I am rebuilding a 400M because after 500 miles it loss oil pressure and took out all the bearings. I have tank the engine and cleans out all the oil passages, found a lot of junk in them. I have 2 problems 1.I am unable to find any flat top pistons at a reasonable price. I want to increase the C/R, the engine is a 1981 with 2V heads. The other problem is when installing the cam it fit very tight in the last bearing you have to use a bar to turn it. Has any one seen the cam problem before.