Topic: 1953 Johnson Seahorse 25 hp RD-15 not pumping water

This topic has 25 replies, 6 voices, and was last updated 4 years, 1 month ago by labrador-guy.

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April 30, 2019 at 7:57 pm #174578
KEVIN RINEHIMER
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US Member - 2 Years
This motor has a brand new water pump housing, impeller and plate. There is no water getting to manifold. It appears the copper water tube doesn’t reach the water channels near pump housing. Is the copper tube supposed to sit on the water channel or is there a grommet missing that connects the copper to the water channel? Several mechanics have looked at this motor and can’t figure it out.
Thanks for the help.
May 1, 2019 at 8:03 am #174603
Buccaneer
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US Member
Not sure what you mean by “water channel”. Are you saying the copper tubing isn’t long enough to
reach the pump discharge rubber grommet? I’ve worked on a RDE-17.
Not sure how much they differ, but don’t remember anything confusing on mine.

Prepare to be boarded!
May 1, 2019 at 11:00 am #174612
fisherman6
Participant
US Member - 2 Years
I think the confusion here is that the RD-17 has the later design water pump where the water tube plugs directly into the pump housing. I have not had an RD-17 apart but I have had a ’54 Big Twin and a couple of RD-16s apart and they do have a water channel in the area between the midsection and the gearcase. On these earlier ones, the seam between the two halves actually forms a channel into which the water pump discharges water. The water tube carries water from this channel up to the powerhead. It makes the gearcase easier to line up only having the shift rod and the drive shaft to be concerned with. It also means that the seam between the two halves must be pretty well sealed. There is supposed to be a gasket between the two halves to seal this cavity up. I have used a gasket in one of the three that I have worked on and the other two I used Yamabond on the joint at installation because I didnt have a gasket and didn’t feel like making one. I tried it once and it worked great so I did it again on the next one. If yours has a water tube that is not connected to the channel, that is likely the problem. So far I have not had one with the tube disconnected from the channel. If it is, it will just pump water into the exhaust housing and out into the lake without the cooling water reaching the powerhead. I do not remember if the water tube is fitted into a grommet in the midsection above the channel or if it is just flared at the bottom. I seem to remember being able to see the bottom edge of the water tube in the top of the water channel though. Someone else can probably fill in the gaps here.
-Ben

OldJohnnyRude on YouTube
May 1, 2019 at 1:34 pm #174622
frankr
Participant
US Member
Yep, what fisher said. The pump discharges into the groove around the rear of the gearcase, which connects to the water tube in the exhaust housing. 302636 grommet seals the lower end of the water tube to the exhaust housing.

I don’t recall there ever being a gasket between the gearcase and exhaust housing. I suppose it wouldn’t hurt if there was one though.

Obviously, none of this is going to work if somebody put a 1955-up lower unit on your ’53 .
May 1, 2019 at 2:11 pm #174625
KEVIN RINEHIMER
Participant
US Member - 2 Years
I attached a rubber hose to copper end and notched it on sides to accept the water through the channels and it sat flush on the water channels. Still no water pumping anywhere up on the block. The plastic groomer that is on the tube is not able to make a good seal so I used rubber braided high temp hose. It’s definitely a 53 lower unit without any water tube opening on pump housing. I did find that the impeller key pin spun below the impeller yesterday and I replaced with a bigger pin today. I noticed that the flat impeller plate became concave downwards after running motor. Not sure if that’s normal either.
Still open to suggestions to move forward.
Thanks for the advice.
May 1, 2019 at 3:22 pm #174629
fisherman6
Participant
US Member - 2 Years
Should be no need for any hose in there at all. I would remove that. As long as the tube is in the midsection properly, if the pump is moving water, it will get to the tube. The impeller plate is not flat. They are actually supposed to sit so the convex side is up (facing the impeller). If the drive key spun below the impeller something is not right. When all is correct with the gearcase, the drive key / pin will be close to the center of the impeller’s thickness. I’m not sure if it is possible to install this particular impeller plate upside down or not. I’m not sure what you have going on that caused that, but it sounds like there is another issue to be sorted out. If the drive pin actually bent the impeller plate down there is definitely another problem that need to be sorted out. I do not have one of these apart right now and for the time being I’m not able to post pictures on this site. When that capability returns, maybe I can post pics of one of mine. In the mean time, there may be someone else that has pics available of theirs and can post them here through an external host.

Frank,
It is likely if you don’t recall a gasket ever being there that there never was one there. I do have one of these that has a gasket installed in there and that gasket was there when I got the motor. It could have easily been a homemade gasket though. I did not look at it that closely and I just left it in place when I serviced the gearcase and replaced the impeller. I know the ones that I sealed up with anerobic sealer work great.

-Ben

OldJohnnyRude on YouTube
May 1, 2019 at 4:55 pm #174632
frankr
Participant
US Member
Any possibility that it is a long shaft with the wrong extension housing?

EDIT: Nope, crazy thinking there. The ’55-up gearcase and extension housing won’t bolt up to the pre-’55 exhaust housings.
- This reply was modified 5 years ago by frankr.
May 1, 2019 at 5:56 pm #174636
KEVIN RINEHIMER
Participant
US Member - 2 Years
It’s a standard length shaft. I wonder if the drive shaft may have been replaced with another or the spring in the gearcase is allowing too much downward movement of the shaft??? This is so frustrating. No wonder Bill Fischer got fed up with it and sent it away from his shop! If he couldnt fix it how will I? We will pull it apart again and see what happened when we ran it today. Next step is to put a liquid gasket between lower unit and exhaust shroud and see if the water will make it up the water tube. I think I needed to gasket seal the under side of plate to isolate the channels better.
May 1, 2019 at 6:46 pm #174638
fleetwin
Participant
US Member - 2 Years
Very interesting, would love to see a picture of this set up….Glad I showed up for school today….
May 1, 2019 at 6:48 pm #174639
frankr
Participant
US Member
With a normally operating water pump, it would take a rather huge leak at the seam where the lower unit and exhaust housings meet to have any significant effect. I just can’t see that being a no-pump problem. But no harm in sealing it anyway.
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