120 v4 1993 - powerhead rebuild

[DimitriH]

Hey, I have a 1993 Johnson 120 v4 that I am getting roughly 80-90 psi on engine compression on all 4 cylinders. My thought was piston rings. Im hoping me and a buddy who's a mechanic can get a power head rebuild kit ($750 on ebay) and knock this out in one day. Gonna get a can of blaster to soak the bolts with before I take them out. Also getting an angle grinder with brass head and clean the head while its off. The kit comes with new pistons so no need to clean. I'm hoping I don't have to take the block off the outboard. What are your thoughts? This will be my first engine rebuild.

 

[racerone]

Well-----I think you need to remove the block from the exhaust housing !----Trying short cuts could be frustrating and expensive.----Have you tried another gauge ??-----What is your motor doing / not doing ???

 

[jonesg]

Well-----I think you need to remove the block from the exhaust housing !----Trying short cuts could be frustrating and expensive.----Have you tried another gauge ??-----What is your motor doing / not doing ???

second that. !
I had a 150 hp that read 35 psi across 6 cylinders, bought a new guage and pressure went up 100psi.
Easiest rebuild ever.

 

[DimitriH]

The motor starts but when I give it some gas it shuts off. I got the powerhead off now I cant get the flywheel off. Used a puller.. Nope, hanged it from a hoist to allow its own weight to pull it off... Nope. Pb Blast, WD40, impact wrench. Nothing.

 

[racerone]

Hurry----Run to an outboard shop.----The proper puller and technique gets it off in just minutes.----Will save you money !

 

[Faztbullet]

Your compression is about normal as these have a decompression port drilled thru sleeve above exhaust port. This lowers compression about 10psi at cranking and helps idling they claim. Compression will rise when engine builds RPM