Ignition modules

[Dusty]

I have the usual broken wire issues with my early 912(1000+hrs)
It has Been suggested I change my plugs to the current standard type for ease of of in field repairs
I am considering relocating the modules only to inside the firewall via an extended replaceable loom.
Thes is to keep then away from heat and vibration.
How much cooling do they need?
Will the extra wiring length upset the ignition?

[WWhunter]

Dusty,

I can't offer you any help other than I had these same 'broken wire' issues and they were a bugger to track down and fix. Ironically, I have wondered the same thing, why couldn't a guy relocate the modules to a less vibration prone area.

Also, does any one make a replacement harness for these old modules that have updated, or better made wires?

[Dusty]

I have installed a 200 hr second hand stator, the wires are long enough to reach inside he firewall.
We found one broken wire in the pickups(there must be another we can't find). The electrical engineer is looking to use if possible "tinsel"?wire which is used in high flex applications.
Once this is done we will cook the pickups in an oven and retest the resistance as the ignition problem only occurs after 10 minutes of high power flying ,which we can't reproduce it on the ground
We will beat this gremlin!

[WWhunter]

I found a couple of 'breaks' under the part of the harness that was encased with steel braiding. It took a day or two to chase down the breaks since they were intermitent. I don't remember right off hand how many breaks there were, but do recal 2-3 at least.

I was just lucky I realized the problem on one of my run-ups! I had noticed am occassional roughness while flying, but attributed it to carbs/bad fuel.

This problem arose when I first got the plane flying after its 11+ years in hibernation.

Good Luck!!

[HighWing]

When I built the First Model IV, there was talk of the module issue. One of the guys then - A Northrup Grumman engineer - talked about the wire as being "Junk Wire" as in not aviation grade. The picture shows my current IV with the modules mounted to the firewall side of the engine mount but I did a similar thing to the first one. That one I flew for 900 hours with no electrical module/ignition issues.

What my mod amounts to is a piece of .032 Aluminum bent I to a close fit to the module stack. Then an angle bent from a bit stouter stock was riveted to that to serve as a wire cradle as the wires to the engine exit the module. The assembly is then attached to the topmost module with stout Nylon Zip Ties. my thinking was that if I had a wire break, I would want it a distance from the modules for ease of detection and repair. On the first version with the modules on the typical engine mounting, the wires to the firewall were in the cradle with all connections within the cradle structure so only Tefzel insulated wire was in the vibration zone. whereas on this version, only the engine connected wires are in the cradle. All the wires to their respective destinations were tightly bundled for mutual support.

With the first install, I finally had one of the stainless steel module mount legs break. It was then that I moved everything to the firewall side of the isolators. The only thing I had to do is buy a length of ignition wire for a single plug as by juggling the wires, I was able to get 7 plugs wired with what was already there.

[egp8111]

What's the best way to check for broken wires? I can hear static on the radio on one ing. module that goes away when I switch to the other. Obviously something is going on with that circuit. It also runs rougher on the module making noise.

Thanks
Skip

[WWhunter]

I was searching my issue and found old posts relating to these 'bad' harnesses. This research started me in the right direection.

I hate to say this, but I inspected each individual wire by tugging/bending it. I guess I got lucky because when mine quit, I figured it was a connectivity issue. I first looked at the wire bundles and the connectors, I noticed one of the wires bent abruptly, as in the internal wire was broken. I started checking and found other places that were near breaking so had several places to repair.

Definitely off topic....As was mentioned, the wire, in my opinion was very substandard. I wonder if this weren't made by a US manufacture, they may have had a recall needing to replace them. Just specualtion but I wonder how many planes were wrecked due to this issue. For a bit of reference, in the past, I built and tested large test systems that were used to test the systems of the FA/18. So I know just a little about wiring and whatis durable or not, at least according to milspec standards.

[kitfox2009]

Hi Lowell
On your photo it looks like you have mounted the module stack directly to the engine mount without using any of the rubber flex assemblies normally used.
Is this correct?
Also did you have to re-plumb the coolant spider? I have been looking at something similar to your system but it seems there would not be sufficient room without re-doing the coolant system.
Mine is a 912UL on a Vixen.
Thanks
Don

[kitfox2009]

Hi again
After reexamining your photo I believe my oil reservoir would also conflict unless I moved the modules further forward than you have shown. Where is your oil tank?
Don

[HighWing]

Sorry about the picture. I tried to find a picture of the wire support fixture I had on the first airplane with the standard Model IV mount. The posted picture shows my new IV with a custom ring mount, but was intended to illustrate the fixture I made to support the wires as they exit the ignition module. The oil tank is at the firewall mounted on the passenger side slightly below the carburetor.

On the first IV with the factory engine mount, the modules were mounted to the engine with the typical factory designed mount. What I tried to say is that with the wires supported rather than left to move with engine vibration, I was able to fly for 900 hours with no ignition issues, even with the failure of one of the Stainless module support legs.

[mr bill]

Lowell:
Can you post pictures of your engine and oil tank mounting? Did you have to change the cowl?
Bill

[HighWing]

The short answer is yes, but it amounted to adding a couple of inches to the aft edges of the bump cowls.

Two pictures. The first is what prompted the modification of the firewall forward. I added ribs and gap seals to both horizontal and vertical surfaces and some fairings. It added about six or seven pounds back there. At 11 ft. aft of the datum it added about 65 foot-pounds aft. I did the same on the first IV and for weight and balance purposes, I was limited to 25 lbs. in baggage. To eliminate that restriction on the new IV, I moved the engine forward a couple of inches which provided room for the oil tank in a better location. And rather than putting a bubble on the cowl to accommodate the lower edge of the tank, I did some body work on it by hammering it to clear and then some micro and paint. The ignition module mount is a welded bracket attached to the aft section of the engine mount.

[mr bill]

Lowell:
Really well done! Too late for me now though. In July it will be 5 years on this project and all painting is done. I'll think some more on this.
Bill

[glasseye]

I'm wondering if I have a similar issue, 912 UL when running at 4200rpm on LH ignition unit it misses badly. Increase RPM slightly and it runs smooth. Decrease slightly from 4200 and also smooth.