Vacuum test LU

[MarkHPCA]

I have water in my LU. I did a pressure test and it held 20 PSI for over 1 hour. Now I want to do a vacuum test, what do you guys use to pull the vacuum? Will the automotive brake bleeder hand pump be sufficient?

 

[rick_l]

Re: Vacuum test LU

I don't understand. If you did a pressure test on the lower unit with 20 pounds and it held, why would you need to do a vacuum test. If it's not leaking outward then it can't be leaking inward.

 

[Molaker]

Re: Vacuum test LU

I don't understand. If you did a pressure test on the lower unit with 20 pounds and it held, why would you need to do a vacuum test. If it's not leaking outward then it can't be leaking inward.

Not exactly true, Rick. Granted, it is unlikely but it is certainly possible it could leak under vacuum and not under pressure. Seals will move in opposite directions with vacuum vs. pressure. One way they might seal, the other way, might not.

As for Mark's question, I'd think any vacuum pump that can draw and hold and be securely connected to the LU would suffice. However, I'm not sure how you would measure leakage with the brake bleeder pump other than to just see if it holds any vacuum for a period of time - unless you can come up with some kind of guage.

 

[tashasdaddy]

Re: Vacuum test LU

90% of water intrusion, is because the last time the plugs were removed the washer were not replaced. always replace washers.

 

[ezeke]

Re: Vacuum test LU

My choice of a tool for that is the MityVac Model 04050 which allows you to do both tests and a lot of others requiring both pressure and vacuum.

Be careful not to exceed the pressure and vacuum range specified in your service manual.

 

[MarkHPCA]

Re: Vacuum test LU

I havn't pulled it apart yet but someone suggested that maybe the driveshaft is groved where the seal go and although it will pass pressure/vacuum tests all day long under high RPM the waterpump will force water past the seals. I hope not but, if this is the case, is there somekind of sleeve that can be put on the driveshaft where the seals go ? I realy don't want to replace the shaft ($$$$)

 

[jbjennings]

Re: Vacuum test LU

I havn't pulled it apart yet but someone suggested that maybe the driveshaft is groved where the seal go and although it will pass pressure/vacuum tests all day long under high RPM the waterpump will force water past the seals. I hope not but, if this is the case, is there somekind of sleeve that can be put on the driveshaft where the seals go ? I realy don't want to replace the shaft ($$$$)

Ha Ha! I've been reading your thread and am anxious to hear the answer to your question. If you can wait about a week, I'll be able to answer it myself because I'm going to "bearing service and supply" and see if they can put a sleeve on mine which has the exact problem as you just described. If they can fix it, I'll start a thread and show pictures and such because I think this is a very common problem. I think that 20 lbs. of press. is pretty darned impressive, I would think if it held half of that it would be a great seal job.
JBJ

 

[R.Johnson]

Re: Vacuum test LU

Fore years', many seals' were called parachute seals'. They work fine with upward, or positive prressure. not so great with downward, Here is where the pressure, vacuam test comes in.

 

[iwombat]

Re: Vacuum test LU

That's exactly why there's two seals - one facing in and one facing out on some of the LU shafts.

 

[Vic.S]

Re: Vacuum test LU

That's exactly why there's two seals - one facing in and one facing out on some of the LU shafts

and the outer one is fitted to keep the water out while the inner one keeps the oil in. Similar arrangement on the prop shaft and drive shaft.

The orientation of the seals is shown on the parts diagrams.

The most likely one to fail is the outer one on the prop-shaft as that can easily be damaged by fishing line and other debris. As that is the one that keeps the water out the result is water getting into the LU.

 

[MarkHPCA]

Re: Vacuum test LU

I still havn't pulled it apart yet but I have done some reading. SKF makes a product, speedi-sleeve, which is designed for just this. It is a thin walled sleeve (0.010") that you drive on the shaft over the damaged area. They come in many size increments and cost about $30. I wiil be doing a vacuum test tomorrow and I willl take it apart to examine then.

 

[samo_ott]

Re: Vacuum test LU

A thin walled sleeve? That's cool. I was talking to my local OMC place and they said any machine shop can fill in the grooves and then re turn it for about $50 I think he said... I didn;t go that route though. what engines is this on anyway? Maybe driveshafts are common for it?This is a really good thread though as I bet a lotta folks are in this position.

I'm curious though as to what set up you used to put 20lbs pressure on it and hold it for an hour?

 

[MarkHPCA]

Re: Vacuum test LU

Samo

It's on a 120 looper. I used the screw in fitting that comes with the pump for filling the oil in the gearcase. I added a Tee to the tube, connected my water pressure gauge (30 PSI) to the tee and an old tire valve to the other side and then pressurized it using my compressor. You could also use a tire hand pump.

 

[samo_ott]

Re: Vacuum test LU

Dang, I like that setup. I think I'll make something like that. Thx.

 

[ezeke]

Re: Vacuum test LU

In addition to the other possible leaks that have been suggested, a bent propshaft, unbalanced propeller, or improperly alligned driveshaft can allow for leaks.

As to the grooves in the shafts, a very small spacer under the seal(s) can sometimes improve the situation dramatically, and at minimal cost and effort.

I would like to echo the following by tashasdaddy: "90% of water intrusion, is because the last time the plugs were removed the washer were not replaced. always replace washers."

 

[MarkHPCA]

Re: Vacuum test LU

Well I did the vacuum test and it held fine so I took it apart and the problem is a groove on the shaft just where the seal runs.

http://img148.imageshack.us/my.php?image=shaftre5.jpg.

I guess I will try ezeke's idea as there is good shaft surface with 0.1 " of the groove and I have lots of room in the bearing carrier to miove the seals up somewhat.