since 1940

Magneto attachment hardware loose on Bendix D2000 or D3000 magnetos

In the Mooney M20J-201 there have been reports of the hardware attaching the dual Bendix magneto to the studs in the engine accessory housing becoming loose after maintenance in the field. It is possible that during magneto maintenance, such as timing changes or checks, the attachment nuts are not being torqued to specifications or that hardware has not been installed properly. If the clamps are loose the magneto can move!

The Bendix magneto can also work loose if the Lycoming mounting flange is worn or warped, or the hold-down clamps (part number LW-18378) haven't been updated to the more forgiving design (part number 66M19385). The 66M19385 magneto clamp has a wider bearing area and accommodates variations ( which shouldn't be there) in the magneto base flange thickness.

There have been reports of badly worn clamping surfaces who's hardware was not loose and never had been loose prior to finding this problem. Inspect the mounting flange and the mounting base very carefully for wear. Badly worn clamping surfaces may prevent proper attachment.  Use the newest clamp as outlined in Lycoming Service Instruction 1508A, if approved for your engine model - contact Lycoming for approval and application information. A note to Lycoming: Using a star washer in a critical torque application is probably not the best idea. There have also been  reports of other loose magnetos besides the ones issued in S.I. 1508A.

Any engine that uses the Bendix D2000 (you really should get rid of this dangerous beast and update to the D3000) or D3000 magneto should inspect the mounting flange and attachment hardware. See Lycoming S.I. 1508A for instructions.

Diagram of Bendix D3000 Magneto Installation - notice new style clamp

Damage to mounting pad on D3000 magneto caused by a loose LW-18378 clamp

Old style clamp LW-18378 on the left and new style clamp 66M19385 on the right

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Disclaimer: sacskyranch.com contains abundant information relating to aircraft maintenance. The information provided  is not intended to supercede or supplement the F.A.A. approved  maintenance and/or operator’s manuals. Those F.A.A. approved manuals must be utilized when performing maintenance and/or operating aircraft.