QuestionI need to know piston measurements,ring clearence, and bore diameter. Could you please help me in finding that information? I can't seem to find a site, everybody wants to sell a book.
AnswerHonda 90s are 55mm bore size. There are always 5 sizes of pistons/rings for each Honda model: STD, .25mm, .50mm, .75mm and 1.00mm
Piston clearance should run about .0015" Check bore for roundness, taper and any ridge forming at the top ring edge on the cylinder that would require an overbore to clean up any defects like that.
Back in the 1970s, you could bore/stroke a OHC 90cc engine out to about 160cc, but they were pretty fragile at that displacement size. Engines were used in CS90, CL90 and SL90 street bikes, CT90 offroad models, ATC90s, etc.
I don't have a shop manual for the 90s anymore, so can't give all the rest of the dimensions as far as deck height, piston length. There is some rather cryptic information on this website: http://www.jccpiston.com/manufacturer/16805/16805.html
There used to be another site in China making vintage pistons, but I wasn't able to locate the link again.
Just found this:
http://www.powroll.com/P_HONDA_90EARLY.htm These guys can tell you everything you need to know about them...
Bill Silver
