Low compression one cylinder, steaming

Hi,

I have a 1982 Mariner 3-cyl 70 hp. Was towing tube for awhile and running hard when suddenly lost power, and motor died. Would not turn over until it cooled down. Would sort of run, but not enough to power the boat. Left overnight, and ran a bit today - would run for a few minutes, then begin to die, and eventually the same thing. This time I noticed quite a bit of steam coming from the exhaust, so I suspect a head gasket. When I got home, I checked compression and found that the top cylinder had none (maybe 10 lbs). Other two were over 100 psi.

I have been looking online for a head gasket but cannot find one. Almost seems that this engine does not have one. Found references to water jacket gasket but not head gasket. Surely there must be a head gasket? Hopefully that's all the damage. Water pump is in good shape and lots of flow from the tell-tale. Any help or suggestions appreciated.

Thanks

Re: Low compression one cylinder, steaming

Bad news I guess!
There is no head with head gasket on this engine ,just a cylinder block cover.
You have lost compression on top cylinder, guess you have to split your powerhead to get this fixed.
Most likely cracked rings,seized piston or hole in piston, pull of the spark plug,use a light and inspect the cyl and piston top.

Re: Low compression one cylinder, steaming

Thanks Iceman66,

So it sounds as thought eh cylinder head is not a separate and removable part on these engines? It definitely is not a seized piston, because the engine will still start and run fine when cold. In fact it will run without any unusual noises for about 5 minutes, at which point it overheats and starts steaming through the exhaust. It could conceivably be a hole in the piston or stuck/broken rings. Is there an easy way to examine the rings without splitting the entire powerhead? A side cover on the block perhaps? I will try and look into the cylinder tonight through the spark plug hole and see if there is a hole in that piston.

Thanks

Re: Low compression one cylinder, steaming

With almost no compression on a cylinder either piston,rings or both are gone and you have to splitt the powerhead to see the total condition.
But first ,inspect through the sparkplug hole, turn the flywheel by hand and observe all the cylinders and piston tops,and reply on thread.

Re: Low compression one cylinder, steaming

Does that #1 spark plug look like it's been steam-cleaned? Or like it's got grayish goo (emulsified water/oil) on it? A clue as to whether water is getting into the cylinder.

Double check that compression number, I don't see how it could run OK cold (or otherwise) with only 10psi on one of the cylinders. Well, unless maybe one of the cylinder castings has a crack that only expands once hot? Which I guess could explain low compressioin AND steam in the exhaust. Best way to see those cylinder castings will be to remove the rear water jacket (careful, use lots of penetrant on the bolts...especially if run in saltwater a lot!).

Another possibility as regards steam in the exhaust, there may be a water leak through the inner baffle plate, which is under the port side exhaust cover plate. Basically, that baffle separates the cooling water from the exhaust ports. That baffle can eventually corrode through, especially if run in saltwater a lot. If you can remove those plates (again, use lots of penetrant on the bolts), you can get a good look at the piston skirts and rings through the exhaust ports, as well as examine the baffle for holes or cracks.

Re: Low compression one cylinder, steaming

bluenoseboater said:

Hi,

I have a 1982 Mariner 3-cyl 70 hp. Was towing tube for awhile and running hard when suddenly lost power, and motor died....

Click to expand...

There's the clue. My bet would be a detonated piston. Did you change the propeller to one of a smaller pitch before you started 'tubing'? What you've done is overloaded the engine, raising combustion pressures and temperatures. The crown of the piston has overheated and started to come apart. Have a look at the spark plug from the top cylinder. Does it have aluminium all over it? Time for an engine strip and (hopefully) rebuild. Or a new engine.

Chris........

Re: Low compression one cylinder, steaming

Most motors when you remove the exhaust cover, you can see the pistons and rings from the side.

Re: Low compression one cylinder, steaming

Thanks for all the advice. I decided not to tackle a repair on this motor. I purchased a 1997 Evinrude 90 SPL in excellent shape. Just installed on the transom last night and will be hooking up the controls today and test running. Will post how she performs with this new powerplant. Look very good on there! Hopefully it works out well.

Thanks.