Hi, got her in bits and removed cylinder head to check bore etc. I noticed that I can rotate the piston in the barrel several degrees. every thing else looks clean, no score marks etc. Is the small end bearing shot or is it normal. I have tried to ease barrel away from cranks but I dont want to use to much force. Any advice gratefully accepted,

Cheers,

Myson

A few degrees? Hmm time to take the barrel off and investigate, something is worn I would of thought.

Wayne....

Thanks Wayne, will get barrel off at weekend and post findings then,

Myson

Hi, barrel and head now removed, piston is badly pitted on crown and small end bearing appears to be the problem. There is no vertical play on big end but some lateral movement on con rod. The piston is stamped "73" is this standard bore or oversize as i cannot see any + figures. Any advice welcome,

cheers

Gday, check the side clearance of the rod with some feeler gauges. You should see between around 12 - 20 thou. Someone may have the actual specs for this bike but these are a good rule of thumb. More than this means a crank rebuild, with or without up-and-down play.

Cheers,

Stork

Thanks mate, will do that tomorrow p.m.

Hi, I checked clearance on sides of con rod to crank an they are 11-12 thou so presume it is within spec. I am now looking to order new piston/smallend kit from Bultaco UK so I can get engine back together. Any thing else that should be done before re assembly?

Cheers

Gday, look for the cause of the pitting on the piston. Most likely cause would be ignition timing, but fuel issues could also cause this. Good news on the rod, that will save some work for you. It will also pay to check the ring end gap before final fitting as well and make sure the ports have a little chamfer on each edge.

Cheers,

Stork

Cheers Stork your help is much appreciated, no doubt you will be able to help me in the future,

Cheers