912ULS crankcase fretting

[Hambone]

So my mechanic says that my 912 is suffering from crankcase fretting. It’s done 900 hours toward its 1300 hr TBO. He suggests that a lighter prop will help.

How much fretting is too much? I can feel some resistance between piston compressions when turning the prop, but it’s not that hard to turn.

Experience and recommendations welcome!

[3Dreaming]

There is some information here.
https://www.rotax-owner.com/en/912-914- ... se?start=5

[drseti]

Early 912 crankcases (prior to s/n 06.0020) are prone to fretting regardless of flight hours. Fretting can cause oil leakage along the seam between the crankcase halves. When this happens, it is natural to want to increase the torque on the thru-bolts, but this result in reduced main bearing clearance and increased main bearing wear. At the extreme, you will note increased force required when pulling the prop thru to burp the engine. If you have one of these early design crankcases, lighter props won't help (and the engine will likely not reach TBO).

I have photos of a damaged early crankcase in this webinar (about 12 minutes in):

http://avsport.org/webinars/videos/past_tbo.mp4

which will also also show you how to identify affected crankcases.

[drseti]

I've noticed that in the 11 year old thread on this issue at rotax-owner.com, posters are referring to the engine s/n. The only way to know for sure if a given engine will have this problem is to check the crankcase s/n, which is different. Old-style crankcases have serial numbers in the format xxxxxxx, while the serial numbers on new style crankcases are in the format yy.xxxx (where yy is the year of manufacture). For where to locate the crankcase s/n, see the above referenced webinar.

[GBisset1960$]

Hi,

I have had a significant propellor issue with my Evektor Sportstar which maybe implicated in fretting. Only two propellors have been certified. A Whirlwind and Woodcomp SR200. Whirlwinds are very hard to get in Australia even though there are two dealers. Very unresponsive. Took two weeks to get a quote and a week later I still can't get an invoice to pay!

Anyway on topic. I had an SR200 Woodcomp on and it did 1100 hours but ran out of calendar so being happy with the propellor placed an order for a new one. I was dismayed to see they are now only good for 300 hours! As I already had it I had it fitted and balanced by a highly reputable LAME. I immediately detected a difference in resonance. Was always at 5050 RPM quite light and was a very narrow ban. Now it was at 5100 and went to 5200 RPM. About VY RPM. I had the propellor checked and all was well. I hire my plane to a flight instructor and he never detected anything different, although I fly the plane more. However also during this period, my A/H instrument collapsed. This might sound strange but I could more acutely detect the resonance by placing my finger on my Ipad screen attached to the dash. It was smooth with no vibration until it went through the band and then disappeared at cruise about 5300RPM. It seemed to be a resonance and not a vibration as such.

About 50 hours after fitting a weep developed on the through bolt at the top: The leak was never quite as bad but after say 4-hour flight there would be about half fingernail amount pooled in the head bolt area. At times there was none. The plane went in for 100 hourly and the propellor was to be rechecked. During the service, the filter was cut open and aluminium was found. The engine was sent to Rotax in Australia and when it pulled down the crankcases had fretted.

The engine had to be replaced and had only done 1170 hours. The motor was manufactured in 2007 and was in a 2007 model Sportstar Plus. It was just out of calendar hours. It is the new version of crankcase 07.6521 stamped. The engine has a check for metal every service and metals have never been detected and compression etc were all excellent.

My question is has anyone else experienced this? I guess I am very concerned about the propellor so even though it has 200 hours left I am trying to replace it with a Whirlwind. I obviously don't want a repeat. I cannot get any answers from the manufacturer or from the dealer as to why the propellors had hours reduced. I can only think of quality issues. My understanding is Whirlwind propellors are good and actually shouldn't have to be changed in the life of the engine.

Any thoughts would be appreciated regarding Whirlwind propellors and would be interested in others' experiences with SR 200. I have a series of photos but a bit large for this billboard.

Thanks

Gregg

[drseti]

Gregg, I have never seen fretting on the newer style crankcase (which doesn't mean it can't happen). However, I can't tell from the photo you sent me that the oil seen pooling at the top of the jugs is coming from the crankcase seam - it could be from anywhere.

To my knowledge, Evektor approves both the Woodcomp Klassic and the Warpdrive CF. I've used both, and prefer the Warpdrive. I am not familiar with the Whirlwind. As for the resonance you describe, that would normally be an indication of unequal pitching of the three blades.

I'm a little confused about your reference to Vy RPM, since airspeed is controlled by pitch, not power. I'm guessing you mean that at wide open throttle, when you pitch for Vy, that's the RPM you see. In any case, WOT RPM is a function of propeller pitch, so if you're not getting the RPM you expect, recheck your pitch with a protractor (measured with prop backing plate set to vertical using a bubble level, and each blade rotated to leading edge level).

The photo you sent me of the metal found in the oil filter does seem to look like it might be from case fretting (although the only way to know for sure is metallurgic analysis of the fragments). But in the other photos of the torn down engine, I can see considerable scoring of the crankshaft bearings, so I have to wonder if that's the metal being caught in the filter.

Sorry I can't shed more light on your issues - it's hard to diagnose from the other side if the globe!

[GBisset1960$]

Hi,
You are correct. The WOT on take-off at VY is about 5150 RPM and the was just on the edge of the resonance. The oil was coming directly out of the bolt thread and you could see the ever so slight weep running down. My LAME (Licensed Aircraft Mechanical Engineer Aussie term) Assured me wasn't too much to be concerned about at the time. Like most in Australia they still really learning about the Rotax as they deal with everything.

When I flew the airplane straight after fitting the new propellor I checked WOT at 2000 feet straight level 2650 RPM as before. At VY WOT 5150 RPM cruise 5250 RPM right on 98 knots as it was with the old propellor so I was happy that it was set right. I just had some concerns about the resonance shift.

I did read that a person had a problem with a propellor and found one blade flexed a bit more than the other and causing some harmonic-type problem.
As the propellor and hub are still together I will check all blades are equally pitched with the LAME. I did think I wonder with blades in the hub and fixed horizontally if I hung a weight from the tip and see what variation in flexure in the independent blades. I am not sure if variation is normal or not.

Anyway, I thank you for your time and expertise, and whilst I haven't enjoyed replacing the motor I have found investigating possible causes enlighting.
You quickly realize the more you learn the more you don't know! I look forward to following this page as well been most helpful. Just one last question how long would it take for a motor to frett like that in your experience?

[drseti]

The crankcases that had the fretting issue were made in roughly 2004 through 2006, and we began seeing failures about 10 years later. I'm not sure how many hours they had on them, but I would guess the problem shows up at 500 to 1000 hours. I have yet to see fretting on the new design.