MSD 8578 SBF new distributor loose shaft

[cjperformance]

In essence its the upper bearing or bush and the dussy shaft pilot hole in the block that support the dussy shaft. Stock dissys gave no lower bush or bearing at all, just a bush at the top and block pilot below the gear. Vertical end play setup is vital in these but that's another issue.
But!, having a bush or bearing at the bottom of the dissy housing , as long as everything is properly aligned, does help timing reliability at higher rpm by not allowing or reducing shaft whip or vibration.

I'm not sure what stock stuff you're describing here but just about any distributor I've ever disassembled has a bushing or sleeve installed in the lower housing that locates the shaft. Which, unless I totally gaffed it, is why this thread was started in the first place?

Small block ford, Cleveland, 385 bbf, FE all have a top bush and a pilot in the block no bush in the bottom of the dissy ex factory!

[KnightEngines]

They are supposed to be loose at the bottom - to allow for variations in factory block machining.
With the bottom part of the shaft located in the block they don't need a bush in the bottom, if they had one & the block was machined a couple of thou off (they all are LOL) then the shaft would bind in the bottom of the dissy & make a mess.

It's not a flaw, it's what is required.

[cjperformance]

A friend just bought a new MSD 8578 Pro Billet distributor, to my shop, so I could put a melonized gear on it.
When checking the new distributor I have noticed the shaft has a large amount of radial play at the bottom bearing area, I have,nt measured the clearance yet, but its large - and looks to be about .020" .
Has MSD intentionally made this model like this ? because the pilot / spigot diameter below the gear is supported in the block ?
Factory Ford distributors ive seen are not loose at the bottom bearing , I am mostly dealing with GM/Chev stuff
If it was designed to be like this, then all good, but I doubt it, I have seen quite a few new MSD distributors with quality control problems.
Anyone seen this ? Cheers

The factory ford stuff has a bushing in the top of the housing which is aprox 1" long depending on the actual dissy. When the bush is new there is very little play at the bottom of the shaft.
As long as you dont have radial play at the top of the shaft you are fine. That MSD dissy has a ball bearing at the top so radially will have basically no appreciable play at the bearing at all, when new you wont feel any, once run you get just a little.
And as Tony /KnightEngines said regarding alignment, yes you would be worried if the dissy had no radial movement at the bottom!
Fit it into a block and you will see what we mean.
It is fine!

[groberts101]

Thinking that maybe my memory was going faster than it actually is.. I went and checked 2 SBF Motorcrafts and a 351C Mallory unit. All have virtually no radial end play at all. And that has always been my experience with any known good units as well. If they're too sloppy I have witnessed the blocks hole start to become egg shaped as they continuously flop-n-slop around in the hole. I guess it's another one of those.. YMMV.

[Tuner]

A friend just bought a new MSD 8578 Pro Billet distributor, to my shop, so I could put a melonized gear on it.

If you have figured out the lower shaft bushing is the hole in the block on a Ford, the actual most critical dimension in this job is the vertical location of the gear. The distance from the flange on the distributor housing to the thrust flange on the bottom of the gear must be as specified in these Ford instructions. https://performanceparts.ford.com/downl ... lation.pdf

Alternately, you can measure the block from upper to lower flange and set the gear accordingly, but you will inevitably find the FoMoCo instructions are spot on unless the thrust face where the gear seats in the block has been damaged by previous improperly installed gear.

[cjperformance]

A friend just bought a new MSD 8578 Pro Billet distributor, to my shop, so I could put a melonized gear on it.

If you have figured out the lower shaft bushing is the hole in the block on a Ford, the actual most critical dimension in this job is the vertical location of the gear. The distance from the flange on the distributor housing to the thrust flange on the bottom of the gear must be as specified in these Ford instructions. https://performanceparts.ford.com/downl ... lation.pdf

Alternately, you can measure the block from upper to lower flange and set the gear accordingly, but you will inevitably find the FoMoCo instructions are spot on unless the thrust face where the gear seats in the block has been damaged by previous improperly installed gear.

The above instructions are perfectly fine when using a bushed distributor or a needle bearing distributor but not for a ball bearing distributor where you dont have the same shaft end play as a bush/needle! Measure vertical play in a ball bearing dissy then try relating the ford method !

[Tuner]

What is wrong with people's reading comprehension? Did you actually read the Ford instructions? They apply to the MSD manufactured Ford Motorsports distributors as well as stock FoMoCo distributors. Have you never worked on an MSD distributor? The ball bearing is not a press fit to the shaft. The shaft slides freely through the inner race of the bearing and the end play is set by shims, which, by the way, are usually too tight as the distributors come out of the box, so when the aluminum housing expands with normal engine heat the end play against the collar and thrust washer on the shaft below the housing is insufficient for the advance mechanism to move, so it either sticks advanced or does not advance at all until the engine cools. With the engine cool all seems normal, but with the hot engine the hanging advance can cause hard starting or detonation, depending on the situation.

[cjperformance]

What is wrong with people's reading comprehension? Did you actually read the Ford instructions? They apply to the MSD manufactured Ford Motorsports distributors as well as stock FoMoCo distributors. Have you never worked on an MSD distributor? The ball bearing is not a press fit to the shaft. The shaft slides freely through the inner race of the bearing and the end play is set by shims, which, by the way, are usually too tight as the distributors come out of the box, so when the aluminum housing expands with normal engine heat the end play against the collar and thrust washer on the shaft below the housing is insufficient for the advance mechanism to move, so it either sticks advanced or does not advance at all until the engine cools. With the engine cool all seems normal, but with the hot engine the hanging advance can cause hard starting or detonation, depending on the situation.

cjperformance - (aka. , Me! ) The above instructions are perfectly fine when using a bushed distributor or a needle bearing distributor but not for a ball bearing distributor where you dont have the same shaft end play as a bush/needle! Measure vertical play in a ball bearing dissy then try relating the ford method !

Tuner , i wasnt trying to start a riot mate. My apologies for not explaining far clearer but i think we are on about exactly the same thing. Yes I have worked on a couple of msd dissys, and I do a lot of SB and BB ford stuff. I usually like your posts but man you got your grumpy pants on lately !
Smile and the world is a better place