VF4D distributor cap

[skidder58]

Was just wondering how my 71 M600 with the odd fire distributor has an even fire 90-90=90-90 cap? I've known this machine for many years as it belonged to a friend of mine. I know the crank is not evenly phased, and the distributor cam is not evenly phased. the machine actually runs pretty good but on the under side of the cap, it is burned slightly before one of the terminals. When he first got this machine we had to put the distributor back in it. We actually melted a piston playing around with the firing order until I noticed the phasing of the cam lobes. Then we just pulled the plugs and matched up the crank phase to the cam lobes (after replacing a piston of course). This was 20 years ago and it's been running pretty good for years now but it just dawned on me that the cap is evenly phased. It has the prestolite distributor and my new tune up kit matches the old stuff exactly. Is there an odd fire cap for this motor? Any education would be greatly appreciated

 

[SkidRoe]

This is a short cut so that the same distributor cap can be used in many applications. As you stated, the points cam is unevenly spaced, and this dictates when the ignition is fired for any given cylinder, not the rotor's proximity to the cap.
As long as there is overlap between the electrode on the rotor and the cap, the spark will be delivered at the appropriate time. I would imagine that the distributor rotor has an elongated, sweeping electrode on the end that interfaces with the plug electrodes in the cap to help facilitate this.
Make sense?
Cheers - SR

 

[6brnorma]

This is a short cut so that the same distributor cap can be used in many applications. As you stated, the points cam is unevenly spaced, and this dictates when the ignition is fired for any given cylinder, not the rotor's proximity to the cap.
As long as there is overlap between the electrode on the rotor and the cap, the spark will be delivered at the appropriate time. I would imagine that the distributor rotor has an elongated, sweeping electrode on the end that interfaces with the plug electrodes in the cap to help facilitate this.
Make sense?
Cheers - SR

The VF4D is a 90-135-90-45 engine. It uses the same distributor cap as the 90-90-90-90 VH4D but has a different rotor with a large T-shaped contact….just to expand on SkidRoe's correct answer.

 

[skidder58]

The VF4D is a 90-135-90-45 engine. It uses the same distributor cap as the 90-90-90-90 VH4D but has a different rotor with a large T-shaped contact….just to expand on SkidRoe's correct answer.

Thanks so much for the reply. I think I have the vh4d rotor in it as it is not elongated at the tip. you guys are great. Thanks again.