On the top of the piston in my 55 ES2 is a set of pin-dotted data; "JP 1090" and +0.060" NE.I can see that the +0.060" indicates a 60 thou rebore but what about the rest? Any views? George
That's a 7.1/1 comp ratio…
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Also check the weight agai…
Also check the weight against an original type piston. JP's are excellent quality pistons but generally know to be slightly heavier.
Wish I took this into consideration before fitting mine. A bit lumpy but not bad enough have the piston out. High gearing helps to keep the buzz down.
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Well that's very interest…
Well that's very interesting, guys. Many thanks. Given the choice of keeping the revs down or removing then weighing the piston, then not knowing what to do with that info, I'll stick to keeping the revs down. The bike is fitted with a Mod77 which I think is higher geared - any views? George
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That's a 7.1/1 comp ratio 1955 ES2 piston made by J.P. Products in South OZ. If you use it ensure it has ample clearance to bore.Don't rely on the old Norton hand books for this info.