I retreived the newly rebuilt cylinder heads in San Diego yesterday so decided to assemble the engine top end this morning. When I originally pulled the R100S engine apart, years ago, it had cylinder base metal gaskets installed. Unfortunately I tossed them thinking that new ones would be used. I then found out that the base gaskets were not used on these engines. The later engines had an "o-ring" groove on the cylinders for sealing. This engine had no o-ring grooves so sealant was necessary to seal the cylinder to the engine.
I want to reduce the engine compression a bit so I purchased a pair of earlier base gaskets and then trimmed down the interior diameter to fit over the engine cyliders. All I have is a small Dremel type tool so I spent probably an hour on each gasket, trimming down the interior diameter to fit over the cylinder base.
Hopefully the base gasket will not reduce the compression too much. I saw signs of detonation on one piston so reducing the compression should hopefully make the engine run a little cooler and get rid of any "pinging".
The base gasket in place prior to cylinder head installation.