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A Tale of 3 Seals (fixing an oil leak) printer friendly version
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Donald
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Posted Monday, May 2, 2016 @ 09:15 AM  

Because I had come to suspect that my prop hub, and possibly the crankshaft, were not as true as they should be I had my engine inspected. This would involve a strip down and the replacement of any parts found to be worn, out of spec or however suspect. In fact my engine was in remarkably good condition but came home with a new prop hub and, for good measure, main bearings plus fresh seals and gaskets.

Picture, then, my dismay to find, after reassembling and flying my aeroplane, oil washing down the underside, dripping from the undercarriage doors and wetting the cockpit floor around the wheel well.

My first thought was that I had overfilled the sump and this was just the Veedub pumping it out the breather. But how could that be? The breather exits too far aft and too low to have the oil reach the parts it had got to. Prime suspect had to be the seal on the flywheel end of the crankshaft.

With the engine off the airframe again and the magneto removed it was clear from the amount of oil inside the magneto drive housing that this was the root of the problem. I assumed it to be just a faulty oil seal and, luckily, I had a fresh spare so, after a little more disassembly in it went. Remount the engine, make sure all is secure and go fly to check. Back on the ground I had again to clean her bottom like the elderly lady she is becoming and to ponder my next step.

Disassembled again these wear rings are what I found on the magneto drive hub on which the oil seal runs. These marks were very light and could barely be felt but I felt certain they were preventing new oil seals from working properly

I’d seen this mentioned on the VW/Porsche forums as a common enough problem, apparently solvable by a device called a Speedi-Sleeve, a thin wall sleeve specifically intended to put a new seal wiping surface on to rotating parts. SKF have a catalogue to suit just about any size and this is what you get.

The sleeve is sitting on top of the box and the cup that looks like a spray can cap is the installation tool.
Sit one over the other and hammer it on. No, really, that’s what you do and, below, this is it after the hammering.

As can be seen on the box I bought part No.99274 but had I ordered 99275 the height would have been perfect.
I knowingly chose to err on the side of caution and turn the excess off in the lathe, the result being this:

There is a way to completely remove the flange by tearing it off along the visible line, much like a ring pull but I kind of wanted to keep it.

Next job was to fit yet another new seal. Essentially this is just pushed into the end of the crankcase but it has to go in square.
Specialised tools can be bought for this job but the Rectimo engine comes with its own in the form of the magneto coupling housing/magneto mount.

That raised lip on the magneto drive housing fits in the same crankcase opening as the seal so progressively tightening the four retaining screws will take the seal in perfectly square and to the proper depth.

It's also worth using a scraper to put a small bevel on the edge of the crankcase opening to aid insertion, but be sure to keep any shavings out of the works.

To install the magneto drive hub into the seal I removed the magneto drive housing again.

Then refitted the magneto drive housing for, hopefully, the last time.

Next install the magneto coupling, a hard rubber puck within a metal band. Mine is showing a few cracks but I have no idea where to get a replacement. However, it’s not too different to how it looked several years ago when I last photographed it so perhaps it’ll last me out.

Before offering up the magneto I checked that the timing mark in the magneto, the red tooth, was visible to ensure that I had not upset things with all this carrying on.

And lastly, refit the magneto.

With the engine back on the airframe and everything tightened up and safetied, it was time to find out if all this had been effective. I'm happy to report that it was and I no longer have to wipe her bottom after a flight.

[...

[size=small][Edit by Donald on Monday, May 2, 2016 @ 11:34 AM]

Donald
Command Sergeant Major

Gender: Male
Location: Scotland
Registered: Jan 2007
Status: Offline
Posts: 489

Click here to see the profile for Donald Send email to Donald Send private message to Donald Find more posts by Donald Edit or delete this message Reply w/Quote
Posted Monday, May 2, 2016 @ 09:24 AM  

An afterthought on cleaning up the mess of oil.
Cleaning the metal parts was easy enough but the rubber puck was pretty wet with oil and since rubber generally doesn't care for mineral oils I gave that a thorough wash with white spirit then, when dried and blown clean with the air line, I used a rubber lubricant in the hope of adding a little protection and maybe longevity to a component past its prime.

[Edit by Donald on Monday, May 2, 2016 @ 09:24 AM]

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