re: install ignition coils Rotax 912uls

I am installing a Rotax 912 uls 100hp engine into a Model IV. the Model IV Firewall Forward Instructions (dated Dec. 01) In section B. Engine Mount Installation
Number 1. Instructs: Unbolt the ignition coils from the engine-these will be reinstalled later using different brackets. Nowhere do I find further instructions to re install the coils or any reference to "different brackets". Can anyone help me with this, and are there any updated instructions to install this engine to Model IV. John McBaen no help with this matter.

I'm sure the reason for removing the coils and modules is the intake manifolds get swapped from one side to the other. When I installed the 912 in my Kitfox 4, I made a bracket that mounted on the firewall side of the motor mount and the coils mounted on that bracket. They don't get shaken around with the engine then like with the factory set up, and there is less chance of broken wires on the coils or modules. You will need longer sparkplug wires then however. Easy to make new ones up as well. JImChuk

Attachment 28081Attachment 28082Attachment 28083

Thank you!

Your welcome. If you need these scanned send me your email and I can scan and email so you can print easier.

Thank You So much. I was able to reprint beautifully from your pictures. Also is there anything in your Engine mount instructions regarding lengthening the balance tube between the carburetors?

I do not see anything about extending the balance tube but I also do not see anything about switching the manifolds. The pictures in the manual show the carbs and intake in the original inboard position.

Sorry for the late reply, I just saw this question. There is a section on the balance tube and I had been overlooking it. I purchased a balance tube only to remember that it needed extended. I then realized that there was a piece of aluminum tubing in the firewall forward kit that was to be used as the compensation tube. The manual just wants you to run the tube between the manifolds and use rubber fuel line to connect to the fitting on either side. I think I may just use the tube to extend the stock compensation tube since I spent money on it. If you want pics of the actual manual pages let me know and I'll upload them.

T. W.

One fine point on this modification which I don't think there is a lot of published info on. The ignition modules each have their own ground wire; which, on the uls, are each held by separate bolts to the intake manifold. There have been some modifications where the builder has combined the ground wires and fastened them to the top of one of the coil mounting straps using the strap as a single connection to ground - it's easier that way because a person doesn't have to lengthen the ground wires. What can happen; and what has happened in a few cases, is the bracket cracks taking out both ignitions. It is well to be sure that each ground wire for each module ends up with it's separate link to engine ground to preserve redundancy of the separate ignitions.

Right on Dave. I have heard of that happening more than once.

my rebuild project has the 80hp 912 with 280 hours on the hobbs;
the 4 point rubber isolation mounting for the coils has the smallest rubber isulator taking the largest vibration load - it connects to the more rigid side of the large motor mount isulators, whereas the other 3 are connecting to the motor itself, complete with some lever arm to accentuate the difference ..

so of the 4 isulators, only the little one was starting to fail .. but it should have had an easier life on the 80hp ...

the info on cracked mounting brackets for the coil bundle is great to have; and a great idea to separate the coil ground wires in case of failure to make an adequate ground ...

the replacement rubber isulator was available locally meaning not at rotax prices

This topic has triggered a question in my mind as well. I was messing with my ignition system and when I purchased the aircraft, the coil packs attached to the rubber isolators were in no way grounded - the coils remained isolated from ground due to the rubber isolators. When I pull up the wiring diagram for these coils I notice that there is a wire that comes from the top bolt that retains the CDI boxes and connects to one of the intake manifolds - this would provide ground to the isolated side of these rubber mounts - does everyone else running these old ignition units have their coils grounded or free floating?

ground wire I am mentioning is upper right just below the "1T" box

Attachment 29981