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b98 Mercury 175 Piston Problem

ronm

New member
"Hello all.

I have a 98 Mer


"Hello all.

I have a 98 Mercury 175 2-stroke with what looks to be a burnt piston (see pics). I was cursing yesterday and I felt the boat loose power. I pulled the throttle back and the motor shut off. Steam was coming out of the pee-hole so I think it got hot. When I got home and started troubleshooting I found out that the over temp horn was disconnected by the previous owner – not good.

Any idea if this piston damage is due to improper fuel delivery / mixture or excessive heat?

Also, is it possible to replace the damaged piston and hone the cylinder or do I need a complete rebuild? All other pistons look good.

Thanks,
Ron

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"One burnt piston is not over

"One burnt piston is not over temp horn. Either the carb or ign. system had something to do with this. Your pic is not that great, but it looks like the piston is blown off on the exhaust side showing the rings from a fuel problem.

If the head chamber is chiesled up, that the ign. failed. Pretty common problem with these. If the aluminum is built up on the walls than there was no oil. The carbs are going to get gone through on the rebuild any way. I guess you gan do one piston if you have to save some dollars."
 
I to have a 175 mercury black

I to have a 175 mercury black max that has a bad score in number 1 piston pot. My question is can the power head be rebored or resleved. Iam new to this marine stuff and just wondered if it can be machined like a car engine?
 
"steam was coming out of the p

"steam was coming out of the pee-hole just before the motor stopped or the whole time??? may be your water pump went bad causing an overheating problem which later burned your piston, no water coming from the pee-hole means bad water pump"
 
"Kevin, yes can be bored just

"Kevin, yes can be bored just like a car engine. Usually can go .030 over without a sleeve in most cases, and less if the score isn't that bad (the machine shop will decide).

On average it costs about 50 bucks to repunch a hole for ya.

You only need replace the one bad cylinder as well, with an oversize piston and rings without any balance issues etc.

Personally, I don't do that (replace only the bad piston). But to each their own.

I would at least, at minimum, do the one bad cylinder completely, and have the others honed out and install new rings. Most of your cost is going involve the gaskets/seals and time to tear it all down and put it back together. You also need to track down what caused the problem in the first place and usually one bad piston can either be traced back to a fuel issue (dirty/clogged carb or injector) or just plain faulty component (less likely).

So while you have it all torn down, why not give it new life with at minimum new rings in the other cylinders...."
 
"Ron, that hole was running ho

"Ron, that hole was running hot as it got tight...check that head for flattness too. The spark plug in that hole will tell you alot as to why that hole started to seize up. The 3 most likely, lack of oil, no fuel or water getting into that cylinder from a bad gasket. Water will cause steam, steam equals super heat which starts to melt the piston. If it was a bad pump and it got really hot the paint on the heads should look discoloured (both heads) in that case you want to pull the other head for sure and replace those gaskets and check that head for flattness as well."
 
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