Oil leak vs Grease leak MT prop ?

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Rich
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Re: Oil leak vs Grease leak MT prop ?

Post by Rich »

Rich wrote: Fri Dec 11, 2020 8:12 pm Far better than an engine front seal failure would be.
I did some research and, except for needing a special tool or two, engine front seal (part no. LW-13792) replacement isn't too bad. Google and retrieve Lycoming Service Instruction No. 1324 for details.
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Re: Oil leak vs Grease leak MT prop ?

Post by Steve »

Rich wrote: Thu Dec 17, 2020 6:14 pm
Rich wrote: Fri Dec 11, 2020 8:12 pm Far better than an engine front seal failure would be.
I did some research and, except for needing a special tool or two, engine front seal (part no. LW-13792) replacement isn't too bad. Google and retrieve Lycoming Service Instruction No. 1324 for details.
When I had to split my engine for the set screw issue, installing the front seal was easy with the installer tool. It is amazing how much the seal stretches (obviously enough to get around the propeller flange).
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Re: Oil leak vs Grease leak MT prop ?

Post by Rich »

Bryan, if this were my plane I'd remove the top cowl and see if you can trace the oil flow back to its source. Be sure to look at the underside of the top cowl and down at the lower cowl. Also check the prop hub to see where oil appears thereon.

I was looking at my plane today and have some theories about the origin of the oil leaving the hub but it's a bit tricky filling a gap in the simple o-ring theory. An interesting data point is that does not appear to be any oil on the outside of the lower cowl nor the left side of the top.
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Re: Oil leak vs Grease leak MT prop ?

Post by yl472401 »

Rich wrote:Bryan, if this were my plane I'd remove the top cowl and see if you can trace the oil flow back to its source. Be sure to look at the underside of the top cowl and down at the lower cowl. Also check the prop hub to see where oil appears thereon.

I was looking at my plane today and have some theories about the origin of the oil leaving the hub but it's a bit tricky filling a gap in the simple o-ring theory. An interesting data point is that does not appear to be any oil on the outside of the lower cowl nor the left side of the top.
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Hi Rich, I took some pictures while I was at the ship the other day. The first picture shows there’s a great chance there’s a oil trace there. Not sure if that’s the leaking point, but other places around the prop doesn’t show much spillage. What’re your thoughts ?


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Re: Oil leak vs Grease leak MT prop ?

Post by Rich »

I was thinking if this was leaking through that seal we're talking about, it would appear the oil would likely be slinging out of the seam between the prop hub and the mating surface at the front of the flywheel. That's well behind the front of the cowling, though. But the oil could then run down the inside of the top cowl, and airflow would pick it up and spread it over the areas we see. Given the direction of rotation of the prop and airflow being somewhat spiral, this airflow would tend toward the right side of the aircraft. Oil should also be slinging inside the bottom cowl, but would simply tend to run down below and not migrate toward the cowl opening.

The next-to-last photo in your most recent slate of pictures seems to show a crack forming in the prop hub. I could be mistaken, but I'd give that a very careful look as soon as you can.
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Re: Oil leak vs Grease leak MT prop ?

Post by Steve »

Bryan:

The first photo wins the prize. To me, it appears that the source of oil/grease spatter is the small hole at 7 O'clock on the face of the hub. The older versions of the MTV-12 hub (like mine) do not have this hole. MT added it to try to mitigate the grease spatter issue on these props. There was even a service bulletin to drill a hole in the hub of the older S/Ns to try to reduce the spatter. The fix was actually to bore out the hub, and install steel sleeves for the blades, which seemed to allow for better sealing. I had this done when my prop was overhauled about 7 years ago (hub had to be shipped to Germany for this), and it has been dry as a bone since.

The other unusual thing (to me) in your photos, is the gray silicone? around the base of the blades. My blade roots don't have anything like that:
IMG_4339.jpg
although my blades are 180-17f and I suspect you have the scimitar prop with 183-59b blades. The design of the blade root appears much different, but that sealant doesn't look like a factory job...

Your blades do look like they have a very small amount of grease leakage, but I think the majority of leakage is coming from the previously mentioned hole, and running/being blown aft. Now, as to what is causing it, I think that determination will have to be made by a prop shop. Keep us informed as to what you find.

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Re: Oil leak vs Grease leak MT prop ?

Post by Rich »

Stave is probably right. I also see signs of oil on the blade itself in that picture. There is something important to understand: There should be no engine oil in the prop hub, only grease. There is another seal we haven't discussed that is to keep oil from getting into the hub. It slides with the piston contained therein and could be worn.

I also wondered about that goop that Steve mentions. Moreover, I see at least one bolt (last photo) that lacks safety wire. Who when last overhauled this prop?
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Re: Oil leak vs Grease leak MT prop ?

Post by Davestation »

There is next to zero chance it’s oil. The crank flange is well aft of the cowling opening and the air flows rearward from there. It will surely be grease from one of the blade roots, cause for a prop reseal.
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Re: Oil leak vs Grease leak MT prop ?

Post by Rich »

Davestation wrote: Sat Dec 19, 2020 5:14 am There is next to zero chance it’s oil. The crank flange is well aft of the cowling opening and the air flows rearward from there. It will surely be grease from one of the blade roots, cause for a prop reseal.
Bryan's pictures show little evidence of leakage out of the blade seals. I've had several bouts of grease-slinging and it has always been apparent on the blades themselves. And it didn't look like this. More like a bunch of little black dots with very localized smearing. This is a prodigious amount of stuff.

The seam between the hub and the front face of the flywheel is about 1.5" behind the front edge of the cowl. With the position of the spinner and cowl I suspect that that area inside the cowl is probably dead air, allowing oil that would hit the inside of the upper cowl to drip down to the front edge. With the air flowing across that small gap between the spinner and cowl, there should be a low-pressure area that would draw the oil collecting on the lip of the upper cowl up and out the top to be blown back. Yes, this is conjecture. How to check it out? Remove the upper cowl and inspect the hub/flywheel interface and inside of the cowl, both above and below. Confirmed or eliminated.

The other route for engine oil to find its way out the propeller involves failure of the internal seal that keeps engine oil from getting to the innards of the prop hub. This seal travels with the activating piston and is inside the hub itself. That bit of a smear from the vent hole that Steve pointed out would be an exit point, allowing the stuff to flow back along the inner surface of the spinner. The picture doesn't show much in this area but it's a possibility. From the MT manual:
MT Piston Seal.jpg
Any route for grease or oil that's from within the prop hub itself would show up on the inside of the spinner.

Bryan, Yous should examine the inside of the spinner for any oil or slung grease deposited there. Also remove the top cowing and see if there is any sign of oil coming out of the hub/flywheel interface area and on the inside surfaces of the cowling halves and cooling intake air ducts.
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Re: Oil leak vs Grease leak MT prop ?

Post by Rich »

Steve wrote: Fri Dec 18, 2020 12:00 am
The other unusual thing (to me) in your photos, is the gray silicone? around the base of the blades. My blade roots don't have anything like that:

IMG_4339.jpg
This gray collar between the blade ferrule and the blade itself is present on mine. It's referred to in the MT manual (6.2.2.4) and is to be kept intact. It's to keep moisture from seeping into the joint between the blade and the ferrule. Quote:

Check that silicone, sealing the blade to the blade ferrule, is not damaged. If a damage is obvious, repair that no moisture can enter into blade body and blade ferrule

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