Compression and Leak down results. Help
 

HELLO , well i guess what i have been told is ,,you want your numbers to be in certain range...
say you dont want leak down numbers to be more than 5 or 10..........different from each other.
your number 4 cylinder may have some sort of issue...
what will cause lost compression,,,rings ,,,valves,,,head gasket...
is there water in the oil???
you will have to get into the motor to resolve issue.

can you run boat rest of season...hmmmm..good question
not sure if i would,,although you maybe fine running easy rest of season
see what others say.
u should post this in the DO IT YOURSELF LINK...OR FORUM..

I'd pull port head and have a peak.

The leakdown readings are incorrect. Maybe the method used ?

Was the engine run within a week or a few days or that day before the tests ?

BTW: 185 compression is a very high # if this engine is stock. Same with 172. Was Method changed between these and others ? # of spark plugs out if not ? What I'm getting at is the faster an engine cranks over (with all else being the same) the higher the compression # will be.

I think you are reading the leakdown tester incorrectly. Lower numbers are better and there is no way you have that high of a leakdown. The numbers are probably backwards. In other words your 92% on #1 should be 8% and the 28% on #4 is actually 72% which is not the best.

When you have the leak-down tester blowing into the cylinder you should be able to hear the air escaping somewhere. If it is coming out of the intake then you might have a leaking intake valve. If it is coming out of the exhaust a leaking exhaust valve. If it is coming out of you valve cover breathers then it is going past the rings.

Also, I would run it some and do the test again. I have seen valves stick and not quite seat when you are turning the engine over by hand. That can give you a false reading. If you run it for an hour and then get the same readings, then they are probably correct.

Just thinking out loud :)

Throttle should be blocked wide open during compression test. I always hook up a battery charger to ensure consistent crank speed, and recheck the first one after I'm done with the rest, should get same reading as first time. Your compression readings are all over the place. I would recheck before tearing it down. I don't think 1 qt in 10-14 hours on a 502 Mag is unusual, especially if you are running 3500 and above for extended time. Some of them don't use any, but some used from day 1.

neither test is 100 % conclusive by no means. A broken rocker arm is a good example that a leak down would show nothing and there many more failed parts and or failed areas a leak down is not a test all - tell all .

I sat in on so many of Dart U classes back in the day.

Us marine techs would always have the topics and even disagreements about leak down tests and compression tests plus leak vs comp. Even many marine techs leakdown test 2 stroke outboards. I never did, we would pull the heads for those but compression check beforehand. Anyways this is a good one I sat in on years ago Dart U.

I actually like vacuum testing better