Hi Douglas...The easiest fit I know of is the low compresssion T140 piston. This still has to have the head machined to reduce the 'lump' but it's easy enough...basically flatten out the top a little and machine a chamfer on it....You will still need to use a decoompression plate under the barrel though...or a machined plate between the barrel and head to maintain the 'squish' under the head..There is a Honda piston that is used in Holland for this conversion but I don't know which one it is..The guy that sells them keeps that information to himself...That one is flat topped but will still give a reasonable compression ratio with the small B31 head. Ideally you should pop a B33 inlet valve in there, open out the port to about 30-32mm with matching carb and run a pair of 65-2446 Goldie scrambles cams to get it going. (you can still use the std. valve springs with these). Also lighten the flywheels the next time it's apart..that is key when tuning these engines.(assuming you haven't done that already).....Ian
hi ian beautiful engine parts seems to be a shame to hide them i have got my B31 400cc engine together and in the frame maybe i might get it running when the weather warms up a bit i have seem to have lost interest in rebuilding bike since i retired will not start anymore once i have finished the B31
Hi Roger...I sometimes get periods where I 'run out of steam'...The trouble is my head is full possible of new projects and I always come back to it...You have to do something with your spare time and need to keep the mind occupied..and if I did stop building bikes I'd just find myself another expensive hobby!... ..It's also in my nature that I never think I have built the best one I can, though after 40 years I have now accepted they are usually a reasonable effort!....Ian