Compression issues

[tomandjen43150]

-Took it out on the water today, had some smoke but sounded good and was pretty smooth. Started to accelerate and then bogged down and died. Had a backfire while attempting to restart, blew the exhaust hose to pieces. Ran a compression test when I got home and this is what it was.
87 Bayliner capri, It is suppose to be a Force 125, I beleive the power head has been replaced and is now a 120 (according to wiring diagrams it is an early 120). Compression on to 2 cyl is 110 and 111,
bottom 2 are about 30psi. Any help on where to start?

 

[foodfisher]

Re: Compression issues

Decarb per sticky and hope

 

[tomandjen43150]

Re: Compression issues

Decarb per sticky and hope

What is worst case scenario? Piston's? Power Head Rebuild?

 

[chitownborn]

Re: Compression issues

worst case, power head rebuild, as food fisher says try a decarb and hope

 

[tomandjen43150]

Re: Compression issues

worst case, power head rebuild, as food fisher says try a decarb and hope

- will do

 

[jerryjerry05]

Re: Compression issues

Your past a decarb.You didn't fill in your profile.Your location can make a difference.Salt or fresh water??? Pull the head and check the pistons,check the gasket for failure.If two piston next to each other have low comp then it's possible that a blown headgasket is the problem.That is a LOT cheaper than a rebuild.If the pistons are ok and the gasket is ok then the decarb might help.
Post some pics.J

 

[tomandjen43150]

Re: Compression issues

So I pulled the head off. I was amazed at what I saw. What really shocked me was 110 psi on cyl # 2 despite the ring falling apart and a piece being lodged in the center of the piston. I have allready torn it down. I am guessing a PO has used gas without oil. Hard to say.
Here is a pic of the #4 cylinder. - Now the fun part - there is no ID # or any info to tell me if I have a 125 or 120. The cover says 120, according to clymers the ignition sys wiring is for a 120. The carbs I beleive are from a 125.
Any tell tale signs to help. I had it a local marina. I do know it is a pre mercury Force.

 

[Force 120]

Re: Compression issues

Measure the cylinder. It is 120 Hp with 3-3/8" bore and 125 Hp with 3-5/16" bore.

 

[tomandjen43150]

Re: Compression issues

Measure the cylinder. It is 120 Hp with 3-3/8" bore and 125 Hp with 3-5/16" bore.

How much over can i bore? Are the cyl heads any different between the two? If it is a 125 can I switch to 120 pistons and bore accordingly?

 

[tomandjen43150]

Re: Compression issues

How much over can i bore? Are the cyl heads any different between the two? If it is a 125 can I switch to 120 pistons and bore accordingly?

I noticed something that may tell me what engine I have. The 125 has a
more square cyl head and the 120 has a more round cyl head. So if this is true I believe I have an early (1990ish) 120.

 

[jerryjerry05]

Re: Compression issues

Post a pic of the cowling and the head and sides of the motor.Usually the boat and motor are the same year unless it a repower. 120 and 125 pistons are the same.J

 

[tomandjen43150]

Re: Compression issues

The engine cover says 120. Pics aside, the CDI is either 89-90 120 or 125, so I beleive it has been replaced as the boat is an 87, the casting # is 720010. I would take pics but it is completely disassembled. If i go .040 over I think I will be ok.