912 Nightmare

[art.o]

Hi guys Well I went ahead and bought that series6 on anfibs wounderd why the guy had a heater on the engine at 32` engine started with modest problems that was the last time I have since put on a new battery 250 cca new cables new soft start new plugs new gold starter new oil and filter checked gaps in mag trigers now told probley needs new sprag clutch and housing for yet another 900 or so I thought that the 4 stroke was a much better engine then the 2 stroke, does everyone have the problems with these engine, it only has 250hrs what I thought was quite new is this the wrong choice should i have gone with the other choice ? Im thinking the preowner got a price and said i'ts time to go anyone have any sugestions am i stuck with a enginering screw up Cheers art.o:mad:

[Newkid]

We just replaced the sprague clutch on our Rans which has a 912S. Right around 250 hrs it started "kicking back" on us. We put a soft start on it and that solved the problem for about 20 hrs. I think we have had that engine off of that plane 3 times to mess with the sprague clutch. We finally bought a used sprague clutch and put it all back together. Starts like a dream now. I've been told that having a heavy prop will ruin the sprague clutch, but ours just had a Warp Drive. If your mechanically inclined it isn't very hard to change, but you do need two people and a puller from Rotax.

[Av8r3400]

The Warp Drive props are the HEAVIEST props you can put on a 912! Warps are not a lightweight prop. This might be something that is not widely known.

A three blade Warp, with square tips and nickel inlays is too heavy (per the Lockwood and LEAF seminars I attended at Airventure) for a 912. They said bearing, gearbox and sprag-clutch damage is a sure thing with that combination. If the tips are tapered, that lowers the weight to the absolute maximum allowable. Still, at that weight, sprag-clutch problems should be expected on a 100 hp 912ULS (with the violence of the start/shut down on that model). The soft start modules should help, some. The new 912S motors have them from the factory now.

[Newkid]

I totally agree with that as far as a ground adjustable prop. When I said heavier props I meant props like the medium IVO or the Airmaster constant speed props which weigh upwards of 20 lbs.

[art.o]

thanks again guys my engine doesn"t have the Warp Drive I have the IVO in flight adjustable don"t know if it"s better or worse but the hours are about the same as others that are also having trouble seem to me it"s not the prop but an engine fault, if one has to put a sprag clutch in every 250 hrs that gets real expense on an engine that wasn"t cheap to start with.Cheers art.o

[Newkid]

Not too many 912s have this problem. I know that Rotax put out an AD for 912Ss that fall with in a certain range of serial numbers. You might have one of these engines, anyway if you replace it once it shouldn't ever be problem again.

[RobS]

Could someone clarify which end of the motor we are talking about? Is this the sprag associated with a gear reduction unit between the engine and the prop? Or is it the sprag clutch between the starter and the flywheel?

I thought art.o's original post was related to the starter and can see where the Rotax soft start module would help prevent kick-backs and, in turn, lessen the risk to the sprag on the starter. I can also see where a heavy prop could cause more problems with the gear reduction unit and all of its components including any clutch mechanism.

If it is the starter end of the motor, I would think it highly unusual to have to change the sprag clutch very often unless you are regularly getting “kick backs” on start up. I know that’s what happened to the sprag clutch on my Continental O-300. The clutch was old and more susceptible to “slipping” and compression kick-backs and sure enough a kick back did in the sprag completely. If the motor is kicking-back on start up, I'd work on solving that problem before install a new starter sprag.

[Newkid]

The sprag clutch is on the back of the engine on the crank.