Hi folks,

I thought I would share my recent experience on an issue that may affect a few of you out there.

I have a 2005 912 ULS installed on a P&M GT450 Quik trike in the UK. It has 875 hours on it and has been very well looked after. S/n 5645111.

Recently I noticed an oil leak between no2 cylinder and head. I have also had for some time a miniscule wet patch (just one droplet) appear on top of the engine case after a long flight. I came across a thread on this site which describes a problem know as fretting and read that somebody else had similar symptoms...and a similar engine serial number.

I had the oil in my engine spectro tested...it's clear.
I removed the 60 hour old filter ....it's clean.
I've had no abnormal oil temps and pressures and no vibrations which would lead me to think there's an issue.

After more googling, I found a simple test that helps diagnose this fretting issue, and on its own has been the only real definitive evidence of a problem. Essentially, arrive at the airfield on a cool morning, remove a plug from each cylinder, and use a spring gauge/scale/Newton meter to pull the prop over. The tips of my prop are around 83 cm from the prop shaft, so the math is fairly easy.

The manual says that this torque test for a free running crank should read below 150NM. I'd like you to just have a think about how much torque that is for a moment....to turn an engine over that has had compression removed by removing the plugs...all you should be fighting against really is the springs in the valve gear!...so this number seems very high to me...anyways, I did the test, and my reading was around 8-9kg of force required to initially move the prop...doing the maths this works out at about 75NM. After this initial movement, the prop turned freely at around 3kg (or approx 25nm). Wait 5 mins, do the test again, same numbers.

Some folks have explained that backing off the cylinder head nuts on cylinder #2 and redoing the test will confirm the issue as pressure on the crank will be released with the slackens head nuts. This test made no real difference to my crank static torque test readings... I still had a 'stiff prop'. A friend performed the same test on his engine ...his numbers were half of mine.

With a big trip scheduled for a month's time which involve some very inhospitable terrain, I decided to get an iRMT to pull the engine.

The fretting is very severe. Pics attached.
I probably wouldn't have made it home from that trip. Block and crank of this engine are scrap....so I am replacing with a new shortblock.

Safe flying...
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IMG-20190531-WA0004.jpg (You do not have access to download this file.)
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  • Re: Fretting 912 ULS - my experience

    by » 6 weeks ago

    Thanks for sharing this info.  I have a 912 with s/n 5644xxx, 2005.  I am getting more concerned as my engine is getting tight, especially when hot.  I think the the rotax spec for torque test is interesting, and very high.

    There has been lots of discussion on crankcase fretting on this site.  It is a very concerning safety issue.

    More research in my future.

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