Are exhaust housing gaskets on my Johnson 80hp necessary?

[BonairII]

I want to replace the middle section on the leg of my motor. It's got some kind of white corrosion all over it and is unsightly. I have a good leg section on my parts motor and just want to swap them out.

After looking at the parts diagram, I noticed that there are supposed to be gaskets on the top and bottom of the middle section. I'm sure that I don't have a gasket between LU and middle section....and I'm not sure I have one between the middle and top portion of the exhaust housing.

The bottom gasket is only $6 bucks, so if I need that one I'll order it. BUT, the middle gasket is labeled(on marineengine.com) as a "Vintage seal" and they want $37 bucks for it! If that one is necessary, I won't bother swapping out the leg sections.

The gasket in question is on Page 16(Part #42) in the diagram
http://www.marineengine.com/parts/v...ntage-evinrude-johnson/382096/38209600001.htm

 

[yorab]

Re: Are exhaust housing gaskets on my Johnson 80hp necessary?

Neither gasket is necessary. Water fills up that area anyway when the motor is in running position. About the only thing that a gasket may do is to keep the unburned fuel from seeping out along the mating surfaces when the motor comes out of the water. Since I painted mine, I replaced both gaskets to keep the "gunk" segregated to only those areas where it is supposed to leak out. If I remember correctly, I ordered 2 of the bottom gaskets and used them at the top and bottom.

 

[Joe Reeves]

Re: Are exhaust housing gaskets on my Johnson 80hp necessary?

That #42 that you mention is not a gasket.... it is a absolutely required heavy duty rubber seal that goes around the outside of the long exhaust housing (Hsg between the powerhead and lower unit). The purpose of this seal is to keep the exhaust fumes of the engine from traveling back up into the powerhead area where they will get drawn into the carburetor which effectively kills the engine.

Perhaps you are giving that item a wrong part number?

The gaskets you should be speaking of would be on page 18, item number 17 which is part number 305312, sells for about $10.00 each. One goes on top of that 5" extension, one goes under it. Two are required.

If gaskets are unavailable, you can use:

Marprox Sealer 1000 or OMC Adhesive or Boat Armor Sealer 1000 (same substance)[See Below Note] should be used on any metal to metal or metal to plastic surface (such as impeller hsg to plate, and plate to lower unit surface) to eliminate air leaks. It should also be used on the Spaghetti tubing that is used on many powerhead crankcase halves, lower unit skegs, etc. I have found that this substance works quite well on various "O" Rings such as what are found on lower unit carrier and upper driveshaft bearing housings (Note that this substance is obviously not to be used on all "O" Rings). This substance also works quite well in sealing the surfaces between the lower unit and the exhaust housing to which it attaches, eliminating the unsightly water spray between the two after completing a water pump installation.

NOTE: OMC Adhesive is now Bombardier 3M Product #847 .

 

[BonairII]

Re: Are exhaust housing gaskets on my Johnson 80hp necessary?

That #42 that you mention is not a gasket.... it is a absolutely required heavy duty rubber seal that goes around the outside of the long exhaust housing (Hsg between the powerhead and lower unit).

Just to be clear....This "rubber seal" is INSIDE the large exhaust housing just under the powerhead? And will not be disturbed if I drop the 5" extension piece?

I see that Sierra sells the gaskets I need in a 2-pack, so I think this will take care of sealing the 5" extension piece.
http://www.marineengine.com/newparts/part_details.php?pnum=SIE18-2869&ptype=&Engine=&Model=

 

[F_R]

Re: Are exhaust housing gaskets on my Johnson 80hp necessary?

That is correct. The large rubber seal will not be disturbed. All you are contemplating is replacing the 5 inch extension housing. Now, back to the original question---are the gaskets necessary? The answer is no. Want proof?? Look at the following year, 1968. The gaskets are were longer used by the factory on the '68 models. If "necessary" means leakproofing the seam, then they are of value. There undoubtedly will be some seepage without the gaskets. But as already pointed out, anything that seeps out there is destined to go out the exhaust outlet anyway. The difference is you can't see it.

So, it is up to you. Use them or don't use them. The motor won't care, but you might.

BTW, much more important than those gaskets is the #305762 foam rubber seal ring on top of the water pump cover plate. That keeps exhaust smoke from going up the drive shaft tube, where it comes out the vent hole at the top and is drawn into the carburetor. That results in a lousy running condition that will drive you nuts, trying to figure out what is wrong.

 

[BonairII]

Re: Are exhaust housing gaskets on my Johnson 80hp necessary?

BTW, much more important than those gaskets is the #305762 foam rubber seal ring on top of the water pump cover plate.

I just swapped out the housings. Pretty simple. There was only a gasket between the lower unit and bottom surface of the extension section. It looks a lot better now.

F_R, Is the black gasket in the pic the part that you're talking about? Water is getting into the gearcase, so I plan on pressure testing the LU soon to see where the water is coming in from. Should I test the LU first with the water pump housing on....then with it off? Last season, in the handful of times I took the boat out(cause I got it running late in the season)...I changed the LU oil after EVERY time I ran it. I'm getting the equivalent of 2-3 shot glasses full of water each time out.

 

[F_R]

Re: Are exhaust housing gaskets on my Johnson 80hp necessary?

That is the seal I was referring to. It has NOTHING to do with keeping water out of the lower unit. But it has everything to do with keeping exhaust out of the drive shaft tube.

The oil seal for the drive shaft is below the water pump.

 

[Joe Reeves]

Re: Are exhaust housing gaskets on my Johnson 80hp necessary?

The seal that you are pointing to (if it is the one that is installed "within" that 4 bolt housing)...... it may be in perfect condition BUT if the bearing within that driveshaft bearing/seal housing assembly is worn, leakage will take place at that point, allowing water to enter the lower unit.

With the lower unit drained, applying 7 to 12 psi to the unit and having the unit in an upright position, grab the driveshaft and try to move it sideways, to and fro, etc. If you can observe leakage when trying to move the driveshaft, replace the bearing and the associated seal(s). Some housings have 2 seals, some only have 1.