1950's to 1970's 22 cubic inch powerhead swap.

[samo_ott]

So who knows the 22 cubic inch engine well? It has a long great history. I recently picked up a 20BA75B which seems to be quite a rare bird. It's a Johnson 20hp from 1975 made in Canada. It appears to be the same as the 25hp engine from that same year other than the fact that the 25 revs at 1,000 rpm faster. The 20hp came missing most of the ignition parts up top including the flywheel and looking in pretty rough shape. It also has external coils. So my question is two fold, a) can an older 22 cube engine from the late 50's with magneto's bolt up if I wanted to change the power head outright, or can I move the entire ignition plate and flywheel over off a similar vintage engine and get it up and running? Any ideas or comments would be appreciated. Thanks, Steve.

 

[levi_tsk]

Re: 1950's to 1970's 22 cubic inch powerhead swap.

check the powerhead gaskets samo if theyre the same itll bolt up as for the driveshaft and other stuff i dont know but id count the spines and compare -my guess would be no as omc was always tweeking and refining the designs of their engines ESPECIALLY in the fifties and sixties some things changed every six months....

 

[1946Zephyr]

Re: 1950's to 1970's 22 cubic inch powerhead swap.

One thing to look for, is the water circulation. Newer motors from 1959 on have thermostats. so, if you go that rout, make sure the water circulation system is the same. And yes, sammo, the 22 cube is probably the best ever built, in my book.

 

[samo_ott]

Re: 1950's to 1970's 22 cubic inch powerhead swap.

I did check the power head gasket #'s and they are different but they could just be a part # change as they looked the same. And Zephyr, good point about the thermostat, forgot about that part but no problem thought as I could just use an early 60's power head. I prefer the idea of just changing the ignition plate over to magneto's though if I can. No idea if all the same holes are bossed onto the block though. If I get the time it could be an interesting experiment.

 

[1946Zephyr]

Re: 1950's to 1970's 22 cubic inch powerhead swap.

yea, early 60's oughta work. I think the older ignition system will work, if the components will mount up. Yea, I think it's worth a shot

 

[F_R]

Re: 1950's to 1970's 22 cubic inch powerhead swap.

The powerhead bolt pattern was changed, accounting for the different gasket. There were so many other changes from year to year, that it is pretty hard to keep up with them. Is there a particular reason you don't want to simply look for the correct magneto and flywheel for your motor? It has the Low Tension mag, which some people are not too fond of, but hey, they work.

BTW, the 20-25 have more differences than the RPM. Different pistons, different head, different crankshaft, different carburetor, etc. It is those differences that allow it to make the extra horses that make it rev up higher.

 

[samo_ott]

Re: 1950's to 1970's 22 cubic inch powerhead swap.

The main reason for doing it is that I have all the older parts, lots of older mag plates, coils, etc and I like and know the system reasonably well. So if it bolted on it'd be great.

 

[samo_ott]

Re: 1950's to 1970's 22 cubic inch powerhead swap.

Good news. I checked the ignition plate part numbers today and they matched from the '75 20hp to my '65 18hp parts motor even though the 20 had the later ignition and the 18 had the magneto's. So I believe I can make it work as now I know everything will bolt up. The 20 also came without a flywheel so I also got a spare from the 18. And I see the reason the PO took the flywheel off (and subsequently lost it). The key was sheared off. So once I got the new flywheel on I got to turn the engine over for the first time and compression seems reasonable (by hand).

The top of the casing is broken above the main bearing though I found out. Does anyone think it will be an issue? It does not look like it to me but I could JB weld it some. Photo attached.

 

[samo_ott]

Re: 1950's to 1970's 22 cubic inch powerhead swap.

Success! Runs like a top. I love nice n easy magnetos (other than a minor lean sneeze - gotta clean the carb I reckon) Everything fit on well. Strong blue spark. Much cleaner, simpler engine with everything under the flywheel. I like the streamlined look! I even took the flywheel ring off. Those things are heavy. Had no idea it was that heavy.

Oh and also the timing cams were different so I kept the one from the magneto plate figuring that the timing curve for the magnetos would be different from the timing curve on the external coils plate. But so far this is just a guess as I have only run it in a barrel.

 

[jbjennings]

Re: 1950's to 1970's 22 cubic inch powerhead swap.

Nice work Steve!

I just made a trade and got a '75 25hp electric start johnson. It appears to run good in a barrel as well, but no lake test yet.
Mine looks just like yours.
Later,
JBJ

 

[samo_ott]

Re: 1950's to 1970's 22 cubic inch powerhead swap.

Yep, that's pretty much the same engine. Should be fast. I paid $50 for mine but needing parts.

And if you want to make the ignition simpler it's pretty easy!