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 MSD-Delco Distributor Weight Modification For Less Advance 
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Joined: Fri Feb 08, 2013 2:37 pm
Posts: 1702
Using a big bushing to limit travel in an MSD stops the travel of the weight lever arm at a location on the advance cam further from the distributor shaft center and closer to the weight pivot pin and results in transmitting more of the oil pump torsional noise to the ignition timing, causing “spark scatter”.

Bending the weights like this limits the travel of the mechanism in the retard direction because the weights hit the back side of the football shaped cam on the top of the shaft. This provides a shorter advance curve and limits the travel by moving the bottom of the curve up instead of the top of the curve down.

This has two advantages.

One, it gives more consistent function because it provides a greater offset angle of the spring pins at the fully retarded position so the springs have better leverage to pull the mechanism toward retard when very soft springs are used.

Two, because the oil pump causes a torsional oscillation (the pulsing you feel when you use a speed handle to prime oil pressure) in the distributor shaft which causes “spark scatter” it is very advantageous to have the advance mechanism travel reach the end of the weight lever, so the travel of the lever on the advance cam (football shape on the end of the shaft) moves as close to the shaft center as possible and still remain on the flat face of the lever at the tip (but not roll up on the tip).

The shaft drives the rotating pole-piece (reluctor) through the weight and weight pivot pin.

The torsional oscillation in the distributor shaft is greater in amplitude further from the shaft center.

When the contact between the cam and weight lever is further from the shaft center, the leverage of the weight and pin more efficiently transmits the undesirable oscillation to the reluctor, causing greater error in the spark timing, “spark scatter”.

When the weights are bent like this a small limit bushing can be used (I usually use the smallest red one)which allows the weight lever to travel all the way to the tip and the curve is limited on the retard end to the required amount, which can be as little as desired.

Heat the weights to red-orange heat and bend. Take care to keep them flat and parallel. Put 3/16" stainless tubing or an old drill bit shank through the pivot hole to keep it round.


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MSD-Delco Distributor Weight Bend.jpg
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MSD-Delco Distributor Weight Modification W-Notes.jpg
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Mon Feb 23, 2015 1:33 am
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Joined: Wed May 08, 2013 11:22 pm
Posts: 17
great info Tuner

Is it worth while to weld/fill the retard side of the slot where bush run to limit travel also?


Thu Jun 11, 2015 5:30 am
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Joined: Fri Feb 08, 2013 2:37 pm
Posts: 1702
MELWAY wrote:
great info Tuner

Is it worth while to weld/fill the retard side of the slot where bush run to limit travel also?
I don't see any reason to do that if you heat and bend the weights as described above because the motion of the advance mechanism in the retard direction is limited by the weights coming to rest against the back side of the advance cam. One benefit of bending the weights in this manner is because nothing is welded the mechanism can easily be restored to original condition by replacing the weights or bending them back to the original shape.


Sat Jul 16, 2016 1:01 am
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