sprag clutch 912uls

[Slyfox]

I'm posting this because I need to make a decision. The decision is I have a damaged sprag clutch. This was caused by troubles I had last year with the running of my engine. It had severe kick back on starting caused by over flooding caused by a bad needle seat. move forward and the engine now runs great but has a sprag clutch problem. I have a 912uls 2008 or there abouts. There is a bulletin from Rotax to change to the newer modules which I did, it also says to put in the newer flywheel that retards the timing on startup. I called Lockwood and have all the parts and tool needed to replace the sprag but they are claiming the flywheel is not needed. I only want to do this once and am thinking that the newer sprag and the flywheel should be changed. yes my engine when it's below 60 degrees does slip out. when it's nice and warm out the engine starts up real fast with no choke, hence the reason for replacing the sparg. I want to hear what everybody thinks about adding the flywheel to the list. the cost doesn't bother me, just want it right.

[jiott]

I have heard on this forum (but don't remember who) that the new soft start modules are most of what makes the soft start function. The new flywheel adds a small additional benefit to the soft start function, but very little and can easily be done without. Can't verify, but this is what I remember hearing. Hopefully some others will verify.

[Dave S]

Slyfox,

Jim has a pretty good call on the issue.

According to Rotax documentation

Normal timing (without soft start feature) is 26 degrees BTDC

The soft start feature provides a 3 to 8 second delay period when the timing is retarded.

The old flywheel and soft start modules will retard the timing to 4 degrees BTDC during the delay period

The New flywheel with soft start modules will retard the timing to 3 degrees BTDC during the delay period

Interestingly enough, Rotax lists the normal timing as 26 BTDC for both flywheels once the soft start delay times out.

The difference between 3 and 4 degrees BTDC is insignificant.

[Slyfox]

putting a closer to this one. I pulled the motor off and changed out the sprag clutch. I didn't replace the flywheel, only 1 degree change, not worth it like mentioned. The first bolt was tough but doable. The big nut on the sprag housing was a 46 mm book wasn't clear on this, they mention 36mm but that's the thread size of the nut. After scrabbling and finding a socket that was deep enough, at least 60mm deep inside. I used a heat gun 1300 watt and softened the locktite and it came right off, reverse threads so be careful. Everything else was straight forward. The only thing to warn is to empty all your oil before doing this. Yes I had a mess for all the oil came out the tank and out the bottom of the engine, what a mess. lol It starts really nice now with no kick back. You have to know what you are looking for to know if you have a bad sprag clutch but basically the spring that goes around the sprags stretch out and makes it so the sprags don't engage. but if you have any kick back on startup, that sprag is gone.

[Av8r3400]

I have always been scared of kickback and damage to the sprag. I don't want to do the job you just did.

To mitigate this, I installed new "soft-start" ignition boxes from Rotax when I first finished the rebuild of the Mangy (also fixing another problem detailed on the forum).

I still had a few instances of kickback, so I also changed my starting procedure to spin the engine on the starter with the ignitions off until the engine is turning at "full speed" then turning on the ignitions. Not solely relying on the starter to overcome the pulse of the ignition. I also leave the ignitions off while "enrichening" during a cold start. Since implimenting this procedure, I have never had any kickback.

Another reason the "Left-Right-Both-Start" switch has no place on a Rotax powered aircraft.

[avidflyer]

The aftermarket ignition modules sold by the guy in Wisconsin that advertises on Barnstormers has a built in soft start system, you connect a wire to the starter solinoid that supplies power to the module whenever you are cranking over the engine. After startup, the module is powered by the engine, just like the original rotax modules. I put one of these modules on my new Kitfox build with a ULS on it. Haven't ran it yet, but expect it will be fine. Reason I mention this, is if someone is looking to do the soft start module, it may be something to consider. JImChuk

[Slyfox]

Larry, I replaced both my modules to the newest and hooked up the soft start. I also replaced the battery cables to #4 wire on the long runs, 24inch wires for the pos and neg. the shorter runs #6. I use to have the 912ul engine and originally had really skinny wires, like #8 lol. I now have the 912uls and even though things have worked out for 800 hrs. , last year things went south. biggest reason is I had a flooding issue with the right carb, which originally went on the left side, but because of the 4 needed the manifolds turned to outside, it is on the right side now. should have kept the carbs on the proper side but I didn't. Anyway, the flooding problem which occurred after running a half hour was do to a bad seat for the needle and seat. I replaced the carb and problem solved. But in the meantime it caused hard starting and kick back, which took out the sprag. I now can pull the choke out and start and it fires right up. I also have the earthx battery and that really spins the starter. love it. I too have switches for the mag, no way would I have a combined switch for mags. so many benefits to cranking with mags off.