Rotax 912ULS starter sprag clutch...

[proemer]

I have a Rotax 912ULS in a Sky Arrow SLSA, which shows signs of a slipping starter sprag clutch on cold starts. It fires once, then if the starter is held in I can hear the starter turning, but the engine is not turning. If very well pre-heated, or on a hot start it starts more or less normally. (800 hours/ 15 years old.)

If the sprag clutch needs to be replaced, is this a "factory authorized only" type service, or can a local AI do it?

Also, if the airplane continues to be flown with this condition, with a slipping sprag clutch, is there a risk of further engine damage... bits of metal, etc?

Thanks!

[David]

Yes to more damage

I found this and post on the forum before, view this video and see if the symptoms are similar. I did have a sprag clutch go bad at 400 hours

https://youtu.be/wOVwB5EmtRg

Edited I found my YouTube of my rv12 trying to start with a bad sprag.


https://youtu.be/A4g5kJnuFcM

[proemer]

Thanks, David -- Looks like my sprag clutch is indeed the problem.

Were you able to do the repair yourself or have it done locally, or did you have to send in the engine?

Pete

[David]

Thanks, David -- Looks like my sprag clutch is indeed the problem.

Were you able to do the repair yourself or have it done locally, or did you have to send in the engine?

Pete

I had a Rotax mechanic assist me. I believe we also rented a tool from Lockwood and then returned it. I would not do it my self and still get a Rotax certified mechanic to do the repairs.

[ShawnM]

Thanks, David -- Looks like my sprag clutch is indeed the problem.

Were you able to do the repair yourself or have it done locally, or did you have to send in the engine?

Pete

On various airplanes where the engine isn't shoehorned into the cowling this can be repaired with the engine in place. You certainly don't have to send the engine anywhere. I cant imagine what that repair would cost.

I assume the cowling comes off your engine on the Sky Arrow. I would think this repair would be very easy AFTER you make some sort of temporary work platform behind the engine.

[proemer]

The engine access on the Sky Arrow to that area may be a bit tight, but it would be good news if we don't have to send the engine anywhere.

Thanks, Pete

[drseti]

I would think this repair would be very easy AFTER you make some sort of temporary work platform behind the engine.

Actually, in front of the engine. (Remember, the engine is mounted backwards in the Sky Arrow)

[drseti]

Replacement of a sprag clutch requires a couple of Rotax specific tools, which my factory-approved Rotax heavy maintenance shop doesn't happen to possess. Thus, I have had to send my own plane to a larger facility to have this work performed.

On a related note - you have doubtless heard of the current global supply chain disruptions, variously attributed to the Coronavirus and the prevalence of Just-In-Time inventory control policies. Our industry is not immune. As of yesterday, there were zero sprag clutch housings found in calling all of the Rotax parts distributors in the US and Canada. Lead time was cited at 4 to 6 weeks.

[ShawnM]

I would think this repair would be very easy AFTER you make some sort of temporary work platform behind the engine.

Actually, in front of the engine. (Remember, the engine is mounted backwards in the Sky Arrow)

Yes, of course I remember they mounted the engine backwards but technically it’s still the back side of the engine. I have not seen the cowlings removed from the engine on a Sky Arrow but assume it exposes most of the engine for servicing like other aircraft cowlings. Other than it being high up in the air I would think any service would be fairly easy.

As for your “supply chain” comment and on a non-aviation related item, I waited just over 3 months for a Hypertherm plasma cutter for my CNC table. They are US made and the plant shut down because of covid and they are now playing catch up. Ordered it in early March and it came last week.

[FastEddieB]

I have not seen the cowlings removed from the engine on a Sky Arrow but assume it exposes most of the engine for servicing like other aircraft cowlings. Other than it being high up in the air I would think any service would be fairly easy.

Most things pretty straightforward. Carb balancing is tricky, and of course nearly everything requires at least one ladder.

[ShawnM]

Most things pretty straightforward. Carb balancing is tricky, and of course nearly everything requires at least one ladder.

Great pic, thanks Eddie. It does appear that service would be very easy once you climb up there.