MSD Pro Billet Dizzy “top” shim washers

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73c34me
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MSD Pro Billet Dizzy “top” shim washers

Post by 73c34me »

Getting ready to re assemble my SBC pro billet dizzy with a new gear. Noticed the the out side corner of the pick up housing is worn down from the advance mechanism pin anchor rubbing against it . I have 2 thin shim washers that I ASSUME fit between the top of the reluctor and the bottom of the advance plate, that would raise the shaft up. However. Don’t remember seeing them there before. I can’t find a diagram for assembly, so looking for assistance. Much thanks. Note : not to be confused with the shim washers between the gear and the housing; these are at the other end.
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Re: MSD Pro Billet Dizzy “top” shim washers

Post by Lizardracing »

OR hand file the pin down to clear.
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Re: MSD Pro Billet Dizzy “top” shim washers

Post by Tuner »

You sure it's not the rotor screws are too long?

There are small shims that go between the reluctor (rotation pole piece) and ball bearing. They go above the bearing and below the advance part with the weight plate and the 8 legged reluctor. No shim goes above the weight plate and below the cam on the top of the shaft. The cam is directly above the weight plate with nothing between.

As assembled by MSD, most usually the end play is shimmed nearly complete out of the assembly and this results in hastening the eventual sticking of the mechanism. When the engine heats up to operating temperature the aluminum housing grows twice as much as the steel shaft, so if the end play is too tight the end play dissappears completely and the advance mechanism sticks or drags until the engine cools off. Factory GM distributors have .060 to 090 thou end play and work just fine. The oil pump load on the distributor gear thrusts the gear up against the housing, so that ensures the advance mechanism can move freely. You need at least .030" end play.

MSD designed the distributor copying a GM distributor with the end play shimmed completely tight with shims between the gear and the bottom of the housing, pulling the shaft down, which closes up the clearance the advance mechanism needs to move, and worse, also pulling the rotor blade down from making good contact with the carbon button in the cap. This is why we see so many MSD distributor caps with the carbon button burned up, the rotor blade doesn't touch the button. It is a good idea to bend the rotor contact leaf spring up a little to be sure it touches the carbon button when the cap is on.
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Re: MSD Pro Billet Dizzy “top” shim washers

Post by 73c34me »

Tuner. Thank you much. To clarify. Both shim washers go above the bearing directly below the bronze bushing?
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Re: MSD Pro Billet Dizzy “top” shim washers

Post by Tuner »

Bronze bushing? What part number is this distributor?

There is a .500" ID x 1" bronze washer and .500" x 1" steel washer above the gear that goes against the aluminum housing. From the housing down, aluminum housing, bronze washer,steel washer, gear, in that order.

On the top, ball bearing in top of housing, small washer(s) .500 ID x .625" (? approx) OD, then reluctor (advance part with 8 legged reluctor and advance weight pivot pins that the shaft goes through). The shims above the ball bearing, between the ball bearing and the advance mechanism, sometimes vary in thickness as they fit the original end play and are optional as required to achieve the desired end play, which is looser than MSD assembles them. The assembly needs enough end play so when the housing grows in length when it is 250F or more at operating (racing) temperature it doesn't bind up the advance mechanism. MSD fits them too tight, they need some, at least .030", end play. Better the end play be too loose than too tight.
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Re: MSD Pro Billet Dizzy “top” shim washers

Post by 73c34me »

Part 8572. SBC w/ vacuum advance
Bronze bushing approx 1-1/4” long sits on top of the bearing
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Re: MSD Pro Billet Dizzy “top” shim washers

Post by 73c34me »

73c34me wrote: Fri Aug 16, 2019 1:38 pm Part 8572. SBC w/ vacuum advance
Bronze bushing approx 1-1/4” long sits on top of the bearing
. Something is not correct. With the cam gear on with 2 shim washers (original) I have 0.070” play. I also have to push the shaft up toward the top or the reluctor “wheel” hits the pick up. I would love to see an assembly diagram cause I am missing the boat on this.
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Re: MSD Pro Billet Dizzy “top” shim washers

Post by 73c34me »

Thought. It is a tach. Drive dizzy. Perhaps the bevel gears are what limits shaft travel by self centering?
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Re: MSD Pro Billet Dizzy “top” shim washers

Post by Tuner »

You are correct, the small washers do go between the sleeve and ball bearing or above the sleeve, between the sleeve and the advance part.
73c34me wrote: Fri Aug 16, 2019 1:38 pm Part 8572. SBC w/ vacuum advance
Bronze bushing approx 1-1/4” long sits on top of the bearing
I think you will find the "bronze" is chormate coated steel, use a magnet to confirm although it It doesn't matter what it is made of as it is just a sleeve.

Tach drive has nothing to do with this. Just position the washers to give the required clearance for the pickup coil and leave some end play. Are you sure the screws for the rotor are not too long, protrude down though the plate too far?
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Re: MSD Pro Billet Dizzy “top” shim washers

Post by 73c34me »

Been a while ,Update. I shimmed between the top of the tach. Drive gear and the bottom of the reluctor with a 3/4” oil impregnated bushing. This allowed some vertical play and centered the reluctor to the pick up. Installed a new Chris Straub supplied gear and shimmed to .040”. Flushed the motor thoroughly etc.
installed the distributor, the motor has never been so quiet. It always had some gear noise previously. I have an hour run time and the oil pressure has not degraded. I hope I dodged a bullet. Thhnx to those who helped
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Re: MSD Pro Billet Dizzy “top” shim washers

Post by ProPower engines »

73c34me wrote: Sun Sep 15, 2019 2:41 pm Been a while ,Update. I shimmed between the top of the tach. Drive gear and the bottom of the reluctor with a 3/4” oil impregnated bushing. This allowed some vertical play and centered the reluctor to the pick up. Installed a new Chris Straub supplied gear and shimmed to .040”. Flushed the motor thoroughly etc.
installed the distributor, the motor has never been so quiet. It always had some gear noise previously. I have an hour run time and the oil pressure has not degraded. I hope I dodged a bullet. Thhnx to those who helped
Was the dist. depth into the oil pump checked with the intake installed before you installed the oil pan??
This is what I do to confirm the amount of end play in the drive shaft and also check the dist. gear for proper engagement or mesh before the pan is installed.
In todays market where companies get bought and sold several times like MSD has the QC seems to differ a bit and when stuff is made off shore the spec's can change without notice. I have had a couple drop in units that needed a slip collar made and the flange machined off to get them correct lately.
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Re: MSD Pro Billet Dizzy “top” shim washers

Post by 73c34me »

Depth checked prior? No. I forgot to mention. I had the “fixed” collar machines off and installed a slip collar. Surprised I forgot that, as the slip collar is a main point of the fix!
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