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HIGH-PERFORMANCE PARTS AND SERVICE FOR NORTON TWINS |
JS Motorsport 4480 North Academy Avenue Sanger, CA 93657 Phone/Fax: 559 875 0659 Email: jim@jsmotorsport.com |
JS Motorsport Technical |
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COMPRESSION |
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Copper cylinder head and base gaskets in various thicknesses are now available to adjust compression. Standard thickness is approx .040". Adding .040" to a head or base gasket will lower the CR approx one point. Going to a thinner .020" head gasket will raise it 1/2 point etc. Never use a paper base gasket because they can loosen and cause damage - use Yamabond (Permatex Motoseal #29132). Note that Hi compression pistons generally require racing fuels. If you want to use high compression pistons on a street bike then you must use a thicker head or base gasket to reduce the compression to avoid detonation ("pinging") or risk failure. 9:1 compression is average for carefree street riding. To prevent head gasket oil leaks, use Yamabond and lay a loop of dental floss around the pushrod tunnels and the oil return hole. |
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Special extra high compression .003" thick head gasket rings (glued down with rubber contact cement) and dental floss for sealing around pushrod tunnels and oil return hole. When done properly - this is a very reliable and leakproof headgasket system. It is the easiest way to raise your compression approximately one point (10%). For example - you can start with our 10:1 C.R. pistons and raise them to 11:1 for racing by using the thin rings and cutting the tops of the pistons to clear the squish band as in the photo below (see diagram). |
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