Pressure test criteria - Lower Units

[Caseyuconn]

I researched the old posts and could not find a solid anwser for this.

I tested my lower unit today at 15 psi.

The unit lost one PSI in one hour.

I redid the test and in two hours it lost 1.5 psi.

I soaped the vent and drain with no resulting bubbles.

Question is, what is the test criteria on a lower unit, does this small incremental loss mean a leaking seal that could allow water infiltration?
Thanks

 

[Daviet]

Re: Pressure test criteria - Lower Units

I usually test mine at 9-10 lbs, not sure if it is a manual spec. You need to also check the drive shaft and propshaft seals. I would think if it held that kind of pressure for that long, you don't have any problems. I usually pump mine up and submerge it in a water tank and look for bubbles, rotate drive and prop shafts, no bubbles, good to go.

 

[Caseyuconn]

Re: Pressure test criteria - Lower Units

Repeated the test again, this time rotated and messed with the prop. Much different results. Lost a lb a minute. Turns out the prop seal is bad.

The static test isn't a very good indicator of seal. Definitely turn the prop while testing. Although this keeps my boat out of the water for yet another day it will save me some headache later this season.

 

[Daviet]

Re: Pressure test criteria - Lower Units

Yep, whenever you do a pressure test move every shaft with a seal on it, drive, prop, and shift shaft if you have one. Do the same with a vaccum test also.

 

[boobie]

Re: Pressure test criteria - Lower Units

I hope more people on here read this when doing pressure/vacuum tests. Daviet hit it right on the head. 'nough said.

 

[Mas]

Re: Pressure test criteria - Lower Units

If you load up the gearcase with high pressure (15psi), this may actually help seal a bad seal by forcing the seal against the shaft. Also, a vacuum test is the most useful with shafts that use two back-to-back seals...one for pressure and one for vacuum. A lot of the older motors only have a single seal. Try a lower pressure (4/5 psi) over a longer duration of time..24 hours.

Mas