70 350/350 distributor advance weights & shaft bearing play - NCRS Discussion Boards

70 350/350 distributor advance weights & shaft bearing play

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  • David L.
    Expired
    • July 31, 1980
    • 3310

    #16
    Re: 70 350/350 distributor advance weights & shaft bearing play

    Originally posted by Joe Lucia (12484)
    Dave------

    Yes, these weights were widely used in Delco-Remy distributors. By far, these are probably the most common weights. Note the sharp edges on these weights. This is how all GM weights I have ever seen appear. The weights on the distributor shown in the original post here are more "beveled" indicating a different sort of stamping process was used to manufacture them.

    One thing, though: these weights appear to be zinc plated. I've never seen original GM weights that were plated.
    Joe,

    These weights are original. I cleaned them off years ago with my wire wheel. I have many other Chevrolet distributors with the same 1881371 weights. I weighed the 2 weights and they weigh 38 grams (1.34 oz.) or 19 grams (0.67 oz.) each .

    Dave

    Comment

    • Duke W.
      Beyond Control Poster
      • January 1, 1993
      • 15672

      #17
      Re: 70 350/350 distributor advance weights & shaft bearing play

      Originally posted by Stephen Byrd (12641)
      Duke,

      I believe the side play may be a little more than barely perceptible. I had recently shimmed the shaft end play to between 2 an 7 thousands. Could the side play cause 2 to 4 degrees of spark scatter. This distributor is a points distributor with Pertronix. I need to check the hole for the VAC.


      The mechanical advance is providing only 4" of advance at a maximum rpm of approximately 2,000 rpm's. I wonder why. I posted 2 pictures of advance weights that might be originals. I wonder if I should change to the original weights (if original,, or change to original type weights) and the springs you recommend in other posts.

      Thanks
      Yes excess side play can cause spart scatter. I assume you mean the centrifugal provides only 4 DEGREES advance at 2000. Is that where it stops? How much at 4000. As I think I requested earlier, post the centrifugal and vacuum advance specs from the CSM/AMA specs.

      Install the other weights. Clean the corrosion off everything and wipe down the parts with WD 40 and manually pull the weights to the limit to check that they move freely and don't get hung up.

      Duke

      Comment

      • Stephen B.
        Very Frequent User
        • April 1, 1988
        • 876

        #18
        Re: 70 350/350 distributor advance weights & shaft bearing play

        Both sets of advance weights I have are 17 grams and have a zinc coating. However, they do measure .057" at the widest part. I know one set is not original as I remember purchasing the weights and springs as a high performance set decades ago.

        Comment

        • Stephen B.
          Very Frequent User
          • April 1, 1988
          • 876

          #19
          Re: 70 350/350 distributor advance weights & shaft bearing play

          Here's the advance data from the GM Specifications. Isn't this the same information as the CSM/AMA?



          As mentioned in another update that's part of this post, I used a set of aftermarket 17 gram advance weights with the black springs from your recommended Mr. Gasket 928G kit after cleaning and lubrication. The distributor has full mechanical advance at 1,800 rpm's with total advance of 38 degrees. The mechanical advance accounted for approximately 24 degrees.

          I determined that the majority of the ignition splatter was from the distributor cap not being property secured.

          Is this the rpm for full mechanical advance that you like to see?

          Thanks
          Attached Files

          Comment

          • Duke W.
            Beyond Control Poster
            • January 1, 1993
            • 15672

            #20
            Re: 70 350/350 distributor advance weights & shaft bearing play

            Centrifugal all in at 1800 is more aggressive than most engines will tolerate, but if there is no detonation or driveability issues like bucking/jerking at low revs, light load then it should be okay.

            I'm assuming that you are measuring centrifugal advance with VAC hose disconnected and plugged. That's the way it MUST be measured. You should give the throttle a good blip to about 5000 to ensure that no more advance is added.

            Most aftermarket weights are not hardened and wear, so you should obtain a set of hardened OE weights.

            If you haven't already done so you should convert vacuum advance to full time. You'll need to swap out the VAC for a 12" B26 in order to pass the Two-Inch Rule, assuming an OE equivalent cam. Check idle vacuum. It should be in the 14" @ 750 ballpark.

            Duke

            Comment

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