Noticeable vibration at 200+ hours 912iS Sport

Have a 912iS sport on a Sling airplane and after about 200 hours there is a noticeable vibration in the RPM range of 4000 to 4300. It is enough that I am trying to avoid that RPM range. Any other similar situations? Cure/ Thoughts?

Perhaps you should contact the west c0ast Rotax rep, Kevin Kane at California Power. 1-800-247-9653 ext 302 . He was very helpful when I upgraded my iS to iS sport.

Hi!
Have you check your magnetic plug?

Check it.

Regards

Talked to the airplane manufacturer, and it is some known problem with the 912iS gearbox which can be bandaged under warranty but another R&D hassle for the iS. So far it sounds like just fix the symptom every 200 hours or so but no fix for the real problem by ROTAX. Not Happy. I have 3 912iS engines in service now that I have to deal with.....

Just curious, did this get resolved?

my 912iS vibration was finally cured at about 130 hrs when the gear box went to the Rotax shop for the third time and 10 items were replaced including the prop shaft. I now have 160 hrs and no vibration since. All was in warranty.

To close out my thoughts/findings on this issue:
It turns out that this problem exists on "some" but not all 912iS engine installations. When I went to the Rotax maintenance course at Lockwood with Dean Vogel I complained LOUDLY about this issue and the iS engine. This is what "Dean said".

Depends on the installation. Perhaps mounting stiffness, motor mounts, prop or any combination. Maybe 20% of installations have this problem. Apparently there is no dog leg in the slip clutch so it is a direct connection which creates wear in SOME installations (and my installation is one of those, lucky me). Yes I had it fixed by warranty but a hassle. Apparently ROTAX is working on this but it looks slowly. For now we have to live with this and have the gearbox rebuilt about every 200 hours under warranty....

Paul, thanks for the information about the percentage of engines with vibration issues. My vibrations started first flight after the sport upgrade. It was an intermittent event which occurred as the engine/prop system loaded or unloaded as in turbulence. If vibration was present commencing a climb would stop the vibration,or reducing the power would stop the vibration. I am using a whirlwind RZ 3 bladed prop. The engine mount is the same one used by Kitfox on 912 engines for years.Hope it does not start again in 50-100 hrs.

We had to overhaul a 912 is gearbox in a flight design CTLS that had only done 126 hours, symptom was a vibration, problem worn dogs, managed to get parts under warranty, we will see how long this one lasts.

I have a vibration that began at approximately 30 hours. The sudden onset suggested that it was the result of some change brought on by a maintenance event, however I couldn't think of anything that preceded the event. The vibration occurred when the airplane reached cruise airspeed. Usually after the airspeed reached or exceeded about 90 KIAS at engine RPM's of 5400 and above. Climbs, yaw, roll or slips would not stop the vibration. Only slowing the airplane to 80 KIAS or below or reducing the RPM to below 3000 or 4000 would stop the vibration. Increasing the throttle to MAX would not change the vibration. Changing the prop pitch didn't change the vibration airspeed trigger- only the engine RPM (i.e.- the vibration still began at about 90 KIAS the RPM was lower/or higher).
All the customary fixes were done- balancing wheel/tires, making sure wires and hoses were isolated, balancing the propeller (.029 isp), downloading engine diagnostics and fault/error codes, checking control surface rigging and cable tension,
At 71 hours I pulled the gearbox and had it serviced. The only fault found was a 1mm under-shim and adjustment of the friction torque. The vibration persisted after reinstalling the gearbox.
Propeller experts advised me that airspeed related vibrations are usually caused by harmonics of airframe parts and not by the propellers. I embarked on a long list of possible sources. I installed a video camera on the tail and on the wing to view the main and nose landing gear, control surfaces, antennas, and sheet metal. I then installed a video camera in the empennage to observe the strobe, elt, and rudder/stabilator controls. Without any obvious signs visible, I added some stiffeners to some belly skins. I added supports to the battery box and oil tank. The vibration persisted. I rebalanced the nose gear tire/wheel and adjusted the linkage (nose gear steering) and tightened the nose gear bushing. I individually removed the wheel pants thinking that the change in mass or aerodynamic load would change or eliminate the vibration. Still the vibration persisted. I finally came to the belief that the vibration has to be in the engine/propeller and not any other part of the airframe. The vibration is a "BUZZ", felt mostly in the rudder peddles. Imagine if a vibrating sander or orbital sander was attached to the nose or tail of the airplane- that is what it feels like. The airplane has nose wheel steering and has a direct linkage to the rudder peddles. The nose wheel is part of the steel tubing frame that the engine is mounted to, so any vibration transmitted from the engine through the mounts would be felt in the rudder peddles and airframe. The engine mounts (new airplane/new mounts) don't appear to have any faults and obviously do a good job of isolation until the airplane reaches about 90 KIAS. There is only one other airplane model like mine with a 912 iS in the U.S. and the owner says that he doesn't have any vibration similar to mine. The only difference between mine and his is the design of the cowling. Visual observations don't seem to identify the cowling as the source of the vibration.
I was faced with replacing the Warp Drive propeller or doing more diagnostics on the engine. Downloading the diagnostics in flight didn't show anything unusual. I did notice that the vibration can usually be "triggered" by turning OFF lane B. Once the vibration starts it usually can be stopped by turning OFF lane A? (usually but not always)
After speaking with the service center and with Eric Tucker during Heavy Maintenance training, they advised me to pull the gearbox again for replacement of the gear set and dogs. So with about 150 hours on the engine I pulled it again and sent it to the service center.

Hi James,

You should try to to verify the rubber lords at the engine mount to see their integrity and elasticity.
Another possibility is that there is a contact between a part of your engine and the cowl, sometimes hard to see.

The service center just got the gearbox today. I will probably will have it back and installed by next Thursday. I will post the results then.

Re: Motor Mounts- Since they were installed new in a new airplane they are probably OK. These are not Lord mounts- manufacturer produces them. Visual inspection while on the airplane does not reveal any sagging or cracking. Dis-assembly would be required to see anything more. Again, since they do a good job of isolation the motor mounts are probably ruled out.
Re: Engine to Cowl contact- checked and verified many times.
Thanks for the replys.
James Porter

Do not know why but On my 912iS I get a vibration at about 4000 RPM but only in a gradual decent at about 90 knts. I also avoid getting into that condition.

Are any of these vibration problems associated with engines listed in the latest service bulletin? Just a potential owner who is interested.

legacy.rotaxowner.com/si_tb_info/serviceb/sb-912-070.pdf

Mine is not affected.
James Porter

Paul Hamilton wrote: Apparently ROTAX is working on this but it looks slowly. For now we have to live with this and have the gearbox rebuilt about every 200 hours under warranty....

Any idea where Rotax is on this?

I had a strange vibration during my last flight. I'm hoping it's not the gearbox. (PS - I'm at 320 hrs)

Jim Flock wrote: I had a strange vibration during my last flight. I'm hoping it's not the gearbox.

What level of urgency should I be giving this?