smurf hunter

I've got a Shimano 105 FC-5603 triple crankset (https://techdocs.shimano.com/media/te...9830646645.pdf)

I bought it "new" (allegedly) on eBay for a steal. It shifts wonderfully, is stiffer than my stock Bontrager crank - but every 500 or so the opposing pinch bolts loosen up a bit resulting in a "click" during rotation.

I've taken this apart and even replaced the M6x19 pinch bolts. I don't have a small precision torque wrench to measure the exact torque, but tightened with alternating 1/4 turns until it was firm using a hex key. I've also adjusted the outside fixing bolt. I've made this "better", but after some time I've got to re-tighten.

I was passing through a high-end bike shop during my lunch and asked the mechanic his opinion. He said this never happens and I must have stripped the female thread(s) in the left crank arm. He said for a price they could use a thread gauge to determine this. I've seen posts and videos on MTB sites explaining this is somewhat common issue on XT and XTR cranks.

Here are the questions:

1) If I can assemble this and have it work wonderfully for a few hundred hard mile (I weigh 200lbs and live in a hilly area) - how likely is it that threads are stripped?
2) Is there really a reliable way to mechanically measure if the full run of the inside threads are in good shape?
3) Any way I can determine this myself without spending 1/2 the cost of the crank at a fancy LBS?

Honestly it's not a huge ordeal to tighten this all up once a month or so, but I want to know I'm not doing something totally wrong.

Thanks

pointatopointb

cheapest way I can think of is to drop into your hardware store/machine supply store, pick up a tap of the same diameter and pitch. turn the tap in slowly, and if it binds or is loose, there might be problem. If there is, get the next size up screw, tap and drill to go with it, re-drill and tap your holes. way cheaper than paying someone else to do it.

or, since my mind is now wandering, try some loctite or t-tape to fill the holes.

DaveSSS 

If the bolts screw in without much resistance and can be tightened to a reasonable torque, the threads are not stripped. Stripped threads would have had a good amount of aluminum stuck to the bolts at some point and the bolt would no longer tighten.

If you're unsure of your torque, invest in a cheap beam type torque wrench. Use blue loctite (242) on the pinch bolts.

If the cranks have been ridden for very long when loose, the fit between the splines can become loose. Try the same loctite product recommended by FSA for their lousy splines - loctite 641.

smurf hunter

Thanks for the tips - I have some things to try out now.