MSD 8578 SBF new distributor loose shaft

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RT Machine
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MSD 8578 SBF new distributor loose shaft

Post by RT Machine » Tue May 22, 2018 7:20 am

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

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Re: MSD 8578 SBF new distributor loose shaft

Post by mag2555 » Tue May 22, 2018 7:34 am

.020" of play gear to body is fine as .008" to .010" will go away when the Aluminum body expands!

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Re: MSD 8578 SBF new distributor loose shaft

Post by groberts101 » Tue May 22, 2018 8:09 am

mag2555 wrote:
Tue May 22, 2018 7:34 am
.020" of play gear to body is fine as .008" to .010" will go away when the Aluminum body expands!
Your logic is reversed.. the aluminum hole will get bigger. I would never accept a sloppy part like that. Sleeve it or send it back.

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Re: MSD 8578 SBF new distributor loose shaft

Post by Steve.k » Tue May 22, 2018 9:31 am

I will say msd quality control has gone south. Last cleveland dist. We got came with smaller windsor gear. You really have to inspect their stuff from top to bottom. Some guys i talk to will not buy their products after to many issues.

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Re: MSD 8578 SBF new distributor loose shaft

Post by 427dart » Tue May 22, 2018 5:41 pm

I bought one of those years ago for my Ford 351W and it was an over priced piece of junk. It had one real ball bearing at the top and a loose bushing at the bottom...sloppy as hell.
So I then ordered an Accel Billetech Race distrib which was 10 bucks cheaper and it had 3 high speed ball bearings and the inside advance setup was rock solid. The top part of the distrib you can remove from the body to change advance curve.
Still running it today!!

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Re: MSD 8578 SBF new distributor loose shaft

Post by RT Machine » Tue May 22, 2018 10:14 pm

Thanks for replies,
I will send it back, I have sent back 3 in the past for similar quality control issues, cheers

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Re: MSD 8578 SBF new distributor loose shaft

Post by Geoff2 » Wed May 23, 2018 5:03 am

RT,
Do you mean side to side play, or up/down play? I thought you meant side to side, in which case 0.020" is waaaaay too much.

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Re: MSD 8578 SBF new distributor loose shaft

Post by Circlotron » Wed May 23, 2018 6:20 am

Geoff2 wrote:
Wed May 23, 2018 5:03 am
RT,
Do you mean side to side play, or up/down play? I thought you meant side to side, in which case 0.020" is waaaaay too much.
RT Machine wrote:
Tue May 22, 2018 7:20 am
the shaft has a large amount of radial play at the bottom bearing area,
Across the shaft.

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Re: MSD 8578 SBF new distributor loose shaft

Post by Tuner » Wed May 23, 2018 2:23 pm

The sideways slack at the gear is not important because it has a ball bearing in the housing and the shaft bearing surface below the gear pilots in the block. The vertical slack is important so the thrust surface on the gear can contact the thrust flange in the block with no interference of the advance mechanism end play. The advance mechanism must not be bound up when the gear is pulled down against the thrust flange by the load of turning the oil pump. Measure the distance from the upper flange where the distributor housing seats on the block to the thrust flange where the gear seats. That measurement must fall between the maximum and minimum of the shaft end play.

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Re: MSD 8578 SBF new distributor loose shaft

Post by groberts101 » Wed May 23, 2018 2:42 pm

Tuner wrote:
Wed May 23, 2018 2:23 pm
The sideways slack at the gear is not important because it has a ball bearing in the housing and the shaft bearing surface below the gear pilots in the block. The vertical slack is important so the thrust surface on the gear can contact the thrust flange in the block with no interference of the advance mechanism end play. The advance mechanism must not be bound up when the gear is pulled down against the thrust flange by the load of turning the oil pump. Measure the distance from the upper flange where the distributor housing seats on the block to the thrust flange where the gear seats. That measurement must fall between the maximum and minimum of the shaft end play.
Ah hell.. I seem to be on a roll disagreeing with you today(which is unusually odd :wink: ).. so while I'd agree that the upper bearing is far more important, I'll still say that relying on the upper bearing and block itself to keep the shafts radial play in check is not the best way to go here. In essence, you're basically implying that lower bearing has no relevance towards operational integrity.. or is really even needed in the first place. Too much play on the lower shaft bearing sleeve will only serve to increase the loading requirements on the upper ball bearing and impose additional and unnecessary block and gear wear as a likely result.

Seen lots of damage due to sloppy distributor shafts through the years so I always check radial, and quickly return if necessary, while shimming most down to the bare minimum end play #'s to avoid it. Never ceases to amaze me at the level of quality some brand spanking new parts will sink towards for the sake of increased profit margin.

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Re: MSD 8578 SBF new distributor loose shaft

Post by MadBill » Wed May 23, 2018 4:05 pm

I preface this with my usual "Not a Ford guy, but..." : doesn't the lower end of the distributor shaft locate in a bore in the block? (I know there's a bore; can't think of any reason for it other than shaft lateral location.) In which case either it or the lower shaft bushing, but not both, should do the locating. :-k
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Re: MSD 8578 SBF new distributor loose shaft

Post by Tuner » Wed May 23, 2018 4:40 pm

MadBill wrote:
Wed May 23, 2018 4:05 pm
I preface this with my usual "Not a Ford guy, but..." : doesn't the lower end of the distributor shaft locate in a bore in the block? (I know there's a bore; can't think of any reason for it other than shaft lateral location.) In which case either it or the lower shaft bushing, but not both, should do the locating. :-k
This is the deal ^^^ MadBill is not Mad at all. The shaft is supported on each end, the center is redundant and could actually cause misalignment, were not all three on the same axis as the shaft. The hole in the block pilots the lower end of the shaft and sets clearance between the cam and distributor gears, and the ball bearing (or bushing in stock distributors) in the top of the housing locates the top. That's all it needs.

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Re: MSD 8578 SBF new distributor loose shaft

Post by groberts101 » Wed May 23, 2018 7:42 pm

MadBill wrote:
Wed May 23, 2018 4:05 pm
I preface this with my usual "Not a Ford guy, but..." : doesn't the lower end of the distributor shaft locate in a bore in the block? (I know there's a bore; can't think of any reason for it other than shaft lateral location.) In which case either it or the lower shaft bushing, but not both, should do the locating. :-k
It works like any other bore and shaft setup in motor.. via oil film. BUT.. it is not nor ever was intended to be the sole contributor to stabilizing the entire lower shaft of a distributor. Doesn't take much imagination to think about the torsional vibrations of the spinning cam and potential side loading that occurs causing additional wear of the sprocket and shaft/bore when you take the lower bearings support out of the equation.

I'll say it another way to make the point. Take the lower bearing or sleeve out of a distributor and run the piss out of it. Inspect for wear and post back here about how that lower bearing support has little relevance.

And yeah.. nothings ever in perfect alignment. But a tighter lower bearing or bushing takes some of the shafts side loading off the block.

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Re: MSD 8578 SBF new distributor loose shaft

Post by cjperformance » Wed May 23, 2018 8:22 pm

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.
Craig.

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Re: MSD 8578 SBF new distributor loose shaft

Post by groberts101 » Wed May 23, 2018 9:53 pm

cjperformance wrote:
Wed May 23, 2018 8:22 pm
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?

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