So, bearings in old XT HTII BB were shot.
After consulting the STW hive mind I got them replaced with Enduro bearings.
Reassembled bike. Was riding to work when there was a "hang on, something is wrong feeling" backed off pedalling just in time to see the off side crank fall off and go bouncing down the (fortunately empty)road.

I immediately realised that I'd forgotten to put that little black plastic cap on the offside crank.

So, we're all agreed that I shouldn't do any spannering late at night in an unlit garage.

However, I went to sort it last night but there's still a lot of side-to-side play with the crank on.

How far should the splined shaft come through the crank – should it be flush with the face? Because it isn't at the moment regardless of what I do.

Is there anything that I need to do differently, taking into account that the Enduro bearings are a different design to the original shimano ones?

Am thinking that maybe I need to use one less spacer than usual?

should be a 2-3mm gap at the left hand end of teh crank and axle for the black cap to preload with

Can't be sure that this is what you've done, but you might have stripped some of the splines that create the interface betwen the crank arm and the axle.

I've done exactly the same thing myself with a Saint crankset. Basically I had screwed the whole thing up by using the wrong spacer assembly with the chaindevice I was using (fitting the chain device behind the BB). The net result was that the axle was not through the BB far enough and was only binding with the non-drive side crank arm on about 50% of the arms surface.

In answer to your question then, yes, the axle should be more or less flush with the non-drive crank arm.

Mine fell off half way around the Pass Porte Du Soleil and required me to 'borrow' a crankset from a repair shop, which I then had to return the next day!

Park Tool HT11 how to

threadlock on the crank bolts is my tip. and use a torque wrench.

the little black plastic cap (isn't it metal?) is (if you're talking about what I think you are) used to pre-tension the cranks, before you do up the pinch bolts on the crank arm. If you didn't use this, how did you do the crank up? just slot it on and tighten the allen keys?

http://www.cyclistno1.co.uk/features/maintenance/shimano-ultegra-hollowtech-ii-crank-service.htm

Same HTII systm just road cranks 🙂

The black cap is to pre-tension the bearings. That's why it has a little tool to do it up that you just use your fingers for – a tool would be too tight. You can remove it if you want after you've done it – it serves no purpose in keeping the cranks on. That's why it's plastic!

Put on cranks, do up cap with thumbwheel, THEN tighten allen bolts.

There is a chance you have damaged the splines on the crank arm, although you might have been lucky if you noticed the crank arm coming off before you put any power down. The little black preload screw is plastic, but you can buy replacement alloy ones off ebay, which might be stronger.

I would try assembling it correctly, go for a ride, see what happens. If the crank arm is working loose, no matter how tight you do the bolts, then you've knackered the spline (probably on the crank arm). A new crank arm is £60.

I think Molgrips is correct about the preload screw being just for pulling everything together correctly, I road without one on my xt cranks for quite sometime with no problems. However, if you didn't make sure the cranks were pulled together properly, then that is why they came loose quite easily. As I said above, if you've now knackered the spline, then it will keep working loose, the bolts won't hold the crank arm on anymore. First, you need to put it together properly and go out and test it.

The black cap is to pre-tension the bearings. That's why it has a little tool to do it up that you just use your fingers for – a tool would be too tight. You can remove it if you want after you've done it – it serves no purpose in keeping the cranks on. That's why it's plastic!

Put on cranks, do up cap with thumbwheel, THEN tighten allen bolts

see, I'd always been told you have to be really careful not to overtighten the crank bolt – however truvativ cranks use the same BB (or one that looks *very* similar) and the only way they're held together is by tightening a big fo bolt (8mm allen key) that tensions the bearings. no pinch bolts or anything

I don't think you can overtighten it, the preload screw breaks quite easily, presumably that's why it's plastic. These aftermarket alloy ones, I'm not sure about.

Thanks all.

I'll take it all apart again this evening and see how much of an expensive mess I've made of things.

Bugger.

So, in the worst case – think I saw Ribble selling SLX chainsets (minus BB) for £70 or so, or some other alternative cheapy singlespeed cranks that work with HTII BBs.