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  • Distributor end play

    Can anyone offer an expanation for the difference in end play specs. between the Prestolite (.003-.010") and the Delco for V8's (.036-.068"). The Stude manual for the Delco specifies no less than .036". There has got to be a reason for the difference.

  • #2
    No explanation for the difference...but within reason...the tighter the better.

    A shaft that can move up and down, "will" change the timing as the shaft rides up and down the bearings in the distr. body. Why...because the gears are of a helical design and rotate as the shaft goes up and down.

    The Prestolite dimension is good figures for most ant distributor...though I'd go no tighter than about .005" or .006". It gets only spashed oil down there, need to have some room to have it sneek in!

    That's what I try to do anyway.

    Mike

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    • #3
      There may be a book somewhere that explains it all, but I've been going by what a racer-tuner told me many years ago, before the days of HEI...........
      The window distributor is sort of a 'fits-all' design. It was originally made to be used on engines where the distributor goes through the intake manifold. Since the manifold height could vary by an unknown amount, they gave it more end play to compensate for height differences. It's claimed that much clearance causes 'spark scatter'. He said the shaft might float at a slow idle, but as soon as the rpm picks up the shaft moves up or down because of the angle cut of the drive gear and stays there. The shaft is pushed upward in a clockwise rotating distributor, and is pulled downward in a counter-clockwise distributor.
      You can buy shim sets for these distributors, but if you shim a CCW distributor you must be certain you haven't pushed the gear downward so far it binds the cam gear, or the oil pump drive. In any event, don't fit it too tight. Try to keep around .010" end play.


      Dwain G.
      So.....if I'm 'pre-approved' why do you want me to fill out an application?

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      • #4
        The reason of the difference is based on factory tolerances. I see a post cautioning against having so little endplay that the distributor gear is pushed down against the cam gear causing wear. I also see advice to limit endplay to a minimum. Neither one of those address the issue of factory endplay and the reasons for it. If you are concerned about endplay changing your timing; forget it. A worn distributor shaft will change timing; as will worn bushings or loose point plate. Here's the problem not discussed so far. Endplay is to protect the TOP of the distributor shaft and the area where the spinning elements will come in contact with the housing. There is no type of thrust washer in that location, so any contact will cause damage and contaminate your oil with metal particles. So, install your distributor tightly, THEN check the endplay. Do not remove any more endplay than you can measure at that point or you will have metal to metal contact wear. Have one person turning the crankshaft back and forth while the other person measures the endplay. I myself would rather have more endplay than less to lube the bushings better and to have the rotor wear on the cap in a wider pattern.

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        • #5
          Thanks for your comments all, but I still wonder why Studebaker specified that the end play must not be less that 36 thou. Note the word "must". Must be some reason peculiar to the Delco.

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          • #6
            WCP -

            As for your question about why the difference....unless someone has a time machine...none of us "really" knows!

            If you take apart both distributors...from the upper housing bushing down to the lower bushing...the housings are the same. From the upper bushing to the oil pump...the shaft, gear, gear pin, lower shaft, these items are also the same.

            Despite some of the wanderings here stating the shaft endplay will not change the timing as incorrect...that is "factually"...incorrect!! Otherwise, MSD, Mallory, Crane, et.al. have sought to minimize the endplay for....for what...timing reasons!
            Want proof....it takes a little work on your part, but with locking out the machanical and vacuum advance...then watching the timing flucuate during RPM changes...you'll see why minimizing shaft play is a good thing.

            Along with the min. value I mentioned above... .010" to .015" is a good number to work with.

            NOW...it has been mentioned that distributor height can effect other things. This is correct.
            But...the only thing it will effect negativily, is the oil pump and the upper part of the gear vs. the lower part of the distr. housing. This can happen if the deck has been milled and the center block surface has been milled to match. Which "isn't" nesessary by the way on a Stude...
            One way to check is to drop the distributor into the block "without" a gasket. If the housing goes all the way to the block surface....you have no...problems. Now if for some strange reason the distr. housing flange does not solidly touch the block...solid shims will be in order to gain the above noted, solid clearance...along with the gasket thickness.

            There is no other reason to worry about, negative endplay

            Mike

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            • #7
              There are no posts on this thread stating that shaft endplay will not change timing. Timing won't change during sustained rpm or rpm increases; only during rpm decreases... and who cares about that? If your timing does change during sustained rpm or rpm increases, then your bushings or shaft are worn. Anyone care to address the wear factors involved with the shaft rubbing against the top of the housing when factory endplay dimensions aren't followed?

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              • #8
                quote:Originally posted by WCP

                Thanks for your comments all, but I still wonder why Studebaker specified that the end play must not be less that 36 thou. Note the word "must". Must be some reason peculiar to the Delco.
                __________________________________________
                Studebaker was merely quoting the specifications given to them by the manufacturer, Delco-Remy Div. of GM, who built them all alike.


                Dwain G.
                So.....if I'm 'pre-approved' why do you want me to fill out an application?

                Comment


                • #9
                  On closer examination of the Delco drive gear, compared to Prestolite ones on (R2 & R3), the Delco gear is different in that it lacks the lead-in and lead-out ramps on the helical face of the teeth. Also the root width appears slightly narrower. This makes the mesh of the teeth more critical (less lash). I suspect the greater end play allows the distributor shaft to "float" or find the position of least interference, given the probable tolerance variations of the block. I have 1000 miles on a Delco set with .018" of end play and contact pattern on the teeth seem normal. Before I go any further with the engine reassembly, I will install the distributor and feel the mesh by rotating the unloaded cam. If there is interference I should be able to feel it.

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                  • #10
                    No problem. Lots of gear lash. With the distributor seated on the gasket, the rotor can be moved up and down approx. the amount of the set end play (.018") and ditto when the ditributor is shimmed upward .016". Completely smooth feel to the cam rotation. As Dwain G. points out, the usual .055" end play is what GM supplied along with the specified range. Probably no other reason!

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