curttard

FC-RS500 crankset. I was riding along and the left crank just fell off. I have no clue how that happened; the pinch bolts are still there. I've got about 5000 miles on the bike. I couldn't find the fixing bolt. I haen't checked yet to see if the stop plate is still there.

So I think what I need are the fixing bolt, the stop plate, and the "ring" (part #5 here: here). Do I really need the special Shimano tool(s) for the fixing bolt? TL-FC16 and TL-FC18?

Can the splines be worn down and is there a way to check?

sch

Splines can be damaged, but the spindle is steel and the crank aluminum so crank more likely to be damaged.
Sounds sort of like the crank was not far enough in, and the pinch bolts failed to fully grip or were not tightened
to specified torque.

TL FC16 OR TL FC18 (which is just the shop variant of FC16), not both, are helpful. You might find Park BBT9 more
useful as it has the equivalent of the FC16 on one end and the BB cup tool on the other. FWIW the 'fixing bolt"
is plastic.
Basically the plastic fixing bolt just moves the crank in on the splines to the proper engagement depth and then the
pinch bolts and clip actually grip the spindle. The fixing bolt is simply an in/out adjustment method and fills the hole
in the end of the crank otherwise.

https://www.parktool.com/product/bot...ttom%20Bracket

curttard

Thanks. Is there any way to do the fixing bolt without the Shimano tools, and do I need both those tools for it?

Pridedog

Same thing happened to me last week. Had only 1500 miles on new bike. I found fixing bolt cap as it had broken off. Rest of bolt still in axle. This was a new Shimano 105 crankset on a new Orbea bike. My assessment is that the pinch bolts were never tightened properly, either by the factory in Spain or place I purchased it from. The arm worked loose and fixing bolt only thing holding it on. Finally the bolt cap broke and off came the arm along with some of my leg. While waiting for warranty being sorted out, I checked on Ebay and you can find replacement fixing bolts, although not OEM. In over 220,000 miles of riding, never had a crank come off. This is also only the 2nd bike that I didn't build up myself. The other one I lost 4 of 5 chainring bolts in first 100 miles. I guess any new bike you need to double check all bolts.

SethAZ 

I've heard of people using a pair of scissors or something for this. I just use the little plastic wheel on the back of the Park Tools tool that's made for this. It's not very expensive, and works well. That fixing bolt is only tightened finger tight anyway, so any method that allows you to turn it without mucking it up should work.

curttard

Thanks for the in-depth answer! I'll probably pick up the Park Tool.

veganbikes

It sounds like what you might really need is a torque wrench and to double check the torque on your cranks. The fixing bolt tool can be had fairly cheap or with other tools but is important. If you had a crank arm fall off completely while riding making sure everything is put back together correctly is pretty important.

curttard

I've got a torque wrench and will certainly check that before hopping on! I was lucky in that I was just crusing along a slight uphill and not hammering or flying downhill, so no crash.