95 mercury 2 stroke rusty water on top piston

[dvincik]

I have a 1995 2stroke 4 cylinder mercury elpto 100 on a wahoo hull that has served me well for few years now. Out in the bay this weekend while at about two thirds throttle the engine started sounding funny. Like revving higher but less power. I thought smething was wraped on the prop so i throttled higher to free it. Then I looked back at the engine to see it had stopped spitting water out of pipe. I shut off immediately. The motor had overheated and I had a bad feeling. I blew out vent lines and tilted motor up to check prop. Cooled down and it did start and was spitting water again.Ran rough, smoothed some after a while but would not idle. Back at dock checked plugs and #one had water sludge and what looked to be mud on it. Next day new plugs & took it out ran better of course but still wont idle. Checked plugs again #1 plug has what looks to water on it. #3]plug same just not as much. I was thinking my next step (besides crying lol) is to check.compression. Bad gasket maybe? Can anyone tell me how to proceed or what problem could be...

 

[Mi duckdown]

I would always check compression simple and cheap

 

[dvincik]

okay I checked compression. All four right at 150. So compression is good. hhhmmm..... so how does water end up where the sparkplugs fire? Anybody out there ever have this problem?

 

[dvincik]

So mechanic says(without looking at it) definitely cracked the block. Major ouchy!

 

[emckelvy]

Usually a cracked block won't pump 150 psi in the bad cylinder. Since he's condemning your motor, you have nothing to lose by pulling the exhaust manifold cover/baffle and perhaps also the cylinder block cover, for inspection. Pulling the cyl block cover gives you access to the tops of the cylinder domes, and surrounding area. Any cracks bad enough to suck water into the cylinder should be obvious.

Another thing that can happen in an overheat condition is that the heat fries the exhaust manifold gaskets, then they start leaking. Potentially a way to spray water into the cylinder. And one your mechanic should have considered before blindly declaring the block to be cracked.

Now, that doesn't mean there isn't a crack somewhere, but if your manifold bolts aren't all seized from salt, removing the exhaust cover/baffle is pretty easy to do and a quick way to see into the exhaust ports & check for damage to the pistons/rings. Likely any bad cracking will either be found around the exhaust ports, or at the tops of the combustion chamber domes.

Note that the old 65hp Merc 3-cyl was almost guaranteed to crack a cylinder when overheated, but that's a specific design flaw and I ain't heard of that in the Big Bore Fours! And when that did happen, you'd get Zero psi in #1.

Maybe some of the other Guru's have anecdotal evidence to the contrary. I do know some of the early Big Bores had problems with the cyl sleeves shifting but don't know if that caused a water intrusion problem.

HTH..........ed

 

[dvincik]

Thank you for your response. I appreciate that. I was not completely satisfied with that mechanics opinion either. I spoke to another mechanic yesterday and he more or less says what you confirm in your response. several of the bolt heads are rusted and it is not going to be easy. I think I will let the mechanic tackle this he said it would cost around 2 hundred dollars possibly more with difficult to remove bolts to find out if its gaskets or a crack. so far my best deal on a good condition used motor replacement is around $2500 so this looks like a good option to start at.