rotax 912s engine failure

[wilsron]

In flight the other day, my 912s in my Kitfox 4 went rapidly from running perfectly, roughly for less than a minute, to totally quiet. Multiple attempts to restart were completely unsuccesful. Folded wings after forced landing on highway and towed home to hangar.
Rotax 912s, about 200TT
Abundant fuel in plane, so much so that it flowed out the vents with the wings folded. Drained fuel sample, no debris or water.
Removed Carb bowls, they were full, and fuel gravity flows at a rate that appears adequate to produce power without the pump working.
Removed a plug, grounded on engine and engaged starter- NO spark on either system.
Reviewed Rotax Heavy MX manual measurement values for the ignition unit, values WNL.
Generator coil Yellow to Yellow 1.5 ohm
Charging coil Red to Ground 4.6
Trigger coils .240 .240 .238 .238

Thoughts?

Thanks

Ron

[Av8r3400]

Do you have the "ACS" style off-left-right-both-start ignition switch?

There has been some debate here, but LEAF (Leading Edge Airfoils - Midwest Rotax service facility) has recommended not to use these with the Rotax's CDI style ignition due to failures.

[wilsron]

Wired with separate individual ignition switches, tested with P leads disconnected at the ignition boxes.

[Dave S]

There is a Rotax Service Bulletin on flywheel washers in some 912/914 series engines. If the washer crunches, the flywheel can loosten resulting in complete ignition failure.

Not saying this is what you experienced; however, here is the link to the SB.

http://www.rotax-owner.com/index.php...article&id=243


Sincerely,

Dave S
KF7 Trigear Flying
912ULS Warp Drive
St Paul, MN

[wilsron]

Thanks Dave
I had wondered about that one as well.
I'm not included in that sb according to my sn.
I was hoping to avoid find a problem that didn't involve pulling the engine, but it certainly looks like a possibility

Ron

[DesertFox4]

Ron, sorry to hear about your engine-out and forced landing.
Glad you skillfully got her down and you were unhurt. Nice job.
Rarely does a 912 have a total ignition failure and you've checked fuel issues so I'll be following this one.
Dave S. posted something new to me. Must have missed the washer problem associated with possible ignition failure. Check your serial numbers guys. Thanks Dave.
Good luck with the investigation and keep us posted.

[wilsron]

Thanks to each of you who have given suggestions on the problem.
Primary credit goes to Kevin at California Power Systems for suggesting a ground problem.
A Jumper across the aluminum break makes it work. I believe this was the way Kitfox suggested it be done on the original 912 back in 1993. It will go back together with different ground paths, and wire to complete the circuit in case of a similiar break in the future.

Thanks
Ron

[Dave S]

Hi Ron,

Looking at my engine, I see the current Rotax hookup has each of the two ground wires going to separate bolts on the starboard manifold. That way the chance of loosing both mags at the same time is unlikely.

I can see where the aluminum bracket combining both would cause both sides to fail at the same time if the bracket failed - probably not the best patent in the world. Your fix with separate grounds is the way to go.

Your photo helps in understanding the situation. Thanks for sharing.

Dave S

[DesertFox4]

Glad your Rotax is still healthy. Good info for everyone using Rotax engines.
I installed an extra ground when my engine went on back in 2003. We forget these things so long after our builds are completed. At least I do.

[kmach]

Hi,

I am very glad to see you found the smoking gun !