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Dave S
10-18-2008, 02:55 PM
Good afternoon,

To date, I have a bit over 1/2 of my required flight testing accomplished on my series 7 with the 912 ULS (100 hp) with the slipper clutch. Absolutely happy about the fuel burn and performance. The engine starts instantly and runs smoothly.

Here is my question about what is normal for this engine.

Aside from getting accustomed to the rather sudden stop of the prop on shutdown, there are a few unique noises that I am curious about. I have visited with an A & P who has done a number of annuals on commercially produced light sport aircraft with the 912 ULS. He says that they do make a few noises that you don't hear from a direct drive conventional engine (conventional meaning lycoming or continental).

1) When hand spinning the prop to burp the oil, the gearbox makes a very slight but audible noise (hard to describe, but a slight scratching noise is as close as I can come for a description) which appears to be in agreement with the gear teeth passing each other. Anyone else experience this?

2) On Shutdown, the engine makes a slight "clunk" as the prop jerks to a stop.

3) The gearbox makes a slight squeek after the engine is warmed up, after stopping, when a person rocks the prop a few degrees back and forth - seems to be the slipper clutch, but not sure - does not make this particular noise when cold.

For the record, I have religiously checked the gearbox magnetic plug, which has always had very little accumulation. The oil filters have been opened with a very few almost microscopic metal particles on the oil change. Also have monitored the gear lash which has not changed since new.

Are these observed noises "normal" for this engine; or is it anything to be concerned about?

Sincerely,

Dave S
St Paul, MN
Kitfox 7 Trigear, 912 ULS

DesertFox4
10-18-2008, 11:03 PM
Dave, nothing you mentioned has me concerned that you have any problems. I've noticed that some Rotax sound slightly different from one another at times like shut down. Some have the little "squeak" or "chirp" during shut down and some don't. Just know the engines I've heard do these things are well and thriving.

If you start seeing metal fragments in the filter or on the magnetic plug pay attention. Sounds like you're getting a normal break-in to me.

Regarding shut downs there is a little trick you can use to smooth the sudden stoppage against the compression stroke especially if you run a lighter weight prop.

When you get your rpms. down to about 2000 or 2200 keep your hand on the throttle and at the same time you cut the ignition , start to pull back on the throttle to full idle. It should spin down to a smooth stop without the "clunk".

I also hear the gearbox when I turn the prop by hand before start up. I have about 690 hours on my 912S and it sounds the same as it did when new. :)