18 mod

Sirrobin53

Sirrobin53

Petty Officer 2nd Class
Joined
Mar 13, 2012
Messages
189
good morning. I have found Dad's old crestliner and want to use a 1957 johnson tp power it. Seeing that those old motors were plain bearings i was wondering if a 1972 25hp block could be coaxed in that wonderful aluminum cowel. I am certian some one of the whizzes here can guide me.

Thanks
 
D

Daviet

Fleet Admiral
Joined
Sep 24, 2008
Messages
8,958
Re: 18 mod

Welcome to the forum.
I can't answer your question directly, but if you look up the part number for the power head gaskets for both engines, it would tell you if they would bolt up.
Nothing wrong with those old motors, as long as you used the proper oil/fuel ratio, lots of them still providing great service to many people.
 
Chinewalker

Chinewalker

Fleet Admiral
Joined
Aug 19, 2001
Messages
8,902
Re: 18 mod

Not without some significant cobbling together. The 25 doesn't have the cowling support brackets, and the 18 doesn't have a thermostat, so the heads aren't interchangeable. The major differences are the 25 has a counter-balanced crankshaft, higher compression head, and different pistons, as well as porting.

The 18 is not plain bearing. It has roller/needle bearings on the crankshaft top to bottom, and on both ends of the rods.
 
Sirrobin53

Sirrobin53

Petty Officer 2nd Class
Joined
Mar 13, 2012
Messages
189
Re: 18 mod

Chinewalker said:
Not without some significant cobbling together. The 25 doesn't have the cowling support brackets, and the 18 doesn't have a thermostat, so the heads aren't interchangeable. The major differences are the 25 has a counter-balanced crankshaft, higher compression head, and different pistons, as well as porting.

The 18 is not plain bearing. It has roller/needle bearings on the crankshaft top to bottom, and on both ends of the rods.
Click to expand...

Some info i have read suggests that in 57 they were plain bearings and in 58 were upgraded to caged bearings. I never blew one up so have not had one that far apart. I was just wondering if a newer 25 block could be squezzed? in the cowl so oiling would be an easy 50:1 (also a little more hp as i have gained a little WAIT:) I understand that there may be a small amount of fab work to get the mounting of the hood right but if i stay as close to 57 maybe like 68-9 some of the old bosses and mounting positions may still exist. May be a foolish idea but I seem 2 B quite the fool these days. I want the 57 look with 25 fa tass pushing horse power:) I believe that the 22 ci 25 was full circle stuffed crank higher compression and about the finest made by omc. Would be a great upgrade if it could be done. Good idea on the gaskets. I am looking them up now. 18 and 25 hp in 1969 use the same gasket so there is hope........
 
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