Help Pls 1973 OMC 120 GM will not turn over

[Karl 027]

Ok the guy said it was last in the water 3 years ago and that he started it 1 1/2 years ago. I came across this 1973 Larson 1650 shark with a OMC 120 GM eng. sitting under a tree for $200.00 with a nice trailer and tires. Well i'll go ahead and tell ya this is my first boat. She would not turn over - new batt - starter ok - so I pilled the head off and found that water was getting into the back two cyls and I think the rings are rusted to the walls, I have had about an inch of PB BLASTER on top of the pistons for a few days and still locked up - guess i should mention the top of the head looked great, no deposits at all, it looked like it was well taken care of. I have tapped pretty good on each piston trying to free it up - any suggestions? Thanks in advance <br />Karl.....

 

[Don S]

Re: Help Pls 1973 OMC 120 GM will not turn over

We call blocks with the piston and rings froze to the cylinder wall Junk. May even have cracked block if it wasn't winterized properly (Perhaps that's how water got in the cylinders?)<br />Even if you could get it to turn over, the rings would need replaced (most likely the piston also) the block bored new bearings and $$$$$$$$<br />It would be cheaper to just find a short block assembly if your head is ok.

 

[Karl 027]

Re: Help Pls 1973 OMC 120 GM will not turn over

Thank you Don for your reply. Ok that sounds like the realistic answer I needed to hear....BUT isnt there some small chance I let everything soak for a few weeks and maybe get lucky and have some small pitts on the cyl walls and maybe the rings will free any rust on or in them after being started and ran for a while? Ok your prolly thinking how cheap is this guy lol, well this is my first boat and it doesnt need to run perfect, also I do know the water was not getting in from the head or block, it was from the manifold elbow gasket, the entire engine looks great, the oil is nice and clean. Like I said the top end looks like new money. The water drains were open. <br />Thank you again for your reply.<br />Karl....

 

[Don S]

Re: Help Pls 1973 OMC 120 GM will not turn over

Try this, put water in half the cylinders of your cars engine, then free it up with what ever method so you can get it started. I won't run worth a dime, but who cares. Now put it in low gear and pull a heavy trailer up hill at 3000 rpm and see how long it lasts. that is the kinds of loads boat engines see all the time. It's not like running a car on flat ground at low rpms.<br />Then pull over to the side of the road and thumb home because parts of the inside of the engine is now on the outside.<br />Being as it's a 70's engine, it may have a hole corroded through the manifold that caused the water to get to the cylinder. It wasn't drained, or the water couldn't have leaked to the cylinders.<br />Free boats are usually the most expensive to fix.