[Closed] Worn XT crankset splines - Will it keep coming loose?

tightened the pinch bolts significantly

Not the best option, they don't need to be tight, all you're doing is compressing a hollow shaft, and all that is supporting that is a nylon preload adjuster.

One last throw of the dice, worked for me when I allowed someone to overtorque mine - get an alloy preload adjuster, fit that, and don't horse everything up. You'll get one off ebay for a few quid.

At the same time as that see if you can find the most suitable gap filling threadlocker or bearing seating product.

Cheers for that. Mine come loose from time to time, though certainly not with that regularity. I wasn't even aware you could get alloy preload adjusters. Just ordered one.

I often wondered why, usually as I was tightening mine up again, why Shimano made such a critical part out of cheese.

As above. We had one go like that at the start of an Alps holiday. Managed to find an alloy one in the bits box with a view to getting through the holidays and fitting new cranks when we got back.
Worked a treat and never got round to swapping before the bike was stolen two years later.

I havnt done it, but i have heard of people wrapping the splines with some aluminium foil to take up some of the wear.

I am not an engineer

Ian

Alloy Preloader order. Well worth a try. Thanks everyone.

The preload bolt is not there to hold the cranks on, its there to very gently take up the slack between the cranks. Once you've done up the two pinch bolds, the preload cap serves no purpose.

If you've goosed the splines in the crank arm then its too late, aluminium foil might work as a temp fix. An alloy preload cap might help keep the crankarm on, but you'll probably end up killing the BB instead by over tightening it.
Replacement crankarm time.

Shimano Saint cranks come supplied with an aluminium preload bolt. Can't just be because they want them to look fancy can it??

Quick question, Are you riding flats or clipped in?

I've had this problem twice now on two separate XT cranks and not on a third I have. The two I have had issues with are ones I ride flats on and I think it might be something to do with a slight side force I exert when pedalling from not having my feet perfectly centred. The bike I ride clipped in has never had an issue and they've been on longer and get more miles.

Once it starts it gets worse so just get a new crank. Interestingly, the drive side and the actual splines on the shaft are still perfect on both the failed sets. Just the non drive side that failed.

Typically the last one failed 1 week out of warranty and Shimano basically told me to do one.

They'd tell you to do one anyway I suspect, as it's basically caused by user error.

What, putting them on a bike and peddling on them? 50% of the lads I ride with ride flats (Raceface or Hope though) so It's not uncommon or wrong to be riding flats. Shimano don't say cleats only with these cranks. What I was suggesting is that with flats, your foot isn't always central when riding potentially causing off axis stress. That could be a design oversight and necessarily not user error.

Their reason for the "do one was that it was one week out of warranty which I accept. It's at their discretion. Other companies handle things better, others worse. EThirteen replaced a whole wheelset for me just out of warranty with a smile and a bag of sweets as an apology. Amazing service.

I just find it interesting that someone else has had a similar issue and am curious to know if there are further similarities. Apologies if that caused you to stand up and fight the keyboard warrior fight and respond with a dig.

Happened to me a couple of times and always ended up buying new cranks in the end. Over tightening the pinch bolts results in the spline being out of shape apparently, thus making the problem worse. I always remember this video when putting cranks back on.

"Nip it up, back it off"

Quick question, Are you riding flats or clipped in?

I ride SPD’s but don’t think that’s the issue.
Plastic preload cap has gone AWOL. I can’t remember, but maybe I reinstalled the crank without it present, possibly causing the problem.

There’s still good spline in the middle of the interface, if the alloy preloader helps keep all stable - great. If not, it’s a new crank, with the added bling of the accent colour matched cap.

Bigyinn, yes, that's the theory, but in my experience, and others too, the preloader also works to hold the whole assembly together.

I always fit the gold shimano Saint cap now, looks good, and is just better.

IME your cranks are goosed. Yes, it'll soldier on, but it'll let you down at crux points, like landing in a turn, or standing on it for traction when you've got the bike laid over. Chances are high you'll injur yourself due to the point at which it fails.

I often wondered why, usually as I was tightening mine up again, why Shimano made such a critical part out of cheese.

It doesn't have to be made any tougher. In fact, doing so is more likely to result in trashed BBs as it seems some folk can't read the bloody fitting instructions and end up over-tightening the pre-load. It's only supposed to be finger-tight.

I had an old bike I bought 2nd hand with a square taper. The previous owner hadnt installed the crank arm properly and it came lose on a ride. Rather than replace it, i tried to fix it. Next ride out it did it again, ruined a ride.

I went to my lbs and they went in the spares bin. Found me a replacement which worked perfectly.

I suggest the risk of injury or a ride being ruined isn't worth it. Visit your lbs and see what they have kicking around.

Yes, but that was a square taper, a completely different interface, of which there really was no fix once it was gone.

Mine did exactly this, refitted them with low strength loctite, which took up the wear in the spline, and they stopped coming loose.

It doesn’t have to be made any tougher. In fact, doing so is more likely to result in trashed BBs as it seems some folk can’t read the bloody fitting instructions and end up over-tightening the pre-load. It’s only supposed to be finger-tight

I don't doubt what you're saying as you are correct and the bolt shouldn't  be too tight, but there must be a reason that Shimano supply the Saint cranks with an alloy bolt and not a plastic one.

Personally I think it cos its less likely to move whilst gnarlyness is insuing as the threads are stronger. It also makes me think they know the plastic ones can be shit.

Probably a daft weight/cost consideration, plastic ones will be way cheaper, especially considering the 000's of cranks they sell.

the bolt shouldn’t be too tight, but there must be a reason that Shimano supply the Saint cranks with an alloy bolt and not a plastic one.

It's not a bolt, it's a preload adjuster. It does not retain the crankarm, the pinch bolts do that.

Personally I think it cos its less likely to move whilst gnarlyness is insuing as the threads are stronger.

If the pinchbolts are correctly torqued, it shouldn't matter whether the preload adjuster moves or not.

Which is all fine and dandy, but as soon as the 2 bolts are over torqued, the shaft effectively becomes a splined taper, and the alloy preloader works to counter this.

You're 100% correct btw, if the bolts are torqued correctly, there's no issue....

Some people clearly dont understand the intended function of the preload cap...
You wouldn't expect your headset top cap to hold your stem on would you?

Which is all fine and dandy, but as soon as the 2 bolts are over torqued if the crankset is installed incorrectly, the shaft effectively becomes a splined taper, and the alloy preloader works to counter this as a temporary bodge.

FIFY

It’s not a bolt, it’s a preload adjuster. It does not retain the crankarm, the pinch bolts do that.

TBF it is called a "Crank arm fixing bolt" https://www.wiggle.co.uk/shimano-fc-m582-crank-arm-fixing-bolt/

And I understand exactly what it does and how it should be used, I just think they supply the Saint cranks with a alu one as a kind of safety net, which is sort of admitting the plastic one is not great if you bash your pedal on a rock and get a touch of movement, and the threads on the plastic one squash and you ride home 20 miles oblivious to what has happened as your splines are now getting more ****ed with every crank turn. I also appreciate I may be talking crap....

But yes, torque it all properly and check them regularly there shouldn't be an issue.

I don’t doubt what you’re saying as you are correct and the bolt shouldn’t be too tight, but there must be a reason that Shimano supply the Saint cranks with an alloy bolt and not a plastic one.

I think 'because bling'

A mate of my 'fixed' his old Hone cranks (remember them) by using an slightly longer alloy bolt (might have been a saint one) they still had play in them, but at least they didn't fall off.

I'm sure it'll work, but if you're using the bolt to retain the crank arm it'll probably be too tight, which is a sure fire way to knacker the BB very quickly, but at least they're cheap and on the shelf in most LBS.

I think ‘because bling’

You're probably right.

TBF it is called a “Crank arm fixing bolt” https://www.wiggle.co.uk/shimano-fc-m582-crank-arm-fixing-bolt

Shimano fitting instructions describe it as a "cap", not a "bolt".

You wouldn’t expect your headset top cap to hold your stem on would you?

If the stem/steerer were splined you might, if you didn't read the instructions

if you didn’t read the instructions

So, if you didn't read the instructions, you might not understand the function of the different parts and install it incorrectly, potentially damaging the incorrectly installed parts.

So the OP asked if they they were a few crafty fixes. Ours was a crafty fix, has anyone seen the price of buying new XT cranks in Verbier. The alloy end cap wasn't over tightened and was still intact a few years later, as was the bottom bracket. May still be for all I know. The Saint ones come with the alloy end cap for a reason, not because it looks better.
Out of interest has anyone tried the bodge job and had a fail.

So the OP asked if they they were a few crafty fixes. Ours was a crafty fix

Exactly.

A mate of mine did exactly that ( replace pre-tensioner with alloy ) and went from two sequential rides last year where his crankset came loose, and has ridden the same set since then without problems. It's just helping the shaft maintain it's shape.

OP
Forget all these half measures,get the welder out 😉

The Saint ones come with the alloy end cap for a reason, not because it looks better.

That reason is probably that it looks better after the bike's been dropped a few times. Saint users are not going to be worried about a few grams extra weight, but much more likely to be abandoning ship on a regular basis. Other groupset users probably will be worried about weight and much less likely to be bashing their bikes around. AFAIK, the bearing preload on all the Shimano cranks is the same, so the Saint cap doesn't have to deal with any extra loading when the cranks are fitted. Once the pinchbolts are tightened, the cap no longer has to support axial loads, so it's functionally irrelevant whether it's made from plastic or metal. As long as it's strong enough to preload the bearings, it's fine.

If the cap is required to support axial loads during use (i.e. if the splines are worn and the crankarm is rocking on the shaft), that axial load has to be supported at the other end by the bearings, so requiring a stronger cap means that the bearings must be subjected to axial loads exceeding the design specifications. Whether this is enough to cause premature bearing failure is another question, but it doesn't strike me as a permanent solution to damaged cranks, just a bodge to allow you to ride long enough to replace the damaged crank.

No one has said its a peminant solution. We had every intention of putting on new cranks when we got back from the Alps. The fact is we didn't and it worked so just left it and eventually just forgot about it. Not really bothered about the difference in weight over it working right and if I were to fit XT cranks again I would fit another alloy end cap,just in case. As an habitual bike basher, I destroyed one in the Alps, I don't want to worry about bits falling off.

Worn XT crankset splines – Will it keep coming loose?

No one has said its a peminant solution.

So, the answer to the OP's question is that it can be bodged but nobody can guarantee that it won't come loose again.

Tracey, its no good telling people that as a solution it works in practice, they 'know' that in theory it doesn't work. 😉

Aye, it's pointless Tracry, putting forward your experience of a fix that actually works when someone clearly knows better. I've worked in Engineering in a few forms for 26 years now, and I find myself quite surprised on a regular basis by things that just shouldn't work, but they do.

It's only now at 43 that I'm actually studying the theory behind it all!.

Here's something to try. Do your little plastic cap up finger-tight to preload the bearing, fit NDS crank, torque to recommended setting, and then try and undo that finger-tight cap.

Then tell me it's not taking any load. 🙂

Tracey, its no good telling people that as a solution it works in practice, they ‘know’ that in theory it doesn’t work.

So, do you guarantee that it won't come loose again? I'm not saying it isn't a useful bodge, but you have absolutely no way of knowing how long it will last because you don't know how much the splines have been damaged, or how heavy the riders are, etc. It might last for years in one case where the splines aren't badly damaged and the rider isn't a heavyweight and it might last a few minutes in another case where the splines are badly damaged and the rider is much heavier.

So, to answer the OP's question as to whether it will keep coming loose, nobody knows. It's probably worth trying, but just because it worked in one case doesn't mean it will work in another. If you want a guarantee that it won't fail, you need to replace the crank arm. If you don't mind taking the risk, try the bodge and see how long it lasts.

In practice it worked for me and in theory it shouldn't have. Others have said its worked for them or people they know. It may or may not work for the OP. You cant guarantee the new crank arm wont fail. We have damaged another XT crank beyond repair on a rock strike but did wait at the pub whilst it was pushed back.
I wont fall foul of it again as most of the bikes are on X0 and when we go away in the camper, holidays or competing, have enough spares to build a bike except a frame. And have a spare bike just in case.

We have bodged a few things in the 30 odd years of mountain biking, some worked some didn't. I think the best was at the top of the Brazilian in Switzerland. We had done the hike a bike up the back and just set off on the down when the little rubber grommet on the top of Abigales Hayes 9 rear brake lever popped out. We bodged an allen key held in with tyre cement and duck tape to get her down to the valley bottom. It worked but it shouldn't have.

Hope it all works for the OP and is saves a bit of cash.

Im going to leave it, my excuse is been a girl.

It may or may not work for the OP.

Exactly. So the answer to "Will it keep coming loose?" is "Nobody knows because it's impossible to know".

Funnily enough, exactly the same answer if you fit a new crank

Thank you everyone for your responses, I had no idea it would spark so much debate!

To be honest I was pretty much resigned to buying a new crank, but thought it was worth an ask before buying.
An alloy cap has been purchased and installed. I loosened the pinch bolts for installation and could immediately feel the lateral play on the NDS arm, however as soon as I screwed the cap in place the arm would no longer wobble. With the pinch bolts retightened to the instructed 12nm it feels completely stable.

I'm off out on a 30km loop on Saturday, so if the problem remains it will become evident.

Thanks again.

Best of luck mate.

Funnily enough, exactly the same answer if you fit a new crank

If a shop charged you to fit a new crankset and it came loose, you would expect it to be repaired under warranty. No mechanic with any sense would offer any guarantee that a bodged repair to a damaged crankarm would last 5 minutes. Very different answer.

Im going to leave it, my excuse is been a girl.

Tracey, you're one of the few folk I'd happily let work on my bike! 🙂

Folk have been getting very het up in here and I don't think there's been any real disagreement. Just some folk saying "you're not supposed to expect it to do X" and others saying "yes, but it can do X" 🙂

Here’s something to try. Do your little plastic cap up finger-tight to preload the bearing, fit NDS crank, torque to recommended setting, and then try and undo that finger-tight cap.

Then tell me it’s not taking any load

It's being pinched by the pinch bolts, which are squeezing the tube of the axle. I always, without fail, try and undo the torque cap before releasing the pinch bolts, 'cause I'm a numpty.

I'm going to leave it

I don;t think there's any shame in removing oneself from a thread when it's getting a bit repetitive 😉

And good luck OP, if you keep everything nipped up it'll hold on for quite a while.

🙂