Power-head Swap on 84 Evinrude 115 to 91 Evinrude 115

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dracer33

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I have a 84 Evinrude 115 with lower unit issues and i also have a 91 Evinrude 115 with power-head issues. The question is can I swap power-heads to make one good power unit?
 

lmuss53

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I'm not certain on the power heads, but the lower units will probably swap out and it's a much easier project. Look at a site that sells powerheads and see if the years use the same part number. I think the short blocks are the same, but the electrics might be somewhat different.

I started to swap an '89 or so 50 powerhead onto a '91 I have and found out the new motor uses a different CDI box than the old one, Since the previous owner kept the CDI box and the external electric parts from the '89 I have to pull the flywheel off the blown motor to swap out stator, timer base, coils, etc.
 

emdsapmgr

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The powerheads will interchange. Keep in mind that the 84 is a flatback 115. Hp rated at the crank. The 91 is a bubble back performance engine-hp rated at the propshaft. So the bubble back 115 will put out maybe 15% more hp than the flatback. Not a big deal, but you will probably have to run the 84 prop in order to get the performance you are looking for. Ther ignition systems are slightly different, so keep the ignition with the powerhead.
 

rothfm

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I did something Similar this past spring, and its still my runner....Blew up my 1993 bubble back 115, and already had a 1984 freshly rebuilt that came out real nice. I needed to get back on the water.....

While putting the '84 block on the existing setup...I Notice the block didnt sit fully flat onto the adapter plate (lower unit on). It rocked back and forth a bit. and it was binding when I rotated the flywheel. I removed the lower, to reinstall, and it wouldnt go in all the way.

If you search my posts, you will see that between those years there is a difference in the Crank portion that accepts that drive shaft, or vice-versa. I had to cut a bit off the top of the drive shaft, and grind in the "shoulder step-area" at the top of the driveshaft.

Only then, did the head sit flat on the adapter, and not bind the shaft...I knew I took enough off, when I couldnt feel the shaft binding anymore when turning the flywheel and/or prop.

I dont know if this applies to the 1991 also, But its just about identical to the '93 so I imagine it would.
 

emdsapmgr

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You can also have this problem if too much grease gets onto the top of the driveshaft as it goes into the bottom of the crank. That grease won't compress and that problem will cause the powerhead to not seat fully. You just can't overcome a hydraulic lock in this area. Just be sure any grease is sparingly applied to the vertical splines only. And that it won't accumulate onto the top of the driveshaft.
 

racerone

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Not a grease problem.---There were changes made in the early 1990's V-4 and you might encounter this binding when doing these swap outs.
 

dracer33

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Thank you All for you Knowledge. I will consider all your advise before I tear into this project. Thanks Again
 

Jackbrown08

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I did something Similar this past spring, and its still my runner....Blew up my 1993 bubble back 115, and already had a 1984 freshly rebuilt that came out real nice. I needed to get back on the water.....

While putting the '84 block on the existing setup...I Notice the block didnt sit fully flat onto the adapter plate (lower unit on). It rocked back and forth a bit. and it was binding when I rotated the flywheel. I removed the lower, to reinstall, and it wouldnt go in all the way.

If you search my posts, you will see that between those years there is a difference in the Crank portion that accepts that drive shaft, or vice-versa. I had to cut a bit off the top of the drive shaft, and grind in the "shoulder step-area" at the top of the driveshaft.

Only then, did the head sit flat on the adapter, and not bind the shaft...I knew I took enough off, when I couldnt feel the shaft binding anymore when turning the flywheel and/or prop.

I dont know if this applies to the 1991 also, But its just about identical to the '93 so I imagine it would.
Will this work
Can I Put my 84 evinrude vro power head on my 93 johnson vro... both are 115 hp
 
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