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Recently replaced the chainset and BB on my 456 to a HTII chainset. Bought second hand, had two spacers, i put them both on the driveside to get the chainline right. All was fine, couple of local rides, went to Afan, everything worked a treat. Then realised that as it's a 68mm shell, i should have three spacers - two driveside, one non-driveside. Got hold of one, and put it on the bike. Couple of rides later, rear end was feeling very sketchy, and I realised the crankarm was coming loose from the axle (non-driveside)
Had a look, it appeared that the pre-load cap thread had broken, so it was no longer holding the crankarm tightly, which was letting it work its way loose. I assumed i'd tightened it up too much, so when I bought a new preload cap, i was careful not to overtighten it - just did it up finger tight. I'd removed the non-driveside spacer too, just in case that was meaning the crank wasn't fully on to the axle. Once again, everything was fine for a couple of rides, then at Cannock today the same thing was happening, the crankarm working it's way loose. Sure enough, the thread had cracked again.
Surely this sort of thing shouldn't happen regularly? Anyone else had any experience of this kind of thing happening? Am I just overtightening the preload cap, or does anyone else have any ideas as to what could be wrong? I'm not the smoothest rider in the world, but i haven't exactly been doing 6' drops to flat either.
Cheers
Phil
Silly question, but you did tighten the pinch bolts on the crank arm?
Yes, the pre-load adjuster is simply that, to get it tight enough that there is no play in the bearings. The two pinch bolts are to hold it on.
Sorry if i'm teaching the sucking of eggs but it's a common mistake apparently.
Yeah, i did tighten up those pinch bolts - can you overtighten those too? I had them done up pretty tight, i thought!
Yeah, i did tighten up those pinch bolts
Did you push the little plate that goes between the two bolts down into place before you tightened them? They only need about 14 Nm IIRC.
little plate that goes between the two bolts
Hmm - don't appear to have anything that fits that description - they're Deore LX cranks, should they have one of these plates? There's nothing in the gap that the bolts go through
LX have the plate just like the other HT cranks. As above though, the preload doesn't hold your carnks on, the pinch bolts do. Tighten gradually and evenly but they shouldn't need to be very tight. They're a small bolt screwing into alloy so you [i]can't[/i] get them very tight.
you are doing the pinch bolts up too tight friend,and its crushing the plastic cap.
much like a headset with its top cap, once the pinch bolts are done up correctly the plastic cap is doing nothing, this is why its only made of plastic, Its purely there to correctly seat the non drive arm fully on.
Make sure you tighten the pinch bolts evenly, I tend to do half turn on one, then the other, etc - until tight.
If you nip up one side then the other, it won't have an even seat onto the splines. Failing that, you could have particuarly worn splines that mean the pinch bolts can't do there job properly.
As has been mentioned, the plastic cap is just to put a small amount of preload onto the bearings. The tool I have is just like a thumb screw, so that you can't overtighten.
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Part No. 9 is the one to which I refer fella.
that's just there to stop the crank actually falling off. as above - tighten the pinch bolts evenly. if you can't get it sorted like that, i'd begin to suspect there was a reason you only two spacers with them...
Yeah, definitely don't have that part labelled 9. I'll get down my LBS, see if they have any knocking about - other than that, seems i've probably been doing the pinch bolts up a bit too tight.
Thanks all
Early cranks didn't come with part 9 as far as I know, and the 12-15Nm recommended for HT11 crank bolts is quite high for an M6 bolt (tighter than you would normally expect)
Yeah, the early cranks never came with part 9.I have a set without this part.Use a torque wrench, but don't go by the reccomended figures! I think they say something like 12-15Nm on the two bolts.I do them up to 12Nm.I know people have done them up to 15Nm and have stripped the bolts out!
Thanx Max
I had a similar problem which occurred after about 4 years of trouble free riding.
The non drive crank came off and consequently the plastic cap was destroyed. I went into my LBS for a replacement and they claimed that even though it is a only a plastic preload cap, that cranks do have a habit of coming off if is removed.
I have since reinstalled the cranks with a new preload cap and done everything up as tight as it should be with no further problems.
(Mine is an older HT2 crank without the plastic spacer)
I hope that you get it sorted - definitely make sure you tighten up the bolts evenly on each side. Overtightening one bolt will remove the tension in the other as mentioned by Hallsy
Part 9 isn't that important tbh, by the time it's doing something things have already Gone Wrong.
UPDATE
Got hold of another preload cap thingy, went about re-installing the crank, first of all using all three spacers, as suggested for a 68mm shell. Definitely haven't overtightened any of the bolts, but all done up pretty snugly. However, same problem seems to be happening - there seems to be some sideways play in the crank, so much so that even after a quick 2min spin around the block, dropping off a kerb or two, the crank already seems to be coming away from the bottom bracket.
So. It occurs to me that sideways play means that the crank doesn't have enough of the axle in it, so it can wobble free. Without the end cap on, i'd say there's a 1-2mm gap from the end of the axle to the end of the splines on the crank. Is that normal? or should it be almost flush with the end of the axle? I thought about trying to just do everything up a bit tighter, but i don't want to ruin another end cap!
For more info, here's a photo of the crank pushed full onto the axle, showing the gap at the end:
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sounds about right actually,if it's still coming off then i'd suspect that either the splines in the arm are damaged, or you've not tightened the bolts correctly(apart from carbon fibre components, they're the only bolts I always get the torque wrench out for).Edit-just saw the photo, looks not far from normal to me, not sure about the splines though, they look a bit iffy in the photo and that's on a part that normally doesn't engage on the crank. Bit difficult to be sure without seeing in the flesh though.