Lower Unit Pressure Test

[Greecy]

Engine: 2004.SR.Johnson.2-stroke.50HP

I have been getting water in the gear lube in my lower unit. I rebuilt this unit two years ago including a new water pump and the leak started gradually then got serious. I removed it and immmediately discovered that the nut around the shift rod was very loose. Hah, I was sure I found the problem. I put a small amount of gasket sealer on the threads and tightened it down.

Instead of putting it back on the engine, I did a pressure test according to the manual with the LU submerged in a tub. A steady stream of bubbles emerged from the shift rod pivot screw. The O ring on this screw is nearly microscopic. I ordered a new one, gave it a dab of gasket sealer all around and did the pressure test again. At 18 psi, the shift rod shaft and shift rod pivot screw do not leak. The water pump outlet gives up a bubble every 45 seconds. If I turn the shaft, a few bubbles come out every third of a turn (impeller has three spokes). It must be leaking at the O ring on the shaft inside the impeller housing. At 6 psi the LU does not leak. When I pull a vacuum, it will hold 15"Hg for at least 15 min.

I don't know what the internal pressure inside the LU is under load but I doubt that it is anywhere near 18 psi. Should I be concerned about this leak?

 

[racerone]

Remove bearing housing under the water pump.----Replace oil seals on that housing.------These gearcases are not robust in my opinion.----Very important to keep water out of them.----Use top quality gear oil.

 

[Vic.S]

As Racerone says replace the driveshaft seal below the water pump. ( only one seal, but a double lipped one according to the parts diagram) # 36 in the attached diagram. Also replace the housing O ring ( #34)


Also consider replacing the shift rod O ring seal. #45 in this second diagram. Also renew the housing O ring , #47, if you disturb it.



If necessary you can replace the prop shaft seal ( another double lipped seal) at a later date without removing the gearcase.

 

[Greecy]

Thank you both for the sound advice. It would not have been wise to put the LU back on with this very small leak.

What I did not mention in my original post was that I had flushed the LU with kerosene followed by methyl alcohol to remove any residual water. Overnight, I woke up with the thought that the seals were dry.

Today I put about half a cup of Evinrude gear lube in, inverted the LU, then turned the driveshaft a few times to make sure the lube was reaching the drive shaft seals. I reconnected my pump, turned the LU upright and put it back in the tank. It took 8 hours to drop to from 18 to 11 psi. No bubbles in the water pump when I turned the shaft.