What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Check this at your next annual

This bracket breaks because of vibration. Putting a thicker bracket on is a
band-aid to the main problem. We need to fix the cause and not the result.
This vibration is usually from poor carb sync, gearbox vibration (maybe it needs to be shimmed), the prop (either blades out of pitch from each other or the prop is out of balance). It can also be bad or old rubber engine mounts or engine mount bolt torque too lose. These are the common causes. There are over 50+K engines out there with well over 5 million run hours and most don't have this issue. Best to find the cause because if it breaks this bracket it's working on other parts to. You may not feel a vibration as a human, but all engines vibrate. It you can feel it then it may be bad. Even if you think an engine feels smooth it just has a fine vibration that a human can't feel.
 
I agree that vibration is the problem, however, 4-cyl engine behaving as two separate, but coupled power sources, is difficult to minimize vibration especially at harmonic frequencies. I could have easily bought a Rotax replacement bracket and begin a process to reduce vibration but I?d rather not wait for same bracket design to fail again and perhaps end with a bad day. My new bracket gives me confidence that ignition coils will not shake loose.

Rubber engine mounts and mounting bolt torque, prop pitch, and carb synch will be checked again at next condition inspection. Prop balancing is outside of my budget and not specifically required by Van?s or Rotax.
 
Brad, everything you said about vibration causes is correct. However, what does not make sense to me is that all LSA models with 912s should have the same issues, but from the two ROTAX mechanics I have talked to it seems only the RV-12 is having a common bracket problem. I wonder if Scott would comment about whether the prototype ever had these bracket failures. If it didn?t with all the hours it has I would be nclined to agree it?s not specific to the RV-12.

Rich
 
Unfortunately, without a larger sample of data on failures/flight hours by model, one cannot support claims that the RV-12 is any worse that other 912ULS installations. All the reports on here are anecdotal. That said, my carbs are (and always are) balanced with gauges, prop pitch is within 0.1 degrees etc... I've done everything expect having the prop balanced which I'll probably do in next few weeks. I'm glad that this possible failure was noted on VAF as I likely would have missed it.
 
Here's an "out-of-the-box" thought: Builders of early RV-12s were required to partially disassemble the ignition modules to install the fiberglas engine plenums. When the builders reinstalled the modules did they inadvertently induce a torquing stress on the module mounting bracket? Could such a twisting stress contribute to premature failure of the bracket?
 
Brent, I agree it is certainly not a comprehensive sample from which positive conclusions can be made. That?s why I thought it would be helpful to know if the Vans prototype had bracket failures. Would that have prompted a service bulletin on the brackets?
 
Add me to the list, back bracket broken, at 192 hours.

Will check pitch of prop, and balance the Carbs. Plane is a 2012 build. Is this less common on newer 912 ULS motors or newer RV-12 builds?
 
Last edited:
My German cousin is a ROTAX mechanic. He got me a couple of replacement brackets, and he said this issue is not common to other aircraft types. Seems weird we are so ?blessed? in the RV-12 world.

I took all the dimensions on the ROTAX parts so I can make replacements in the future.

You have the measurements handy? I'm in either need to fabricate something more stout or buy again. Part is also available at California Power Systems in Corona, CA
 
Mine broke early on, around 100hrs or so from memory. Looked like a manufacturing fault. It had been pressed so hard when forming the bend that the thickness on one side had been reduced by roughly half. Perhaps a bad batch? The replacement has a ?normal? bend.

Jack
 
See my post #49 above. Photos are no longer available on photo sharing site.

You should also check mounting bracket for front of ignition modules. This bracket bolts directly to top of engine case with (I think) 8mm socket head bolt.



 
Last edited:
I've seen two of these brackets break. One on a Tecnam P2002-JF (around 500 hours total time) and one on a Tecnam P2006T (twin - but only on one engine affected), TTAF around 200 hours.

A right pain to replace on certified aircraft with the single airbox in the way!

It's a right pain to replace, even with dual K&N air filters, too. Access is tight, to say the least.
 
As I recall I had to cut down some box wrenches to access the nuts and bolt heads. When I made the replacement I increased the distance of the holes from the edge and slotted them. Slots allow for minor misalignment without stressing the bracket. My guess is they crack due to minor misalignment.
 
And when you do replace this bracket......be sure to place a cloth under the bracket work area so that an errant nut or washer doesn't fall into the magneto/generator assembly and its voracious magnets. No, this didn't happen to me but the potential for a major headache is great.
 
Mine broke early on, around 100hrs or so from memory. Looked like a manufacturing fault. It had been pressed so hard when forming the bend that the thickness on one side had been reduced by roughly half. Perhaps a bad batch? The replacement has a ‘normal’ bend.

Jack

I've observed the same on mine. Part #33 on this diagram.

851-267 BRACKET


https://www.cps-parts.com/catalog/rtxpages/912914dblignition3.php

I know my plane was getting uneven throttle at full rpms, the throttle cable on the left carb was jamming against the fuel line hose, not applying full throttle.

Very, very time consuming to get in there to change this part out. Removed the K&N right air filter for easier access to the bits that needed un threading. Miserable in there, if you have large hands.

Temporarily, I've wedged and glued some hot water insulation foam around the engine mount and between the ignition coil. Will address the problem when it's a bit cooler, both temperature wise, and frustration wise, dealing with fixing this right. In my case, I'm sure the cause was the throttle cable on the left carb not going to full throttle, while the right hand side did. It was jamming into the heat proof fuel line.

Rotated the heat proof fuel line away from the throttle linkage, and resecured with zip ties. Now I get full throttle from both carbs.
 
Last edited:
Back
Top