Mercrusier 260 Low Compression

[hogcat]

I just purchased a 1980 Century Arabian 200, with the Mercruiser 260 Chevy 350. The boat was left uncovered, with the engine hatches off (can you believe someone would do that) for over 6 months. It was winterized, as the engine plugs were pulled, but we have confirmed low compression (0-10) in at least 2 cylinders. I am not very mechanical, but we guess that rain leaked in through the manifold, and has fouled some of the cylinders. The oil in the dip stick looks fine - no water, but a couple of the plugs show some thinning of the oil from water.

I would prefer not to pull the engine yet unless I have to, but was wondering if anyone has any possible solutions. The previous owner swears that it ran fine before the long term exposure.

Thank you very much!

 

[Haut Medoc]

Re: Mercrusier 260 Low Compression

Drain & refill the oil.....
See if it will run.....
My guess is bad valves......
You could most likely replace the heads without removing the engine.......​

 

[ziggy]

Re: Mercrusier 260 Low Compression

http://www.boatfix.com/merc/Bullet/97/97_25.pdf

ya might try the air test part of this service bullitin to try and fig. where the loss is comeing from......

 

[Don S]

Re: Mercrusier 260 Low Compression

no water, but a couple of the plugs show some thinning of the oil from water.

Not sure how that is even possible. What is the signs of thinning of the oil due to water? If you see rust, That is water in the cylinders.
Besides, water in the oil makes it thicker (like a milk shake) not thinner. Gas makes oil thinner, but there are no signs of it on the plugs that I am aware of.

 

[Bondo]

Re: Mercrusier 260 Low Compression

but we have confirmed low compression (0-10) in at least 2 cylinders. I am not very mechanical,

Ayuh,...... Welcome Aboard to the forums here at iboats,......

Exactly How,+ by Whom was the loss of compression diagnosed,..??

You're going to have to dig deeper,+ do a Leak-down Test to see where the compression went to......

 

[hogcat]

Re: Mercrusier 260 Low Compression

Thanks to all for the quick replies.

The compression test was done by my boat mechanic, who is very experienced and very good (although he really doesn't have time to rebuilding engines, etc.) What he did was put in a new starter, and then removed one plug at a time inserting a compression gauge and turned the motor over. Some were ok, some were not. He guessed that the one's left open the last time the engine was running, got some water in them from being left out and therefore the valves were stuck.

A friend of mine who is mechanical told me the same thing happend to his 350, and he put Marvel Mystery Oil in all of the plugs and carburetor, let it sit for a couple of weeks, then ran it and it was ok...Could this work?

 

[Bondo]

Re: Mercrusier 260 Low Compression

Could this work?

Ayuh,.......

I suppose Miracles can happen,..... But I wouldn't be holding my breath......

 

[Haut Medoc]

Re: Mercrusier 260 Low Compression

Pull all of the plugs, squirt some oil into the cylinders, ground the coil & crank the engine to get the oil in the pan moving....
Put the plugs in & see if the engine will start.....
It should still start with low compression....
I don't see how water could get into any cylinder by just sitting....​

 

[Don S]

Re: Mercrusier 260 Low Compression

The boat was left uncovered, with the engine hatches off (can you believe someone would do that) for over 6 months.

This might explain the water Haut

 

[Haut Medoc]

Re: Mercrusier 260 Low Compression

This might explain the water Haut

Oh, I guess it could get in through the carb then....:redface:

 

[dcg9381]

Re: Mercrusier 260 Low Compression

You can try oiling the cylinders, starting, and then repeat to see if your compresison improves.

If you're trying to determine head/rings/etc - have your mechanic run a leak down test on the cylinders in question.

 

[achris]

Re: Mercrusier 260 Low Compression

.... and then removed one plug at a time inserting a compression gauge and turned the motor over. ....

This is NOT the right way to do a compression test!!! Find a mechanic who know what he's doing....

Chris.........

 

[Don S]

Re: Mercrusier 260 Low Compression

You can try oiling the cylinders, starting, and then repeat to see if your compresison improves.

That would really make me want to take my family out on the water.
That might work on a car that you can pull over to the side of the road, but if you go out on the water, you should have something that is a little more dependable than something you unstuck and made run a little bit.
No biggie though, there are plenty of boater out there that want to spend a part of their day towing in someone that started out with a bad motor.

 

[hogcat]

Re: Mercrusier 260 Low Compression

Thanks to all for the information. We will try the 'oil the cyliners' approach first, and I will let you know the results.

btw Dan, thanks for the concern but the family will not be in peril, as they ride in my Sea Ray....the Arabian is just a project/toy for me