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Would be appreciated for some of you prop guys


Steve1300
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We are currently working on some pump housing showing leaks. The plane has been in cold weather, so we also have some blade leaks, but nothing abnormal.

The other herk forum has lost the old posts from back when this question was asked, so I am hoping that some of you ol\' prop guys will repost your answers.

The pump housing actually looks simple when the covers are off, but they aren\'t simple when tracing the source of leaks when part of the propller assembly. I am interested the causes of \"lip seal leaks\" and those that just look like lip seal leaks.

We have three props now that appear to be lip seal leaks and none of them were overserviced.

Perhaps, when we get some of you to post some help for me here, I can save the whole thread so it doesn\'t get eaten up by the ether-net.

Thanks in advance........:)

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I\'m sure the prop shaft seal leak has been mistaken for a rear lip seal leak many times. My rule of thumb is if the prop shaft leaks with aux pump pressure, it\'s the prop shaft seal. If it leaks as soon as you let off the aux pump, it may be a clogged breather preventing the venting of pressure out of the atmospheric sump or simply a worn rear lip seal.

I\'m kind of ignorant though when it comes to clogged internal passages/filters/screens causing leaks.

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Thanks for your input on that. We are having to deal with front cover leaks which I can only attribute to a pressurized atmospheric sump. We never find bad o-rings,but the fluid is getting past them.

I am thinking that most \"lip seal leaks\" are not lip seal leaks at all. That\'s why there are other actions that have to be taken instead of changing the lip seals.

Anyone else willing to get into the discussion?

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I\'ve had a Guard guy tell me he found an atmospheric dipstick mounting nut loose cause a leak from that area. Unfortunately, you have to take the front cover off to retorque it.

Another thing to look out for is to make sure before installing a rear lip seal that the drain holes on the pump housing are at 6 o\'clock, otherwise there will only be one way for the vented fluid to go, and that\'s out of the rear lip seal.

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  • 2 weeks later...

We had a period of time that one of the guys in my shop was putting the double lip seal on without putting the greese in between the lips. If the first lip seals works then the second one will heat up due to lack of lubrication and distort both lips. That cost us a few manhours but after he learned the correct way which is to read the book we have taken care of most of our can seal leaks! This is just one of the possible causes I have seen.

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  • 6 months later...

I believe the cause of on an over pressurized atmospheric sump is the pitchloch regulator. I have had prop lip seal leak one after another so I took out the pitchlock regulator and disassembled it. Found the all the cups to be pretty blocked. Cleaned each individual one and put her back together. Installed and hasnt leaked from the lip again. I hope this helped?

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This has been a LONG time problem and there really is no exact fix to the problem. It may any one of many problems associated with that cover. The lip seal not being pressed in properly, dip stick seal or nut not torqued, cover plate seal, valve housing cover breather being clogged. A long time ago Hamilton Standard did a big study at Pope AFB in trying to determine exactly what the cause was. Out side of the normal stuff discussed earlier they found that almost 80 percent of prop leaks are caused by an over serviced propeller. During the study at Pope we found that some of the propellers had almost an extra gallon of fluid in them.... This is why it is so important to not just throw 2 quarts in everytime the low oil light comes on with out checking the servicing first. The book has the established way of checking servicing but you will find that a lot of the old heads do it differently. Remeber that a little fluid goes a long way.

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An interesting \'aside\' to this story - in the cell, one of the things I watch during servicing, is

the 115v 400Hz digital voltmeter. In a properly serviced and functioning prop, there is a drop

of 0.6 volts when feathering or unfeathering. Yesterday I noted the voltage drop was still

1.1v. I believed that during servicing an air-lock had occurred, which is normally cleared by

running the engine for 10 minutes. However after an hour of run time, I had some streaking

down the inside/back of the blades and some mess on the lower afterbody. I decided to

deservice/remove half a gallon of fluid. Lo and behold!! the voltage drop is suddenly 0.6v and

the feather time dropped to 17 secs from 19. All this from a prop initially refusing to take more

than 4.5 gallons of fluid .....

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