Topic: 1956 Johnson 30 HP casual q’s – Antique Outboard Motor Club,Inc

This topic has 10 replies, 6 voices, and was last updated 5 years, 9 months ago by 1946zephyr.

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June 6, 2018 at 10:01 pm #10180
olcah
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Looking at the photos the powerhead is primed but not painted. it has no serial number and the exhaust cover and transfer covers are not even primed. The intake manifold is painted. Also the lower crank seal is the carbon type. I think this is a replacement powerhead?

The exhaust has the earlier type silencer with the tubes. It also had the large baffle plate and so it used two exhaust gaskets. I am going to discard the large baffle plate and go with one gasket. Looking at the photo of the powerhead exhaust the old gasket is the thinner type and in good condition. I am thinking of just putting 847 or Johnson/Evinrude gasket sealant on the mating surface of the leg and putting the powerhead and leg together.
Will I get into trouble if I just seal the gasket like that ?? 😎

I notice that the inner exhaust plate (under the exhaust cover) appears to be aluminum. A second similar motor appears to be aluminum also. (checked by just scratching the edge of the plate.) Seems somewhere there was comment that such a plate may erode. Is that so?

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June 7, 2018 at 12:04 am #77562
chris-p
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Looks like it was put together from a few different motors?

Yes the inner exhaust plates can corrode and form pin holes in them. They need to be checked during tune up.

Are you saying you want to just use 1 thin gasket with no baffle? Is that just to save on the cost of a gasket?
June 7, 2018 at 12:25 am #77565
dan-in-tn
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This would be typical of a replacement powerhead as you stated. The parts used from his original motor are painted.
The crankcase, heads, etc were pressure sealed in red primer before machining up through mid 80s. OMC didn’t paint their replacement P/Hs until they went black across the board. Different assy. process. The red primer process went away. If the dealer didn’t move the chip or paint the powerhead before installation it looks just like this. Lots of customers were not happy when this happened to their new engine.
Not making excuses, but think about it. Inventory of powerheads would have been a nightmare. You would have had to have copper colored ones (Johnson), blue (Evinrude), not sure about Gale, Sea Bee, or other makes. This would have been for all horsepower lines. It could change each year even if the powerhead didn’t? That was the reason they gave later on. When the P/H assy. went black, no problem.
The baffle is almost a matter of personal preference? I put them in. I never saw a SB that said take them out. If there is one I would be interested in seeing it.

Dan in TN
June 7, 2018 at 12:34 am #77566
olcah
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Chris,
Not to save the cost of a gasket. There is an earlier extensive discussion about the use of the big baffle plate here viewtopic.php?f=2&t=10757 . From that I put together another RD18 without the baffle. I used that a lot last summer and had no problems. That was the experience of others too. It is the same as the original setup on the 1955 RD17s. Not to revisit that long discussion but RD17s and RD18s have run fine with and without the baffle.
I would like not to replace the existing exhaust gasket if that is possible. Prefer not to deal with removal (asbestos) although in the past I always used new exhaust gaskets.
Appreciate the comments Chris and Dan.

Can anyone address the question of reusing the gasket?
June 7, 2018 at 12:46 am #77567
frankr
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Agreed, a replacement powerhead. The early 1956 30hp motors had the troublesome 303804 lower seal, which was continued from the late 1955 25hp motors. Lots of powerheads got replaced because of that seal letting water into the crankcase.

I found out about that aluminum inner exhaust cover the hard way. That was an expensive come-back job. You can spot the aluminum cover easily. It is thicker. The stainless steel ones are only about as thick as a credit card.
June 7, 2018 at 12:53 am #77568
olcah
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Frank,
I see the plate is thick although I am running in fresh (not brackish) water here. Sounds like I still need to check.
Thank you.
June 8, 2018 at 12:17 am #77621
fleetwin
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I would replace the gasket, use the baffle plate and second gasket as well…
June 18, 2018 at 9:44 pm #78138
olcah
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Today I removed the old engine exhaust to exhaust leg gasket and will use a new one. Also opened up the exhaust cooling to check for corrosion and after cleanup the plate has numerous small pinholes that are not deep. I saw one larger area that could be corrosion. The two arrows on the tape in the photo point to it. It is maybe 0.015/0.020 inch into the material. The plate is (looks like) made of aluminum that is 0.093 thick before forming. So I will replace the exhaust cooling plate gaskets and put it together. I plan to use 3m 847 to seal the cooling plate gaskets . Does that seem reasonable?
Thank you.

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June 24, 2018 at 6:32 pm #78380
olcah
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Update – I took two other parts motors apart and checked the exhaust cooling plates. Both were in worse condition than the one in the photo above. The parts engines are a 1956 RD18 30 HP and a 1953/54 Evinrude 25 HP. Both of the plates had one or more deep pits that are not through. I will probably use JB Weld on the one above or look around for a NOS part. The part number is 302549.
July 17, 2018 at 8:39 pm #79670
olcah
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Just to close this out for reference, I put in a NOS exhaust cooling plate obtained from ede (Ed Elliot). Thank you Ed.
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