Engine problems

Thanks for the reply Paul, I'm hoping it will be at worst maybe carbon build up on a valve stem! It's confusing that the problems don't affect a cold engine only hot. I'll find out soon enough. Crankshaft has covered 130,000 miles and the followers are approx 80,000 miles old. Out of the two I guess the crank would be under the most stress and most probable suspect. Hope it's only a sticking valve!!

Thanks for the moral support and advice guys. Spoke to a friend today who races a heavily modified Commando and apparently has a lot more experience at breaking standard Commando's than myself. He suggests it could be the drive side main bearing based on my report. I'll be chuffed if that's the only problem. Going to remove the sump filter to see what that shows and then strip the engine tomorrow to see what that reveals. I'll start with the primary drive and timing side and progress to the top end if necessary. Plan to leave for Austria on the 28th, that gives me 17 days which is plenty of time......no problem......I hope.

Pretty sure I've found the cause of the engine vibration and noisy valve train. It was the timing side exhaust valve getting too big for the guide clearance, which was partly due to a slight build up of carbon and that the original clearance was too small. The clearance cold appeared to be zero so I ran a Flexhone through until there was approx. 0.002" clearance on both exhaust guides.

Previously checked primary drive and timing cover. Everything as I'd assembled it apart from worn pad on the primary chain auto adjuster. Clutch plates got a wash.

Well happy! I was working out cost of a new crank at possibly £1800 ! So saved myself a few quid there. Had the barrels off and all appeared sound except cam follower to tunnel clearance was 0.004", which ideally could be nearer 0.001". All good on rest of cylinder head too. Didn't see the point of going any further as crankcase oil came out clean with no bits of any kind. Sump mesh filter clean as well. Panic over. Thanks for the advise guys, see you in Austria and France!.....as long as my passport turns up.

Thanks for the reply Phil, insufficient clearance between valve and guide explains the tight spot when turning the engine over hot. Cold no tight spot. This would be enough to produce vibration as the crank turned it would momentarily meet with resistance for half a crank revolution out of every two complete revolutions. A bit like applying a brake on off very quickly. That's my theory although not very well explained.

I've not stripped the gearbox as there was no problem hot or cold. Everything else I have checked (inc. all the above) is fine. I agree a road test will be the proof.

Completed 90 miles on the bike today and everything seems ok, hooray! Valve train is definitely on the noisy side and I think this is the cam followers to tunnel clearance at 0.004", or maybe the PW3 cam, but nothing to worry about. Happy the bikes back on the road.