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Ignition coil wire chaffing

bbaggerman

Active Member
I have been running down an intermittent problem with one mag with occasional large RPM drop on my 1400 hour 912 ULS. Poking around the ignition coils I found *lots* of chaffed wires going in and out of the coils as well as near the connectors. In most cases chaffing was to the point of wire to wire or wire to metal contact.

For the most part wires in this area are loose. If it were me I would have laced them up initially but frankly I am surprised there was enough mass and vibration to result in the extreme chaffing I found. It is kind of a PITA to get the coil assembly out for inspection but it might be worth taking a look at yours if you are chasing down a rough engine (isn't everyone?).

The low voltage ignition leads all have a field splice between the wire molded into the coil and the wire that goes to the connector. Is this standard? It would have been nice if this were a single contiguous wire.

I have been thinking about trying to repair these with heat shrink. From what I have seen the wires themselves looks intact. But the more I think about it the more I think I'll just pull out the check book and write one for $1500+.

Thoughts?

Bob
 

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I see from the photos what you are saying about the wire condition and considering a repair to the wire sheath. However starting from new/replacement might give you an opportunity to better secure these short runs and know the wire integrity is sound.
Thanks for posting your experience and as I work through my condition inspection I’ll give this are a special look.
 
It’s an airplane, so if it were me, I would replace with new and secure them very well. Bare conductors can start fires. :eek:
 
Here is a follow up on my original post about the chaffed wires. Looking around the coil assembly a bit I find that there is a mounting bracked for a rubber shock mount (Rotax calls it a rubber buffer) that is not a Rotax part. The angle bracket is shop made.

Note in the picture that the bracket is too short as evidenced by the metal bracket above hitting the head of the rubber buffer mounting bolt below. This causes the fabricated angle bracket and rubber buffer to be somewhat cocked. You can't see it here but the shortness also causes one coil to push on the motor mount frame below.

When I dug into this coil assembly I found this rubber buffer broken. It is the aft-most rubber buffer mount. It is clear that it has been broken for a good long time but I can't tell how long. I believe the cocked mounting and/or the contact with the motor mount frame caused enough stress in this rubber part to make it fail prematurely.

With the rubber buffer broken this allows the coil assembly is move up and down quite a bit. I believe this extra (and probably severe) vibrating motion caused the coil wires to rub a lot more that they would have normally, causing the severe chaffing I found.

So at a very minimum I will change out these parts with the correct Rotax parts but I think there is a larger lesson here. If you or a shop decides to go rogue and save a few bucks over a genuine part or faithful replica you had better be sure you know what you are doing. Looking at this bracket it should be clear to anyone that it isn't fabricated right but the person doing the job (not me!) couldn't be bothered to slow down and do it right. Sometimes there are no consequences but in this case I think there was a cascade effect that was slowing rendering my ignition system into junk. All four ignition coils showed damage. I am glad I caught this before it failed in the air.

Bob
 

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