Author Topic: Engine Compression Figures? (Read 2223 times)

Serge · « **on:** July 24, 2009, 12:03:18 AM »

Just did a compression test on my m42 and all cylinders showing 180psi, is that a good or a bad reading, what is the factory spec? cheers.

phrunt · « **Reply #1 on:** August 05, 2009, 08:50:17 PM »

Normal Compression is 142-156 psi, cylinders should not differ more than 7 psi. The reason for your high readings may have to do with the temperature of the engine, take the reading when the engine is slightly warm, about a quarter way down the temp gauge.

bbarnumboy · « **Reply #2 on:** August 20, 2009, 05:05:58 PM »

142-156? wow i just did a head job on mine and used the stock thickness head gasket etc. and with the engine slightly warm i just blew a 215 on 2 cyl and a 220 on 2 cyl anyone explainw hy it is so high? before the head job i blew a 200 180 190 and a 90....the 90 was because of a cracked head. ad now after the had job it is 215 215 220 220

JP 91iS · « **Reply #3 on:** August 20, 2009, 06:45:09 PM »

Mine were 220 across all 4. I searched and most people were showing 180 and above so that lead me to believe that the figures listed in the Bentley are the lowest acceptable numbers.