QuestionI HAVE RECENTLY REBUILT THE ENGINE IN A 1980 RM 50 (NEW PISTINS,RINGS,BEARINGS,SEALS AND GASKETS). THE COMPRESSION WHEN CHECKED COLD IS ABOUT 105 PSI. WHEN I CHECK IT HOT I ONLY GET A READING OF 70 PSI. IT ALSO IDLES HIGH AFTER IT IS WARM AND SEEMS TO LACK POWER. WHAT COULD THE PROBLEM BE? AND, WHAT SHOULD THE COMPRESSION PSI BE? THANKS FOR ANY HELP YOU CAN OFFER.
AnswerHi Randy,
Q: "...I HAVE RECENTLY REBUILT THE ENGINE IN A 1980 RM 50 (NEW PISTINS,RINGS,BEARINGS,SEALS AND GASKETS).
A: Why was this work necessary? Was the cylinder machined to fit the new piston?
Q: "...THE COMPRESSION WHEN CHECKED COLD IS ABOUT 105 PSI. WHEN I CHECK IT HOT I ONLY GET A READING OF 70 PSI.
A: Perform a cylinder leak-down test. A leak-down test will indicate by percentage or air leaking from the combustion chamber the condition of the engine. A leak-down helps locate the source of the combustion chamber sealing property failure by listening for escaping air.
Q: "...IT ALSO IDLES HIGH AFTER IT IS WARM AND SEEMS TO LACK POWER. WHAT COULD THE PROBLEM BE?
A: Air leak is my guess. Lack of compression=lack of power. I suspect the cylinder is worn beyond service limits and not sealing. Measure cylinder, piston, etc... and verify they are within service limits. Repair or replace accordingly.
Q: "...AND, WHAT SHOULD THE COMPRESSION PSI BE?
A: I don't have the service manual either and I could not locate the specs on line. Sorry!
I return tech information files by email. There was no email address with your question as requested in my instructions.
Respectfully,
Mark Shively
