Fried piston

Tomb77

Cadet
Joined
Apr 25, 2009
Messages
29
I have a 1984 OMC SEADRIVE same as a 115 Johnson ran all of last summer problems here and there with power and idle but seemed to have that all worked out. Last October the lower unit went out and it sat for a few months until I could get it going again. In the process I pulled the crabs and intake everything looked good put on a different lower unit and started up good. Ran in the drive way several time no problems when I took it out I tried a different propeller and it was no good but motor ran fine. Put the old propeller back on and ran a few miles and burnt a piston. Damage is not bad no scoring on the cylinder wall.
Not sure where to go from here I figure it will run after I cleaned to the piston not much is gone but why did it burn. I premix. I tried to make sure the fuel was mixed up prior to running and after a fifty mile drive it should have been well mixed. When I first started it was running as good as it ever has for me. IT is old motor and boat with a 70 gallon tank last year we ran it out 30 miles several time have a few problem but always got it worked out.
My question is where should I go from here I can tear everything down no problem putting in a new piston is no big deal just time and a few bucks. I ran two stroke motor cycles for years and burnt a many pistons but could always figure out why this on has me scratching my head I see no problem.
 

emdsapmgr

Supreme Mariner
Joined
Dec 9, 2005
Messages
11,551
Re: Fried piston

Possible that hole was running lean. Two things to check fuel and overheat. Pull the carb and inspect that side of the carb which feeds the low compression cyl. Check for debris in the jets or elsewhere in the carb. Any debris can cause a fuel restriction and run that one cyl lean without you knowing it. Also possible it was overheated-pull that head and check for proper placement of the powerhead water diverters. If they swell they can cause poor water flow on that side of the block-without causing an overheat warning horn.
 

Tomb77

Cadet
Joined
Apr 25, 2009
Messages
29
Re: Fried piston

When I pulled the cylinder covers off which was shortly after it was run both top and bottom cylinder cooling flow seamed good. It could have been a lean out situation I will clean both carburetors again from what I can tell so far that must have been the problem it just surprises my when it was running so good. I just picked up a 1900 evenrude 120 HP in very goop shape I am planning on putting this one my seadrive and will most likely take the other motor completely down and use for parts.
 

Dhadley

Supreme Mariner
Joined
Feb 4, 2001
Messages
16,978
Re: Fried piston

How old was the fuel and what spark plugs are you using?
 
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