motor bit the dust

[johnson89]

1989 Johnson 90hp....last sunday ran fine all day,today got to the ramp,started right up,idle for a few minutes then went to take off and got up to about 3000 rpms,then started dying,,,,got boat home,and my first guess was a carb. problem....I checked spark with timing light and all 4 were good,took carbs . off and they all looked good....then pulled all 4 plugs and the last plug I pulled out was damaged,,,ran compression test,25lbs(122lbs on the other 3)....took cover off, then took head off,what a mess....this motor I mix my own oil...have no idea what caused this,1st time I have ever had a motor tear up like this,,,no idea what my next move is going to be....the sleeve inside has a nice little grove in it also,not sure if it can be fixed or even worth all the money....is a powerhead change out a simple task,I am pretty good with tools but a complete motor just seems like to much, am sure there are a lot of special tools needed

 

[Bosunsmate]

easy job, the hardest part is actually lifting the powerhead off if its a salty- the bolts get salt frozen in over time.
the only special tool is a puller for the flywheel and a torque wrench which you probably already have.
You will need to find out if you have oversized pistons in there, if its the original pistons then just get the cylinder bored out a bit to take the slightly bigger piston on that cylinder.
reasons for failure can just be wear and tear, but check the water deflectors if that motor has them.
replace top and bottom seals too as that can lean out a cylinder

 

[emdsapmgr]

You can replace just one piston. Bore that one cyl and put in an oversize piston. You will need to replace all 4 ringsets. I'd probably pull the carb apart to look for the source of the problem. Possible that some debris got into the high speed jet and caused that one cyl to run lean. Also, check the position of the rubber water diverters by each cylinder inside the block. If they get out of position, that could be a reason for an overheat and lean condition also. In any event, you'll want to know the source of the problem before you overhaul it and plan to start it back up.