1987 OMC 4.3 Hydrolocked

[hilgeman]

I have a 1987 OMC Cobra 4.3 liter engine in my boat. This engine runs great, well at least it did. It starts everytime with just a bump of the key so starting is not normally a issue. It was running fine 15 minutes prior to the problem which I will describe. I was pulling my son on the tube for about 300 yrds slowed down and turned off the engine to switch tubers. When I went to restart the engine it made the most god awful metal on metal grinding noise. I thought it was the starter so I pulled it off to test it and noticed about 2 inches of teeth missing from the flywheel. I talked to the marina and they said it was hydrolocked probablly due to water rushing in through the exhaust manifolds. I guess they seem to think the flappers in the Y pipe are missing. They said they would have to pull the engine to change the flywheel, install new flappers, pull the plugs to crank out the water and change the oil and filter all for the low low price of $1200.00. I checked on parts and I can get them for around $300.00. I have the means and mechanical skills to pull the engine and change the flywheel and flappers and all the other stuff. I just don't have the marine knowledge to diagnose if there is some thing else wrong as to why it got water in the cylinders. Do you think it was related to the water rushing into the exhaust and just fix it myself or should I talke it to the marina? It just seems like alot of money and mostly labor.

 

[Kainon]

Re: 1987 OMC 4.3 Hydrolocked

You definately need to find out where the water is getting in, could be from Cracks in the Exhaust Manifolds ( especially if you have the gull wing style ) so when running the water is kept out of the cylinders, but when you shut it off, any water in the manifold drains through the exhuast port into the cylinder.

Or a Cracked cylinder head, but would typically show up as a miss fire too and running rough

could also though very rare, have a cracked cylinder.

If you dont have the marine knowledge but are mechanically inclined and have or can get a basic set of tools, you can do it.
else, you'd need to find someone that can.

remove the spark plugs (all) and turn the engine over by hand if you can, put the starter in and get the rest of the water out and see what cylinders it shoots out from. ( left or right side of engine, 123456 etc.. ) then take that exhaust manifold off.

look inside you may or maynot find someone that does and can.

Flywheels are expensive, I recommend having the RING Gear Replaced which is the toothed part of the flywheel which can be purchased through some auto parts stores ( have to count the teeth ) like NAPA ( I bought one from a 69 Mustang for a 1980's Ford 302 Boat Engine. )

Could be the flappers, if you stopped quickly, yea the water can rush in..

could just be the flywheels/ring gear is bad due to the starter or the starter staying engaged too long either due to the operater or starter.

It is a lot of labor, but to change the flywheel or ring gear you have to remove the engine, and either the starter or gear in the starter needs to be replaced ( there are starter/altenator repair places that can do this )

 

[hilgeman]

Re: 1987 OMC 4.3 Hydrolocked

Thanks for the info. If there was a problem with the exhaust manifolds wouldn't of I had some kind of problems prior to this, like hard starting or running bad? It worked perfectly up to the point that I stopped to switch tubers and restart the engine.

 

[Howard Sterndrive]

Re: 1987 OMC 4.3 Hydrolocked

pretty sure OMC came out with a bulletin at one time saying those flappers didn't do enough to warrant even bothering to replace them if they failed. It does depend on hull design, waves and yeah, it isn't a good idea to just kill the engine via the key when a wave is washing up behind the boat (flappers or not)
I'd be looking at the manifolds.

If there was a problem with the exhaust manifolds wouldn't of I had some kind of problems prior to this, like hard starting or running bad?

I don't really see why necessarily. A crack could form/open up when running under load (e.g. tubing). If they're 25 year old manifolds, they have gone 15 years longer than anyone ever expected them too.
I'd pressure test the cooling system. That will eliminate everything except the manifolds as far as water ingression from the cooling system. (e.g. intake manifold)

That $1200 seems pretty reasonable to me if $300 is parts.
But it's a ll DIY doable if you can lift the engine.
You'll need to get an alignment tool for aligning the engine if doing it yourself.