snapped ultra torque crank bolt... [Archive]

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cash05458

10-30-2019, 12:09 PM

dddd

10-30-2019, 12:27 PM

I've known mechanics to install similar hollow, large-diameter bolts from Shimano Octalink cranksets in the UltraTorque cranksets.

I have an UltraTorque Chorus crankset sans bolt and am considering doing this myself, but I can't vouch for the adequacy of using any of Shimano's bolts.

rain dogs

10-30-2019, 12:28 PM

I don't think that's very common. It's a hirth joint, so the splines are load bearing, the is basically no movement in the joint when installed (no slack) and very little sheer..... your bolt likely was loose and installed under-torqued ... or waaay over/torqued and damaged, but I doubt that.

I don't know of there being an aftermarket bolt.... it's hardly that expensive for a campy part... just buy the legit one and torque it to the recommended setting.

slambers3

10-30-2019, 12:38 PM

Just out on a ride and snapped the crank bolt....campag UT chorus etc...any of you folks ever have that happen and is it a common one? And this wasn't even when I was doing one of my human dynamo write home to Mom about it 400 watt sprints either...:)

After a good long walk home then checked out buying a new one and they seem to go for like 25 bucks if you can find them...that something that is going to be campy specific? (Not sure why I ask as I think I already know that answer...)...any suggestions on a cheaper route would be appreciated...

I wouldn’t use anything less than the proper campagnolo bolt. Why risk it to save a few bucks? Also, acquire an adequate torque wrench if you don’t already have one. This is too critical of a part to mess around with “alternatives”

Nomadmax

10-30-2019, 12:47 PM

I'd pay 25 bucks for the specific bolt. I don't know what testicle and tooth repairs go for these days but it's GOT to be more than 25 bucks. Moreover, my BB cups and UT bolts are installed using a calibrated torque ratchet.

cash05458

10-30-2019, 12:54 PM

yeah, prolly correct and right on the proper bolt...and 25 isn't going to kill me...just asking...and yeah, I torqued it to proper load etc...just went bang...stuff breaks after all. Could have gotten loose I suppose tho...hadn't checked it in a few months I would guess...

dddd

10-30-2019, 05:10 PM

This bolt is somewhat like a brake caliper bolt, or at least the portion of the bolt that passes through the fork crown and simply pre-loads the caliper mounting face against the mounting surface sufficiently to prevent any movement in use.

As such, there should be no cyclic force input reaching the bolt, thus making a bolt fracture during use highly unusual.

It is only during tightening, when the combined tension- and torque-imposed shear forces reach a maximum, that such fasteners would be most likely to fail.

I have to wonder if Campagnolo's technical representative might be interested in seeing such a bolt after an on-the-road failure, and might be willing to trade you a new one for the failed sample.

Red Tornado

10-30-2019, 05:31 PM

If it was me, I'd spring for the correct Campy bolt.

A little OT, but several weeks ago had both the hidden chain ring bolt on a Veloce Power Torque crank - and - another chain ring bolt come out on the same ride. Chain jumped due to the inner ring getting bent, due to the fact only 3 bolts were holding it on. Never heard the bolts come out but it was windy. Got back home and a 3rd one was coming loose.
Needless to say the replacements went in with some semi permanent Loctite on the threads.

oldpotatoe

10-31-2019, 05:40 AM

Just out on a ride and snapped the crank bolt....campag UT chorus etc...any of you folks ever have that happen and is it a common one? And this wasn't even when I was doing one of my human dynamo write home to Mom about it 400 watt sprints either...:)

After a good long walk home then checked out buying a new one and they seem to go for like 25 bucks if you can find them...that something that is going to be campy specific? (Not sure why I ask as I think I already know that answer...)...any suggestions on a cheaper route would be appreciated...

Wow, installed a bunch of these and have never heard of that happening..Specific to the 'system' and not hard to find. Make sure ya grease the threads and hirth fitting 'teeth'...

Billybob62

10-31-2019, 07:00 AM

Just out on a ride and snapped the crank bolt....campag UT chorus etc...any of you folks ever have that happen and is it a common one? And this wasn't even when I was doing one of my human dynamo write home to Mom about it 400 watt sprints either...:)

After a good long walk home then checked out buying a new one and they seem to go for like 25 bucks if you can find them...that something that is going to be campy specific? (Not sure why I ask as I think I already know that answer...)...any suggestions on a cheaper route would be appreciated...

I broke mine shortly (<1,000 miles) after initial installation but I think it was because I hadn't installed it properly. The torque spec on that is 42 nm

cash05458

10-31-2019, 07:59 AM

"hirth fitting 'teeth"

Pete, not sure what you mean here...might you explain? Does that mean the teeth between the drive and non drive side, in the middle maybe where they join?

ah, looked it up...yes, I see what you mean...so that is called a "hirth" joint...did not know that...good to know...

old fat man

10-31-2019, 08:14 AM

I might have a spare at home from a campy crankset whose pedal inserts stripped. I'll look tomorrow.

cash05458

10-31-2019, 08:19 AM

I might have a spare at home from a campy crankset whose pedal inserts stripped. I'll look tomorrow.

Hey, that is kind of you...I ordered one this morning...15 bucks from flea bay so not bad really...maybe someone else here might need it? Tho it does sound fairly uncommon...

Mark McM

10-31-2019, 09:01 AM

This bolt is somewhat like a brake caliper bolt, or at least the portion of the bolt that passes through the fork crown and simply pre-loads the caliper mounting face against the mounting surface sufficiently to prevent any movement in use.

As such, there should be no cyclic force input reaching the bolt, thus making a bolt fracture during use highly unusual.

I'm not sure that's true. The bolt diameter is a significant fraction of the shaft diameter, so it will experience a meaningful portion of the bending stresses on the shaft. Also, due to the ramp angle between the teeth, the bolt will also experience tension increases when the shafts are torque. So there will be some cyclic stress on the bolt during use (and that cyclic stress will be added onto the static stresses from the pre-load).

YesNdeed

10-31-2019, 11:57 AM

I've never heard of that happening, but I wouldn't replace it with any other bolt than a Campagnolo replacement bolt.

dddd

11-01-2019, 08:54 AM

I'm not sure that's true. The bolt diameter is a significant fraction of the shaft diameter, so it will experience a meaningful portion of the bending stresses on the shaft. Also, due to the ramp angle between the teeth, the bolt will also experience tension increases when the shafts are torque. So there will be some cyclic stress on the bolt during use (and that cyclic stress will be added onto the static stresses from the pre-load).

It seems you must be right, since the bolt did fail in use after all.

Difficult to quantify I would say, since there is not enough "extra" metal in the assembly to fully isolate any part of the joint from the flexing.
I was assuming zero movement of the Hirth joint, but that was a simplistic assumption since the cyclic stresses do actually flow through so as to induce a bit of torsional stress, as well as at least some tiny bit of bending stress, in the center, where the bolt resides.

At least we know that Campagnolo apparently didn't grossly over-design the bolt, which is subject to it's own sample-to-sample variations(?).
Maybe a Shimano bolt is an improvement, I can't say. Some of the Shimano Octalink bolts are noticeably heavier than others FWIW.