1970’s to 90’s OMC 60 to 75hp - worth rebuilding?

[ShoestringMariner]

Can we talk about the 60, 70 and maybe the 75hp OMCs from the 70’s through the 90’s?

I hear that these motors are revered by quite a few people.

I’ve acquired a few older ones as of late in the hopes that I’ll find gold, but all are parts motors.

Are these motors typically good candidates for complete rebuilds?

Or or are there better motors out there, or better money spent on newer technology?

 

[flyingscott]

The 86 and newer 56 cid blocks are the best of the OMC 3 cylinders. They are a significant power improvement over the earlier 49 cid blocks. The 75 hp was always built on the carbed 49 cid block. I also consider the 75 hp the least desirable of all of them. The 75 hp is best suited to light hulls and the 70 is a much more user friendly motor. Tilt and trim is almost mandatory for them nowadays. People just want it.

 

[ShoestringMariner]

The 86 and newer 56 cid blocks are the best of the OMC 3 cylinders. They are a significant power improvement over the earlier 49 cid blocks. The 75 hp was always built on the carbed 49 cid block. I also consider the 75 hp the least desirable of all of them. The 75 hp is best suited to light hulls and the 70 is a much more user friendly motor. Tilt and trim is almost mandatory for them nowadays. People just want it.

Interesting about the 75, I don’t see many of them to begin with. Can I ask what makes the 75 different? is it only the carbs? I’m starting to have several pre 80’s parts motors here and it would be good to know what crosses over. I’m assuming bottom ends are all the same through this era?

 

[flyingscott]

The carbs, block and head are different. The block has different porting.

 

[ct1762@gmail.com]

Ditto on the 75 being for light light hulls only! Had a 1982 70hp and a 1980 75 that I fully rebuilt. The holeshot way waay stronger on the 70, and top speed was about the same. The 56 cube blocks are a whole different animal as well! Huge power jump from the 49's. My theory is OMC was trying to catch up to Yamaha and Suzuki who were leaving the 49er's in the dust.

I think it was 1975 that the rods and bearings were beefed up. The older rods were like chicken legs and alot of them got thrown. you can still use them, but I wouldn't.

 

[ShoestringMariner]

Great info. Thank you.