piston clearance

John Turnbull. · Post by **John Turnbull.** » Mon Apr 15, 2002 9:59 pm

anyone know the clearance between piston & bore in a G3LS.......

33d6 · Post by **33d6** » Thu Apr 18, 2002 3:16 pm

Much harder to answer than you would expect. The answer can vary according to the make and type of piston, the part of the piston measured and so on. Usually this is only a matter of concern to any firm boring out a barrel to fit an o/s piston and the info is provided with the piston. In effect it is usually beyond the skill and facilities of the home mechanic to change anything in this area. (Depressing answer isn't it.) BOB

Biscuit · Post by **Biscuit** » Fri Apr 19, 2002 11:01 am

According to F.W.Neill's book, the cylinder bore is 2.7187" + or - .0005. the piston is 2.7180" at the bottom and 2.7176" at the top, both + or - .0005. The wire wound pistons are said to be oval, so these dimensions apply only to the front and back, not either side. These dimensions give a nominal clearance of .0007" and .0011" at the top and bottom respectively. You will need good quality internal and external micrometers, reading to 10ths to measure these clearances, plus the ability to use them.

33d6 · Post by **33d6** » Fri Apr 19, 2002 4:14 pm

Hello again,John.
Alan's answer merely confirms what I was trying to explain. He gives the clearance figures for the original wire wound pistons only. The factory obviously only gave information on what they fitted when the bike was new. To my knowledge these haven't been available for a long time and the figures aren't particularly relevant for the types of piston now available. He also has a very good point in saying that to check clearances you need the right measuring equipment and the skill to use them. (Sorry, I continue to be depressing). Why do you need to know anyway? BOB