Uh-oh! Motor locked!

[Mechmagcn]

1990 48 Johnson. This has been a very dependable motor for almost 6 years as a daily commuter.
Went to leave the dock and it died at idle in reverse. Tried to restart and it was locked.
Pulled the boat out of the water and pulled cowling. The motor would turn most of the way and then lock. Pulled plugs and could see where something had made contact with the bottom piston, the mark was straight and about 3/4" long. Ran a piece of stiff wire through the spark plugs and hole and heard something move, but evidently it fell through the exhaust port.
Reinstalled the plugs and it fired right up, but is now coughing back through the bottom carb.
Does this sound like one of the reeds broke and made it's way to the cylinder?

 

[racerone]

Drain gear oil just to have a look there.------Also remove cylinder head and post some pictures of any damage that might be seen.

 

[Joe Reeves]

In agreement with racer... time to remove that cylinder head.

 

[F_R]

Do not attempt to start it again until you establish what the problem is. Things can get real ugly, real fast.

 

[harringtondav]

Mechmagcn I thought you were using that 3.0L Merc Alpha set up by now. Maybe time to shake a leg with that project

 

[Mechmagcn]

Mechmagcn I thought you were using that 3.0L Merc Alpha set up by now. Maybe time to shake a leg with that project

I wish I was, haven't had time to finish it yet. Might have to get it going this long weekend.

 

[Mechmagcn]

Drain gear oil just to have a look there.------Also remove cylinder head and post some pictures of any damage that might be seen.

The only damage can be seen through the spark plug hole, just a straight mark across the piston crown towards the bottom that is probably .010 deep and maybe .75" long. Whatever was in there evidently fell out the exhaust port because I had the motor tilted up and couldn't see it. I swapped out motors with a 35hp spare for now and will check this one out when I find time.

 

[racerone]

But, but these motors are know to have less than ROBUST gearcases.-----A wise owner would check gearcase oil at this time.

 

[Mechmagcn]

But, but these motors are know to have less than ROBUST gearcases.-----A wise owner would check gearcase oil at this time.

The problem is not in the lower unit. Whatever had it locked was imbedded slightly in the head and I dislodged it with the wire I ran in the spark plug hole.

 

[juno pierrat]

ok not lower unit , but the head should be removed for better inspection

 

[Bosunsmate]

Pull your bottom carb without further ado and check the reeds

 

[Tim Frank]

....and read FR's post again.....twice.

 

[Mechmagcn]

Well folks, finally found time to dig deeper into this motor, it's not the reeds. The bottom piston crown has started to chip off and it was a piece of it stuck between the piston and head.
The motor is not worth the $$$ it would take to rebuild, so I decided to hone it and replace the bad piston with a used one. Ordered from eBay, a piston #391798, which should be correct and they sent a 390457. The cutouts on the sides are way bigger on the replacement, but the seller states that these will interchange. Told them it might if I was replacing both, but not a direct replacement.
They seem to be helpful in trying to get me the correct part, only time will tell.
I know that patching 2 strokes will usually come back to bite you, but this is just for a back-up. Just bought a new Tohatsu to replace the worn out 60hp Johnson on my pontoon, so replacing this one is out of the question for now.