Armen
Serious Thumper
Offline
Half-Witted Wrench-Jockey from Jersey
Posts: 1452
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On early Airhead BMWs, there is an aluminum base gasket. By the mid-70's, the gasket was eliminated, and 2 o-rings were used on the top stud holes. When I work on the early ones, I eliminate the base gasket and counterbore the underside of the cylinders for the late style o-rings. This does two things-it eliminates 2 gasket surfaces, raises the compression a tiny bit, and tightens the squish band a bit. Always a happier bike. When Norton went to 850ccs, they had trouble with the cylinders murdering the base gaskets. They worked with Loctite to develop a gasket goop that could be used in place of the base gaskets. That product still exists. So, IIRC, there aren't any o-rings on the cylinder base. Lose the gasket and goop it up. I believe Lancer skimmed the head and the cylinder. And used a high compression piston. Kinda tells me the bikes can tolerate a lot more compression and a much tighter squish band. Start with measuring the squish band with the stock used head and base gaskets. Then measure the used base gasket. In there somewhere it would be good to actually measure the combustion chamber and calculate the compression. My guess is that the bike could tolerate about .040"/1mm of squish. If this results in a really high compression ratio, start to lose the sharp edges on the valve pockets in the piston crown. My 2 cents.
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