io-540 governor idler retainer cap stripped threads
 

We thought an oil leak was from the prop flange seal. After removing the prop its pretty clear the oil leak is coming from here. This cap is the governor idler retainer cap, right?



The cap was covered in some hard epoxy / goop that I had to pick away. Under that was some RTV. It's obvious someone did a shoddy job a long time ago.

The guys at the local shop think it is B 1/2 (B-Half) or some sort of pro-seal that has cured rock hard. I picked all of it away and we aren't sure what we are seeing here.



The threads in the copper inset piece are completely stripped. The epoxy (B 1/2, whatever it is) was gooped in there and the plug was installed.

Is that copper piece removable? It almost looks soldered in. We couldn't find any reference to a removable / replaceable plug in the overhaul manual.

Is there an approved / recommended repair procedure here?

I don't remember copper threads there when I pulled my 540 apart, but it has been a couple of months. The purpose of that cap / plug is to cover a hole placed for machine access for the bore at manufacture and to create a path to remove the shaft supporting the governor gear that is driven off the Cam gear. Nothing structural here and I am sure that's why they tried the epoxy hack. I would possibly consider epoxy again, though RTV or similar material may be a better alternative. If using a sealant instead of adhesive, you may want to fabricate a pin to hold the shaft in. There is no real axial load, but a sealant alone may not hold it. You can drill and tap this to a lager thread and make your own cap, if you have a lathe. And you would need a bottoming tap and some caution to stay out of the shaft carrier ID. You can also see if you can find a helicoil in the thread size you are working with. The problem here is the depth of only 2-3 threads. The big problem will be capturing the chips. I am not sure that you will have access to block the chips from falling in the case. I would have to go examine my case half to see if you could get a rag in through the main governor opening. Though I suppose it wouldn't be that difficult to fabricate a plug that went where the gear shaft was to block the chips.

I am sure Divco or other shop can weld and repair it at the next overhaul and it is unlikely you will need to pull that gear before the next overhaul, making a sealant approach realistic. The threads in the case are definitely aluminum and the copper you are seeing is probably a damaged male thread of some sort. I am guessing you should be able to pick this out and salvage it.

EDIT: based upon your picture, it really appears that the threads may be intact and what you are seeing is remnants of something (copper or brass) that was cross threaded and drilled out. The ID of the threaded area should be larger than the OD of the shaft you see in there. If the thread ID appears to be smaller than the OD of the shaft, it is not the virgin case threads, but some remnants of a crappy mechanics work. That shaft should be able to slide right out of that threaded hole.

Larry

The copper your seeing may have come from a copper crush washer, threads do appear to be intact ,maybe someone previously didn?t replace crush washer and just overtighten and added goop may be worthwhile to thourghly clean and reinspect. If OK install with proper crush washer.

It's not a crush washer with an inner crush material, it's looks a solid copper washer that is quite wide -



Perhaps the washer (70455) is embedded in there and the black goop was between the pulg and the washer?

The threads are most certainly destroyed. The epoxy was 90% of the thread material when we removed the plug.

There was one washer under the plug, but perhaps there is still a second copper one in there.

The gasket that is recommended by lycoming is not a crush washer, it is a ring of gasket material.

I haven't found a solid answer on this, and my response that was originally here was incorrect.

The cap threads into the case, those are the threads that are destroyed.

We ended up getting a 3/4"-16 helicoil kit and new gasket for the cap.

It looked at first as though the leak wasn't any worse than it had been. Flew the plane and it was much worse. 2.5-3qts on the fresh paint.

Now that we have good threads there, any suggestions on sealing this up?

How was the case surface under the gasket?

I looked at those parts after remember incorrectly. The seal has to seal on both the outer shaft and the case, though only the seal with the outer case is relevant. However, the shaft does limit the travel of the cap, so the two surface need to be on a relatively level plane. In your picture, the case flat area seems pretty rough. Is that just the picture or is there some pitting or gouging there? If there is, you'll probably need some sealant in additon to the gasket.

Larry

In the above pictures, there is no gasket. There was some remaining B1/2 that was cleaned off with a scotch brite wheel.