vacuum test question

[reeldutch]

i have a outdrive from a friend (ALPHA gen2) and it holds good pressure 15 lbs but it only holds may be 5 hg of vacuum.

is this how it is suposed to be?


thanks.

 

[Don S]

Re: vacuum test question

They usually hold between 5 and 10 hg of vac. If they hold 5, then you are probably ok. It's probably pulling thru the input shaft seal. It's inside the bellows and doesn't have another seal in the opposite direction to keep the water out. The bellows does that. So, only one seal.
You can tilt the drive backwards and pour some thick gear lube around the seal and try the vacuum. It will probably build, and slowly suck the gear lube in then go back to leaking.
It's all very normal.

 

[wire2]

Re: vacuum test question

No, something isn't right with that.

15 psi is ~1 atm, which is approximately 30" of vacuum in reverse.
The OMC stringer drive I had used back to back seals at all shaft entry/exits, I expect that's an industry standard for marine.
If that's the case, I believe one of the 2 seals in one location on your drive is defective, allowing leakage at only 5" vacuum.

And once again, Don, you snuck an answer in there while I was thinking about it. And your experience outshines my theoretical logic. But that's ok, every day I learn something new is a good day.