Timing mark Chamfered tooth Figure 4-43.  Timing marks indicate the number one firing position  of a magneto. Figure 4-44.  Checking magneto E-gap. Figure 4-45.  Installing timing kit. 4-26 Red marks visible through vent hole must align Timing pin In a third method, the E-gap is correct when a timing pin is  in place and red marks visible through a vent hole in the side  of the magneto case are aligned.  [Figure 4-44]  The contact  points should be just opening when the rotor is in the position  just described. Bench timing the magneto, or setting the E-gap, involves  positioning the magneto rotor at the E-gap position and  setting the breaker points to open when the timing lines or  marks provided for that purpose are perfectly aligned. The following steps are taken to check and adjust the timing  of the breaker points for the S-200 magneto, which does not  have timing marks in the breaker compartment: When replacing magnetos on aircraft engines, two factors  must be considered: Timing the High-tension Magneto to the Engine High-Tension Magneto E-Gap Setting (Bench  Timing) 1.  Remove the timing inspection plug from the top of  the magneto. Turn the rotating magnet in its normal  direction of rotation until the painted, chamfered tooth  on the distributor gear is approximately in the center of  the inspection window. Then, turn the magnet back a  few degrees until it is in its neutral position. Because  of its magnetism, the rotating magnet holds itself in  the neutral position. 2.  Install the timing kit and place the pointer in the zero  position.  [Figure 4-45] 3.  Connect a suitable timing light across the main breaker  points and turn the magnet in its normal direction of  rotation 10° as indicated by the pointer. This is the  E-gap position. The main breaker points should be  adjusted to open at this point. 4.  Turn the rotating magnet until the cam follower is  at the highpoint on the cam lobe, and measure the  clearance between the breaker points. This clearance  must be 0.018 inch ± 0.006 inch [0.46 millimeter  (mm) ± 0.15 mm]. If the breaker point clearance is  not within these limits, the points must be adjusted  for correct setting. It is then necessary to recheck and  readjust the timing for breaker opening. If the breaker  points cannot be adjusted to open at the correct time,  they should be replaced.