Swap 1958 Evinrude 18 HP powerhead onto 1956 Johnson 15 HP exhaust housing

[olcah]

Has anyone tried this swap?  I may be able to put together an 18 HP powerhead from parts to replace a bad 15 HP one.

Thank you.

[Olypopper]

I have not but have you compared base gasket part numbers between the two?

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olcah

[opposedtwin]

I had a friend who put an 18 hp johnson on a 15 hp johnson.

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olcah

[olcah]

Olypopper,

Both motors can use base gasket 304588.    That’s good, but possibly connections may still not line up.

Opposed twin –  I wonder what the motor and exhaust duct years are.

Thank you both.  I am hoping to hear from someone who has tried this swap.   I know to use the Johnson hood would require changing the 18HP Evinrude head to an 18HP Johnson one.

[olcah]

Just put an empty 1958 Evinrude crankcase onto the 1956 Johnson leg.  The powerhead attachment screws all went in fine.  I will look for useable crankcase internals next. 🙂

[outbdnut2]

I think that Swap will work, but since you are putting an Evinrude powerhead on a Johnson lower,  if your plan is to put the Johnson top case on, you will have to swap whatever hardware necessary to mount the different clamshell case, including carb knob adjustment parts., but you probably already knew that.

Dave

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olcah

[olcah]

Yes, outboardnut2, I do have cover, faceplate, lower pan parts from the 15 HP Johnson and hopefully they will fit.

[fleetwin]

olcah wrote:

Yes, outboardnut2, I do have cover, faceplate, lower pan parts from the 15 HP Johnson and hopefully they will fit.

Yes, but the head mounts are different.  The Johnson hood has bumpers in the back, the Evinrude bumpers are on the side.  In later years, the 18HP heads might have had a common head casting with mounts for both brands.  The forward starter mount brackets are probably different as well, but you could use the brackets from the 1956 15hp, on the 18hp block.

Please don’t try to swap the cylinder heads though, the two engines have different bore sizes

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olcah

[olcah]

Fleetwin,

Thank you.

So I would need a 1957 or 1958 18 HP Johnson head.

I also need a crankshaft, pistons, rods, and bearings to go into the 1958 crankcase.  I have a damaged 1961 powerhead.  Maybe the crank and pistons will be useable and will interchange.

Like working a puzzle.  🙂

 

[fleetwin]

OK, I think I understand now.   You have an empty 18hp crankcase??  So yes, you will need a cylinder head from a johnson 18hp, 57-58.  I think your forward side recoil cover brackets from the 15hp will work, they have the rubber bumpers on them.  Unfortunately, the 1961 18hp crankcase is set up for a thermostat, so the original style cylinder head will not fit properly.  I’m pretty sure the crank/rods/pistons could be used in a different/older 18hp crankcase though.  Don’t forget, your original 15hp carburetor will probably have to be changed as well.

Why is it that you want to convert this 15hp to an 18hp??

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olcah

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