Topic: 1956 Johnson 30hp, RD-18 – Antique Outboard Motor Club,Inc

This topic has 22 replies, 9 voices, and was last updated 5 years, 1 month ago by jeff-register.

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March 19, 2019 at 11:21 pm #171564
bobw
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I’m looking at a 56 Johnson RD-18 with a total junk powerhead, but I have access to a good condition 57 Johnson RD-19 35hp powerhead. Will the RD19 powerhead mate up to the RD18 exhaust leg and driveshaft or is there some trickery involved in making that work?

Bob

1937 Champion D2C Deluxe Lite Twin
1954 Johnson CD-11
1957 Evinrude Fastwin 18
1958 Johnson QD-19
1958 Johnson FD-12
1959 Johnson QD-20

“Every 20 minute job is only a broken bolt away from a 3-day project.”
"Every time you remove a broken or seized bolt an angel gets his wings."
March 20, 2019 at 1:43 am #171569
frankr
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No problem that I can think of, doing the whole powerhead. Of course there are internal differences though.
March 20, 2019 at 1:52 am #171570
frankr
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The 35hp has the compression relief. No law saying you have to use it though. In fact, many of them get disconnected.
March 20, 2019 at 8:38 am #171579
mas
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Because of the compression relief…hoods are different lengths? Might be other issues too.

Mas
March 20, 2019 at 12:01 pm #171593
bobw
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Hadn’t thought about a difference in the cowls between the 2 models. My parts listing for both motors does show different cowl part numbers between the 2. The parts lists indicates both models share the same crankshaft and pinion gear numbers, but the driveshaft numbers are different?? Maybe need to keep looking for a ’56 powerhead….

Bob

1937 Champion D2C Deluxe Lite Twin
1954 Johnson CD-11
1957 Evinrude Fastwin 18
1958 Johnson QD-19
1958 Johnson FD-12
1959 Johnson QD-20

“Every 20 minute job is only a broken bolt away from a 3-day project.”
"Every time you remove a broken or seized bolt an angel gets his wings."
March 20, 2019 at 12:43 pm #171596
olcah
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I’d be surprised if the cowls do not interchange. Can you borrow/try your cowl on the RD19 powerhead?
March 20, 2019 at 1:22 pm #171597
bobw
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I don’t have the RD18 in hand yet and a friend of mine has the powerhead for the RD19 but not the cowl. I was going to pick up the RD18 if I can verify the possibility of making this swap ahead of time. The lower pan numbers on both motors appear to be the same so it seems the cowls would interchange. I suppose there’s always a possibility that the cowl part number from my original RD18 parts list has been superseded by a new number that I don’t have.

Bob

1937 Champion D2C Deluxe Lite Twin
1954 Johnson CD-11
1957 Evinrude Fastwin 18
1958 Johnson QD-19
1958 Johnson FD-12
1959 Johnson QD-20

“Every 20 minute job is only a broken bolt away from a 3-day project.”
"Every time you remove a broken or seized bolt an angel gets his wings."
March 20, 2019 at 3:01 pm #171613
frankr
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The numbers would be different if for no other reason than the color/decals. I’d be surprised if the comp release made a cowl change, but never say never.
March 20, 2019 at 3:05 pm #171617
frankr
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Well sure the drive shaft numbers are different because the pinion gear is different in the lower unit. But that’s got nothing to do with the upper end.

EDIT: You said the pinion gears are the same?? One of got the wrong info.
- This reply was modified 5 years, 1 month ago by frankr.
March 20, 2019 at 3:08 pm #171619
bobw
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Best case scenario is I can salvage the existing powerhead. Latest news today is that the current owner only called it “total junk” because he can’t turn it over. I asked if he thought it was a powerhead or a lower unit problem. His response was “I don’t know anything about these motors, I’m not a mechanic”. In the pictures he sent me it doesn’t look to be all that bad. I’ll go look at it and see what the real story is.

Bob

1937 Champion D2C Deluxe Lite Twin
1954 Johnson CD-11
1957 Evinrude Fastwin 18
1958 Johnson QD-19
1958 Johnson FD-12
1959 Johnson QD-20

“Every 20 minute job is only a broken bolt away from a 3-day project.”
"Every time you remove a broken or seized bolt an angel gets his wings."
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1956 Johnson 30hp, RD-18

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