Thursday, July 21, 2011

Slick Magneto Inspection Tip

Slick magneto arching damage
Slick Magneto Arching damage

Engine roughness has many causes. Here is one item to  check; quick and easy:

Remove the harness caps and inspect the distributor block. Look for:
  • Erosion or burning on towers
  • Color differences in lead contact buttons
  • Carbon dust
Notice the burning (arching damage) and color change. Lots of erosion;  this engine had a miss for a long time.
Slick Magneto Arching damage Closeup
This damage is caused by the electrical arc bypassing the spark plug and finding an easier ground path along the lead tower and to the magneto housing. The magneto below has a different problem.

Slick Magneto Carbon Dust
There is a layer of black carbon dust shown by the red arrows. Carbon dust is conductive and can cause arching to ground inside the magneto instead of at the spark plug. Lets take a look inside this magneto.

Slick magneto carbon brush
This is the worn carbon brush inside the magneto. Just as we suspected from all of the carbon dust on the distributor cap. Here is what internal arching does to the insides of the magneto. That carbon dust is bad stuff.

Slick magneto arching damage
 Notice the white residue. You will find this inside the magneto cap. If you remove the harness cover and see white residue on the lead towers then there is lots more inside. In case you're interested; this magneto did run and pass a mag check -- it just crapped out at full power and resulted in an aborted takeoff.

Slick Magneto white residue

There have been improvements in the Slick magneto. The picture below shows the carbon brush and the insulating portion of the distributor block. Notice the "dams" (yellow arrows). They are new as of about 2010.

Slick magneto distributor block closeup showing dams
These "dams" serve the same purpose as the ones below on a electrical transmission tower insulator. You might have also seen these on some spark plugs.

Electrical Tower Insulator
Original (old) style
This older style has no dams. The dams capture the dust and provide a longer electrical path to ground.

Removing the harness cap and inspecting the top of the distributor block can be quite revealing and save you  troubleshooting time; it can find problems early and at little cost.  Of course all of this stuff I write about here is part of Mechanic's Toolbox Software.

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