Crankcase Fretting

[mcomeaux53]

Can anyone chime in on Crankcase Fretting. I looked up on the Rotax site and not sure what resolve was. Is it just insuring that torque is checked periodic to prevent such a thing to occur? Any help would be appreciated.

[Av8r3400]

Crankcase fretting is almost unheard of in the Rotax world.

Can you elaborate on your problem?

[mcomeaux53]

I read several posts on Rotax site regarding this issue and it mentioned a particular run on serial numbers. I'm going to try and contact Rotax today and get some clarification on this and I'll post what I find. Just curious if any members here had any experience with this. I personally do not own or have this problem but considering purchasing one. I never heard of this prior to my research and was concerned. The serial number run was starting with #5645 that was produced on or about 2005.

[jiott]

I remember seeing that on the Rotax site also. But I think it referred to CRANKSHAFT fretting on some older serial numbers. Maybe it had something to do with the pressed together sections of the crankshaft moving very slightly with respect to one another (that is the definition of fretting, and it causes fretting corrosion).

[jiott]

I'm sorry, you are right, it is Crankcase fretting.

[Dusty]

I am aware of 4 fretting failures here.
Generally indicated by an increase in effort to turn the prop when hot.
One aircraft wouldn't turn on the starter until the next day!
These engines were all 100hp,but that may be distorted figures as most use the 100hp here,the cost to rectify(new cases)is around 1/3 the cost of a new engine and I doubt these engines would be suitable for line boring.
An easy test is just get it hot !
If it is ok then it won't happen immediately of at all?
912's are a little tighter when hot,but a fretted case will be easy to pick.

[Jerrytex]

Curious to know if anyone has heard anymore stories about 912 fretting. The Rotax owners show a few but there are 1000's of these engines flying with only a few reports. I am looking at a 2004 ULS with 300 hours. It's serial number is before the listed "effected" cases but it's before the 2006 case change. I read about lugging the engine etc. causing it, or the different sealant used. Just weighing in on the risk vs. value.

[jiott]

My understanding is that it is not engine lugging that causes it, but a design error that allows microscopic rubbing movement (the definition of fretting) between engine crankcase halves. This movement over time causes corrosive wear on the sealing surfaces, which in turn causes the thru bolts to lose torque. This then allows leakage, but more importantly it relaxes the squeeze on the crankshaft bearings, allowing them to turn in their mountings and accelerate wear. If you retorque the bolts it does not fix the problem because then you put too much squeeze on the bearings and they then often cause the engine to seize. Its a bad situation with no easy fix other than an expensive engine teardown and crankcase replacement. Personally I think the risk is too great and I would not touch it with a ten foot pole, unless the engine could be had for nearly zero cost, then fly it until it gives up, which may be a few or many hours.

[patrick.hvac]

There's lots of info out there on fretting of Rotax cases. Even some documented failures.
My personal mentality is to stay away from any old style cases to reduce risk. I think they changed in 2007.
Best bet is to discuss with your mechanic. I keep hearing about people dropping 5k for new cases though.

[rv9ralph]

This week I watched the EAA Webinar "Operating your Rotax On Condition". Early in the Webinar, the presenter explained, with images, the issue and causes of case fretting. If you are operating a Rotax, I recommend watching this Webinar. He addresses the 5 Year Rubber Replacement with some logical thought on the issue.

Ralph

[jiott]

Ralph, I also watched that webinar and as you say it is quite good. I am attempting to operate my 912uls "on condition" also. I did my "5 year" rubber replacement at about 7.5 years because I had the engine dismounted for other reasons which made it very convenient to do the rubber at that time. However, I will say that every rubber hose, etc. that I removed was in perfectly good condition, in my opinion, and could have easily lasted until 10 years. I fly at least once per week even thru the winter (few exceptions) and keep my plane hangared.