Non-Stock Distributor Question

buckyAugust 4, 2008

Fellas: Bucky here; still alive and kicking. Haven't posted in a long while but still check this great list now and then. Anyway:

I have now acquired an old 56 Ford TBird with a 312 Cu In Y block engine. A previous owner installed a real neat Mallory dual point mechanical advance distributor sometime back. I am about to do a tune-up on the old girl and am thinking that the dwell and point gap settings shown in the shop manual no longer apply due to the totally different distributor set-up now in the car. (Timing should be the same?) Am I thinking correctly or do the standard gap, dwell and timing specs still apply? Thanks a lot: Bucky

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A way back in 1957, I believe that the standard distributor for Fords had both a centrifugal advance and a vacuum advance. (I would think that a thrid party distrubutor would have the same.) Probably the reason a prior owner changed to an after market distributor was to get the dual points setup. The dual point setup should be similar the the dual point distributor used on the Dodge Red Ram (hemi) engine of the same era (I owned one a long time ago.)

The dual points operate in parallel, one set delayed a bit after the other. The first point to close starts the current in the primary coil and is followed by the closing of the second point. Then the first point opens followed by the opening of the second point. It is the second point that controls ignition timing. The thinking behind this setup was to spread the contact wear between two points and to gain some dwell time. Dwell time becomes critical in an 8 cylinder engine as RPM climbs.

The point gaps should be about the same as for a single point. Adjust the distributor rotation to produce proper timing (opening of the second point), and then adjust the point gap of the first point to adjust dwell time. Too much dwell time is just as bad as not enough. If the first point closes on the circuit while the ignition circuit is ringing, it will increase its wear. As engine speed inreases, the first point will march into the ringing period and that is unavoidable. (You'll need an ignition analyzer oscillscope to see the point action and circuit ringing.)

The drill for setting the timing advance at idle was to disable the vacuum advance to set the mechanical advance (Remove the vacuum line from the vacuum advance unit and plug the line). Most carbureators were designed with the vacuum advance port positioned just above the edge of the throttle plate when at idle position with little to no vacuum is present at idle. As the throttle plate opens beyond idle, it passes the vacuum port and this ports begin to see the intake manifold vacuum. In a 'messed up engine', the throttle plate can be at or above the port at idle and some vacuum will be present.

Soon after 1960, kits became available to convert to capacitive discharge ignition using the original ignition coil and rotor in the distributor. The early ones were prone to failure. mostly due to burnout of the SCR. Expensive SCRs were required at that time - oridnary ones failed. The SCR had to have an exceptional short rise (full turn on) time. If you like to tinker, think about convering to capacitive discharge.

By 1973, the ignition electronics became reliable and the underhood temperature was addressed. I bet that you could lift the ignition electronics out of a 1973 Chrysler V8 product and apply to the Ford with little trouble. In 1973, Chrysler mounted the power unit for the ignition on the fender to heat sink it and combat underhood temperature. Use heat sink grease under the unit to insure good thermal contact with the fender.

The only thing I'm not sure about is when did Ford switch from 6 to 12 volts. All the electronic ignition systems designed after 1960 were for 12 V systems.

    Bookmark   August 5, 2008 at 3:17AM
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The link below may be helpful for Mallory distributor parts.

Here is a link that might be useful: Mallory Distributors

    Bookmark   August 6, 2008 at 4:48PM
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Thanks for the replies guys. Gem Dandy: In anwer to your question about when Ford changed over from 6 volt to 12 volts it was the 1956 model year. Up to 55s were 6 volt.

    Bookmark   August 25, 2008 at 10:13PM
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