35 omc

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08-22-2011
JohnsonM50

35 omc

Question on the OMC 31.8 motors. Ive modded a few of these & always look for more performance. Ive heard the 82 year model was the best [at least of the older ones]. I finally get one to rebuild in a trade & find the sleeves loose. What got my attention is the head, there's many subtle & a few major differences in these motors over the years & hp's but this is the 1st of this type head Ive seen.

http://i35.photobucket.com/albums/d1...5/DSCN1078.jpg
http://i35.photobucket.com/albums/d1...5/DSCN1083.jpg
http://i35.photobucket.com/albums/d1...5/DSCN1084.jpg

The difference is on the intake side of the head [3rd pic] & Im pretty sure it had the same deflector piston as usual. This looks to be padded there more than the other & is different at the plug too. Could this be why the '82 is said to be stronger? The timing spec for motors with this head would be of interest.
08-22-2011
Powerabout

Didnt the 78's come out with high ring pistons, they went well.

I think most of the later mods were to make them more durable so they could replace the old 40 that the military used around the world.

If anyone still has the dealer notes from those years its all in there
08-23-2011
JohnsonM50

Quote:

Originally Posted by Powerabout

Didnt the 78's come out with high ring pistons, they went well.

I think most of the later mods were to make them more durable so they could replace the old 40 that the military used around the world.

If anyone still has the dealer notes from those years its all in there

, 1 I have with high rings does run a little faster, I don't think the 82 had them from what I can see at BRP.. Im thinking about a combination motor of all the improved performance parts. The head in question has more material in the combustion chamber on the I side but is dug out a little more around the plug hole. Ill cc it to compare. There is a 35 of this type used for military, the a Navy Seal version that has a high efficiencey enclosed prop set up & a crank case purge valve to evacuate & quickly start a motor that was submerged.
04-22-2012
JohnsonM50

I saved a 2nd effort list of parts for the 35hp's to be a mod C.
http://i35.photobucket.com/albums/d151/mes355/modc.jpg
The head I found on this motor appears to be the 2nd effort version. Put it on & try it out is the temptation but from the condition of the motor it came from I want to ask. Is there a timing spec change needed to run this properly? or did this motor end up with holes in the pistons & badly scored & loosened sleeves from overheating, plugs too hot, gas w/o oil? Or could the head have been run with improper time, wrong gas & detonating? Any help or information direction appreciated, Thanks.