This is my first season with a used M-1 (5#psi) installed on my used 7.4 Mpi (600hrs). I have 125-135#'s compression in 1,2,7,&8 and 110-1153s in 3,4,5 & 6. I squirted oil in all the cylinders and found aproximately a 10# increase in all cylinders. The leak down however is 50#s/ 80#s in 1,2,7,&8 and 20#s in 3,4,5 & 6. I can hear leak in the exhaust. I also have oil backing up the dipstick under full power. I plan to pull the heads and re-work if necessary, replace the factory gasket with better gaskets designed for blower applications and re check the leak-down to eliminate gasket and valve leaks. If I still have leak problems I will tear down further to the pistons and rings. I was planning to hone, re-ring and replace the pistons with forged pistons. Any suggestions for pistons/rings. If the bearing surfaces are good is it worth the expense to replace rods? rod bolts? and go to a steel crank? I plan to stay with 5#s of boost and keep my rev limiter @ 4750 RPM. The application is a Bravo III on a heavy cruiser.
I would get with a machine shop (if you are going to assemble the motor) And let them tell you what needs to be done. I would recondition the stock rods (add arp rod bolts)crank, and heads. Add a mild blower camshaft a set of forged pistons. Put it together and have fun.
Sounds like it still runs ok,i'd wait till winter and tear the whole motor down instead of taking the heads off,then on, and still may have to go back into it.Do it once and do it right.
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