'70 20 or 25hp to '57 18hp Pwrhd transfer?

[jbjennings]

I was just curious if anyone had tried to transfer a 22cub. inch 25 hp powerhead or a 20hp 22inch powerhead to an old '57 johnson 18hp. Would it bolt in? I'd love to put a 25 hp on my old 18, especially if the 25hp had electric start. Anybody tried such a thing? It sure would be fun to run off and leave some of these newer motors with one of my oldies.....
JBJ

 

[samo_ott]

Re: '70 20 or 25hp to '57 18hp Pwrhd transfer?

JBJ, you sure like mixing and matching engines eh!

BTW, why don't you just get an electric start for your '57 18?

 

[River - Runner]

Re: '70 20 or 25hp to '57 18hp Pwrhd transfer?

You can also include 1969. The first year for 25 hp. years with the 22 cubic in.

 

[jbjennings]

Re: '70 20 or 25hp to '57 18hp Pwrhd transfer?

Steve,
Is it easy to find a setup for electric start on the '57 18? I probably won't put a bigger hp. setup on my 18 'cause they're too nice like they are. I just saw some interesting cheap parts the other day and started "thinking". I would like to have e-start on one just for fun. I like to pull on 'em anyway. You don't know if a bigger powerhead from '69 or '70 will bolt on, though? I thought it might since the mid sections look so similar, and you know that a lot of people just junk their old motors when the lower unit goes out. I guess the drive shafts might not match though even if the bolt pattern did. I probably better give up on the plan before I get started after this debacle with my QD-14. It's been cold so I haven't cleaned the carb yet.....I'm pessimistic about the fix, though. I wish F-R would get back from his holiday so we can sqeeze that computer-brain of his for some more outrageously obscure info. that he'll probably immediately know the answer to.
Later,
JBJ

 

[jay_merrill]

Re: '70 20 or 25hp to '57 18hp Pwrhd transfer?

Actually, I was kind of thinking about an Allison T-58 for one of my Bigtwins!

 

[cc67]

Re: '70 20 or 25hp to '57 18hp Pwrhd transfer?

I'm using a drive shaft from a 67 Johnson 20hp in my 58 fastwin right now. It drops right in.

 

[Chinewalker]

Re: '70 20 or 25hp to '57 18hp Pwrhd transfer?

However, you can't just drop a 1959 or later 22-cube powerhead onto a 1958 & prior lower unit. Your cowlings will no longer fit without some serious modificaitons. 1959 & up had thermostats in the cylinder heads and lacked the ears to support the cowling, so there is no swapping of parts that will achieve what you want... except if you take the 1968 & up 20hp innards, intake & carb and swap them into a 1957 & prior cylinder block & crankcase. That would give you the later style pistons (2-rings) and improved bearing arrangement on the rods, plus the bigger bore carb & intake. Might notice a bit of an improvement in performance, particularly on a light hull with a good prop. The 25hp pistons have a different dome and can only be used with the 25hp cylinder head - which will not work on a 1958 & prior block...
- Scott

 

[samo_ott]

Re: '70 20 or 25hp to '57 18hp Pwrhd transfer?

Steve,
Is it easy to find a setup for electric start on the '57 18? I probably won't put a bigger hp. setup on my 18 'cause they're too nice like they are. I just saw some interesting cheap parts the other day and started "thinking". I would like to have e-start on one just for fun. I like to pull on 'em anyway. You don't know if a bigger powerhead from '69 or '70 will bolt on, though? I thought it might since the mid sections look so similar, and you know that a lot of people just junk their old motors when the lower unit goes out. I guess the drive shafts might not match though even if the bolt pattern did. I probably better give up on the plan before I get started after this debacle with my QD-14. It's been cold so I haven't cleaned the carb yet.....I'm pessimistic about the fix, though. I wish F-R would get back from his holiday so we can sqeeze that computer-brain of his for some more outrageously obscure info. that he'll probably immediately know the answer to.
Later,
JBJ

Most of them are set up for electric start. Do you have a toothed flywheel on it? If so then you only need to bolt on the starter, electric choke solenoid and wiring harness.

FR's away? I had no idea. where'd he go that has no internet? Bora Bora?