Johnson 150hp rust in cylinders & piston damaged

[TNBassManCKV]

Engine Model: J150TLCDC Serial: R7308812 Year: 1986Engine is on a 1987 17' Phantom Panther3rd owner - as far as I know garage keptNoticed loss of power the last 4 fishing trips.Last trip, when through some leaves on top of water and engine over-heated / shut down. Cranked back up after cooling and notice a significant lost of power. Went back to ramp and then heard a rattle in the engine.Back @ home removed all spark plugs. 2 cylinders on the starboard side had moisture on plug. Removed head on the starboard side. Middle and bottom cylinder had small patch of rust on cylinder wall. Middle piston look very clean and beaten. (small dents and chipped places). Removed port side head and all 3 cylinders look fine.Would like to get 5 to 6 more years out of engine.

[Solittle]

Welcome TNB - Unfortunately it has got to come apart and be rebuilt. If the 2 cylinders are next to each other I would guess you blew a head gasket. It is important to find out why it overheated or it will blow again. Spend a few hours reading here and get familiar with the search. It all has been done before. Oh and you need to get the OMC shop and parts manual if you are going to do this yourself.

[rodbolt]

you may also wish to test your alarms, that motor,like all other major brand outboards, does not have a "shut down" feature. some has a feature that will reduce RPM when the alarm sounds but if it got so hot it shut down its time for a complete teardown and a careful inspection of all the pistons,bores and head surfaces.

[TNBassManCKV]

The 2 cylinders are next to each other.Main Question??? Can I get by with replacing the damaged piston in the one cylinder and only the rings in the other cylinder?Thanks TNB

[OBJ]

Yes you can TNB. But be sure that the five cylinders are measured and will still be in specs after honing. You only have about .004 to play with fron standard bore.