The Knowledge - Velocette Owners Club

# 4829 Correct, split to the front.
L # 6041 I Have just purcased what looks to be an original, plus .020 oversized piston for my
iorn barrel 1937 MSS 500. This piston (81.5mm)from the Goodman Co. has the conventional ring set
up with two compression rings and an oil control ring on the top but also has a fourth ring near the
bottom of the skirt. The piston is very solid with no expansion slots at all. I have been told that iron
barreled MSS bikes had a lot of seizure trouble with "stock" pistons and were sometimes fitted with up
to .012 thou clearance to prevent seizing up though this seems like way too much. The book says
maximum wear on the cylinder is .008. My question is how much clearance ought I allow for when
reboring the cylinder?
# 6056 As standard the bore is 3.189" with clearances of: Top land .0178" to .0185 Top skirt .0092 to
.0105 Bottom skirt .0052 to .0065 but if you’re worried you can go up a thou or so on this without any
worry. I leave off the orphan ring on the bottom of the piston, but it's your choice.
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