Rtax912 issues

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Rtax912 issues

Postby BucF16 » Thu Jul 26, 2018 4:38 pm

Hey Guys, I'm preforming a condition inspection on a friends Highlander. I'm very versed in the airframe part, but am a little new on the Rotax nuances. The only issue for the airframe is the tail feathers. The flying wires seem a little loose. Data is scarce, and most say tight>>>>>> I used a tensiometer and got a average of 25 Lbs. My real issue is that the "burp" on this 912 takes 30-40 blades........ on some forums, that is normal, and some say only 5-10 blades is normal.

The top spark plugs are very caked with carbon. He uses 90 Oct no ethanol farm fuel.

I've heard that those who use farm fuel, add 10% 100LL, and some use straight 93 Oct car gas with 10% ethanol (but don't store it for any length of time).

What are you all using.

Any advise would be appreciated!

Cheers,
Bruce
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Re: Rtax912 issues

Postby kenryan » Thu Jul 26, 2018 4:56 pm

There is a very good Rotax forum at https://rotax-owner.com/en/. From that forum I have gleaned that the number of blades required to burp an engine is quite variable, depending upon tank height relative to the engine, method or "technique" used to burp the engine, and probably other factors as well. I also learned that dark sooty plugs is quite normal if the engine was idled before shutdown. You might want to replicate your post on that forum.
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Re: Rtax912 issues

Postby alan » Fri Jul 27, 2018 9:24 am

Technique with the prop rotation for the burp is key. Turn the prop to top of compression stroke and hold it there for a second or so until the pressure has time to blow by the rings. That is what blows the oil from the crank case. It takes far fewer blades to get the burp that way. Straight from Phil Lockwood.

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Re: Rtax912 issues

Postby BucF16 » Fri Jul 27, 2018 1:15 pm

Thanks! How about the fuel issue. What are you all using?
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Re: Rtax912 issues

Postby ja30driver » Fri Jul 27, 2018 3:06 pm

According to my research and reading... which I've spent quite a lot of time looking at this...
A mixture of 90 Non-Ethanol with 100LL Av Gas seems to provide an excellent fuel for the ROTAX
According to what I've found that combination leaves everything cleaner than both MoGas only or 100LL Only.
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Re: Rtax912 issues

Postby BucF16 » Fri Jul 27, 2018 7:29 pm

What percentage? 90/10?
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Re: Rtax912 issues

Postby alan » Sat Jul 28, 2018 8:36 am

I've been using 91 octane auto gas with 10% methane for 12 years now with no problems. Every time I check my plugs they were light tan with no carbon buildup. I change them at every annual, which, except for the first year, has been less than 100hrs. The only time I use any 100LL has been when I've flown a cross country.

Just finished my 11th annual and will do the recertification, and $100 hamburger flight this morning.

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Re: Rtax912 issues

Postby alan » Sat Jul 28, 2018 9:44 am

Oh yeah. I almost forgot. Stabil fuel stabilizer. Phil Lockwood highly recommends it. I put my fuel in a 33 gallon drum and add 1/2 of a large bottle of Stabil to it before I pump the fuel into it. Phil says it will keep the fuel good for a year. So far, so good.

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Re: Rtax912 issues

Postby BucF16 » Sat Jul 28, 2018 7:23 pm

All of on target condition inspection aircraft spark plugs have the light tan "bottom Plugs",,,,,,,, but the top plugs are very carbon coated!!!!! So some sort of change needs to occur.

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Re: Rotax912 issues

Postby gkremers » Sun Jul 29, 2018 8:27 am

Buc,
I have also been using 93 auto fuel with Ethanol from day one. Very unlikely the black carbon is from the fuel you are using. As someone else mentioned the upper plugs getting black is more likely from idling before shutdown. I’ve spoken with Rotax extensively on the fuel subject. Nothing wrong with running up to 10% ethanol, the engine doesn’t care. The bigger issue is the fuel system and how often you let the plane sit without flying. If I could buy 91 octane or better without ethanol I would, just not available by me. Below is how they rank which fuel to use.

1. 91 octane or better with no ethanol
2. 91 or better with ethanol
3. 100LL

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Re: Rtax912 issues

Postby BucF16 » Sun Jul 29, 2018 8:55 am

Thanks Gary!
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Re: Rtax912 issues

Postby BucF16 » Thu Aug 01, 2019 2:42 pm

2019 Highlander condition inspection is going well. Last years sooty spark plugs have given way about 50%. We added 1 gallon of 100LL to each 10 gallons of 90 oct farm non-ethanol fuel. So new plugs this year, and we'll fly it a few hours to see if there is any change.

I do have one question? Does anyone recognize the piece of rubber in the picture below. It was laying on the top of the engine in from of the coolant collector (not the overflow). I'm looking through the manuals to see if I can figure it out. It looks like pieces of both loops, that would go around a 7/8ish hose, have broken off.

Thanks in advance.
Bruce

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Re: Rtax912 issues

Postby AV8R Paul » Thu Aug 01, 2019 9:24 pm

The piece of rubber is a wear pad that goes on the bottom of the Radiator Thermostat housing. See attached photo from catalog, Item 12. Mine looked more like yours than the one in the catalog drawing. It there to prevent wearing a hole in the bottom of item 9 causing a water leak. If you don’t have a rubber wear pad under it, which I doubt you do, it needs replaced.

If you are using 100LL you need to be adding Decalin to the fuel to strip out the Lead. The Rotax engine does not run well with Lead. I had a server problem with lead build up on my heads, and had to have the heads walnut steel blasted to clean it out. I live in North Texas, I could not get gas without alcohol, and it destroyed my fiberglass fuel tanks. The alcohol sripped epoxy out of tanks (from the slosh baffles) and coated carbs, inside of heads, air box, etc. That story is a saga. I ended up running 100% 100LL. If you run 100LL, you must use Decalin, or some other additive to strip out the lead.

To burp 10 to 15 is all you should need. I never got mine to burp in 5 turns.

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Re: Rtax912 issues

Postby BucF16 » Wed Aug 14, 2019 8:35 pm

Paul, I'm sorry I didn't respond sooner. Thank you! Yes this item was the rubber protector you indicated. I fabricated a new attachment.

The last area that I inspected were the brakes. Whoa! metal to metal. These tricycle gear Highlanders need a lot of brakes to keep them going straight!!!

So new linings, maybe new rotors. 240 hours. Wow.

Your mileage may vary!

Cheers,
Bruce
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Re: Rtax912 issues

Postby Winston » Tue Aug 20, 2019 10:36 am

I have double calipers and changed my pads and rotors at 874 hours. The disc thickness was just below Matco's minimum (which I don't remember) and the pads were very thin. I once had a rotor loosen up and sheared two of the three bolts that hold the rotor to the wheel hub. Now checking the security of the rotors is part of my preflight. I'm now at 1158 hours - pads and rotors look good.
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