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Magneto Overhaul / IRAN (inspect & repair as necessary) and USA or Europe?

Hello,
I am not sure that every body complies with the D3000 overhaul every 4 years. A lot of people do only 500h inspections coupled with AD 2005-12-06.
I usually also send my D3000s to QAA and had just once a bad internal timing from them ; 8 degrees difference between left and right!

This magneto needs to be taken care by shops that are really used to work on it. And I don’t think there are so many in Europe nowadays.
I just had very a bad experience with a French engine shop. It seems that some unexpected thread lock Loctite was discovered under the contacts assembly that could have caused continuity defects which resulted in nylon cam melting and total loss of ignition on one side.
Please see TB10 F-GNNL accident investigation BEA report about how maintenance induced failure can happen easily on this mag.

In Europe, I now send my mag to the Swiss shop Mecanair, they are used to work on D3000.

Thomas

LFPE

Weird story, it’s normal to use loctite 242 or 243 on the screws securing the contact assemblies, some loctite underneath the contact is probably the result of a mechanic using a bit too much on those screws and the surplus coming up when tightening the screws, under normal circumstances this shouldn’t cause any problems (I can’t even think of a reason how this could affect anything). Also the cam in a D3000 (or any Bendix/TCM) mag for that matter is full metal, not nylon. Overheating is something that seems more likely to be caused by using the wrong or insufficient bearing grease.

Also as far as I know, there aren’t many shops in Europe who still service Bendix Dual mags. (I know 3 who do).

Belgium

There is not any thread locking loctite use mentioned in the service support manual.
These products can affect the continuity.
And good continuity around contacts and capacitors is essential on this mag.
I am talking about the nylon cam that belongs to the contact assembly between the rotating cam and the contact spring.
Please have a look on TCM sb651 and F-GGNL accident report so that you may understand better what I am talking about.

LFPE

Alright, so you are talking about the cam follower (not the cam).
I see what happened here, the heat in this case is the result of electrical arcing, not overheating due to friction.
The cause here has nothing to do with loctite or the contact assemblies themselves. It’s the capacitors. The capacitor should be connected to the contact assembly through it’s wire (flag terminal). The other end of the capacitor is connected to the housing cover and secured with a nut. In the case of F-GNNL, the electrical arcing between the breaker points and cam follower/felt was caused by either a capacitor no longer being connected to the contact assembly or the capacitor shell no longer being grounded (being connected to the harness cover).

  • I will check regarding loctite on contact assembly screws being in the maintenance manual or not, however, applying a tiny bit of (blue) loctite to those screws is a good maintenance practice, the position of those screws is what controls the internal timing and even a very tiny bit of movement of those screws will change it.
  • Regarding the accident of F-GNNL and SB651, something I have seen A LOT is bad wiring inside of magnetos. Also, there are many people with a D-3000 who, when shipping their magneto for overhaul or 500Hrs or/IRAN take the magneto cover off, and some even leave the capacitors, and then just ship the magneto without cover. This is just dumb, on a dual mag, the harness and magneto cover, are one and the same thing, and it should be considered an integral part of the magneto. Besides the cover not getting inspected, it’s also bad for transport/easily damaged. As for the capacitors, during overhaul, they get replaced, during inspections, both their resistance and capacitance get measured, and there really are quite a number of service bulletins related to just capacitors on Bendix magnetos.

Extra note: Although not mandatory per the maintenance manual, any good shop will replace all contact assemblies during 500Hrs inspection and install new ones (same goes for carbon brushes).

Last Edited by Eagle20 at 20 Jun 17:55
Belgium

Yes you’re right I missed the word follower. Bad translation sorry.
About the contact assembly. One side of the contact point is linked to the capacitor and the coil thanks to the flag terminals and the other side is grounded.
A bad grounding to this side due maybe to unapproved and excessive use of loctite is suspected to have caused electrical arcing and hence overheating of the contact spring.
Nothing else bad was found and capacitors are replaced frequently and installed as per sb651…
Thank you
Thomas

Last Edited by TomTom at 24 Jun 18:51
LFPE
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