Rotax 912ULS flywheel upgrade

[herman pahls]

I was told by the technical department at LEAF that the pre 2010 Rotax 912ULS engines will start easier with less damage to the engine and gearbox after installing a Rotax produced flywheel that retards the timing at start up more than the flywheel that came with the engine.

1. Has anyone tried this flywheel that can report on how worthwhile the modification is for smoother starts?

2. The flywheel seems like a bargain for $370, but removing the flywheel requires a $200 puller.
Does anyone of this puller for rent or for sale?

3. I have also learned that I need to live in fear that the all mighty 912ULS sprag clutch will prematurely fail if your starting system, starting technique and gear box are not perfect and if your prop exceeds the moment of inertia of the gear box.
Makes me miss my Lycoming already.
I just replaced the starter with a Skytec since the Rotax starter was worn out (brushes and armature) and want to make sure the rest of my starting system is ideal since I am new to flying with the 912ULS in a model 4 Kitfox.
My current battery cables are size 6 wire with crimped on eyelets.
The Aerovoltz 12 cell battery is on the left side behind the firewall so cable distance is quite short.
I will be installing a Bully Hawk delayed timing device and the slipper clutch tests out with in normal limits for torque when tested with a fish scale at 24" from prop center.
My 72" tapered tip, nickle leading edge Warp Drive prop probably exceeds the recommended inertia limit.
What prop does not exceed the limits of the gear box?
Should I consider going to size 4 cables and should the eyelets be soldered for better conductivity?
Would I get better starting performance with the Odyssey 680 battery that many 912ULS owners seem to be using?
Should I be using a block heater.
I live on the Southern Oregon coast which has mild temperatures.
Any other suggestions from those who have years flying the 912ULS without fearing the "sprag" clutch.
Sounds like I need sprag clutch therapy or quit talking to "tech" departments.
Thanks
Herman

[Dave S]

Herman,

Being a pre 2010 912ULS user who does not have the flywheel upgrade and who does not have the "soft start module either"......I have to admit that the engine has never caused me any anxiety over starting.......and it is still running well with no crud on the magnetic plug, no decrease in the slipper clutch torque and no increase in prop gear backlash.

Starter and battery do have to be up to snuff.....if the RPM generated by the starter is less than what it should be, I can see the possibility of a kickback given the compression ratio of the ULS.

IMHO - correct starting technique and a healthy starting system seem to make this engine start up just fine

I don't know much about the "Bully Hawk delayed timing device" - however, the name seems to indicate it may have a similar function as the Rotax devices. Long ago in my mechanic's career, I learned to change only one thing at a time so there is some hope of knowing what causes what.

I have to admit that I had a few moments of adjustment regarding the differences between a C or L and an R.....after quizzing one of my favorite tech counselors about much of this stuff, he retorted..."Relax, you just haven't spent enough time behind a Rotax to understand it is not like a C or L". I think I have made my peace with the ULS and its original configuration certainly does not cause me any concern with starting.

There is a lot of stuff you can do a list search on with regard to preheating a rotax...FWIW...I live in a climate which can be colder than a witch's pump handle (if I can mix my metaphores in the name of political correctness)...Preheating is something I routinely do if the OAT is less than freezing. Then startup is a matter of using the Rotax recommended procedure. Making sure the throttle is closed and the choke (or whatever Rotax likes to call it) pulls shut completely before hiitting the switch seems to work just fine. When doing the pre-start rotax burp, it is apparent that in cold weather it takes more torque to flip the prop at first so I am inclined to believe "loostening up" the engine by rotating prop has some merit with regard to how much work the starter needs to do.

I also have my idle stops set so I can roll back to 1400 before shutdown to eliminate most of the "non-lycoming" abrupt stop a Rotax is famous for on shutdown - no timing delay device will help with that at shutdown anyway since the ignition is off to shutdown.

Sincerely,

Dave S
KF7 Trigear
912ULSWarp Drive
St Paul Minnesota

[Av8r3400]

Herman-- I'm glad to hear your troubles seem to have been solved with your starting circuit.

I'd agree with Dave with regard to changing the flywheel. Obviously pulling the starter and flywheel are not simple tasks, needing to move the engine off the mount, but now that you have done the starter once, you know the tricks of the task. But in the grand scheme, "If it ain't broke, don't fix it."

Dave also makes a good points on starting and shut down procedure to help matters. There have been a couple threads over the years here on managing starting and shut down. Preaheating, especially on the 100 hp motors is a great idea once temps get down into the 40s and lower. I personally don't believe that this requires expensive heating systems. I use a $20 cube heater from the hardware store mounted on the top of an old work light stand. This works great for me even down to the single digits. (From a couple years ago)

I hope you cleaned and added high temp anti seize to the exhaust joints so that they separate next time easier. A lesson I learned, too late. Check with the local EAA chapters to see if someone may have the flywheel puller tool you can borrow, (A reasonable machinist can make one, too.) if there's a need next time.

[jiott]

I have the Aerovoltz 12 cell battery in my SS7 with 912uls and have been happy with it so far. It holds a charge far better and longer than other types of batteries; no need for a trickle charger. It saves about 10 lbs of weight (no kidding). Its only down side is it doesn't seem to have the "staying power" of a conventional battery; if your engine doesn't want to start easily for whatever reason and you do a lot of cranking, the battery will fade out quicker than you might expect. For this reason, some guys have been going to the Aerovoltz 16 cell, or just carry a spare 12 cell battery (it doesn't weigh much) if you are going into the back-country.

[War Eagle]

I was told by the technical department at LEAF that the pre 2010 Rotax 912ULS engines will start easier with less damage to the engine and gearbox after installing a Rotax produced flywheel that retards the timing at start up more than the flywheel that came with the engine.

1. Has anyone tried this flywheel that can report on how worthwhile the modification is for smoother starts?

2. The flywheel seems like a bargain for $370, but removing the flywheel requires a $200 puller.
Does anyone of this puller for rent or for sale?

3. I have also learned that I need to live in fear that the all mighty 912ULS sprag clutch will prematurely fail if your starting system, starting technique and gear box are not perfect and if your prop exceeds the moment of inertia of the gear box.
Makes me miss my Lycoming already.
I just replaced the starter with a Skytec since the Rotax starter was worn out (brushes and armature) and want to make sure the rest of my starting system is ideal since I am new to flying with the 912ULS in a model 4 Kitfox.
My current battery cables are size 6 wire with crimped on eyelets.
The Aerovoltz 12 cell battery is on the left side behind the firewall so cable distance is quite short.
I will be installing a Bully Hawk delayed timing device and the slipper clutch tests out with in normal limits for torque when tested with a fish scale at 24" from prop center.
My 72" tapered tip, nickle leading edge Warp Drive prop probably exceeds the recommended inertia limit.
What prop does not exceed the limits of the gear box?
Should I consider going to size 4 cables and should the eyelets be soldered for better conductivity?
Would I get better starting performance with the Odyssey 680 battery that many 912ULS owners seem to be using?
Should I be using a block heater.
I live on the Southern Oregon coast which has mild temperatures.
Any other suggestions from those who have years flying the 912ULS without fearing the "sprag" clutch.
Sounds like I need sprag clutch therapy or quit talking to "tech" departments.
Thanks
Herman

You might read this thread to get some insight into using the 72" WD taper tips.

I fly with these blades on an Airmaster CS and have 7 other Kitfoxes in the area that use the same. There is some test data results from Airmaster included.

I don't think you should any trouble with your sprag clutch just because you are swing the 72"WD.

[herman pahls]

I appreciate the 4 responses and PM that I received today.
So this is what I learned from your posts and I thank you for sharing.
If all is in good condition and I use good starting technique;
I do not need to replace my 12 cell Aervoltz battery,
I do not need to replace my prop,
I do not need to replace my flywheel,
I may not need the Bully Hawk soft start or new generation ignition modules,
I do not need an expensive pre heat system,

That advice just saved me a ton when I was starting to believe that I may be abusing my 912 ULS engine, gear box and sprag clutch if I did pony up and make those upgrades.

"if it is not broke, do not fix it" great advice Larry.

The only answer I did not get was what gauge battery cables you are using and should the ends be soldered and crimped or is crimping alone adequate?

Thanks again
Herman

[Av8r3400]

I'd stay away from soldering. That makes the wire rigid and more prone to cracking.

As to gage of the wire, again if what you have now is turning the engine fine, not heating up on cranking and in good shape, go with it.

[jiott]

Herman, I crimped and soldered my battery/starter cable ends. I would never do this on the small wires, but figured the large wire was well supported and much less prone to vibration cracking. Just my $0.02 worth.

[HighWing]

I soldered my first set - 900 hours. This time I had a Harbor Freight hydraulic hex crimper - great tool incidentally - and used that. I doubt I would be comfortable with a single point crimper like used on smaller gauge wires. Can't remember the gauge on either, but my experience is with the UL so theoretical there at best.

[Peteohms]

Lockwood rents the tools. Had to replace my stator this summer.