Compression range

[mav6759]

I just did a compression test on my 1988 60hp evinrude, and it read as follows.
cyl 1. 120
cyl 2. 104
cyl 3. 70
Now I don't know if these are good reading or not, could someone explain them to me. I just brought this motor and having trouble with this motor responding on the lake. When I brought this motor I was told that it was just rebuilt.

 

[iwombat]

Re: Compression range

Those are some pretty telling numbers. They likely point to a blown head gasket.

Those numbers should all be within 10% of each other.

Time to pull the head and inspect.

 

[Joe Reeves]

Re: Compression range

If those readings are correct, you have 50 psi difference between the highest and lowest reading...... not good.

Remove the cylinder head in order to do an inspection of the underside of the head, the sealing surfaces, the piston and cylinder wall etc.

Hopefully you have simply had a head gasket fail between #2 and #3 cylinder.

Let us know what you find.

 

[iwombat]

Re: Compression range

It's likely that whoever rebuilt it didn't re-torque the head bolts after break in.

Oops.

 

[mav6759]

Re: Compression range,,,,Thank you so much

Re: Compression range,,,,Thank you so much

Thanks guys this really means alot to me. But I just brought this engine from a marine shop. The owner told me that he couldn't get the lower unit to work with the motor, so after having my boat for almost a year, I went and got my boat and told him that I would put a lower unit on the motor myself. Now after buying a new lower unit, spending a lot of maney to have it rebuilt, (because I was told that the motor was rebuilt), and spending more money at two other marine shops to play with it, nobody did a compression test. Until, I ask the question on this site and was lead in the right direction, now I'm going to return this motor and I need to really calm myself, because I was lie too and I want to thank you guys for taking the time out, and helping me. I owe you guys a beer.

 

[Solittle]

Re: Compression range,,,,Thank you so much

Re: Compression range,,,,Thank you so much

Let usw know how you make out.

 

[hoeser]

Re: Compression range

If it's just a head gasket which is a real possibility you may want to hang on to the engine. I would pull the head and have a look, if you don't see anything nasty going on inside (scored walls, etc) drop $15-20 on a headgasket and torque to specs... You're already this far with the engine... or the better idea would be to make the shop that sold it to you do it.

 

[iwombat]

Re: Compression range

I think you don't touch it at all and talk to the shop about it. A motor with those compression readings should have either been fixed or sold as a parts motor.

 

[jddenham]

Re: Compression range

Was the motor running good before the test?

How did you perform the test and what type of tester did you use?

Have you tried to repeat the test for consistency?

Don't go tearing things apart until you know that those numbers are accurate !!

 

[Deereman76]

Re: Compression range

The first thing I think of when I see numbers like that, is "is the battery good?" I have had many a compression test results be wrong because of a poor Battery slowing down the cranking speed as the test progresses. More so in this case, because as you progress down the line, they keep getting lower. I would retry the test, maybe in reverse order.

Of course, if you tested in an order of 3-2-1, then this makes no sense!