First off, trying a couple more times skews the test. To get the most accurate reading, let the bike set overnight so it is dead cold when you run the test. Next, lock the throttle in a wide open position. Pull all spark plugs, then crank the engine the same for each cylinder. If it cranks five revolutions to get the highest reading on cylinder one, crank exactly five revolutions on all the other cylinders. You have now completed a dry test.
When I worked for Jaguar, they told us that a variation of 8% between the highest and lowest cylinder was normal. More than that is a problem. I've always used the same range for bikes.
Now, squirt two or three squirts of automatic transmission fluid in cylinder one, put your finger lightly over the hole and crank two revs, then check that cylinder again. Now do the same on cylinder two, then three, etc. Holding your finger over it while it pops, spreads the oil uniformly over the cylinder walls. You have now completed a wet test.
Again, 8% is about the limit. If you find your compression higher wet than dry, it means you have weak or broken rings. No change between the two tests but a low reading, indicates a valve or head gasket is probably at fault.
Agreed. Compression testing should be done to a cold engine. Testing a warmed-up engine is essentially cheating yourself out of accurate results.
The manual says what Mike states above -test at room temperature with 5 or 6 revolutions per cylinder. Manual also states if below 142psi or a difference of 15psi between any two cylinders, then a tear-down is in order (your callon that
). Good tips for wet/dry testing. A leak-down test afterwards can confirm wet/dry compressiontesting.
Cylinder testinghas a "first come, first served" type of approach with no averaging in attempts. The first time don't lie, but the second time just might. Third time is a guaranteed "truth" or "lie", depending on what you're wanting to hear your self tell your self.
171 PSI is as new (assuming no carbonization/coking).
In the Real World, both Hot and Cold routes used together
have their merits. Cold testing and Hot testing. With the cold test, you get the base figure facts for referencing tolerences/conditions withing the combustion chamber against a hot tests operating conditions. Compared, there is insight to be gained just as with wet/dry testing. Relying on only one of the two routes should be with the cold test though, ...IMO, as heat-expanded components that are out of spec in a "cold" state are likely in a pre-failure/failure statethough still operational.