Compression Question 110 HP V4 Johnson - 89

[Jzx2sr]

Hello all,

I have a motor that ran great with zero problems, always started up and ran like a champ. I let the motor sit for 3 years and now I am in the process of selling my boat.

A potential buyer requested the motor be tested, having no issues with the motor I agreed and split the cost with him.

The mechanic came back saying the compression is too low: Left side 95, 95 and right 75, 85.

He said initialy he got 55lbs across the board but decided to run the motor for 30 minutes before retesting.

When asked why the motor ran great and no issues, he told me he wasn't there for that and that it needs to be rebuilt.

I called another marina and right away they asked how such a drastic conclusion could have been drawn given that he didn't open the head to have a look at what was going on.

Any thoughts and coments are much appreciated,

Thanks!

 

[Jzx2sr]

Re: Compression Question 110 HP V4 Johnson - 89

Would decarbing raise the compression and can this be done running the motor on land with the muffs on?

 

[Lyle29464]

Re: Compression Question 110 HP V4 Johnson - 89

I would start there. RAFML

 

[Jzx2sr]

Re: Compression Question 110 HP V4 Johnson - 89

Can the decarbing be done in a parking lot?

The boat isn't in the water and I'm reading I have to go WOT, little hesitant to do that with just a garden hose feeding the cooling system.

Thanks again!

 

[emdsapmgr]

Re: Compression Question 110 HP V4 Johnson - 89

The compression between heads can vary due to manufacturing methods. As much as 5-6 lbs between sides. Your readings are beyond the norm. The suggestion to try a decarb on that engine is a good idea. The instructions on the Bombardier Engine Tuner can say nothing about running full throttle-only that the engine is up to normal operating temps before you start the procedure. See what the readings are afterwards. A second application won't hurt.

 

[JB]

Re: Compression Question 110 HP V4 Johnson - 89

Can the decarbing be done in a parking lot?

The boat isn't in the water and I'm reading I have to go WOT, little hesitant to do that with just a garden hose feeding the cooling system.

Thanks again!

Don't know where you read that, neighbor. Really bad advice. Going WOT with no load is very likely to result in an explosion.

I wouldn't recommend decarbing in a parking lot unless your neighbors already hate you and local Fuzz is very tolerant of public nuisance.

Check the Engine FAQs forum for good decarb suggestions.

Fret not. If your engine runs well the PSI will improve and come closer together.

 

[siw]

Re: Compression Question 110 HP V4 Johnson - 89

delete

 

[BonairII]

Re: Compression Question 110 HP V4 Johnson - 89

Is it a "no registration" thing? Or are you no longer near a body of water to drop the boat in? I'd be surprised if the buyer would want the motor unless he can test it out now,

Probably get a much better price for the boat if you can prove performance on the water IMO.

 

[Jzx2sr]

Re: Compression Question 110 HP V4 Johnson - 89

The compression between heads can vary due to manufacturing methods. As much as 5-6 lbs between sides. Your readings are beyond the norm. The suggestion to try a decarb on that engine is a good idea. The instructions on the Bombardier Engine Tuner can say nothing about running full throttle-only that the engine is up to normal operating temps before you start the procedure. See what the readings are afterwards. A second application won't hurt.

Thanks, if the compression goes up, I'll definitely apply another bottle!

Don't know where you read that, neighbor. Really bad advice. Going WOT with no load is very likely to result in an explosion.

I wouldn't recommend decarbing in a parking lot unless your neighbors already hate you and local Fuzz is very tolerant of public nuisance.

Check the Engine FAQs forum for good decarb suggestions.

Fret not. If your engine runs well the PSI will improve and come closer together.

The engine ran well last week for a good 30 minutes, I really hope this will help bring up the compression.


Something I forgot to mention is that the water jacket gasket and exhaust gaskets are leaking water.... I just found out that these are 4 to 5 hour jobs?

I guess I'll take one thing at a time.

Thanks Gents

 

[emdsapmgr]

Re: Compression Question 110 HP V4 Johnson - 89

I'd be inclined to try to retorque the exhaust cover bolts first. They can loosen with age. If that does not do it, you'll have to remove both covers and replace the gasekt. Not a difficult nor time consuming job.

 

[Jzx2sr]

Re: Compression Question 110 HP V4 Johnson - 89

Thanks for the tip emdsapmgr!

I had a feeling it wouldn't be that difficult, the more I think of it the more I think the local mechanic was just not interested in working on my motor. Lucky for me I have some handy ability! (And a great source of information )