MSD advance bushing
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MSD advance bushing
Anyone have an MSD black distributor bushing handy and could give me the OD measurement of one? I make my own because you can't just buy one, you have to get the whole advance kit. I gave away my last one I made and cant remember the diameter. Pretty sure the bore is .187" and they are .187' thick...the od has slipped my mind though.
Re: MSD advance bushing
I measured .187 inside hole, .178 thick, .375 outside , hope this helps.
John
John
Re: MSD advance bushing
MSD-Delco Distributor Weight Modification For Less Advance
https://www.tapatalk.com/groups/racingf ... 1a348ee22d
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.
https://www.tapatalk.com/groups/racingf ... 1a348ee22d
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.
Re: MSD advance bushing
Thanks for posting this again, Tuner. Too easy to forget that you don't always need a "kit" 
Heat is energy, energy is horsepower...but you gotta control the heat.
-Carl
-Carl