chainreka

I have a 3 1/2 year old Trek alloy road bike with Ultegra gear, except for Durace STI and chain. The Ultegra BB is pretty new and the BB shell in the frame was 'faced' by a frame builder to eliminate any problems there.

I'm about 80kg mostly, 76kg annorexic, sometimes carry 8kg pack...pretty strong and hard on drivetrains.

For some time, there has been noticeable slop in my Ultegra 9spd cranks. If you stand on the pedals while cranks are horizontal, and then rotate them 180 degrees to do the same again, there is a very significant amount of movement, rotation (?), by at least one crank arm while BB spindle stays put.

Lately this has been accompanied by severe creaking. I've found the right crank allen bolt has somehow gone quite loose. I've tightened it (possibly too much with a shifter for leverage), which appears to fix the problem completely for about 50km, before it all starts over again.

This has happened a few times, beginning early in their life when I hastily changed over from 175mm to 172.5mm one morning, and FORGOT to make sure the little steel washers were under the allen head bolt. Not a great start, but surely not enough to cause severe damage? I've pulled right crank completely off, and can't see any evidence of major damage to splines in the crank.

I'm beginning to wonder if maybe the main supporting surface is out of round on the crank? Sure the spline transmit drive and would cause this slop if worn, but what if the round section can't hold the crank perpendicular to the BB spindle? An equally ugly thought? If I put the new chain on the new big chainring and rotate it, there seems to be a fair bit of lateral movement during the full 360 degrees.

Either way, is there anything I can do to fix it? I don't really want to buy a new set of cranks...I expect to replace chainrings, but why can't the cranks last 10 Yrs?....not happy!

chainreka

Hmm, quiet so far, so I'll just add a bit.

I've also heard that using a MTB BB can cause this sort of problem. Apparently the splines vary in thickness, with obvious results.

There's only been two BB in the bike. One came with the Ultegra groupset, so I'm 'assuming' no funny business went on there. I still have it. It is in the box the new one came in. I only changed it as a precaution coz it'd done a lot of hard miles in a season.

I measured the spline thicknesses of both as best I could with a micrometer and they seem the same to within 0.08mm. They are pretty small and hard to get a good reading on. The box is marked:

IBB6500B09
BB-6500 110 BC137 68
2-1TJ01100-57

...if that means more to someone than the obvious I can read from it!

So come on, someone rescue the good name of Shimano by telling me I had this coming due to poor maintenance.........or let me know they are weak cranks and not capable of taking hard riding/abuse!!!

I would be interested even in basic torque specs for the allen bolt that holds them on. I figured initially that they shouldn't need to be 'swinging' tight, since once located the splines transmit all torque. Then the local bike shop owner said there is actually a small taper on the round section of the BB/crank faces...he does them up pretty tight Either way, I'm pretty sure I did them up pretty tight, it always 'bottomed' out when I was doing them up.

I wouldn't whinge so much but my only RETAIL solution is to get a new crankset, complete with marsh-mellow rings .....$AUS400
And I thought pushbikes were 'sposed to be cheaper to run than sports motorbikes.

RainmanP

Well, I am certainly no expert in such things, but I would try some blue (the non-"permanent" or removable variety) Loctite on the crank bolt to see if that will keep it snugged up. I think I have even read of using some on the surfaces of square taper bbs. I don't see what it would hurt to put some on the spline surfaces. Since the alternative seems to come to a new crankset, it wouldn't hurt to try.

roadbuzz

I dunno, so I won't waste your time with guesses. Instead, I'll waste your time with links and comments. Here's a link to the torque specs.

You may also want to look and see if Barnett's says anything about it.

You could take a shot-gun approach... If you still have the old BB, try putting it back on and seeing if the shimmy goes away. Of course, even if it does, that only answers the question, but doesn't solve the problem. Also a comment... torque the cranks to spec once when you first put them on. You shouldn't (and shouldn't have to!) tighten them again. The reason is that after some use , they will wriggle a little further up the spindle, making the bolt a little looser. If you then re-tighten, it happens again. Keep it up and you can wallow out crank/axle interface... a recipe for wobble. There's a hack for the old rectangular taper spindles, an Al shim. Octalink would be more problematic.... maybe you could do something with foil. :confused:

pokey

What??? this is not the routine with splined spindle cranks like he has.

pokey

the model 6500 BB is correct for your crank. An XTR splined BB would be compatible with your crank.Other shimano MTB BB would not. It's hard to get around that your cranks are probably toast.Why is another question.Most often cause is improper installation.A crank bolt that will not stay tight is another indication and loctite is not a solution.I am not aware of any reliability problems with your cranks,but a defective one is not an impossibility.

Feldman

An idea for future reference: install splined cranks without bolts, caps, etc., to insure that the cranks are seated on the splined spindle. Push the arms on with your hands, then install hardware and tighten. It also helps to use very heavy, sticky grease to avoid the creak; I like the red stuff sold in auto parts stores under the name "Lucas Red and Tacky #2." Shimano's torque spec is 35+ ft./lb, considerably higher than for square spindle cranks.

chainreka

Thanks for the input guys. Interesting to note the crank bolt needs to be tighter than the old square cranks. I bet a lot of people don't realise that...like I didn't originally. It may be possible that they are best not taken off/on the BB more than is absolutely necessary...more so than even square ones? Again, something you might not think of initially, given how easy it is to take them off.

That is still not to say I think I did them up too loose. I strongly suspected I was in deep doodoo very early on when I realised the steel washer had dropped out of at least one side when I replaced them in a rush early that morning. The bolt probably 'sank' into the crank, under pedaling pressure, and lost its torque which was when the real damage probably started. I've got a washer in there now, but I think at least one of the cranks has gone out of round.

I have used grease to stop the defeaning creaking, on both sides, every pedal stroke when standing. It just seems like a poor solution...they shouldn't be moving in the first place. I might try loctiting the crank bolt in with an appropriate grade of strength Loctite, but strongly suspect that will do nothing if it is simply the crank wallowing on the spindle and riding further and further towards the frame.

Ah well, chalk it up to experience. Nothing else can be done. Thanks again for your comments. I just couldn't believe it was happening and that it was going to cost so much.

chainreka

Might just add that I appreciate Feldman's comment re taking off the crank caps & bolts and pushing the cranks on by hand. True I was lazy (and couldn't find the tool to remove them!) and was forced to start the thread before I could feel the spline. BUT I was pretty careful and could feel the moment the steel BB spline touched the crank...backed it off a hair and turned them to align.

Admittedly that is still a little bodgy, especially given the importance and PRICE of the components we're talking about here. I would now advocate taking the time to remove the caps, just to be sure.