Low compression

[mcgyver6857]

I am looking for some advice on how bad of shape my motor is really in. The motor is a 1970 Johnson 60hp three cylinder. Recently had the boat at a local marina for a spring tune up and they came to the conclusion that the motor runs well but is tired. The upper and lower cylinders have 125lbs of compression as opposed to the center which has 145lbs. They said the boat motor could last 3 minutes, 3 years, or I may never have a problem with it at all. What do you guys think?

 

[dieselcat]

Re: Low compression

I don't know a whole lot about it but I'm sure someone is going to tell you to try a decarb,you can do a search in forum and it will tell you how the decarb process works.Hope this helps

 

[HybridMX6]

Re: Low compression

Yep, what he said above, do the decarb. Tasha just did a new write up on it also, so just do a quick search. It doesn't sound like a bad cylinder or two, just sounds like it needs a "spring cleaning."

 

[mcgyver6857]

Re: Low compression

Thanks for the response. The marina did a decarb with whatever johnson offers for an engine cleaner they said it was pretty nasty but didn't bring the compression up unfortunatly. Is this a serious concern or am I just not going to get the most out of the motor. Even the mechanic said it ran exceptionally well.

 

[lindy46]

Re: Low compression

A minimum of 125psi compression and running good? I wouldn't be worrying about it.

 

[iwombat]

Re: Low compression

If it were mine, I'd pop the head and take a look. You'll probably find nothing, and a new head gasket just may solve everything. Nothing like a little piece of mind though.

 

[HybridMX6]

Re: Low compression

If it were mine, I'd pop the head and take a look. You'll probably find nothing, and a new head gasket just may solve everything. Nothing like a little piece of mind though.

Good advice to be honest. Only thing is to be careful with the head bolts, the like to freeze up and not come out, and they snap off. I'd give each one a try before ordering anything, and if you think they will come off, go ahead and order the head gasket If you get some that don't feel like they will bust loose, it's your decision at that time. If one snaps below the shroud/cowling, it's not an easy fix. I had 2 snap on mine, one below and one above the lower cowling. I was removing the powerhead anyways, so it wasn't a big deal. Is this motor used in fresh or saltwater? Makes a huge difference when trying to get those out.

 

[mcgyver6857]

Re: Low compression

The motor as far as I know has been in freshwater it's whole life. I would rather not crack it open but it seems there is not a whole lot of choice eh. Thanks everyone for the help.

 

[itsaboattime]

Re: Low compression

If it were mine, I would do the decarb again. Won't hurt anything. Then do the compression test. If you still aren't happy, swap out the head gasket. Like iwombat said, it may solve the compression problem.


An impact driver may solve the troubles with stuck or troublesome head bolts.

 

[tashasdaddy]

Re: Low compression

Decarb, take a can of seafoam put 3/4 of it in the gas tank, with only 1 gallon of premixed gas. put the rest in a spray bottle. start the engine, and let it come up to temperature. then remove plugs, and them some real good shot of seafoam into the cylinders, replace plugs, let sit 15 minutes. restart, and spray the rest of the seafoam into the carbs, so the the motor almost stalls, wait and repeat until the seafoam is gone.then take for a wide open spin. then put in new plugs, ad premixed gas to the tank, and take it for a wide open throttle spin. it is going to smoke like a house on fire, during this process.

afterwards compression.recheck