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Prop governor - small oil leak question.

cnoe

By cnoe
in Modern Mooney Discussion

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cnoe Mentor

cnoe

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I've got a small oil leak at the top of my prop governor ('78 J - IO360-A3B6D). It's coming from what I believe to be a pressure-relief adjustment screw/bolt. The prop/governor are functioning perfectly normal with no issues; the minor leak was discovered through routine inspection during an oil change.

I found reference to a McCauley "service letter" (1998-22A 12/10/1998 LEAKING OF GOVERNORS FROM PRESSURE RELIEF VALVE ALL GOVERNOR MODELS) but can't find any more information about this in a short time of searching online. Does anyone have any more info about this they could share, or have a suggestion where I might read a bit more about it?

Though I don't believe this to be a safety of flight issue I do intend to resolve the issue in the near term. The governor has less than 400 hours since overhaul by Tiffin Aire but I'm hoping this can be resolved without having to remove and return it.

Any ideas about this or the service letter?

Cnoe

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cnoe Mentor

cnoe

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Are you sure that did not drop from above when the filter came off?

Sadly it's not spillage but that's a fair question; it does sit directly below the filter nipple. There was once a time when changing the filter meant lubricating the entire accessory case.

I'm hoping there's an o-ring or seal that can be easily replaced. If not a simple IRAN may be in its future. If I don't get any clues in the next few days I'll make some calls.

Sent from my iPad using Tapatalk

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cnoe Mentor

cnoe

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Follow up to my earlier post:

I contacted both McCauley and the overhauler (Tiffin Aire) to inquire about the aforementioned service letter and was pleased to get an immediate reply (phone call) from Mike Baird at Tiffin.

Apparently this is not an uncommon occurrence and  is easily remedied with replacement of the outer locking nut and integrated seal. This can be done on the plane if access permits  as long as the pressure relief valve setting is not disturbed.

I'm very pleased to say that he agreed to send the replacement assembly to my A&P at no cost where we will complete the repair in the near future.

That's great customer service in my book!

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  • 2 weeks later...
cnoe Mentor

cnoe

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Here's a final follow-up on the issue noted above.

We received the service letter and replacement part (which turned out to be only an o-ring) from Tiffin Aire this week and completed the repair yesterday.

On a J model with the IO360-A3B6D this was easily accomplished by removing the oil filter and working from the top to access the governor. According to the service letter the original o-ring was bonded to the locking nut with an adhesive that hardens, cracks, and allows leakage. Field service involves marking the pressure-adjustment plug to maintain proper position, removing the lock nut, then removing the plug noting the number of turns so that it can be reinstalled EXACTLY in the same position. (Note: McCauley stated that this adjustment can screw things up if even 1/8 turn off).  Now here's the weird part... after a thorough cleaning the adjustment plug is to be wrapped in two layers of mil-spec teflon tape before being re-installed into its original position (I've never seen teflon tape used in an aviation application but apparently the o-ring doesn't effectively seal the adjustment-plug threading without it). The new o-ring is then placed over the plug and the locking nut (which captures the o-ring in a gland) is reinstalled and torqued to only 24-28 in/lbs.

I've attached a pic showing the components for your viewing pleasure (old o-ring shown).

FWIW, McCauley wouldn't even send me a copy of the service letter and advised me to seek help from a prop shop. At least they responded to my inquiry.

FullSizeRender.jpg

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cnoe Mentor

cnoe

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The o-ring is a mandatory replacement item anytime the locking nut is removed. I'm certain it was replaced at the time of the governor OH (400 hours ago).

From an engineering perspective I'd say that the design has a minor flaw in that the original o-ring was employed to seal against the plug threads which is not an effective design. By requiring the teflon tape in the service letter they're essentially sealing the interface between the plug and the lock nut with the tape while the lock nut o-ring seals the inner bore.

I'm just glad it took a <1 hour labor hit rather than the expense of a bench service.

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Rick Junkin Mentor

Rick Junkin

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On 2/1/2016 at 7:32 PM, cnoe said:

1998-22A 12/10/1998 LEAKING OF GOVERNORS FROM PRESSURE RELIEF VALVE ALL GOVERNOR MODELS

@cnoe, any chance you still have this service letter, or know where to get it? Or perhaps the part number for the o-ring (or the specs on the o-ring if I need to go a "different" route). I have the same leak, only more severe - I'm losing enough oil for it to be visible on the cowling inlet ahead of the governor after shutdown. I'm not comfortable with that and have grounded my airplane for the time being. Thanks for any help you can provide!

Cheers,
Rick

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Cody Stallings Experienced

Cody Stallings

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1 hour ago, carusoam said:

Seeing if @Cody Stallings May have an answer to the leaky Governor question for a Bravo...

-a-

I can look Monday morning when I get back to the shop.

Im sure I have the SL in some of the Manufacture Data.

Keep in mind, the PR is a very common place for all Govs to leak.

A Dana Seal under the Locking Nut works wonders.

Or so the Elf’s tell me it does anyway.

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Rick Junkin Mentor

Rick Junkin

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22 minutes ago, Cody Stallings said:

A Dana Seal under the Locking Nut works wonders.

Or so the Elf’s tell me it does anyway.

Thanks Cody! My mechanic will need the service letter to effect the repair, and he's having difficulty getting his hands on it.

My elves would like to know which Dana seal your elves use, and where they source it from. My elves are pretty inexperienced in such things and had never heard of Dana seals before tonight.

Cheers,
Rick

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N201MKTurbo Grand Master

N201MKTurbo

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7 hours ago, Junkman said:

Thanks Cody! My mechanic will need the service letter to effect the repair, and he's having difficulty getting his hands on it.

My elves would like to know which Dana seal your elves use, and where they source it from. My elves are pretty inexperienced in such things and had never heard of Dana seals before tonight.

Cheers,
Rick

http://ph.parker.com/us/en/fastener-seals

Dyna seals and Stat-o-Seals are listed in mil spec  NAS1523

Edited by N201MKTurbo
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