it a short distance and retighten. I'd keep my wrench in my back pocket and check frequently for awhile.

tellyho

I'd put it back together and see what happens. Use a LOT of torque. Either way, your worst-case is a new crankset (and possibly BB).

slim_77

I had a similar problem. If you bought the bike new, the shop should do a free "tune up" after a few months. They will torque things down properly.

I, unfortunatly, didn't do that (god knows why!?!?!?!) and I now need new cranks!

glad there is no damage to the square taper...

HillRider

You certainly did the right thing by not continuing to ride when you noticed the problem. I agree, torque the arm on properly (~30 foot-pounds which is a LOT) and hope it wasn't damaged. As noted, a regular length Allen wrench won't get the bolt anywhere near tight enough. You need a long cheater or an Allen bit for a ratchet.

dm-tm

Thanks everyone, I do have a torque wrench, and i'll see if I can find an 8mm socket-hex adapter.

HillRider

You can make an 8 mm Allen bit from a regular L-wrench and a Dremel with a cut-off wheel. Cut off about 1" of the L-wrench, dipping the work in water frequently to keep it cool. BTW, you cannot cut decent Allen wrenches with a hacksaw unless you have a carbide blade.

Put the cut-off length into an 8 mm socket and you're good to go. If you want to make it more permanant, epoxy or super-glue it into the socket. This is a lot cheaper than a good quality pre-made bit.

rebuilt13

I work in a trek shop and we have a lot of issues with left crank arms coming off. most of them have been the suntour's on the 3700's but we have replaced 2 bontrager selects due to damage from them rounding out. i would talk to the shop you bought it from because it is an ongoing problem. torque it down and if it comes loose again talk to your shop to get a new one.

dm-tm

Oh wow, i'll have to keep an eye out for that, thanks for the warning.

Edit: nevermind, they're not select, they're Bontrager Sport cranks, sorry.

jbrians

+1