Hollowtech II pinch bolts self loosen

[tctyres]

I've got a CX70 crankset on a bike which is a standard Shimano Hollowtech II.
The crankset has close to 12000 miles on it. I might have replaced the bottom bracket once a while back, but it doesn't have play now.

My problem is that the pinch bolts on the NDS loosen. Then, the NDS crankarm eases off. I've had this happen twice in the past 2 months.

The Shimano crankarm fixing bolt (part 1 in the diagram) really doesn't do anything, and the safety plate (part 4) is toast.

Has anybody experienced this, and if so, what did you do? I feel like the solution might be a type of locktite on the pinch bolts (part 3).

I will replace the chain and cassette, as they are due for service, but I can't imagine that those are the real problem here.

[Wattvagen]

Those pinch bolts come from the factory with a locking compound. Probably worn off on yours. Blue locktite is your friend here.

[tctyres]

Originally Posted by Wattvagen

Those pinch bolts come from the factory with a locking compound. Probably worn off on yours. Blue locktite is your friend here.

Right... as suspected. I'll clean everything off and try Loctite Blue. If that doesn't work... then it's something else.

I've never had this happen.

[slambers3]

First question- although you seem detail oriented but didn’t specifically mention it, are you torquing the bolts to spec? Usually those are 12-14nm if memory serves. Helps to tighten both progressively, alternating until they’re at spec.
I don’t think adding a little bit of loctite to the bolts would hurt, but it sounds like something else is going on.

[tctyres]

Originally Posted by slambers3

First question- although you seem detail oriented but didn’t specifically mention it, are you torquing the bolts to spec? Usually those are 12-14nm if memory serves. Helps to tighten both progressively, alternating until they’re at spec.
I don’t think adding a little bit of loctite to the bolts would hurt, but it sounds like something else is going on.

I didn't use my torque wrench. They are very tight. I can take another look at this.

I don't recall ever having used a torque wrench, however. I have 3 bikes with Hollowtech II cranksets, and I've had zero issues over the past 5 years. This is the first time this has come up. It's odd.

I agree that it sounds like something else is going on.

[spoonrobot]

With 12,000 miles on the clock I'd be suspect of a crack somewhere in the interface. Do you know if the crankset is painted or anodized? Some years are not in the specifications from Shimano so it could be either/or.

Cracks are extremely difficult and sometimes impossible to see in painted aluminum.

ETA: Also check the spindle for cracks.

[tctyres]

Originally Posted by spoonrobot

With 12,000 miles on the clock I'd be suspect of a crack somewhere in the interface. Do you know if the crankset is painted or anodized? Some years are not in the specifications from Shimano so it could be either/or.

Cracks are extremely difficult and sometimes impossible to see in painted aluminum.

ETA: Also check the spindle for cracks.

Aaaahh.... I will look. I hadn't thought of this.

[benb]

This is definitely really weird.. if it wasn't that you almost surely didn't do this in 1 year I'd say warranty.

I have never had any trouble at all and have probably done > 30k miles on some of them.

That said I always torqued them properly with a torque wrench and followed the directions very specifically. These are all pretty decent bolts but it's always possible you very slightly damage something if you torque it improperly and then ride thousands of miles on it that way and then you're never going to get it to function 100%.

This is not an area to screw around on when setting it up. The amount of torque through there with a strong rider is quite substantial.

[BobbyJones]

IIRC #4 contributes to this. With my first set of hollowtech cranks I thought it was such a silly little piece of plastic but read somewhere….

It’s been a while, so I could be remembering incorrectly.

[reuben]

BTDT. See this thread.
https://forums.thepaceline.net/showthread.php?t=262724

You can get a replacement hook (#4) at Universal Cycles (BTDT). They're legit, reliable, and a great source for small parts.

This is the part I bought from UC. Torque to spec, slowly, and alternate the pinch bolts as you go.
https://www.universalcycles.com/shop...s.php?id=51165

https://www.youtube.com/watch?v=YeNU2HM6iOY

[konstantkarma]

In my experience it is important to tighten each of the crank bolts on the non-drive side a little bit at a time, going back and forth between them until they are really snug. Then finish them off with a final tightening to torque specs. This has prevented mine loosening, and has remedied creaking.

[tctyres]

As much as I'd like to say that piece #4 is responsible, it is not. Piece #4 is essentially a paperclip cast in plastic. It's there to prevent catastrophe. It also spaces out the pinch bolts.

The issue is that the pinch bolts loosen and the whole NDS crankarm jiggles to the left. Piece #4 was there to keep the crankarm on.

I'll look for some cracks later.

[reuben]

Originally Posted by tctyres

As much as I'd like to say that piece #4 is responsible, it is not. Piece #4 is essentially a paperclip cast in plastic. It's there to prevent catastrophe. It also spaces out the pinch bolts.

The issue is that the pinch bolts loosen and the whole NDS crankarm jiggles to the left. Piece #4 was there to keep the crankarm on.

I'll look for some cracks later.

Misery loves company. I didn't have a crack, but the bolts were improperly torqued, and probably not evenly, which likely led to the deterioration of the safety hook. Just throwing out a similar experience. Hopefully some of it applies, notably the torquing of the bolts, and maybe some blue Locite. I didn't have any cracks. Well, not in the crankarm, anyway...

And yes, #4 is a cheap paperclip.

[mjf]

Torque on pinch bolts on hollowtech and similar copies is very important, and you can easily damage the bolts at minimum, but typically the crank fails first with too much or uneven torque because it's the softer material. Check the area surrounding the pinch bolts for any deformation or cracking, and then the female side of the splines for damage (more common here than on the spindle).

However, since it's loosened up twice already, I'd be looking at replacing the left crank arm at the minimum, and crankset at the worst.

On top of that, I'd be buying a torque wrench, since you've stated that you don't have one.

[jc031699]

After inspecting the bolts, crankarm and spindle to make sure they haven't been damaged by either under- or over-torque, I would reinstall carefully to torque spec before calling this one cooked. It is possible that the crankarm-spindle interface has been worn away by being ridden loose (more likely the grooves on the crankarm since that is aluminum and the spindle is steel), and then it may never tighten to spec.

Also, do your bolts have the washers in place? If not, this could lead to you overestimating your hand-applied torque also.

Agree that Part #4 is basically like the lawyer lips on a modern front fork, to prevent disaster in case of an idiotic mistake.

Thankfully the left hand crankarms are all over due to the proliferation of Stages powermeter cranks. I have a 170mm 6700 and a 170mm CX70 left crankarm available to sell if needed (they are basically the same, and you can't see both crank arms simultaneously anyway).

Trainer season seems like a good time to be figuring this out.