Rv12iS gearbox chatter

[seagull]

I had my gearbox rebuilt at 1020 hrs. The engine has used E10 auto gas for the majority of its life, maybe only 50 gallons total of 100LL. I do not let it run below 2000 RPM. There was no indicators to overhaul the gearbox, I just wanted to see what wear was happening and get ahead of it if something was wearing. Wayne Flemmington at F70 did the work and explained the process as I helped. The biggest concern is if the spline starts to wear you need to fix the cause or it can get expensive to replace. My dogs had normal wear, nothing of concern. Since we were already inside the Bellville washers were replaced and the plastic shims. There is a step collar that was also replaced, this is an updated part with slots for better oiling of the spline.

My gearbox ran fine and could have gone a lot longer before rebuilding. The updated step collar is good to have but the original must have been doing OK.

The OP concern about a rattle when pulling off the power is a clue the splines are wearing due to the Bellville washers loosing pressure probably caused by the plastic shim washers deteriorating.

[rcarsey]

Originally Posted by RFSchaller

I do the breakaway torque check at annual that basically checks the spring pack force. It has always been in spec since first flight in 2012.

I should probably add that check to my annual (which I'm doing right now). I can report that there is still virtually no debris in the filter or on the magnets. The only abnormal thing is that I found a few red cloth fibers in the filter which is due to regularly wiping the dipstick with a red shop rag. I don't think that is enough to cause any real problems (but I will stop using shop rags!)

I also learned, just as a FYI for everyone, that gearbox S/N 74000+ has an additional oil spray nozzle. The factory/distributor upgraded my gearbox before shipping (Jan 14, 2019).. So most, if not all -12iS's should have this mod already in place.

[RFSchaller]

Good info, Rob. Thanks.

When I was at the ROTAX course the instructor recommended running the engine at 2500 RPM and then shutting off the A and B ignitions in sequence to stop the engine. He claimed it resulted in less vibration and stress to the gearbox during shutdown. I’ve always followed that advice even though it conflicts with the ROTAX Operator Manual.

[Piper J3]

All rolling elements – gears, ball bearings, etc., can absorb shock and abuse much better when at speed (dynamic Vs. static). This is why car wheel bearings can withstand pot holes…. The Rotax gearbox has a hunting gear ratio for the purpose of spread wear evenly. All that said…. best practice is to keep ground ops at a reasonably high RPM. I start the engine and warm up at 2600 RPM. Cold engine runs much smoother at this speed and prevents gearbox chatter because higher prop loading sets gear lash only in one direction. Chatter is a huge no-no for gears, splines, drive cogs, and overload clutch...

[PEB]

I changed my prop to an E-props and it runs much smoother with no vibrations and a higher cruise speed.
It only weighs 2 kg (4.5 lb) all inclusive and low weight should be better for the gearbox.

https://aircraft.e-props.fr/product_...oducts_id=2452

It is my aircraft in the picture on the e-props site. :-)

[Cyclone]

Originally Posted by RFSchaller

Good info, Rob. Thanks.

When I was at the ROTAX course the instructor recommended running the engine at 2500 RPM and then shutting off the A and B ignitions in sequence to stop the engine. He claimed it resulted in less vibration and stress to the gearbox during shutdown. I’ve always followed that advice even though it conflicts with the ROTAX Operator Manual.

I read with interest your 2500 rpm shutdown procedure. I always cringe when the second ignition goes to off with the low rpm shutdown. The result ranges from benign to a simulated prop strike.
I used the 2500 rpm shutdown the last two flights and will never go back to minimum rpm shutdown. It seems the additional inertia allows the engine to come to a stop without the bone jarring Kerr-Whump. Thanks for sharing.

[Bob Y]

Guys, the current revision of the POH says to reduce power to 2000 rpm before shutting down. It’s the process I follow and it seems to work just fine. Earlier versions said to reduce to idle for shutting down, but it’s now 2000 rpm.

[RFSchaller]

Looks like the info on 2500 RPM I got in 2012 was good. Too bad it took the thunder gods so long to figure it out.

[rcarsey]

Well, to follow up and close out this thread.. I sent (actually, the paint shop I'm using in Tennessee sent) out my gearbox to Lockwood for servicing.

Lockwood's phone support was excellent (9-10a; 2-3p) and they indicated my symptoms were very likely worn dogs. They received, repaired, and sent it back out a day after they got their hands on it. After inspection, they confirmed that it was worn dogs, but couldn't say why it had happened at only 380hrs (they had copies of my engine logbook, and didnt see anything alarming as far as maintenance or 50hr oil changes [100LL]). The problem would just get worse over time, but at no time was it in danger of failing (no power/emerg landing). Additionally, my gearbox had the optional oiler nozzle in it which was supposed to help prevent/delay this problem.

The only thing I could possibly do a better job at is to plan descents farther out, chop-n-drop less, and land with power more often.

As far as removal of the gearbox, Lockwood indicated that careful tapping the back of the prop flange with a soft mallet usually does the trick..but just be sure it doesn't get cocked while coming off, as there are dowl pins which will cause it to bind up. No absolute need for the special Rotax slide hammer for gearbox removal.

Lastly, warranty expired at 200 Hrs, but said they may cover some portion of the parts (not labor) under their goodwill program since this is problem not normally seen until much later in life.. but its at their discretion.. fingers crossed.

The costs were roughly $350 labor, $2100 in parts -- the bulk of which is a new gearset (886-548) at $1300 and dog hub (958-929) at $370. They also did the 600Hr inspection, since it was close enough to 600.

[Jcurry]

Thanks for the info Rob.