powerhead swap

[fsds123]

I'm having a hard time deciding between a partial rebuild and swapping powerheads since I can't seem to find any that are 1979 or newer (I have a 1979 115hp)

Found someone with a 1978 115. I've been told some 1978 115 hp powerheads will bolt on...would a serial number tell? Any other way? Is it a direct swap?

 

[tashasdaddy]

Re: powerhead swap

seems like it will check here http://www.evinrude.com/en-US/Accessories/Literature/?popup=true

 

[Dhadley]

Re: powerhead swap

The powerhead itself will bolt up to your 79 mid section. The block & crank are different than yours in that the 78 has a small center main journal. All that means is that you'll have to keep the block & crank together. You can't use the 70 crank in the 78 block etc.

You'll need to use the 79 intake manifold if you use the 78 block.

 

[fsds123]

Re: powerhead swap

Are the block internals and intake manifold the only differences? I.E. are the carbs, starter, electronics, thermostats etc etc the same for both?

I.E. can I just take the bare 78 powerhead (block with pistons, crank, intake manifold) and bolt all my 79 stuff on?

Again, I really appreciate all the help.

 

[Dhadley]

Re: powerhead swap

The 78 block will bolt right on your 79 mid. use your 79 intake and carbs. Use the 79 ignition. Inside the block - the rods & pistons are the same.

Make sure the motor you buy is indeed a 78, not a 77. Get a base gasket (powerhead mounting gasket) for your 79 115. On the block you're going to buy (78) all bolt holes must match up. If the middle 2 on each side don't match, it won't bolt up. The holes will only be off by about 1/2 the hole. It must be a perfect match.

 

[fsds123]

Re: powerhead swap

So only the crank is different as far as the bare block is concerned...I take it the 78 powerhead has some 73-77 and some 79+ parts...are there some parts you know for sure are the same..i.e. worth keeping to have a spare, like starter, powerpack etc? Or should I just use the block with all my 79 stuff and sell any remaining parts

 

[Dhadley]

Re: powerhead swap

Ok, this will get a little confusing but --
A 1973 V4 OMC is in a year all by itself. The block, crank, rods & pistons are different than a 72 or a 74.

A 74 style block will bolt up to a 73 mid section but you have to use all the 74 internals.

The 74 to 78 blocks all use the same crank, rods & pistons.

The 77 & 78 140 bloocks all have the late model bolt pattern for mounting but still use the small center journal crank.

A 25" 1977 85 & 115 blocks have the late model bolt pattern.

In 79 OMC went to a larger center main on the crank. To use a 79 & later crank you need a 79 & newer block.

If the front lower pan mounts are bolted on the block uses a small crank. If the pan mounts are cast in the block uses the 79 & newer crank.

The rods in all V4 crossflows are the same from 74 on. They also fit 60* V4's & V6's.

All 3.500" pistons are the same from 74 on. Some 85's were a smaller bore.

You can put a 79 & newer powerhead on an older mid but an older block with the old bolt pattern won't work on a newer mid section.

Bottom line -- if you buy a 78 powerhead for parts on your 79 everything will interchange except the cranks. The 78 crank has to stay with the 78 block & vis versa.

No matter which block (78 or 79) you use on the 79 mid section you'll have to use the 79 intake because of the shift linkage.

 

[Benny1963]

Re: powerhead swap

well guys yall lost me well done dh
good luck sounds like your on the ball with your swap.

 

[fsds123]

Re: powerhead swap

Very informative. Thanks!