Loose non drive side crank arm

I’m having trouble with my non drive side crank are keep coming loose.
They are Shimano hollowtech slx cranks with a push fit BB.

I’ve cleaned up the splines,which look to be free from any damage,loaded up the bearings to remove any play and then torqued up the two bolts to the recommended torque.

After a couple of rides the crank arm has play in it.Both bolts are still tight.I then repeat the above process but it’s loose again after I ride.

What am I doing wrong or is there something else wrong?

cheers

remove the axle. feeling with your fingers is there a tiny bit of play in the BB bearings?

Is the black re-tensioning nut thing coming loose? If not, then I don’t see where play can develop, assuming the crank is inserted fully and the black nut is tightened enough. It’s quite easy to think the crank is on fully when there’s a couple of mm of play still left to take up (where the axle hasn’t fully come through the BB shell – I find this is worse on my press-fit BB than hollowtech II.

Only other thing is the bearings collapsing, but you’d notice tons of play in the axle/crank.

If you aren’t sure whether the black tensioning nut is coming loose, put a line of tippex or permanent marker across it onto the crank and check for movement after riding.

I’ve just changed the BB to see if this would solve the problem but it’s not made any difference

bearings fully seated into the frame ?

Possibly the first time it came loose you damaged the crank arm so that no matter how tight you lash up the bolts there will always be a tendency for it to work loose .If that’s the case you need a new crank arm . Having said that the cost of crank arms is silly and I would be inclined to buy a new SLX Chainset , that way everything is new and the problem will definitely be solved.

Bearing are full seated into frame.

Not to sure if the re-tensioning nut in loose or not but I’m guessing it must be but not sure how that can be.Is it worth a bit of loctite on it to see if it helps?

My money is on the crank arm splines being worn or damaged. The arm is softer than the axle so in most cases the damage is to the arm.

Using Loctite on the end cap won’t help, it’s not designed to keep the arm on. All that will happen is the cap will fail and you will be left with bits of it stuck in the axle.

Apply this to make sure the drive side and axle are seated fully in:

Then preload as normal. Also check that the plastic wedge on the non-drive side arm is still loose after torquing the clamp bolts. When torquing up the clamp bolts, nip up 1st bolt, then 2nd, then torque 1st, then 2nd, then 1st again, then 2nd again, until both bolts deliver a click on the torque wrench.

** More suitable hitting tools are available. 😉

windysurfer – Member

Bearing are full seated into frame.

Not to sure if the re-tensioning nut in loose or not but I’m guessing it must be but not sure how that can be.Is it worth a bit of loctite on it to see if it helps?

Once you have tightened the black tensioning nut, there should be no way that play can develop unless that nut comes loose (or grossly deforms). You are creating a fixed distance between the crank arms when tightening that nut and if it’s not coming undone, then I am not sure how that distance can increase to generate play in the crank.

I would take the crank arm off and make double sure that the crank is fully inserted. Give it a tap on the drive side with a rubber mallet if need be. When re-fitting the non drive-side crank arm, the tensioning bolt will drag the axle through if need be.
I would then mark the crankarm/black bolt so you can see if it is coming undone – might give you a clue about what’s wrong.

Probably a stupid question, but you are definitely pre-loading the bearings with the black bolt, then leaving that in place and tightening the crank arms? And you are leaving the black bolt in place once the two crank arm bolts are tight?

I’m definitely pre-loading the bearings with the black bolt, then leaving that in place and tightening the crank arms.I’m thinking the splines being worn in the crank arm is the only answer but I’ll give all the other suggestions a go before I spend any cash

How many spacers do you have fitted to the BB, what width is the BB shell of the frame, and what width is the BB intended for?

If you have too many spacers, then the crank arm will not be able to fully engage on the splines and it’ll then exhibit the exact behaviour that you describe. (And probably knacker the arm into the bargain)

I had the same with a couple of sets of HT2 cranks, both were well used. finally I bought some new cranks and not had a problem since. I also replaced the plastic preload bolt with and aluminium one, just in case. Not had a lose crank since.

I think the splines can become worn and when it does come loose it makes it all worse.

Clean everything, get an alu preload bolt off ebay, try again and if they come loose again it’s new crank time!!

Edit: what balugabob says as well.

The preload bolt being plastic helps protect the bearings as the required torque is very low.

My bet is damaged splines on the arm or distortion to the arm due to over tightening or play.

But do check any spacers first in case you are preventing the splines from fully engaging.

The easiest way to check if the splines are damaged would be to fit them together outstide of the bike & BB. Is there any movement relative to each other with the two pinch bolts done up fully (dont worry about the preload bolt) with the arm mounted more or less in the right place on the axle?
The fact that they are working loose would suggest the splines on the crank arm have been damaged.

This happened to a friend’s bike, once it had come loose and he’d ridden it loose, it would not stay tight again. To the eye it all looked fine but something in the arms had worn enough to mess up the clamping system. (shimano 105 cranks)

Thanks for the replies.I’ve already tried an ally bolt and still have the problem. The bottom bracket is fitted with one spacer as it came from Giant.I reckon the arm has come loose in the past and worn the splines.I’ve just cleaned it all and tightened it all up so I’ll give it a final try before buying a new crank.

cheers