79 johnson 140

[Sandpusher1]

Hey guys
I'm going to post pics and need some input please.
Was running the boat today and all was well.
Then it kept slowing down. No noises. Nothing.
Limped back to shore thinking a fouled plug. Got her home pulled the plugs and found metal on electrode. Thinking, oh no, pulled the head and found this.
Anyone know what the heck happened?
Thanks in advance

 

[racerone]

Broken piston rings on one cylinder ----Will happen to every one of these crossflow V-4 motors.-----One cylinder shows overheating / pre-ignition.-----Motor needs 4 new O/S pistons.

 

[Sandpusher1]

Broken piston rings on one cylinder ----Will happen to every one of these crossflow V-4 motors.-----One cylinder shows overheating / pre-ignition.-----Motor needs 4 new O/S pistons.

Wonder why the cylinder didn't get scored?

 

[Sandpusher1]

Broken piston rings on one cylinder ----Will happen to every one of these crossflow V-4 motors.-----One cylinder shows overheating / pre-ignition.-----Motor needs 4 new O/S pistons.

Also where can these oversized pistons be found?

 

[racerone]

Factory has them-----Many failures.----Lots of demand.----After market has several suppliers as well.-----Easy fix if you do the work yourself.-----I suggest pulling lower unit apart for inspection and seal kit.

 

[Sandpusher1]

Factory has them-----Many failures.----Lots of demand.----After market has several suppliers as well.-----

Factory has them-----Many failures.----Lots of demand.----After market has several suppliers as well.-----Easy fix if you do the work yourself.-----I suggest pulling lower unit apart for inspection and seal kit.

Easy fix if you do the work yourself.-----I suggest pulling lower unit apart for inspection and seal kit.

I would most definitely be doing it myself.
Never worked on a johnson, but have worked on an old mercury.