Lower Unit pressure test 9PSI sufficient?

[rubilacx]

Following post getting this lower unit squared away. I pressure and vacuum tested my lower unit and the results are that the vacuum side holds solid at 10-12 PSI but the pressure test shows that when I get to 10 PSI it leaks down to 9 PSI before holding. I can't go above 10 PSI without a leak down to 9 PSI.

When I put my ear to the propeller cavity, I can hear the slight air leak which leads me to believe it is the prop seals are where the air is releasing.

this indicates to me that water intrusion can't get in up to 12 PSI vacuum, but the oil may leak out when things get heated up pressure past 9 psi. However, I am not totally sure that this test is accurate... is 9 PSI sufficient? Has anyone seen this before? What is the expected outcome for a 2009 Yamaha 250 txr?

[99yam40]

Have you looked for specs on this testing for your motor?

I believe my 99 C40 specs say 14 PSI

[panasonic]

Here is a link for pressure testing a F225 I imagine yours would be close to the same. But you need to know for sure. It says 12 -13 PSI

In saying that, in your first post you said that you were losing oil...no water getting in. So what you are saying makes sense. It could be the prop shaft seals letting oil out.

But in saying that...lol I cant see how those drian plugs were sealing at all.

https://www.boats.net/blog/yamaha-f2...re-test-how-to

[panasonic]

If you are going to run it like that I would be checking the oil before each trip. You know the prop seals are leaking...so replace them. But then you run into getting that apart in one piece, gland nut seal carrier ect.. on a older engine that can be a problem with corrosion.

[boscoe99]

[boscoe99]

Why was a negative pressure test performed?

[rubilacx]

Ok, took me awhile to find it but the service manual says 10 PSI for 10 seconds and not to over pressurize very close to what bosco99 had. I did a negative vacuum test because that's the only way salt water can get in and I just did a patch job on the drain plug holes. I wanted to be sure they didn't have a leak that would let water in. Those were definitely an issue.

So.... now I'm in a conundrum. Spec says 10 psi... I can get 9 PSI and no higher, but it holds forever. That's pretty close. Hmmmmm. Service manual also doesnt say whether or not to check the pressure with or without oil in it. I'm checking it without oil which may make a difference... but then again how would it fail the test without shooting oil out. Get into those prop seals or not.... gonna sleep on it.

[rubilacx]

I went ahead and changed the prop seals. Guess who has 10 psi? <--- this guy!

[99yam40]

good to hear it worked

[panasonic]

That's good..hope your plugs hold up!

[pstephens46]

Want to have fun? Head over to THT and post a question about vacuum testing your Yamaha lower unit. The replies will be entertaining. As Boscoe was hinting, Yamaha never mentions vacuum testing for lower units….