Compression and Leak down results. Help
07-19-2019 | 09:07 AM
#1
Thread Starter
Registered
Joined: Jul 2019
Posts: 2
Likes: 0
From: Virginia
Compression and Leak down results. Help
2000 Formula Fastech 502 mag mpi with 288hours
results:
1) 185/92%
2) 160/95%
3) 160/95%
4) 147/71%
5) 145/28%
6) 167/85%
7) 172/95%
8) 155/85%
what do the results mean?
I don’t have any misfiring. No clouds of smoke. Burn 1qt of oil every 10-14 hours.
If I have a bad ring or two can I continue to run the boat until the end of the season?
What sort of symptoms will I see if the engine is about to bite it as result of the bad rings?
results:
1) 185/92%
2) 160/95%
3) 160/95%
4) 147/71%
5) 145/28%
6) 167/85%
7) 172/95%
8) 155/85%
what do the results mean?
I don’t have any misfiring. No clouds of smoke. Burn 1qt of oil every 10-14 hours.
If I have a bad ring or two can I continue to run the boat until the end of the season?
What sort of symptoms will I see if the engine is about to bite it as result of the bad rings?
07-19-2019 | 10:14 AM
#2
Registered
Joined: Sep 2012
Posts: 523
Likes: 38
From: new baltimore mi
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..
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..
07-19-2019 | 10:45 AM
#4
Registered
Joined: Nov 2004
Posts: 14,094
Likes: 3,684
From: On A Dirt Floor
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.
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.
07-19-2019 | 11:32 AM
#5
Registered
Joined: Oct 2005
Posts: 1,074
Likes: 251
From: Waldorf, Md
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
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
07-19-2019 | 01:37 PM
#6
Registered
Joined: May 2009
Posts: 627
Likes: 408
From: Indiana
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.
07-19-2019 | 09:59 PM
#8
Platinum Member
Joined: Apr 2005
Posts: 2,150
Likes: 15
From: Northport N.Y.
sometimes you need to rock crankshaft a little to seat the ring to the piston. I really don't care much for leakdown unles something is way out. If it don't have a lot of blowby run it don't worry about it.
07-19-2019 | 11:39 PM
#9
Registered
Joined: Aug 2013
Posts: 397
Likes: 134
From: Kemah, Tx
I leak down with all the rockers backed off, at BDC AND TDC. I’ll even let it push the piston down and I watch the gauge and listen to hear if there are ring issues mid cylinder. If I suspect it’s a valve that’s not seated I whack it with a dead blow a couple times, but that still means the valve isn’t seating right when it’s running every time.
if you can’t get good leak down numbers, because rings or valves “aren’t seated” something is wrong. It’s a machine, it’s right, or it’s wrong, period. Every time the leak down #s are not consistent and under 8%, I pull the engines down and find something wrong. Sure it may run ok for a while longer, but it’s not right.
if you can’t get good leak down numbers, because rings or valves “aren’t seated” something is wrong. It’s a machine, it’s right, or it’s wrong, period. Every time the leak down #s are not consistent and under 8%, I pull the engines down and find something wrong. Sure it may run ok for a while longer, but it’s not right.
07-20-2019 | 12:37 AM
#10
Banned
Joined: Jul 2011
Posts: 9,594
Likes: 45
From: Ft. Worth TX
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 .
Last edited by BUP; 07-20-2019 at 12:45 AM.
