Compression reading

[birdgod]

Hi, i just did a compression test on my ob. the readign from top cylinder down are
120
120
110

is this reading good? the manual i have did not said how much it should be.... also since the compression is low on the 3rd cylinder , does it mean that i need to change the ring for the piston?

 

[SweeperForce]

Re: Compression reading

From what I read on this forum, your allowed 10% difference between cylinders. Hopefully someone in here can post the actual psi for your motor.

Tom

 

[Bifflefan]

Re: Compression reading

They look fine.
There really is not set reading for a 2 stroke that I have ever seen. But I have not seen everything yet.

 

[birdgod]

Re: Compression reading

They look fine.
There really is not set reading for a 2 stroke that I have ever seen. But I have not seen everything yet.

i thought the standard for 2 strocks is about 125-135. at lease that is what i read from my jet ski. that is why i am asking, at WOT my rpm is about 4300, from iwhat i read from the post here it should be arround 5000.

 

[roscoe]

Re: Compression reading

Some 2 strokes are in the 120 range, some the 140 range, some older motors are in the 100 psi range.

Your numbers are good for your 85 hp Force.

You could do a thorough decarb and maybe improve those numbers a bit.

See decarb link in the engine FAQ section.

 

[jerryjerry05]

Re: Compression reading

With a GOOD comp tester.You should get about 150# on each cylinder.On almost ALL FOrce/Chrysler it should be that.Some Mercs have lower comp but that is gennerally bigger motors.
My guage set cost $100 about 20 years ago.Mac tools.
The important thing is that the comp be close or even.
10# is not much but I would do a decarb.Try to get it up to the others.
Any difference could be the guage or carbon.They SHOULD be the same.
Since the first 2 are the same.I'd go with carbon.
It might last 1 year or 20 years,or not.It will get worse if nothing is done now.
You can do a decarb and let it set with the chemical in it.That will help.J

 

[birdgod]

Re: Compression reading

With a GOOD comp tester.You should get about 150# on each cylinder.On almost ALL FOrce/Chrysler it should be that.Some Mercs have lower comp but that is gennerally bigger motors.
My guage set cost $100 about 20 years ago.Mac tools.
The important thing is that the comp be close or even.
10# is not much but I would do a decarb.Try to get it up to the others.
Any difference could be the guage or carbon.They SHOULD be the same.
Since the first 2 are the same.I'd go with carbon.
It might last 1 year or 20 years,or not.It will get worse if nothing is done now.
You can do a decarb and let it set with the chemical in it.That will help.J

thanks, that will be my winter project.