Is my motor ruined?

[skaneever]

Hi everyone, my first post, and its not good. My stepson had my boat out this past weekend and while cruising at full throttle the motor suddenly bogged down and immediately shut down. He tried to restart the motor and it wouldn't turn AT ALL. The starter would pop up and engage the flywheel and stop dead. After looking it over I think it mite be siezed up. Is that how it happens? I've never blown up an outboard before so I don't know if thats what happens. I pulled the head off today and the pistons are there and don't appear to be damaged, the cylinder walls look nice and smooth as well, I really expected to see some carnage, but nothing, so I'm really stumped. A few of the head bolts were really sooty and burned-looking in the middle if the threads if that helps at all. The top and bottom pistons both move a little bit, while the center piston barely moves. A little bit being maybe 1/16 of an inch. If anyone could maybe just give me an idea as to what may have happened it would be greatly appreciated. Oh ya, its a 79 or 80 chrysler skier 700. A 70hp. Thanks again in advance.

 

[jkoppe73]

Re: Is my motor ruined?

If the pistons and cylinders look good I suspect the engine may have overheated to the point of seizing up. Although it is strange that they are seized, and no apparent damage....Just verify a couple things, oil actually mixed in the gas, drop the lower unit and check the water pump impeller, check the thermostat and the operation of the overheat buzzer. Is there any sand/debris clogging water passages in the block (easy to check now that the head is off)? Although it may be too late, at least you may find what caused this.

 

[skaneever]

Re: Is my motor ruined?

Thanks for the quick response. I mixed the gas so it was done correctly. I've run the boat about a half dozen times this summer and the water pump was working, but that doesn't mean that it couldn't have quit. I'm going to have to pull the lower unit and check for debris in the cooling tube, the channels in the head appeared clear. I wish it would have happened while i was on the boat, it would be easier to have an idea what could have happened to cause this, i.e. hitting the mud with motor, or something of that nature. Guess i have some teardown to do. I still don't like the sound of things tho. Sounds like a "catastrophic" issue here. As far as an overheating buzzer,I've never heard one. Should a 79 skier 700 have one? Thanks again for the info.

 

[halfmoa]

Re: Is my motor ruined?

The top and bottom pistons both move a little bit, while the center piston barely moves. A little bit being maybe 1/16 of an inch.

Sounds like a classic symptom of a chunk of cylinder wall stuck between the piston and cylinder in my experience.

 

[Jiggz]

Re: Is my motor ruined?

The best way to diagnose these symptom is to open the intake section. Drop the lower unit. Remove the carbs and reeds and look into the rods. spray oil/gas mix into the rod bearings and also into the pistons and cylinders. And now try to rotate the flywheel. If it still does not move check for overheating in the rods. If there is a sign of overheating, you will need to remove all rod bearing caps and inspect the bearings. If there is no sign of overheating in the caps, then the only option is to remove the manifolds to inspect the piston skirts at least.

 

[skaneever]

Re: Is my motor ruined?

Ugh, sounds like I have some work ahead of me. Thanks for the help with the suggestions guys, its greatly appreciated!