Slick Magneto Inspection Tip

John Schwanerwww.mechanicsupport.com

Engine roughness has many causes. Here is one item to check:

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.

Erosion damage (red arrows) 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.

This magneto has a different problem. There is a layer of black carbon dust. 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 is the worn carbon brush inside the magneto. Just as we suspected from all of the carbon dust. 

Here is what electrical arching does to the insides of the magneto. That carbon dust is bad stuff. Notice the white residue.

If you remove the harness cover and see white residue on the lead towers then there is lots more inside.

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

New Style 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.  This is part of Mechanic's Toolbox Software.

These "dams" serve the same purpose as the ones  on electrical transmission tower insulators. You might have also seen dams on some spark plugs.