pressure testing lower unit

[larky]

i have recently installed a complete seal kit in the lower unit of my 1959 35hp evinrude and after running it a little while i have milky colored lower unit oil once again. so to see where i screwed up i was thinking about pressure testing it. my question is what is the best way to do this and at what psi?

 

[BF]

Re: pressure testing lower unit

you can use an automotive valve stem that you cut down the tire end to fit snugly into the oil fill/drain hole... use bike pump to put some air into it.... or use the screw in piece that comes with one of those small pumps for putting lower unit oil in, and again either use a pump or a syringe or whatever to put some air in. I've also done it by siliconing a small piece of tubing into a hole drilled through a small rubber stopper.. Used syringe to put air in.

I've used a little cheapie $5 kiddie pool, or if wifey wasn't home... in the bathtub.... fill pool/tub with water... Drain oil from lower unit. Make water/air tight connection between pump or syringe to fill/drain hole. Put some air in... lay lower unit in water, watch where bubbles come from.

You don't need much pressure... definately do not exceed 10 psi. (you probably don't even need that). If it's leaky it won't hold air anyway... just give it a couple pumps while it's in the water...

good luck... I've done it a few times to find leaks on my outboards... it's always worked. (although it can get a bit McIvor-ish looking at times)

 

[jtexas]

Re: pressure testing lower unit

that's what the manual says...submerge it and look for bubbles...probably don't have to pressurize it for that but it might help.

Manual also says pressure-test using a vacuum pump w/gauge don't have it handy else I'd give ya the PSI don't know if it'd be the same though, but you already know you have a leak.

 

[OBJ]

Re: pressure testing lower unit

Manual says to pump them up 15psi for pressure testing....but it really only takes about 10psi or less to determine a leaky area when you chuck the whole thing into water.

 

[larky]

Re: pressure testing lower unit

well i did as you all sugested and submerged the lower unit in water and put air in. but i had first resealed the screws on the ''cap'' or upside down shark fin of the lower unit before i put it in the water. when i aplied the pressure i saw nothing, so i turned up the psi a little on the compresor, and still nothing. i finally saw some bubbles, but the compressor was set at 38 psi. so the lower unit seems to be able to hold around 35 psi. the only bubbles i can see are coming from the prop shaft seal which is holding more psi than i had expected. i am guessing that i may have it sealed enough to keep the water out. what do you guys think?

 

[papasage]

Re: pressure testing lower unit

that is enough to blow the seals . be sure to change the fill and drain seal. if still gitting water in it you might have to valcum test it .you have 2 seals one is out and the other is in . after running it let it sit and the water will seporate and settle to the bottom if it is leaking . could be just swettting inside

 

[itstippy]

Re: pressure testing lower unit

There's a misunderstanding here. You are not trying to "pressure test" to find out how much pressure it can take before it leaks. You're just trying to see if the seals will hold water out and oil in. 10psi and look for bubbles. No bubbles is good. If you see bubbles, that's where the leak is. Putting 38 psi into the unit will "blow the seals" and you'll probably have to pull it all apart and reseal. Once the seals are blown they won't hold 10psi any more either. You'll get bubbles.
Seals have two "lips", one facing out to keep water out and one facing in to keep oil in. Sometimes, as papasage says, you get two seals in the kit and you stack them like poker ships: one facing out and one facing in. Putting too much air pressure in the lower unit can force the "in"-facing lips to pop "out". Or it can blow the spaghetti seal. Sooner or later something blows. The unit is not designed to keep water out at 100ft under water.