blown piston on a 1978 merc

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paul tracy

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Aug 22, 2010
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hi im a new boat owner of a 1980 glastron i have a 1978 115hp merc on her. my family and i went out on her and it was running good and then it just died right out no power what so ever. WHY, what did i do wrong am i not mixing it right or what PLEASE HELP:eek:
 
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AllAboard

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Re: blown piston on a 1978 merc

There are alot of informative people on here who will help you out, but you need to give more information. Did you lose power like you just shut the key off? Did it sputter out? Did it lock up? Will it still turn over? And what mix were you using?, etc....
 
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paul tracy

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Re: blown piston on a 1978 merc

after it sputterd it went about a mile and quit still turned over , my mix was at 50/1, i got it apart right now and the second cylinder rings sunk in :confused:not relly sure why
 
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paul tracy

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Re: blown piston on a 1978 merc

what is the max pressure you shoud have for that year, and in each cylinder ?
 
Wingedwheel

Wingedwheel

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Re: blown piston on a 1978 merc

Paul, are you saying you already took the heads off? Did you do a compression check first? when you say your rings are stuck, do you mean the've lost their movement in the grooves?
 
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paul tracy

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Re: blown piston on a 1978 merc

Didn't check comp, but seen that spark plug was full of shavings, iv got it all apart right now, i just bougt this motor this year, it sat for 5 yrs inside befor i used it had it out once and it ran awsome, don;t know
 
Wingedwheel

Wingedwheel

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Re: blown piston on a 1978 merc

Very, very odd. What do the cylinder walls look like?
 
Faztbullet

Faztbullet

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Re: blown piston on a 1978 merc

Does your engine have the packs or distributer as the 1978 came both ways? Can you post a pic of piston? Was the aluminum shavings coarse and gritty and is "eyebrow" on top of piston eroded?
 
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paul tracy

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Re: blown piston on a 1978 merc

you are exactly right, and on the gritty side ,my thunderbolt also has a disributer, now i was wondering would cheap oil have any thing to do with this this is the second time this has happend this summer good thing i have a extra motor for parts:(
 
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Moody Blue

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Re: blown piston on a 1978 merc

Have you checked ignition timing ? Incorrect timing will burn up the pistons through pre-ignition.

Any marine 2 stroke motor oil is fine for your motor.
 
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paul tracy

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Aug 22, 2010
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Re: blown piston on a 1978 merc

well i got it out on the water today runs great strange though my rpm is at 6000 now where as befor it was only at 5000-5500:)
 
Faztbullet

Faztbullet

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Re: blown piston on a 1978 merc

Index the flywheel and check timing on #2 cylinder ,if high replace distributer
 
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