1991 Johson 90hp lower unit pressure test

[thos]

Did a pressure test on the lower unit, since it has been quite a few years since seals have been replaced. I put together a homemade tester with a hand pump,an old automotive fuel pump/vacuum tester, and some rubber hose. It held 3 lbs for 5 minutes with no sign of leakage. Pumped it up to 10lbs, and it leaked down to 9lbs after 10 minutes. Is this good enough, or should I just put in new seals?

Thanks.

 

[HighTrim]

Re: 1991 Johson 90hp lower unit pressure test

To pressure/vacuum test a lower unit:

a) drain the gear oil
b) use an appropriate adapter with a gauge tee'd in to apply pressure or vacuum. No more than 15 psig for pressure. You can use a bicycle pump or any other compressed air source for pressure. For vacuum, you need a vacuum pump.
c) LU should retain some pressure or vacuum for 45 minutes minimum.
d) If pressure doesn't hold, submerge LU in water to find leak source [possibilities: drive shaft seal, prop shaft seal(s) (usually two), shift shaft seal and the fill/drain screw washers.]
e) replace offending seal(s) as required.

When were the vent and drain screw gaskets last replaced?

Have you noticed water intrusion into the lu, hence the test?

 

[thos]

Re: 1991 Johson 90hp lower unit pressure test

The fill/drain washers definitely need replacing. No water in oil when the lower unit was drained. I'm going to repeat the pressure test after new washers.

 

[HighTrim]

Re: 1991 Johson 90hp lower unit pressure test

Those washers are very important, as they are of the 'crush' variety. They should only be used once, getting changed with every lu service. Once they are 'crushed', it is very hard for them to get a good seal the second time around, and are the first usual suspect when water is present in the lu.