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Mercury 150 melted piston

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pivanp

New member
Hello froam Croatia

I have a problem with my engine. The first problem is that I dont have the serial number of the engine. i have only the numbers on the engine block and engine heads.
I was looking and i think it is a mercury 150 about 1985.

The engine was running good 2 3 months, one day we run the engine for 2 3 minutes on 5200rpm and the engine stop to work. We couldent turn the engine, so we open it. the first piston was melted. we dont have had any overheating or something else.
Waht can be the problem ? Can some body help me ?

I have some pictures
 
20121107_221721.jpg20121107_221715.jpg20121107_221707.jpg
 
Melted piston could have been caused by detonation in the cylinder OR lack of oil.

Detonation is "often" when there is a carbon build-up and the carbon glows hot like an ember. Then when fuel gets sucked into the cylinder it ignites while the piston is still moving up towards the point when the sparkplug would fire.

Because it "fires" early it causes all kinds of problems including melted pistons, holes blown in the piston etc.

Some of the initial causes are - 1) poor quality fuel 2) old/dirty sparkplugs 3) poorly tuned engine or, if it was lack of oil
4) clogged carb preventing enough oil from getting to that cylinder - to name a few.

And it is important to try and figure out the cause. If you simply repair the cylinder/piston damage and the ultimate cause was maybe the carb, not correcting that problem will result in the same thing happening again...

IF this motor has oil injection it is NOT the cause. If the oiler failed more of your cylinders would look like this. A bad oil pump does not selectively toast one cylinder and leave the rest alone - it is not to blame...
 
I am mixing the oil in the gasoline. i put 2% oil in the gasoline.

the engine was working fine 2 3 months. Every day new gasoline.
The spark plugs are 2 3 months old.
I need a new piston oversize....

But i need to now the problem whay this happen
 
Looks to me like a bearing failed.-----Take it apart and see what the damage actually is.This damage did not occur suddenly and there has been a problem for a while.------------Proof that these 6 cylinder motors will sound good to many folks while running on 5 cylinders.
 
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Bearing of the piston or the conecting road ?
the piston can move and the connecting road also. the problem was that the piston melted and the aluminium go inside of the exhaust. that block the engine when i was openening it.
 
In order to repair this motor it has to come apart.----Once all the pieces are in the open a decision can be made on repairs.------It will need at least one oversize piston and likely other expensive bits.
 
How does the bearing surface of the crankshaft look ??---------Post a picture of the crankshaft and another close-up of the bearing surface for that cylinder.
 
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