OMC Head-block-Piston questions 150-175 HP

[numlaar]

OK, I have the following:
1978' - 175hp (Evinrude)
1983' - 175hp (Evinrude)
1990' - 150hp (Johnson GT)
(Don't have the exact model #'s here with me at work, but can edit them in later if you need them).

The 1978'-175HP ran lean and burned 2 pistons. (Block is immaculate, very very clean, no corrosion, all bolts came out easily, etc.)
The 1983'-175hp overheated pretty badly, locked up, but freed up after it cooled down. (Block is so-so... not sure why it overheated, need to delve deeper, but has quite a bit of corrosion).
The 1990'-150hp I never ran on the water, but assume it overheated. It has a cracked block, and the worst corrosion I have ever seen, (completely salt clogged in every single water passage).(Started it up on the stand and it's spewing water from block cracks).

Between all three engines, I have 2 salvageable heads, 1-Left from 1978'-150hp, and 1-right from 1983'-175hp. I have shopped around and If i need to buy a set of heads, the only ones I can find still available in the range here, are 1982'-235hp heads. (#327124/327125).

Sorry for long back information, but relevant to my question(s). I need to try and take all three of these and put them together into one working motor. The block from the 78'-175hp and the pistons from the 90'-150hp, seem to be the best combination. I am not sure about bore sizes and what parts are good to interchange with what, so... here are my question(s):
1. Will the pistons/crank assembly from the 1990'-150hp fit into the block for the 1978'-175hp?
1.a.(if not, will the pistons/crank from the 83'-175hp fit in the 78' block)?
2. If I use the 150HP-pistons and everything else from the 175hp(Carbs, heads, etc.), will I reduce my HP?
3. Will it be ok to use the intermix year heads? and will the 83'-175hp head be ok on the 78'-175hp block?
4. If I need to use the 1982'-235hp heads, will they just bolt on, or would i have to do additional machine work?

Thanks in advance for any and all help you can provide. I dont want to dump 500+ into putting this thing back together only to find it it locks because something doesnt fit.

[faztbullet]

Will the pistons/crank assembly from the 1990'-150hp fit into the block for the 1978'-175hp?
My book shows 76-77 as the same ,78-85 as a bump crank and 86-90 as a double seal crank. The 83 should fit and pistons are no problem just make sure they are 3.500 pistons.

If I use the 150HP-pistons and everything else from the 175hp(Carbs, heads, etc.), will I reduce my HP?
You will have a 150.......

Will it be ok to use the intermix year heads?
No you need to use a matching pair of castings as CC's in chamber differ from different years

will the 83'-175hp head be ok on the 78'-175hp block?
Yep....

If I need to use the 1982'-235hp heads, will they just bolt on, or would i have to do additional machine work?

Make sure they are true and change t=stats and shoud be a bolt and go deal

[numlaar]

My book shows 76-77 as the same ,78-85 as a bump crank and 86-90 as a double seal crank. The 83 should fit and pistons are no problem just make sure they are 3.500 pistons.

OK I will use the 83'-175hp crank/piston set then instead of the 1990'-150hp set.



No you need to use a matching pair of castings as CC's in chamber differ from different years &
Make sure they are true and change t=stats and shoud be a bolt and go deal


OK cool, thanks! I ordered the set of 235HP heads.

So here is my plan:
take 1978'-175HP block
Use 1983'-175HP pistons/crank
Use new - 1982'-235HP heads.
Use 1990 ignition (Flywheel, timer base, magneto, etc.)(newer and single powerpak style, with easy change coils, plus easier to mount, as the 78 block doesnt have the castings to use the L/R powerpaks).
Use 1983'-175hp carbs (after rebuild).
New waterpump, t-stats, etc.

Sound good? or need any revisions?

IF i am right, I should end up with at least a 175HP like I had previously?

[dzalj1]

everything sounds good but, if your using the 3.500 inch bore block and pistons, the 82 model 235 heads will be useless as they are to suit the bigger bore xflow at 3.625 inch bore (i think them numbers haha) maybe someone can add ther .02?

[numlaar]

everything sounds good but, if your using the 3.500 inch bore block and pistons, the 82 model 235 heads will be useless as they are to suit the bigger bore xflow at 3.625 inch bore (i think them numbers haha) maybe someone can add ther .02?

Ouch. OK I wasnt sure what the bore size on this set was... just assumed was a 3.500... but we all know what assuming does.

Thankfully, another member on the site has a set of 200hp heads I just bought. (It was actually the reason I found this site, because I was doing a search on the head part numbers). But anyway, thanks for the info. I will check them when they come in, and send them back if they are the wrong bore.

New here, but really appreciate the help so far!

Thanks again.