Cycle News - Archive Issues - 1970's

. -$-0 0.. < A little bit of time spent changing gaskets can alter your engine's performance characteristics. Low bucklno buck two-stroke performance modifications By Jim Saddlemire Chances are if you ha ve the desire to improve the performance of your two-cycle motorcycle you can . A minimum of mechanical experience, basic home tools, and an understanding of methods to be considered combined with a minimum of cash outlay 'can produce very .c . respectable per.lo.rmance irn - 16 provements. Start with a perfectly clean motorcycle and a copy of .the u shop man ua l for yo. r m a chln~ . Needless 10 say your engine ~ust be In a ~ood . state of repaIr before mod~ficallons are made. If yo~ need a rebu!ld you ca? do this , and modlfi.callons. which ~pp~y, at the same lime while the engme IS apart, No buck mods Sometimes less ·is more , for insta nce w~e;~ }~~ .,~~a.d. g~ske:, ,9~ :a n I e~~Si, . can be reduced in thi ckness 10 in crease com p ression . In certain cases the head ga~ket ca n be entir~ly rem oved and a thin even layer of silicone-seal er used in its place. This is very effective when the sealing surface of the head has one or more grooves cut into it. Others may require you to find or make a suitab le replacement of the desired . thickness . Most engines of simi lar displacement have some interchangeable parts. This is particularly true of Japaneese brands. where most share the same bore and stroke dirnen sions for a given displacement. Many twi n cylinder models are the same as two singles, ~ 2~~ _t~~~ ~~i.n~. t."';o-;~ ~5. singles and a 350 twin two 175 singles, etc, Stud pallerns of cylinders are ofidentical even disregarding ten displacements , thus there are many in terchangeable head and base gaskets among these machines . If you m ust make new gaskets do so from like materials. Copper is preferable for head gaskets , Aluminum , like that used for home siding or chimney flashing , is also good. Lowering th e cylinder into the cases by using a thinner base gasket ca n provide significant low-mid RPM irnprovements. When the cylinder is so lowered the exha ust and transfer port . timi ng-s are altered whil e'compression is in cr eased as the piston now rises higher in the bore, decreasing deckheight . which is that distance from piston lOp to cylinder lOp at TOC . This mod. is particularly useful when preparing a pea ky m o t o c r oss machine for a winter of hare scram bles . Spa cin g the cyli nder h igh er wit h - - - - - - - _. --- - - ": :"' ':'" - : _ - - - ~ thicker gasket , multipl e gas kets (not over three thin ones) or a sp acer-gasket" sandwich ra ises the exhaus t a nd tra ns : fer ports for ' in cr eas ed breathing"'at

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