Grommet or Plug Needed? 1963 75hp

[yorab]

I have my adapter plate and exhaust housing back together now but something struck me as odd. Should there be any grommets or plugs covering the "3rd hole" and the shift rod hole between the upper cavity and lower cavity of the outer exhaust housing? My first pic shows the 3rd hole that lies between the two holes where the water tubes pass through. The 2nd pic shows the hole where the shift rod comes down through on models with manual shift. I have electric shift. It seems that the designers wanted a good seal between the upper and lower cavities as evidenced by the tube grommets and by the inner-to-outer exhaust tube ring seal. If the two areas should indeed be separated, then I must be missing hole plugs, though my parts manual does not show them.

I know that some exhaust gas must be allowed to pass to the upper cavity while the boat is stationary because the suction effect that pulls the exhaust out the bottom doesn't exist unless the motor is moving through the water. Therefore, the exhaust travels to the upper cavity and then out the bellow in the back of the exhaust housing. That being said, pic 3 shows what appears to be a slit-shaped hole that is probably for just that purpose just under the exhaust bellow. Are all of these holes supposed to be open?

Lastly, as I was thinking about all of this, I realized that no cooling water pours directly into the upper cavity of the exhaust housing. Does anybody know where the mist comes from that spews from the bellow? Thanks.

 

[yorab]

Re: Grommet or Plug Needed? 1963 75hp

I've attached a pic of the upper cavity from my parts motor. It happens to be a manual shift though mine is electric. You can see the two holes for the water tubes to pass through and the "3rd hole" that apparently remains open. Perhaps it is meant to be a drain hole for any water that may splash through the exhaust bellow and into the upper cavity. Since the parts manual doesn't mention a plug and my parts motor doesn't have a plug, I won't worry about plugging that hole.

I'm still curious as to where the water mist comes from that comes out of the exhaust bellow. I can only think that maybe the water comes from the 1/32" hole in the inlet water tube. It would have to then somehow pass up through the slit that is just under the exhaust bellow or the "3rd hole" and then out the bellow. Seems a bit improbable, but it's the only thing I can think of.

 

[F_R]

Re: Grommet or Plug Needed? 1963 75hp

The hole in the water tube is to cool the electric shift cable. The 3rd hole is normal and open. The water tube grommets merely support the tubes and isolate them from the housing.

I believe the water exiting the powerhead goes through the powerhead adapter. Without having one in front of me, I cannot be more specific.

 

[Willyclay]

Re: Grommet or Plug Needed? 1963 75hp

Lastly, as I was thinking about all of this, I realized that no cooling water pours directly into the upper cavity of the exhaust housing. Does anybody know where the mist comes from that spews from the bellow? Thanks.

First, my disclaimer! I am not an expert like F_R but I think ALL the cooling water exits through the exhaust passage. The "valley" between the cylinder banks is where the exhaust leaves the cylinders and it is contained by a two-chamber cover. The chambers are separated by a SS plate. Cooling water is constantly routed through the outer chamber of the exhaust cover to keep that area of the motor cooler. This pressurized water exits the outer chamber into the upper exhaust housing along with the exhaust gases AND the spent cooling water from the thermostat housing by way of the powerhead-to-housing adapter plate.

I have enjoyed your threads about rebuilding this motor because our family had many great years with our 1962 Johnson 75 with electric shift. I still have a 75HP V4 powerhead in my parts bin not to mention a complete 1968 Johnson 100 with electric shift that needs work. Your attention to detail with that great old motor has been very interesting. Good luck!

 

[samo_ott]

Re: Grommet or Plug Needed? 1963 75hp

Yorab, your exhaust housing is spotless! It looks like the engine has barely been run!

 

[Evinrude Boater]

Re: Grommet or Plug Needed? 1963 75hp

My 64 had the same open hole. The adapter plate seals off that area so no exhaust is leaking up into the engine.

 

[yorab]

Re: Grommet or Plug Needed? 1963 75hp

Evinrude Boater, which tube is the shorter inlet tube on your adapter plate-the starboard pipe or the port pipe? I'm 99.9% sure that the shorter tube goes to port side, but I'd like to be 100% sure. Thanks.

 

[Evinrude Boater]

Re: Grommet or Plug Needed? 1963 75hp

The water inlet is on the port side and outlet on the starboard. If you look at my photo, the tube on the right side of the photo is the outlet pipe. It has the bend in it to route it back behind the water pump.The diagrams on the Evinrude web site for the 1968 85hp are generally the same.

 

[yorab]

Re: Grommet or Plug Needed? 1963 75hp

So just to close this up, I'd like to share a few pics that I took. I sure wish that I could change the title of this thread to point out that this is a final update, but I don't think that's possible.

Anyway, I had some time to look at the adapter plate a bit closer. The 'hot' water is expelled from the bottom of the adapter plate just behind the inner exhaust tube as some of you had indeed mentioned. This expulsion hole is directly connected to a thermostat passage. As the water reaches a pre-determined temperature as determined by the vernatherm, the 'hot' water is expelled and 'cool' lake water is pulled into the circuit by the water pump.

I had trouble visualizing this because, for some reason, I thought that the water was expelled from the cooling system further down toward the pump somewhere. I don't know why I thought that; I just did. Of course it makes sense that the water is expelled at the adapter plate since the thermostat is located there and it is what controls the expulsion. So the exhaust gases and the expelled 'hot' water can both end up in the upper cavity of the exhaust tube. It makes sense that a few holes are left open so that water can drain from that area.

Willyclay, thanks for the nice comments. Keep an eye out as I'm soon going to finish my rebuild and I'll post a rebuild thread that takes into account everything that I've learned along the way.

 

[yorab]

Re: Grommet or Plug Needed? 1963 75hp

Yeah, the pics...

 

[boldtr]

Re: Grommet or Plug Needed? 1963 75hp

Before you attach your lower unit, you can hook a garden hose directly to your inlet to ensure that your don't have any leaks in your heads, thermostat, hoses, etc. I used 5/8" heater hose plus a cheap garden hose coupler from Lowe's.

You can adjust the pressure with a valve (see pic). At high pressure, you will see water passing out the water return pipe when the pressure control valve in the thermostat opens. Of course, your vernatherm will stay closed unless you actually run the motor this way, but the valve on the vernatherm has a small pass by (it looks like a small groove). Thus, a small amount of water will pass through the vernatherm valve even while cool. You will see this water run out the passage you noted in your pics. This will run down the exhaust tube and be visible through the water discharge exhaust port. This will provide a visual indicator of water flow when the engine first starts even though the water is not hot. The amount of water discharged will increase significantly when the vernatherm opens. This also changes the audible sound of the motor exhaust.

Note: I have two small holes in my inlet tube. These will spray when using the hose. I believe these help to drain water from the inlet. They may also help cool the exhaust tube.

 

[yorab]

Re: Grommet or Plug Needed? 1963 75hp

Thanks boldtr. I used the garden hose method to test the connection point between the adapter plate and water tubes. I used a non-OEM grommet at those junctions, so I tested it out before I put things back together. I now have the midsection back on the boat so I'll test the whole system using a garden hose like you have shown in your pic.

By the way, those small holes are meant to cool the shift wires on those models that have the wires. Otherwise, the wires may fry since they are close to some hot exhaust.

 

[boldtr]

Re: Grommet or Plug Needed? 1963 75hp

The spray holes cooling the shift wires makes sense. I have a manual shift Johnson so OMC must use the same inlet tube for both manual and electric shift.