I understand it may seem frustrating trying to get your point across on the web.
However, it seems you are missing what I'm claiming.
But, I completely understand what you are trying to say.
I claim there is an advantage to increasing the cap size, if we can recognize it.
This is great and we have discussed a few points as to "why" they changed, to include the push for better emissions by increasing plug gaps up to .060 which increases the resistance the spark must jump to complete the path to ground.
I don't see anything I've claimed that is inconsistent.
Maybe not but maybe we need to look at this a little closer.
All I'm claiming is that the accuracy of the angle between terminals is increased by a longer rotor.
This is an accurate statement and I have no issue with it.
As the arm gets longer the distance between degrees increases.
The width of the rotor tip does not matter, as long as the approach, arc, and departure of the rotor tip from the terminal is the same for every discharge.
.....
If one cylinder fires after 45 degrees travel, then the next 44, and the next 46, the time between those ignitions and the accuracy of the ignition timing will be affected.
This is where I have trouble understanding how the length of the rotor actually has any affect on the actual timing.
As mentioned earlier, the rotor is fixed to the shaft and only provides a means of transferring the energy from the center post of the cap to the end of the cap.
There is no timing function involved in the rotor, only phasing. Which places the rotor in the correct position in reference to the cap terminal.
Let me show a couple things before i get to the rotor itself. We will discuss electronic timing instead of mechanical since it's easier to visualize.
Here is the AMC firing order and rotation.
AMCFiringOrder.gif
Now for timing we need to ensure the reluctor phasing is correct. This sets the position of the reluctor in relation to the shaft that is directly connected to the cam/crank and is referenced to the #1 piston at TDC. So your timing mark should be on 0*
Each tooth of the reluctor...as close to the shaft as it is, is still ~15* of timing for it's full width.
So in this pic we are way retarded.
AMC DS (4).jpg
This is where we want the reluctor for TDC.
AMC DS (21).jpg
So to ensure the rotor is correctly positioned in relation to the cap we also need to set the rotor phasing.
With the firing order CW rotation, if the timing is ADTC or retarded then the rotor will arc over as the rotor is at the trailing edge of the cap terminal.
AMC DS (2).jpg
As the timing increases it fires sooner and sooner so the rotor tip will sweep across the cap terminal. Total timing (base + vacuum + mechanical) is normally around 40*.
DSC01481.JPG
If we go back to the reluctor we said the width was ~15* wide. So if it is .060 wide and then the rotor is twice as long then the same 15* should equal .120 correct? I'll refer to your math skills to verify that one. It's really just for demonstration purposes.
So if we need 40* then the rotor tip would need to be at least .320 wide to still be in direct relation to the cap terminal. But we also have a wider cap terminal so that helps.
If the rotor is increased in length say to 3 time the distance of the reluctor then the tip width would increase.
15*=.180"
30*=.360"
40*=.480"
Note that when we change the timing, the position of the rotor to the cap does not determine or affect the actual timing.
It is the reluctor or points lobes in reference to the shaft and the piston at TDC that affect the actual timing.
When we grab the distr and rotate it we are changing the relationship(phasing) between the baseplate and the pickup or points rub block to change when it fires(timing).
So does the length of the rotor affect the actual timing or timing accuracy?
HTH
Bill
You do not have the required permissions to view the files attached to this post.