Is my crankset borked?

barongreenback

Was doing some maintenance on my bike yesterday and successfully installed some new bearings in my bottom bracket. Decided to tighten the chainring bolts with a torque wrench but unfortunately the bolt sheared. Worse still, a replacement bolt won’t hold - it seems like the internal thread on the crankset itself has stripped at the same time. Christ knows how that happened unless my torque wrench is also screwed.

Anyway, with stripped threads is the crankset salvageable or do I need to bite the bullet and replace? At worst it will be an excuse to upgrade from Ultegra 6800 to 8000 step by step but an irritation nonetheless.

Incidentally for any Trek owners, the state of the non driveside bearing was shocking for a bike that’s only done 2,500 miles in mostly dry conditions.

jgsi

Can you not just re tap the thread?
Screwfix do some cheapish tap and die sets

sloppyschleckonds

I'd probably just run it with one chainring bolt loose

Whats the worst that could happen....?

Matthewfalle

why spend loads and buy an ultegra chainset?

mf says that he would bodge this one then look for something really cool and decent in the sales.

barongreenback

Thanks all. Will try and bodge enough to upgrade the winter bike.

cycleclinic

with one bolt loose you only have three. if you are using alloy bolts they could shear.

The state of the NDS bearing has nothing to do with the bike. Shimano BB's are like that. Shit. I dont bother fitting them any more.

barongreenback

The flimsy bearing cover may have something to do with it too. Lots of muck getting in there. I replaced with enduro bearings and the matching covers. Not a hugely expensive repair but I think this will now be part of a proper annual strip down to keep things running smoothly.

BikerGroveish

It’ll be fine with three bolts. It might creak a bit, but it shouldn’t be a massive problem.

svetty

If the bolt sheared is there a piece of bolt stuck in the threads of the crankset. If so trying to insert a new bolt would result in it bottoming out - and then trying to further tighten it would strip the threads....

Probably worth ensuring nothing stuck in there and then re-tapping as suggested above. Once re-tapped gently insert a new bolt with thread-locking compound and just gently tighten.

timothyw

I'm confused.

Isn't the 6800 chainset the same as every other one in that you can replace the chainring nuts and bolts? Isn't that why products like these exist:
https://www.sigmasports.com/item/Absolu ... olts/G9C4#

Worst case I can imagine is that the nuts are part of the big chainring and you'll need to replace that.

Either way I'm sure the crankset isn't borked.

slowbike

Which bolt did you sheer?

Reading this it seems like people are assuming it was the chainring bolts that hold the chainrings onto the crank spider - but you wouldn't remove those to replace the bottom bracket - and they're nut/bolt combination anyway - sounds to me more like you've stripped the thread in the non-drive side crank arm - the bit the pedal attaches to ... there are 2 bolts (should be tightened to around 20nm I think) - I wouldn't ride with that not tightened because you could end up with the arm slipping around the spindle and that's your ride pretty much done (been there, done that, fortunately not too far from home)

timothyw

Ah, slowbike that would make more sense.

In which case, good excuse to buy a stages/4iiii precision power meter as they come on a non-driveside crank arm.

Or find someone else who has and buy their surplus crank arm.

barongreenback

Slowbike wrote:

Which bolt did you sheer?

Reading this it seems like people are assuming it was the chainring bolts that hold the chainrings onto the crank spider - but you wouldn't remove those to replace the bottom bracket - and they're nut/bolt combination anyway - sounds to me more like you've stripped the thread in the non-drive side crank arm - the bit the pedal attaches to ... there are 2 bolts (should be tightened to around 20nm I think) - I wouldn't ride with that not tightened because you could end up with the arm slipping around the spindle and that's your ride pretty much done (been there, done that, fortunately not too far from home)

No, I was tightening up the drive side crank as just a bit of good maintenance while I had the crankset off the bike. That will teach me for doing things properly.

barongreenback

TimothyW wrote:

I'm confused.

Isn't the 6800 chainset the same as every other one in that you can replace the chainring nuts and bolts? Isn't that why products like these exist:
https://www.sigmasports.com/item/Absolu ... olts/G9C4#

Worst case I can imagine is that the nuts are part of the big chainring and you'll need to replace that.

Either way I'm sure the crankset isn't borked.

That looks perfect! And aerodynamic benefits that will improve my speed over a 100 mile ride by at least 0.00007 seconds!

Thanks for finding that, I didn't know these were easily replaceable parts. I also found some on the Wiggle website (annoyingly, did not appear when I searched for chainring bolts) but the ones you've suggested seem to be less liable to shear.

barongreenback

barongreenback wrote:

TimothyW wrote:

I'm confused.

Isn't the 6800 chainset the same as every other one in that you can replace the chainring nuts and bolts? Isn't that why products like these exist:
https://www.sigmasports.com/item/Absolu ... olts/G9C4#

Worst case I can imagine is that the nuts are part of the big chainring and you'll need to replace that.

Either way I'm sure the crankset isn't borked.

That looks perfect! And aerodynamic benefits that will improve my speed over a 100 mile ride by at least 0.00007 seconds!

Thanks for finding that, I didn't know these were easily replaceable parts. I also found some on the Wiggle website (annoyingly, did not appear when I searched for chainring bolts) but the ones you've suggested seem to be less liable to shear.

Actually scratch that. They are for 3rd party chainrings. Choice would be whether to try a helicoil or just buy a new chainring. I think the latter may be the simpler solution.

Apologies for confusion - I wasn't sure how the 6800 was put together in terms of its construction. So at least the cost of a new chainring, whilst painful, isn't too bad.