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I've just had the Jubilee barrels rebored, but on ftting them with the rings they are very tight, so I checked the ring gap which is 0.15mm. Is it usual to have to adjust the ring gap on ne new heptolite pistons or has the rebore been done too tight? I dont have the tools to measure the bore.
Hello Dan, I suggest you r…
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Thanks patrick, Certainly…
Thanks patrick, Certainly Wossner and wiseco pistons fit perfectly. However I've just read the manual (on the principle that instructions are merely guidelines!) and they say that one of the rings is tapered, i'll have a look, as its highly possible that I but it in the wrong groove or upside down!
My engineer bored each barrel to suite the piston, and labeled them accordingly - I think the error is prob mine, but will check.
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Hello Dan,
I suggest you ring the engineers who did the rebore and get their opinion -.15mm is around 6 thou which is PROBABLY about right but you could mention that you intend to use the engine hard in competion revving to 8/9 thousand.
Years ago it was common practice to size the rings by filing the ends but this is now apparently archaic.When I got my last engine rebored in Yorkshire I was asked to supply the pistons so that the engineers could size the bore to suit the pistons and rings as they said old British stuff was not always 100% accurate in manufacture. Modern stuff (Honda or Yamaha)they say is completely accurate and you do not file rings to size.
That's what I was told.
Patrick