F4 Magneto points cam adjustment

[martinautry]

The cam driving the points on my f4 magneto came loose. How is this adjusted?

 

[rustred]

is this the breaker cup u are asking about? post a pic of the problem.

 

[martinautry]

is this the breaker cup u are asking about? post a pic of the problem.

no, the cam is a sleeve attached to the end of the main rotor and tightened in place by a nut. The cam sleeve can be rotated when loosened.

 

[rustred]

i am not following what u want to do. u say the cam sleeve can be rotated when loosened, is the nut tight or loose on the shaft end ?

 

[wore out]

The cam driving the points on my f4 magneto came loose. How is this adjusted?

The "hottest" spark will be made if the points break at the exact time the movement of the "rotor" is such that the current through the points is at it's peak.

Typically, there's a procedure in the magneto manual as to how to set this up (in this case, point cam orientation).

I took a quick look at the official IH Blue Ribbon manual and don't see any info on this, for this specific magneto. STRANGE!

Hopefully, a GURU on these mags will come forward and fill in the details!

GSS-5035 Service Manual Magnetos

https://farmallcub.com/rudi_cub/www...Magnetos/GSS-5035 Service Manual Magnetos.htm

If you don't have the GSS-5035 manual you can view it at the link above.

 

[Fritz Maurer]

To hitchhike on wore out, the phenomenon he describes takes place when, in the direction of rotation, the trailing edge of the rotor has passed the end of the armature .090”, just before the magnetic field changes direction. This is known as magneto gap. This is when the lines of flux are concentrated in the tightest possible area; precisely where you want the points to open.
The points should open, with magneto gap at .090, with spark advance positioned at maximum retard, right before engine kill, since this is manual spark advance mag. The reason being you want the hottest spark possible for cranking speeds.
As the spark is manually advanced, the magneto gap decreases, fewer lines of flux are cut, and spark voltage decreases somewhat. This is an acceptable trade-off since the mag is turning much faster with the engine running.

 

[martinautry]

Thanks, this makes sense. I actually finally found a general reference to this in the IHF magneto service manual on the first two pages on how magnetos work.

 

[martinautry]

OK, from what I see is that the points are set to open when the calibration dot on the ignition rotor is aligned with the main rotor cam marker. At this point, the magnetic path to the coil is fully broken and the magnetic path of the stator and rotor is fully broken. There are apparently two cycles of this per rotation.

 

[martinautry]

The procedure I used was to align the calibration dot on the ignition rotor with the magnetic rotor gears. Then I backed up two gear teeth. This appears to give the .095" mag gap, and set the point cam to just open the points at this position. This is with the points at full retard. This seems to give me a pretty hot blue-white spark.