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The 66 250 Monza engine I have came with a metal shim between two gaskets at the base of the cylinder. Is this a modification or stock? If a modification, why? Should I remove it or leave it in place?
Thanks in advance.
I have not measured compression. The engine now runs but is unhappy. It has an erratic idle and puffs in the exhaust with occasional carb "farts".

The NC bikes often came with an aluminium shim below the base of the barrel. These come in a range of thicknesses and were there to control the level of compression, especially with the big lumpy pistons and also to stop head or valves coming into contact with the piston!

The last one I played with needed a 1.0mm shim to keep the piston clear of the head and on a 350 we needed something like a 2.0mm one to reduce the compression so we could kick it over!

Off the top of my head WC barrels are longer and dont need shimming.

Chris

Thanks!
What are NC, and WC?

Never mind my NC vs WC question. I figured it out after my coffee kicked in.
Thanks again