A couple of months ago I decided to upgrade from 2x to 1x on my FS Trail bike. Whipped the crank off replaced chainring and refitted. So far so normal. However after a few rides I suddenly found the non-drive side crank arm was wobbling. Upon closer inspection I found the inner and outer third of the splines were very worn leaving only the middle third intact. I refitted and tightened the pinch bolts significantly, however after less than 20 miles it’s come loose again.

Questions for the wisdom of the mechanically minded STW collective mind…

Will it keep coming loose no matter how hard I tighten the pinch bolts?
Is it definitely new crank time, as I suspect, or are there any crafty fixes?
Any ideas why it may have happened? Used for 2 years, having been originally fitted by me, without any problem. Did I just fail to tighten the pinch bolts adequately after the 1x conversion, or is there something else I’m missing?

Your expertise and wisdom is much appreciated.

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 fecked 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”.
https://si.shimano.com/pdfs/dm/DM-FC0003-06-ENG.pdf

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. 😉