# Lower unit- home pressure leak test



## markw4321 (Oct 4, 2007)

View attachment 424297
Had some discolored oil in the foot of my starboard yamaha motor. Made a pressure tester out of a bicycle air pump and the fitting for changing lower unit oil. Here are some pictures;


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## markw4321 (Oct 4, 2007)




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## markw4321 (Oct 4, 2007)




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## markw4321 (Oct 4, 2007)




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## sealark (Sep 27, 2007)

Mark pressure tests on lower units don't work unless the seals are totally distroid then its obvious they leak. think about the two seals that are in the shaft area. One faces inn one faces out. Apply pressure to the seals that are worn a little and leaking water in and the inner seal will be compressed from the test air pressure and not show a leak. put a vacuum on them and the outer seal will suck down and seal. If U got water in the oil they leak.


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## markw4321 (Oct 4, 2007)

Ron

I'm running twin f115's that are 9 years old. About 4 years ago I used this test method to show a leak on the shift shaft seal of one of my lower units that was showing a little water intrusion in the oil. When I pressure tested it there was an air leak (bubbles) coming from the shift shaft seal. I replaced the shift shaft seal and had no other issues. I will pull the prop off and get a better look at the prop shaft seal and test it again. If it is leaking air on the second test I will replace the prop shaft seal and report back if that fixes the problem or not.


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## sealark (Sep 27, 2007)

If it shows a leak with 9 psi on it it is leaking. But if it doesnt show a leak it could be doing what I have had happen with me. 9 psi is way too much psi 1 or 2 is better. Look at a seals construction and picture pressure pushing down on the lip of the outer seal. Major leaks will show up but a minor leak will be sealed from the pressure. Water in oil change all the seals.


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## TheCaptKen (Mar 14, 2011)

Yamaha seals are not reversed. Both face outward. The old rule of thumb was 5 psi for 5 minutes. You also need to vacuum test the unit because the seals can hold in one direction but leak in the other.


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## sealark (Sep 27, 2007)

I still say for a minor wear leak any test is useless. I have had at least 3 minor leaks from wear and was told it passed the pressure test. Changed the seals and leak stopped.


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## DreamWeaver21 (Oct 3, 2007)

sealark said:


> If it shows a leak with 9 psi on it it is leaking. But if it doesnt show a leak it could be doing what I have had happen with me. 9 psi is way too much psi 1 or 2 is better. Look at a seals construction and picture pressure pushing down on the lip of the outer seal. Major leaks will show up but a minor leak will be sealed from the pressure. Water in oil change all the seals.


Yamaha book says use 14-15psi.


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## markw4321 (Oct 4, 2007)

As an update Livingston marine found a bad prop seal had some mono line wrapped up. Bad prop seal was indicated by bubbles coming from prop area in original set of pictures above. 

went ahead and had all 3 seals replaced just because.


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## fish4life (Mar 3, 2008)

Glad we could help.


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## sealark (Sep 27, 2007)

Like i said major leaks will show up with pressure tests. A normal wear leak that allows a small amount of water into the unit will NOT show up and like i tried to explain will cause the MINOR wear leak to seal when any air is applied due the construction of the seals. So go ahead and take a minor leak down to the shop and pay someone to tell you it's not leaking charge you for oil and the test. then next trip you will find water in the oil again. If you have any water in the lower unit have all the seals and most likely the water pump changed while the lower unit is dissembled. Next time you have a seal LOOK at the design of the lip and you will understand my point.


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