Compression Test vs. Cylinder Leak Down Test?

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Author Topic:   Compression Test vs. Cylinder Leak Down Test?

whalersman posted 07-18-2003 08:02 PM ET (US)
I took my 1985 Evinrude 150 to my mechanic yesterday. I was having a charging problem and found out it is the Regulator/Rectifier.
While I was there I asked him to do a Compression Test... He told me that he preferred not to do a Compression Test on a 2 stroke engine as he felt the Cylinder Leak Down Test was far superior. 1000 times better then a compression test...
Anyone have other thoughts on this???
My engine has about 375 original hours on it... After he was finished doing the test, he said this was one of the best used 150's he has ever tested... Just about as good as new as far a Cylinder Leak Down....
This made my day as I bought the Outrage 18 last year with this engine on it... The engine sounded great to me at the time so I didn't feel a need to test the Compression.. Now I feel much more confident that the engine will last many more years barring nothing major of course..
Does anyone feel that a Compression test is better then a Cylinder Leak Down test on a 2 Stroke motor???
I know my mechanic does use a Compression test on a 4 stroke as Valves are involved.. He explained it all to me and it sounded logical, but then I was already excited about the results... I do trust the mechanic as I have know him for over 10 years and he is still in business and still Very Busy.....
Thanks is advance for any information...
Joe Kriz
Dick posted 07-18-2003 10:17 PM ET (US)
Every mechanic has his way of doing things and his way is the best. My mechanics do compression tests. Which is better??? I think that either one is going to tell the same basic story if there is a problem, 2 stroke or 4 stroke.
Dick
ducktwin posted 07-19-2003 12:14 AM ET (US)
I do not really see the value of a leakdown in a two stroke. The test is really meant to guage the cylinders ability to hold compression. Much more important in a four stroke than two.
Two strokes tend to have "blow by" anyway. Plus, the design of the intake and exhaust ports allows both of them to be open for a fraction of a second. That is how two strokes scavange the cylinder of exhaust gases and let in a new fuel/air charge.
Sal DiMercurio posted 07-19-2003 12:44 AM ET (US)
I leak down test gives you a better reading of what shape your rings are in.
A compression test is no good if it only holds compression for 1 second then drops to nothing....sure, you have compression but it's gone in a second
A leak down tells you what shape that cylinder, piston & rings are in if it holds compression for at least 5 seconds or for however long it holds until you release it.
Their both important, but leakdown is more important.
Sal
Bigshot posted 07-19-2003 01:17 AM ET (US)
Depends.....Leakdown on 2 strokes is like said above....more for 4 strokes....but it still can show ring damage...."can" being they key word. In a 4 stroke if you get low compression in a cyl, you squirt oil into cyl and do it again. If comp goes up then rings are soft. If it stays the same then a valve or head gasket,etc.....make sense?
If a compression test is OK and if sea trial is ok....good enough for me.

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Author	Topic: Compression Test vs. Cylinder Leak Down Test?
whalersman	posted 07-18-2003 08:02 PM ET (US) I took my 1985 Evinrude 150 to my mechanic yesterday. I was having a charging problem and found out it is the Regulator/Rectifier. While I was there I asked him to do a Compression Test... He told me that he preferred not to do a Compression Test on a 2 stroke engine as he felt the Cylinder Leak Down Test was far superior. 1000 times better then a compression test... Anyone have other thoughts on this??? My engine has about 375 original hours on it... After he was finished doing the test, he said this was one of the best used 150's he has ever tested... Just about as good as new as far a Cylinder Leak Down.... This made my day as I bought the Outrage 18 last year with this engine on it... The engine sounded great to me at the time so I didn't feel a need to test the Compression.. Now I feel much more confident that the engine will last many more years barring nothing major of course.. Does anyone feel that a Compression test is better then a Cylinder Leak Down test on a 2 Stroke motor??? I know my mechanic does use a Compression test on a 4 stroke as Valves are involved.. He explained it all to me and it sounded logical, but then I was already excited about the results... I do trust the mechanic as I have know him for over 10 years and he is still in business and still Very Busy..... Thanks is advance for any information... Joe Kriz
Dick	posted 07-18-2003 10:17 PM ET (US) Every mechanic has his way of doing things and his way is the best. My mechanics do compression tests. Which is better??? I think that either one is going to tell the same basic story if there is a problem, 2 stroke or 4 stroke. Dick
ducktwin	posted 07-19-2003 12:14 AM ET (US) I do not really see the value of a leakdown in a two stroke. The test is really meant to guage the cylinders ability to hold compression. Much more important in a four stroke than two. Two strokes tend to have "blow by" anyway. Plus, the design of the intake and exhaust ports allows both of them to be open for a fraction of a second. That is how two strokes scavange the cylinder of exhaust gases and let in a new fuel/air charge.
Sal DiMercurio	posted 07-19-2003 12:44 AM ET (US) I leak down test gives you a better reading of what shape your rings are in. A compression test is no good if it only holds compression for 1 second then drops to nothing....sure, you have compression but it's gone in a second A leak down tells you what shape that cylinder, piston & rings are in if it holds compression for at least 5 seconds or for however long it holds until you release it. Their both important, but leakdown is more important. Sal
Bigshot	posted 07-19-2003 01:17 AM ET (US) Depends.....Leakdown on 2 strokes is like said above....more for 4 strokes....but it still can show ring damage...."can" being they key word. In a 4 stroke if you get low compression in a cyl, you squirt oil into cyl and do it again. If comp goes up then rings are soft. If it stays the same then a valve or head gasket,etc.....make sense? If a compression test is OK and if sea trial is ok....good enough for me.