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Technical SBC DISTIBUTOR TIMING SYMPTOM QUESTION

Discussion in 'The Hokey Ass Message Board' started by anothercarguy, Jun 28, 2025.

  1. If you find you need to strengthen the timing chain cover, how does a gut work around the short water pump?
     
  2. I'm thinking if I can figure out how much the cover needs to be compressed...I should be able to come up with a shim that fills the small gap berween it and the water pump. The back of the water pump will then provide the strength.
     
    pprather and scrappybunch like this.
  3. scrappybunch
    Joined: Nov 16, 2011
    Posts: 436

    scrappybunch
    Member
    from nj

    Mine uses the long style pump, so had room to add the support. Shouldn't be a problem for you to use the pump for support.
     
    anothercarguy likes this.
  4. theHIGHLANDER
    Joined: Jun 3, 2005
    Posts: 10,599

    theHIGHLANDER
    Member

    Ok. We're onto something but like has been said, why. My experience to use as you will. My timing in my racer was desired at 34 degrees. All in BTW, 34 at idle or 7400 (it had a start retard box). To get the 34 I had to stab the dist in at 36. Ran a Comp Cams .714 roller, basic MSD 6AL and req'd accessories, all on a solid HEI with no wt or vac assist. From 1400 idle to 4000 it was 36, clean, like a painted stripe under a flashlight, no flicker, no shiver at all. From 4000 to about 5500 it would "pull back" 2 degrees to 34 and stay there. Had a 5000 stall and shifted at 6800, trap RPM was 7400, I didn't care because under foot and on the time slips the car just flat out liked it. This made me wonder, once again, what were the mechanical actions and effects that pulled 2 degrees out? Was it electronic effect? Was it the ign system saying "Hey bitch, lemme catch up!" Was it the cam feeling the metallurgical twist considering the high spring pressures? And from the chain to the distributor gear, did it twist enough to do that? If we could lock up the back and throw a bar on the nose of a roller cam, how many ftlbs would it take to pull a few radial degrees of twist? A lot? Not much? I'm in this thought more than anything based on "...doesn't do it in the distributor machine." How can we tell its "cam walk" in real time and how can we prove it? I'd think 6 distributor degrees could damn near be seen with the eyes on the front cover. I'd prove it with modeling clay. Stuff it in there and measure it. Now do your thing, make it walk, then measure again (if it doesn't fall out). If you get nothing, no change, drive it and forget it. It runs good, doesn't strand you on the side of the road, probably sounds too kool for most as well. Or as they say, "let it eat" and enjoy your hot rod.
     
    Last edited: Jun 30, 2025
    anothercarguy likes this.
  5. Thinking about this further...so, my assumption was related to the potential that the tin timing chain cover was flexing...and further, that making a shim to fit between the water pump and timing chain cover would address the issue. I now believe my thinking on this was not correct...and here's why in a sketch...
    20250630_130812.jpg
    So, follow along if you're still with me. The distributor is located on the right bank side of the block/cam. It rotates clockwise (looking top down). Losing 8-10 degrees of timing, would require the cam to "walk" to the rear of the engine...walking forward would result in advancing the timing.

    Measuring the diameter of the distributor gear (about 1.1" to the middle of the gear tooth)..and using the the formula for circumference (pi x d= 3.456")...and dividing that by 360 degrees = .009" per degree. So, for simplicity 10 degree timing loss would require the cam to walk to the rear by .090" (A LOT!). I figured I would be able to easily see that.

    So I again removed the distributor thinking I should be able to use a long screwdriver to manipulate the cam from the distributor hole. Long story short, I couldn't do it with the engine in the car...not enough room for the firewall, screwdriver, a light, a couple of hands and my fat head all trying to occupy the same space at the same time.

    So, my next thought was to try and duplicate a 10 degree timing loss with a sacrificial distributor (in case it broke). I dismantled another distributor and removed the section that has the lobes the points ride on...made a spacer bushing to remove all up and down movement. I then installed this distributor in the engine.
    20250630_123853.jpg
    I then made a "spanner" type wrench that fit over the advance pins.
    20250630_123928.jpg
    My thinking was that by applying as much for and aft pressure as I dared to the spanner wrench, with the distributor and cam gears meshed, I should be able to force the cam to "walk" forward or rearward. I was not able to "force" anything more than maybe 1 degree of timing change (which btw, is consistent with the .005"-.010" clearance of the cam button to the timing chain cover)...with applying very significant effort!

    So, all this to say, I'm going to put it together, time it below 3000rpm, put the tools away and as @theHIGHLANDER says, "let her eat"!

    Again, thanks all for providing feedback and conversations.
     
    Last edited: Jul 1, 2025

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