Moparts Tech Archive

Elec Topics

MP Distributor Adjustments

I have a MP distributor on my 1970 340. This is one of the units with the adjustable mechanical advance. Since my piece does not have any marks for reference, I tried to come up with an easy way of making an accurate adjustment in timing.
In the last couple of weeks, I have been trying to figure out a way to "accurately" adjust this without just loosening the screws and guessing where to move it, and retesting to give me the total advance and the initial advance that I was looking for.
I have found a way that seems to be accurate and I wanted to throw it past you guys for any other opinions for adjustments.
I have found that by using guage pins inside of one of the square slots, that the mechanical advance can be adjusted with some accuracy. I have found that for every .003" of diameter guage pin I can get 1 degree of mechanical advance/retard. The last two pins that I have used showed the following:
Tested at 3300 rpms with total advance @ 36.
- @ 900 rpms idle, .251" diam. pin equals 14 degrees of initial timing.
- @ 900 rpms idle, .231" diam. pin equals 20 degrees of initial timing.
The above equals .020" difference in pin diameter divided by the 6 degrees difference in initial timing, gives .003" per degree of adjustment.
I made the above adjustment by adding the guage pin inside of one of the square slots as I tightened the inside of the slot up against the guage pin. Then tightened the two screws while maintaining pressure against the guage pin.
Has anyone else run across another way of doing the above?
Thanks
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1970 YO7 A66

You can purchase an advance curve kit for a Mallory YH advance (part number 29014). It comes with about half a dozen
degree keys, a collection of springs and charts showing the approximate curves you will get with the
different spring combinations. The degree keys allow you to adjust the amount of advance without trial and error.

The current MP distributors are made by Mallory and contain a Mallory YH advance. You can identify the Mallory
advance by the brass rotor sleeve.
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RobbMc

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