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Crankcase Fretting


Safety Officer

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Just an FYI for education:

 

Crankcase fretting? What is that and how do you know you have it. You probably don't.

 

It can happen with any engine, but we are only talking about a Rotax in this case. It has just happened to friend of mine with a 2005 912ULS. It seems to happen mainly with older engines and not the new crankcase that came out around Aug. 2006 and later. How do you know if you have it and what are the issues. The easy way to tell is after you shut your engine down go try and turn the prop. If it turns over like it does when it's cold then everything is good. If you can't turn the prop and it seems like you need Godzilla's help to turn it then you most likely have crankcase fretting. Some of the older crankcases will swell and put extreme pressure on the crank journals. After the engine becomes cold again the prop will turn over much easier. Here are a few things to check to determine if that was really the problem. One check the mag plug, it will most likely be clean or have a slight fuzz. Check the oil filter by washing the element like the video posted on this website and check for metal, it will probably be clean. Check the plugs and make sure they are clean. You need to do these last three to make sure you didn't have detonation and have a piston seizure which is a different issue. This last test is the important one. remove the #2 valve cover and loosen the four cylinder head nuts slightly. If the prop now turns over easy again and then when you tighten them back down it gets hard again then you have crankcase fretting. If you loosened the nuts and the engine was still hard to turn over then it most likely isn't fretting, but a piston seizure. Both of these are fairly rare, but can happen.

As far as the crankcase fretting it must be fixed. It will eventually crack the case and could cause a total failure at some point. The fix is an overhaul. The price is around $12K not including the work to pull it off and ship it. This is one reason that some of us have the 2000 TBO extension and others were held back at 1500 hr TBO. The cases were made a little different.

 

Now don't panic because you have a 1500 hr TBO engine or and engine pre Aug 2006. The over whelming number of engines never have any issues, but there have been a few rare cases of fretting. So far the ones I have heard about had around 700-900 hrs. and came from the 2005 time period, but that may not be the rule and only the ones I have heard about.

 

If this does happen to you fill out the Customer Service Information Report(CSIR) and send it in. Rotax may help on parts, but not labor.

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Roger, are you Safety Officer? I personally think it is better when someone puts out information as Safety Officer, which to most of us means a position designated based on training, experience, practice and responsibility that we know the person is speaking in some kind of official, quasi-official or otherwise sanctioned position. I know you own this site so I'm sure you know who Safety Officer is. If it is you, I'd just as soon you'd simply post as yourself.

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This is exactly what happened to my 2005 model at 600 hours. It was becoming harder to turn over to check the oil but it still ran OK. I took it to Lockwood for the 600 hour inspection and they decided to tear it down and discovered the crankkcase fretting. They advised me not to overhaul but to repair as every thing else was fine. Rotax gave me the newer crankcase and the engine was reassembled. It still cost me over $6000 but at least it extended my TBO to 2000 hours.

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Well if I could put in my two cents. First of all the Crankcase cracking has little to do with the actual fretting inside of the case. The issues from cracking has to do with how the pressure was originally distributed across the case itself. This is why even after changing to the 2006 crankcase they had also changed the torqueing specs about 2-3 yrs later, to prevent the fretting. The new cases are beefed up and they had added extra dowels added to them to prevent the fretting. The switch over to the 5910 also did wonders for helping the fretting. This is why if you have a 2008 and older engine, if you look under your oil pump you will see a redish sealant Loctite 274, if you have over 300-400 hrs on your engine I can bet you will pick up some sweating and possibly an oil drop or two. This can be a problem if your crankcase seal is sacrificed but it would need to be more than a few drops and hour leak. The tightness from spinning the prop over is more a problem with torquing and unequal clearances inside the engine. As long as it's less than 10-15ft lbs with out plugs I wouldn't worry about it, Rotax allows up to 100ft/lbs which is way scary!

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Jeremy, it seems that there's a large difference between your allowed torque to turn of 10 to 15 ft-lbs and Rotax 100 ft-lbs. Would you say that one might be OK if one sees a slightly higher rotational torque than your 10 to 15 ft-lb in light of Rotax's allowance of 100 ft-lb or would you stick to your limit? My thought is that perhaps an engine with low hours might require more torque to turn than one with hundreds of horus? Just curious.

 

Regarding the loctite 274 below the oil pump....it is not clear to me if you are indicating that we should see this sealant or we should not see this? Are you saying we will see some oil weeping from the case joint if the loctite can be seen? Or are you saying that once we locate the area where the loctite can be seen, we may see some oil weeping on higher hour engines? Maybe you can help me understand your comments?

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Hey Dick

The 10-15 ft/lbs or less is what would be found on a normal healthy engine. As an engine gets older you should see a slight drop in this value as the clearances between the crank and main bearings increases. This test is listed under the "unscheudled maintenance checks" in the Line M/M. This test is to be performed if an engine is running "sluggish"<-- I feel there was a loss in translation with this word. In the event you run the engine partially out of oil, prop striked it, or just want to test the overall health of your lower end are the only times this test should need to be done. The engine may be returned to service if the force is less than 100ft/lbs but I can tell you if you start to get into the 50+ ft/lbs area you may be running into a partial siezure already that will just get worse. Next time your mechanic is doing a compression test, walk up and spin the prop with your hand, this will give you an idea of just how little resistance there is inside the engine once the compression is no longer a factor.

 

As far as the loctite goes all Im saying is that if you do see a redish/orange sealant on the bottom of the engine where the case halves meet than your engine is more likely to fret and more likely to develop a leak on the higher time engines. Newer cases with the new torquing procedure along with the black glue-like 5910 are much less likely to have any issues. I wouldn't read to much into this unless you happen to have a leak in which case this will help explain why.

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This is why if you have a 2008 and older engine, if you look under your oil pump you will see a redish sealant Loctite 274, if you have over 300-400 hrs on your engine I can bet you will pick up some sweating and possibly an oil drop or two. This can be a problem if your crankcase seal is sacrificed but it would need to be more than a few drops and hour leak.

 

Jeremy,

 

Is this what you mean?

 

6853570571_46242298a7_z.jpg

 

That's the ROTAX 912ULS2 on my 2007 Sky Arrow, sprayed with Desenex and run for a few minutes. After each flight I have a drop or two of oil running down the cowling, and have wondered exactly where it was coming from.

 

Is it an easy fix?

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Yes Eddie, the oil leak in your photos is most likely do to your o- rings in your oil pump assembly. It's an easy fix just make sure you order all (4) o- rings and replace them all at once. The 1" o-ring on the inside of the pump requires massaging loctite 5910 onto the 1 o'clock and 6 o'clock positions where the crank case halfs meet to prevent oil migration. If your getting a leak just aft of the oil pump, or in your case forward of the pump. Then that may be related to the halfs moving in relation to each other. Also be suspect of the M8 bolts on the lower part of the crankcase, these are notorious for oil migration pass the threads.

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  • 1 year later...

We are experiencing this crankcase fretting issue with our 2005 CTSW with a 971 hour engine. I am waiting for a response to the customer service information report submitted on the rotax-owner.com website. Does Rotax respond to such reports? Are we likely to receive a reply?

 

Our only options are to rebuild the engine with a new case or buy a new engine.

 

Thoughts?

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