RD-17 Compatibilities? (Johnson 1955 25hp)

[johnyrude200]

I was trying to find the original topic, but after spending half an hour searching to find the old thread on these new forums I gave up, so apologies for asking this question again (not a fan of these new forums – BARF).

I have a RDE-17 (1955), low compression powerhead.

What other powerheads fit this exhaust housing, flywheel, and carburetor? I’d love to keep the motor original with another powerhead of that or 1954, but was curious where that extra 5hp came from in 1956?

Thanks

[adam1961]

You can use a powerhead frrom ’56 30 HP or 57/58 35HP. The powerbeads from the Gale built 40HP motors will also bolt up, but it must be a gale unit that is not a “super Quite” double wall exhaust leg. The ’62 and up motors had a bigger top end on the crank and will require you to use the flywheel that came with that engine.

The 5 HP increase from ’55-’56 came from a few places. Compression was in crease from 5:1 to 6:1. The area of the holes in the reed plate was also increased. Carns are the same. the 30HP pistons have the deflectors clipped off at the edges to work with teh higher compression head. Adding needle bearing to the small end of the rod also helped.

The earlier 25 HP powerheads will work, but were usually unpainted and had the cable setup for spark advance. You can swap over all of the accessories and make it work.

What is wrong with yours???

[johnyrude200]

The cylinders are badly scored, and soaking wet with fogging oil I can only get 90/95 compression. The motor had ice inside of the crank case too, so I wouldn’t be surprised if the journals and needle bearings are rusted. Not worth putting effort into to try and revive. The rest of the motor is in nice original condition though, and it is a tiller electric model (original), so I wanted to keep it original if possible.

At what point does the lower crank seal get switched over? I seem to remember rumblings about how the different seal wasn’t as good. I also seem to remember that the lower cowel, beneath the carburetor, should have a larger diameter hole put into it to allow the motor to breath better?

Again – can’t seem to find the old thread as I know this topic has been beat to death but I guess every 3 years our forums either get wiped out or ‘updated’ and we have to go through this all over again.

[olcah]

This is the old thread you were looking for.

https://aomci.org/forums/topic/rde-18-powerhead-to-exhaust-plate-gaskets/

[frankr]

Seal was a mid-year change on 1955 25hp, and changed back again to first version at mid-year 1956 30hp

[phil]

You can use a powerhead frrom ’56 30 HP or 57/58 35HP. The powerbeads from the Gale built 40HP motors will also bolt up, but it must be a gale unit that is not a “super Quite” double wall exhaust leg.

At least in 1958 weren’t there BOTH “super quiet” and single wall (super noisy?) models of both Evinrudes and Johnsons?

Was there EVER a “super quiet” Gale? I thought the Gale 40 had the single wall exhaust housing. as did the mid-sixties 28 and 33hp models. And didn’t the single wall (Gale) 40hp come back in the early seventies?

http://www.omc-boats.org
http://www.aerocraft-boats.org

[adam1961]

Phil,
You are correct. The Gales (Viking, Sea King, Wards, Elto, See Bee, Brooklure ETC) were always single wall.
In ’58 te regular RDs were single wall and the Lark/Susper Sea Horse had the double wall.

Johnyrude,
1955 was the last year for the tiller coming standard on all models. For ’56, they only put the tiller on manual models.
THere is a diffence in the top seals also. I learned teh hard way that if you getthe wrong bearing in the top of the motor, the seal sits too high and the flywheel won’t sit down right. I would have to go back and find my notes, but there was a thread on the old forum and we chased that issue for weeks.

I have built a lot of RD17s. I have torn down many powerheads and it is most likely that something in those motors is worn. Either the top or bottow wrist pin bushing, Bores etc. I have had much better luc finding good usable ’56 powerheads.

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