Ted Russell
Member
Hey all,
I pulled apart my drive to put in a new pump and found some corrosion between the exhaust and cooling water chambers. It appears the drive had never been apart (1998 with 950 hrs).
Here’s the damage:
The wall is very thin here, and even in freshwater, I was told the combination of stray currents from shorepower and the stainless water pump causes the aluminum to corrode away. I spoke to a Mercruiser mechanic and he said at the marina they add beads of silicone and slam it back together but I thought that wasn’t really the best way. I also had seen some rebuild the wall with JB weld, but I was afraid a piece could break off and wedge in the impeller, which would consequently overheat the engine. So I opted to replace the metal itself and make the wall thicker.
First step is to take a dremel and remove the damaged material.
I bought a piece of 1.5" x 1/8" thick aluminum stock and cut two pieces, one to fill the damaged area and one to go behind it on the exhaust side.
I drilled and tapped with 4 mm stainless steel screws to attach the two plates together and attach the plate to the lower unit.
After that, I ground a notch on the exhaust side plate to ensure the relief hole from the pump wasn't partially blocked.
The rubber block was cut down so it would fit with the thicker plate in place. I used JB Marine weld to coat behind the plates, in the screw holes, and in all the gaps to make sure everything was sealed and would stay firmly in place. After that it was a coat of zinc chromate primer and black epoxy paint.
Then, when I installed the pump on the bottom side of the steel gasket I used some silicone to take up any small irregularities as the surface wasn't 100% like the factory machined surface. Other then that I followed the regular procedure for the pump.
All this cost less then $30 in material, and I have enough to do two drives. Much better then replacing a lower!
I pulled apart my drive to put in a new pump and found some corrosion between the exhaust and cooling water chambers. It appears the drive had never been apart (1998 with 950 hrs).
Here’s the damage:
The wall is very thin here, and even in freshwater, I was told the combination of stray currents from shorepower and the stainless water pump causes the aluminum to corrode away. I spoke to a Mercruiser mechanic and he said at the marina they add beads of silicone and slam it back together but I thought that wasn’t really the best way. I also had seen some rebuild the wall with JB weld, but I was afraid a piece could break off and wedge in the impeller, which would consequently overheat the engine. So I opted to replace the metal itself and make the wall thicker.
First step is to take a dremel and remove the damaged material.
I bought a piece of 1.5" x 1/8" thick aluminum stock and cut two pieces, one to fill the damaged area and one to go behind it on the exhaust side.
I drilled and tapped with 4 mm stainless steel screws to attach the two plates together and attach the plate to the lower unit.
After that, I ground a notch on the exhaust side plate to ensure the relief hole from the pump wasn't partially blocked.
The rubber block was cut down so it would fit with the thicker plate in place. I used JB Marine weld to coat behind the plates, in the screw holes, and in all the gaps to make sure everything was sealed and would stay firmly in place. After that it was a coat of zinc chromate primer and black epoxy paint.
Then, when I installed the pump on the bottom side of the steel gasket I used some silicone to take up any small irregularities as the surface wasn't 100% like the factory machined surface. Other then that I followed the regular procedure for the pump.
All this cost less then $30 in material, and I have enough to do two drives. Much better then replacing a lower!
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