Help to identify the cause of piston destruction

[spybot]

I got hold of 1980 Johnson V4 140
The PSI was down on pot 3 @ 70psi
Once i had the head off i then seen the problem.
Scored cylinder and piston destroyed

What could have caused this ???
The piston seems to have been roasted but how i can make sure this doesnt happen again ?

The other 3 pots still have factory hone marks on it.
All i was told was the motor had a electrical problem with no spark on one side.

[Motv18]

I’m thinking their should be a retainer on the wrist pin. But theirs enough carbon and blow by it’s been sloppy for a while.

[spybot]

Heres the cylinder.

[spybot]

Not sure if the exhaust shows any clues

[flabum1017]

Looks lean.... dirty carb................. check the jet for that cylinder

[flabum1017]

I’m thinking their should be a retainer on the wrist pin. But theirs enough carbon and blow by it’s been sloppy for a while.

Looks like the retainers are there.....

[flabum1017]

how do the water deflectors look? Take a pick of the water jackets around the cylinders

[spybot]

They look pretty shot

[powerabout]

can we have a shot of the piston top, has it detonated the edges off the piston?
then it go hot and did a uniform seize.
lean, timing, fuel?

[spybot]

can we have a shot of the piston top, has it detonated the edges off the piston?
then it go hot and did a uniform seize.
lean, timing, fuel?

I think thats what has happened
The corners are rounded.

Regards the lean side how can i check this ??
I will strip the carbs to night and check the #3 barrel in case there was anything in it.
I cant check the timing till its rebuilt, since the deflectors seem in not to bad a sate but must have failed hence the state of the piston. where else what else can i check for cooling issues.
Why only the #3 pot ???

[flabum1017]

check the impeller too. when water starts to boil, the bubbles start at the bottom................. I had a peice of impeller stuck in the block on mine years ago, burnt up a couple pistons before I found it.

But yours looks more like it ran lean

[spybot]

I will check the full cooling system out.
Would running lean only effect one pot ?

[flabum1017]

One little piece of crap blocking the high speed jet for one cylinder would...............

[spybot]

Got to the bottom of what had caused the piston damage.
2 things
1 The #3 main jet was clogged by a piece of grit/debris
2 The water pump cup had been epoxied in with WAY too much epoxy this had clogged up the water pick up tube.
You can see its almost 3/4 covered this would have lead to an over heat and the clogged jet to a lean situation.
This motor was doomed from the start.

[Capt.Insane-o]

That's not epoxy, it's melted housing.