Help Modifying OMC 31.8 cid

[Smokin' Joe]

Was the 1982 motor..a 35 or 30 hp motor?

35 at the crank, 30 at the propshaft. They started calling it a 30 in 1984. The 35 is listed in
the parts book through 2001 but no one has ever seen one. Maybe was still labeled 35 in some other part of the
world outside U.S. and Europe.

[LakeRacer99]

35 at the crank, 30 at the propshaft. They started calling it a 30 in 1984. The 35 is listed in
the parts book through 2001 but no one has ever seen one. Maybe was still labeled 35 in some other part of the
world outside U.S. and Europe.

I have a 82 25hp, which I am pretty sure is 31.8. I wonder if it has the 360Deg head on it. I should go out and check the PN on it. It had the pin drive lower.

[calvin]

The 1982 gearcase with the .53 ratio.....does it have a part # ....tell by looking..or do you have to spin it over to find the ratio?

[JohnsonM50]

I have a 82 25hp, which I am pretty sure is 31.8. I wonder if it has the 360Deg head on it. I should go out and check the PN on it. It had the pin drive lower.

Far as I know the pin drive was last made for a 31.8 in in 84 & on the 25's not 35's, the thru hub[s] I think were always on the 35's. However the 31.8 powerheads as far as I have seen will all interchange at the block/tower location. Your '82 is a 31.8 The # I found on the water jacket of the head I pictured is: 327673 D2 I
1
Its a raised #, not stamped & I coudn't find anything on the actual head. [under the jacket?] That head or not? perhaps you could tell thru thr spark plug hole?.

[JohnsonM50]

The 1982 gearcase with the .53 ratio.....does it have a part # ....tell by looking..or do you have to spin it over to find the ratio?

BRP Parts cataloge has expandable exploded views, you could ID the type for sure. As for ratio, spin the propshaft once & count flywheel spins is the best bet. From what Ive read the gearcase difference is more about aquadynamics than ratio since prop choice can improvise to some extent ratio difference. From what Ive read about the 2nd Effort case, stock parts of whatever years applicable are used in it.

[Smokin' Joe]

BRP Parts cataloge has expandable exploded views, you could ID the type for sure. As for ratio, spin the propshaft once & count flywheel spins is the best bet. From what Ive read the gearcase difference is more about aquadynamics than ratio since prop choice can improvise to some extent ratio difference. From what Ive read about the 2nd Effort case, stock parts of whatever years applicable are used in it.

I think 1980-83 vs later gearcases is only about gear ratio. I'm not Ware of a different gearcase shape
or size there.

[JohnsonM50]

I think 1980-83 vs later gearcases is only about gear ratio. I'm not Ware of a different gearcase shape
or size there.

The pin drives are .571:1, never worked with thru hubs on this motor.

[LakeRacer99]

I haven't but wish I had noted all iIve looked up [duh] A good place to start is BRP parts catalogues [on line]. There is broken down all the parts & part #s. No 2nd effeot stuff tho.. Sea Way Marine is the best bet to call & ask. Ive found 2nd effort solid mounts & this head I thought was.. or might be?, but never saw one of those neat gearcases.

This is what I started last year when we were talking about the 25/30/35 carb differences. This is nothing more than me writing down the numbers on 3 of the 31.8 motors I have. I do plan to add more columns for additional parts. If anyone is interested, I could add their motors and part numbers to this.

OMC 2cyl 31ci parts comparison.pdf

[calvin]

Was there ever a carb with adjustable high speed jets?

[Tim Weber]

You guys seem to be expert on this motor.

I have a 1993, 25 hp on my Lund fishing boat. To bump it up to 30 or 35 I've read to change the carb and the intake manifold. Is that it?

Tim