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 ?403608403609403610403611403612403613403614

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]

403615403616403617

Heres the cylinder.

[spybot]

403618
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]

403682
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.403692403693403694

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.405646405648 405649405650405651

[Capt.Insane-o]

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

[spybot]

That's not epoxy, it's melted housing.
Do you think the motor has got that hot that its melted the housing ?

[rudderless]

Yup...doesn't take long either...seconds with a bone dry impeller and plastic housing...

[flabum1017]

a lean cylinder will raise exhaust temps...... cooked housing

[spybot]

Chit i cleaned the crap out of it and refitted it. Looks like i will need to order a new housing then.

[powerabout]

do you still have a standard mid with can etc in it?

[spybot]

Yeah still have the whole lot.
Can i ask Why you asked?
Should i be looking for trouble some where ?

[powerabout]

Yeah still have the whole lot.
Can i ask Why you asked?
Should i be looking for trouble some where ?
just clarifying if hot exhaust heated up the water pump but in a stock engine no effect

[spybot]

I just cleaned up the water pump housing it looked OK once it was done but should i have replaced it ?

[Bruce2]

I just cleaned up the water pump housing it looked OK once it was done but should i have replaced it ?

I would replace it, being it's been hot and it's plastic, yep replace it.

[roadkill636]

Yup...doesn't take long either...seconds with a bone dry impeller and plastic housing...

Yep. Iv seen people start their outboards dry . And tgey always say. "I only let it run for a little bit. Not enough to overheat the engine " they have no clue that the wp is being toasted.
Also get in them cyl cooling passages with a small wire brush and scrape out all the ol debris