Base timing for Boyer install.

Jan 18, 2004
Thanks to all for your past good advice. This question concerns how to correctly set the initial timing when installing a Boyer ignition. As many of you know, the '72 Commando has two notches on the rotor. How do I know which is the right one? Here's what I have done to this point. Please tell me if it sounds correct.

a. Removed both sparking plugs.
b. Removed all three rocker inspection covers.
c. Completely removed points and advance mechanism hardware.
d. Removed timing cap to view degree scale. (My goal is to set the initial timing to 31 dgrees as per Boyer instruction.)
e. Turned the engine over until the right (timing side) piston began to come up on the compression.
f. At this point my son peered through the timing hole and told me when the very first mark on the rotor came into view.
g. I then set this very first mark to 31 degrees and then installed the Boyer unit per the instruction.

Does it appear that I am OK so far?
Here is my one concern: I am not a novice when it comes to static timing an engine, but, when I base my timing on the very first mark, the piston appears to be just moving up on compression. In otherwords, it seems that the piston is too far down in the cylinder and may be advanced much greater than 31 degrees.
However, the second notch on the rotor does not even appear until the piston has passed TDC. Also, as a remider to all, this is the same bike that we determined was too far advanced and was causing the kick starter to kick back when I was attempting to start it. This is my first attempt at trying to get it started since I posted that question.
Is it possible that the cam may be installed incorrectly?
As always, appreciate all replies. Thanks.



Since both pistons rise and fall at the same time, TDC on one piston is TDC on the other. One is on the compression stroke while the other is on exhaust. The Boyer fires both plugs at the same time, so for static timing it does not matter which is on which stroke.

Take the cylinder up to TDC turning the engine forward with the rear wheel. Then back the engine to 32-33 before TDC and carefully bump it forward again to 31 degrees.

The cam has nothing to do with the rotor scribe mark or the piston position. Rotors have been known to come loose on their centers which can cause inaccurate timing, but more importantly can come apart at speed. Take the primary cover off and remove the stator and the rotor securing nut and grab the rotor and try to turn the rotor while holding the engine with the brake or rear wheel. If you can rock it back and forth replace the rotor.

The little scale on the outer primary can also move somewhat. If this is in doubt, find TDC and mount a degree wheel. Set the engine at 31 by the degree wheel and check the timing mark. It should agree with your degree wheel. If not either scribe a new mark on the rotor or re-align the degree tab.

Ron Leisner


The timing scales riveted to the inside of the outer primary chain cover are notoriously erroneous. I have seen one off 12 degrees. Check for this using a degree wheel and a TDC tool, then adjust your timing allowing for the error of the timing scale.