Brightspark Magnetos

Now that the slip ring has dried off, replace the pick-up(s).

Nearly all magnetos have a gasket between the pick-up and the magneto body (a) to prevent water entry and (b) to set the correct clearance between the pick-up holder and the slip ring. Ensure that you have the proper gasket fitted.

• Single-cylinder magnetos:

  • Turn the armature in its proper direction of rotation until the contact-breaker points are just starting to open.

  • Measure the resistance between the magneto body and terminal in the plug cap.

  • The reading should be substantially the same as the reading you obtained in the 'internal HT continuity' section.

• Twin- and multi-cylinder magnetos:

  • Turn the armature in its proper direction of rotation until the contact-breaker points are just starting to open on one of the cam lobes.

  • Measure the resistance between the magneto body and terminal in one and then the other of the the plug caps.

  • One of the plug caps should give a reading which is substantially the same as the reading you obtained in the 'internal HT continuity' section.

  • The other plug cap should give a reading that is infinite (OL) or extremely high.

  • Turn the armature in its proper direction of rotation until the contact-breaker points are just starting to open on the other cam lobe.

  • The readings for the two plug caps should now be swapped around.

• If you do not obtain readings substantially the same as the reading you obtained in the 'internal HT continuity' section, and if everything else you previously checked is still good, it indicates that the pick-up brush(es) is/are not making good electrical contact with the brass of the slip ring. This could be because:

  • the brush isn't projecting far enough to touch the slip ring, so check that as best you can.

  • the brass is in the wrong place, as a result of a magneto with a segment-type slip-ring having an incorrect cam fitted or having the wrong direction of slip-ring fitted. You can check the latter by removing the pick-up(s), rotating the armature in the proper direction until the points are just opening, and checking that the brass is visible directly underneath the pick-up hole (or one of the pick-up holes) in the magneto body.