Logo
FULL SITE MENU

1974 Johnson 135HP Rebuild?

M

Michael Bergum

New member
Hello All!

I have a 1974 Johnson V5 135HP - One of the pistons has recently thrown a ring (3rd cylinder). I am debating on whether I should attempt repair. The motor is in great shape otherwise. I am concerned that once I open up the powerhead, it will be like opening a can of worms.

Has anyone attempted this?

Any advice? Is this type of repair listed in the haynes manual?
 
Factory manual is best.--This type of repair is done all the time.--Take it apart for inspection first.-----Best to use 4 new O/S pistons ( WISECO ) and it should run like new again.
 
racerone said:
Factory manual is best.--This type of repair is done all the time.--Take it apart for inspection first.-----Best to use 4 new O/S pistons ( WISECO ) and it should run like new again.
Click to expand...


Will the factory manual walk through the procedure should I need to hone or bore out the cylinder? It appears that the ring may have scratched the cylinder wall - I don't know how bad until I take it apart though.
 
Factory manual is best and all you need to do this job.----I recommend 4 new pistons with different style piston rings !
 
I've never taken apart one quite of that vintage but with one exception I'd say the engine you got there should be fairly easy.

Most likely you will find you need to bore at least 1 cylinder. Being a V4 most shops can figure it out even if they have never seen an outboard. Be weary of the care they put into the block since they may not understand the crankcase is a non gasketed precise fit (and could ding it up sliding it around on steel tables and such). Also it's good to bring the pistons in and specifically show them what the tolerance should be instead of letting the shop just go at it based on a bore size. You may find the ".020 over" piston sets you buy are actually .019 or .021 over.

What is a gotcha with OMC's is the rod cap alignment; it can be a real bummer. Those that have done tons do not seem to mind it so much. I've done a few and it drives me nuts every time. Some caps you just can't align and will want to replace the rod. Some are probably fine but are in a grey area and without the experience you will not know how to call it. If you have time it's not a big deal, you can figure out you need another rod and can hunt one down (Ebay is great for this).. If you don't have time and want to get the engine done on a schedule I recommend buying a couple extra rods, used one's are only like 20 bucks. I will say though new rods are easier to line up - #1 they come perfectly lined up so you can see how they need to be #2 nobody has messed them up by torquing them down unaligned.

Jon
 
Back
Top