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912 UL dieseling

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Dick Maddux

Joined: 24 Jun 2008
Posts: 516
Location: Milton, Fl

Posted: Sun Jul 27, 2008 5:06 am Post subject: 912 UL dieseling

I have a 912UL on my Kitfox and for the second time, it dieseled on shutdown. It went backwards aprox 3 revolutions. This time I was at a remote airport with no one there (totally locked up) It was about 94 degrees outside so I elected to fly the aircraft 20 minutes back to my home field. 

  I know there is a possibility of injecting air into the lifters when this happens.(should purge the oil system) When I started the engine the oil pressure came up but there were some fluctuations in the pressure indications on my Westach gauge. This could have been air bubbles or normal oil pressure fluctuations in this hot southern weather.(as it does when hot at low rpm's) In any case I had smooth normal oil pressure at cruise.

  At my home field I changed the oil and checked the filter element for contamination. It looked fine. I am running a Rotax oil filter and it has a rubber diaphragm which I believe will prevent reverse oil flow.Wether this would prevent air entering the lifters, I don't know.

  Today I am going to do the lifter clearance check before further flight.

  I had been using 87 oct gas then switched to 89 after the first event. I am now going to use premium (93) in hopes of stopping this from happening again. The recent manual says I can use 87 on the 912UL (although my original 1994 manual says to use 97 or premium)

  Has anybody ever had this happen or am I the only one? I called Dean at Lockwood(the Rotax guru you see on the Lockwood DVD) and he said that he had never heard of this happening.

   The engine temperatures on shut down were perfectly normal. I know the timing on the engine is fixed, my idle is 2000. The only thing I can think of is fuel. Even my fuel was fresh midgrade. Total engine time is 175 hours. The engine is an early 1994 .

    Any opinions would be greatly appreciated!

  

                                                      Dick Maddux

                                                      Rotax 912UL

                                                      Pensacola,Fl



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  [quote][b]

lucien

Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM

Posted: Sun Jul 27, 2008 8:34 am Post subject: Re: 912 UL dieseling

[quote="Dick Maddux"]I have a 912UL on my Kitfox and for the second time, it dieseled on shutdown. It went backwards aprox 3 revolutions. This time I was at a remote airport with no one there (totally locked up) It was about 94 degrees outside so I elected to fly the aircraft 20 minutes back to my home field. 

  I know there is a possibility of injecting air into the lifters when this happens.(should purge the oil system) When I started the engine the oil pressure came up but there were some fluctuations in the pressure indications on my Westach gauge. This could have been air bubbles or normal oil pressure fluctuations in this hot southern weather.(as it does when hot at low rpm's) In any case I had smooth normal oil pressure at cruise.

  At my home field I changed the oil and checked the filter element for contamination. It looked fine. I am running a Rotax oil filter and it has a rubber diaphragm which I believe will prevent reverse oil flow.Wether this would prevent air entering the lifters, I don't know.

  Today I am going to do the lifter clearance check before further flight.

  I had been using 87 oct gas then switched to 89 after the first event. I am now going to use premium (93) in hopes of stopping this from happening again. The recent manual says I can use 87 on the 912UL (although my original 1994 manual says to use 97 or premium)

  Has anybody ever had this happen or am I the only one? I called Dean at Lockwood(the Rotax guru you see on the Lockwood DVD) and he said that he had never heard of this happening.

   The engine temperatures on shut down were perfectly normal. I know the timing on the engine is fixed, my idle is 2000. The only thing I can think of is fuel. Even my fuel was fresh midgrade. Total engine time is 175 hours. The engine is an early 1994 .

    Any opinions would be greatly appreciated!

  

            ï¿½            ï¿½            ï¿½           ï¿½   Dick Maddux

            ï¿½            ï¿½            ï¿½           ï¿½   Rotax 912UL

            ï¿½            ï¿½            ï¿½           ï¿½   Pensacola,Fl



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   	  Quote: 	
		  [b] 	




I had my 912ULS pop once on shutdown a while back (tho it didn't spin backwards). I've never had another instance of that happening before or since.



The only variable that there could have been is the fuel - everything else, the weather, etc., was exactly the same as it had been many times before when there wasn't a proble.



So, the fuel is my vote. 



There was another thread recently on ethanol and at the risk of dredging that up again..... 



I very seriously question the quality of the E10 gas - I did a "water test" on some local E10 yesterday and was shocked at the results. The gas remained thickly cloudy after mixing it up with the water, clearly indicating the presence of some other kind of contaminate. I tried some E10 from another station (this time 87 octane instead of 91) and got the exact same results with the water test.



No way I'd want to run that stuff through my 20,000 dollar motor .



So all that said...... try running some gas of known quality through the motor for a while. I.e. 100LL which doesn't have ethanol in it and also has a lower vapour pressure, and see if that doesn't cure the problem.



I know the quality of gas is quite variable in my area, so I'm reasonably sure that's why I got the dieseling event I got.....



LS

_________________
LS
Titan II SS

rparigor(at)suffolk.lib.n
Guest

Posted: Sun Jul 27, 2008 8:35 am Post subject: 912 UL dieseling

Hi Dick



"Any opinions would be greatly appreciated!"



I had a 1972 Yamaha RT-2 360 that used to run on after shut down if it was

real hot, I always used hi test fuel. As a matter of fact I once did a

compression test and the cylinder fired! It only has 1 spark plug, it must

have been hot glowing carbon somewhere in combustion chamber.



On cycle it is easy to prevent just put in gear and drag clutch on shut

off, but I would sometimes choke it for a few seconds before shut down,

easy to try on 912. You may also want to have a very close look at spark

plugs, are they the right heat range? Do they have excess carbon on them?

Are you using thermal conductive compound on plug threads and are they

torqued properly?



Are you certain that your ignition ground is not intermittent?



Is your alcohol level infuel whacked like 15% because distributor

overmixed? 



Add 25% 100LL next hot day and see if that helps?



Ron Parigoris

Dick Maddux

Joined: 24 Jun 2008
Posts: 516
Location: Milton, Fl

Posted: Mon Jul 28, 2008 4:15 am Post subject: 912 UL dieseling

Thanks for the tips Ron and LS. I will check the ground wires.We don't have alcohol in the fuel here yet.(not for another two years) I am pulling the plugs today and will check them for carbon.I always use the silicone compound on the plugs and torque to the book. 

  Hopefully the premium auto gas will do the trick ,if not then on to a mix of avgas.I have just started using the new Aeroshell Plus 4 oil and it will handle either fuel. It's a 10w40 oil but pours like water.

                                 Dick Maddux

                                 Kitfox 4

                                 Rotax 912 UL

                                 Pensacola,Fl  

                                

  



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  [quote][b]

rparigor(at)suffolk.lib.n
Guest

Posted: Mon Jul 28, 2008 7:39 am Post subject: 912 UL dieseling

Hi Dick



I just remembered hearing from Lockwoods years ago that if you get the

ignition modules hot you can not turn motor off. I wonder if one of your

ignitions give you a spark or 2 out of phase on shut down??



Ron P.

b.carl@sympatico.ca

Joined: 20 May 2008
Posts: 77

Posted: Sun Aug 03, 2008 8:31 am Post subject: 912 UL dieseling

Dick

 Try Idle power for 1-2 minutes before shut-down.

 Carl

 [quote]   ---

Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Sun Aug 03, 2008 12:57 pm Post subject: Re: 912 UL dieseling

If your timing is advanced too far that will also make engines diesel.

_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056

jackandval

Joined: 18 Jul 2007
Posts: 21
Location: blairsville, GA

Posted: Mon Aug 04, 2008 3:03 pm Post subject: Re: 912 UL dieseling

I didn't think you could adjust timing on a 912 Rotax? I thought it was fixed?

Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Mon Aug 04, 2008 3:51 pm Post subject: Re: 912 UL dieseling

Hi Jack,



For the most part you are correct that timing is not something to mess with , but if the ignition coils are not set up correctly or go bad there will be a change. There are 5 coils. The 5th. is the trigger coil for the tach.

_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056

rlborger(at)mac.com
Guest

Posted: Mon Aug 04, 2008 3:53 pm Post subject: 912 UL dieseling

Jack,



Yes, that's correct.  The timing is fixed, controlled by a set of lugs  

on the flywheel and sensors on the frame.



I guess you could get in and grub around with the sensor position but  

you are treading on thin ice at that point.



Good building and great flying,

Bob Borger

Europa Kit #A221 N914XL, XS Mono, Intercooled 914, Airmaster C/S

http://www.europaowners.org/N914XL

(99.9% done) Presently fighting gremlins in the starting circuit.

3705 Lynchburg Dr.

Corinth, TX  76208

Home:  940-497-2123

Cel:  817-992-1117

On Aug 4, 2008, at 18:03, jackandval wrote:



 	  Quote: 	
		   

 >



 I didn't think you could adjust timing on a 912 Rotax? I thought it  

 was fixed?





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