Rotor/Reluctor Phasing Question

Electrical and Ignition

  1. Reddartowner

    Reddartowner UCF Alumni....Go Knights!

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    While attempting to check the reluctor to pickup clearance in my son's '68 Dart 318, we found the following anomaly. With the balancer set to 18 deg BTDC (our idle timing setting), we found that the reluctor was not aligned with the pickup. Since the car runs fine, we're a little confused. Shouldn't the reluctor be aligned with the distributor pickup at the idle timing setting? The photo shows the alignment at 18 degrees BTDC. The balancer markings have been verified with a piston stop, so I know the balancer is correct. Also, the vacuum advance is not hooked up.

    Anyone have any thoughts on this...???
     

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  2. 67Dart273

    67Dart273 FABO Gold Member FABO Gold Member

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    Depending on idle speed and your distributor curve (spring tension) the mechanical advance may already be somewhat advanced when you are checking that running

    Only way to check rotor phase is to take an old cap and cut it open so that you can see at least one cap tower. It does not HAVE to be no1, but whatever tower you cut open, you need to hook the timing light to that tower.

    [​IMG]

    [​IMG]
     
  3. BillGrissom

    BillGrissom Well-Known Member

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    Sounds wrong. Drill a hole in an old distributor cap, aligned with #1 post, and view the rotor tip position with a timing light (on #1 plug). It should be near the hole. The position changes slightly (~10 deg) with vacuum advance, but shouldn't change with centrifugal advance. If it isn't close, you can get mis-fire to another post, termed "rotor phasing".

    For more info, look for youtube videos, or download the Crane XR700 manual online. There are after-market distributors (MSD, ...) where the mechanical advance does vary the rotor position. Those have a solid shaft and a wide rotor tip, unlike the factory Mopar distributor which has 2 shafts, spring-loaded.

    If you have a phasing problem, Rick Ehrenberg sells a fix on ebay for your distributor.
     
  4. Reddartowner

    Reddartowner UCF Alumni....Go Knights!

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  5. KitCarlson

    KitCarlson Well-Known Member

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    The picture of the distributor shows perhaps an advance of 40 degrees based on the reluctor. A better guess if the picture was taken over the rotor shaft.

    I think you have a phasing problem related to a swap of the pickup coil connections. I think the pictures shows a splice at the 2-wire connector. If the connections are reversed, both the timing and rotor phasing will be off in a way, that cannot be corrected by just setting distributor.

    Reverse the connections, significantly re-time and you should be good.

    Attached is a picture of a VR sensor signal (top) and ignition trigger(falling edge on bottom). The VR signal needs to go low then high, in your case the signal is flipped, creating a significant problem.

    The other problem in phasing is often caused by the reluctor being installed wrong, one position for SB, the other for BB that has reverse rotation.
     

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  6. Reddartowner

    Reddartowner UCF Alumni....Go Knights!

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    OK, now we're getting somewhere.... Is it possible to tell whether the timing would need to be advanced or retarded once I swap the wire connections..? Or do I just have to swap the connections and try to start the car and take it from there...
     
  7. 67Dart273

    67Dart273 FABO Gold Member FABO Gold Member

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    I agree, and had completely spaced that out!!
     
  8. KitCarlson

    KitCarlson Well-Known Member

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    I think it will be best to static time it to start it. You will get close enough to start it, by setting the crank at about 10 degrees BTDC at #1, and a reluctor tooth on the pickup. Then check where the rotor aims, and use that for #1. To check engine phase for sure, pop valve cover and see that #1 valves are both closed. Use timing light to adjust timing, when running.

    I think you may find your engine running much better.
     
  9. Reddartowner

    Reddartowner UCF Alumni....Go Knights!

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    I have a degreed balancer, and know the position of the rotor for #1, so I'll static time it as you recommend. No need to pull the valve cover...

    Thanks much...
     
  10. KitCarlson

    KitCarlson Well-Known Member

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    That sounds like a plan, however double check rotor to #1 plug terminal.

    If the VR curve is flipped the - to + zero crossing lies in the nearly flat part of the wave about 40 degrees from normal. A typical rotor to terminal span, is about 40 degrees, so it is possible, there may have been a shift at the cap terminals, to get it running. Timing may have been uncertain, because triggering on the flat zero crossing varies with noise, and other undesirable variables.

    Good luck, you will like the difference.
     
  11. Reddartowner

    Reddartowner UCF Alumni....Go Knights!

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    That would make sense based on how the car was when we bought it. When we first got it home, we found it was running almost 30 degrees of static timing. We have since changed that to 18 degrees static, and had noticed that the engine's response to throttle was a little "lazy". We just accepted that, as all the other tuning parameters seemed OK, and engine compression was good at 150 across the board. The PO had installed the electronic ignition, and I guess got the two reluctor wires backward, and then bumped the timing to get it to run acceptably. We never checked that wiring because the car was running, and I had assumed it would not run at all if the wiring was reversed. When we installed an HEI conversion a few weeks ago, we simply duplicated the existing connection. Considering how far off the phasing probably is, I'm amazed how well it runs..... Learn something new everyday. Guess its not true what they say about old dogs......
     
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    • KitCarlson

      KitCarlson Well-Known Member

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      Please let us know how it works.

      I woke up thinking about carbon tracking in the distributor cap due to the offset. I trust my sleeping mind, it seems to be on target.
       
    • mopar head

      mopar head Well-Known Member

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      Where is this splice?
       
    • TrailBeast

      TrailBeast Slightly Twisted Member

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      I assume you saw the instructions on that HEI kits that mentioned "If the engine runs crappy, then swap the reluctor connections to correct possible rotor phasing problems" :D

      It never occured to me that it might have already been out of phase.

      Still, doesn't really matter though at this point I guess.
      Just swap the reluctor wires and see if things line up better, and the engine runs better.
       
    • Reddartowner

      Reddartowner UCF Alumni....Go Knights!

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      Yes, I did see the instructions. But the car was running smoothly enough that it never occurred to us that the wiring might have been reversed from the start. Looking forward to seeing how it runs when its in phase...... :cheers:
       
    • TrailBeast

      TrailBeast Slightly Twisted Member

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      Your going to LOVE it.:D
      I wouldn't EVER go back.
       
    • Reddartowner

      Reddartowner UCF Alumni....Go Knights!

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      Well, we got the wires switched and the distributor re-phased. 12 degrees static timing. The idle is noticeably smoother than before, and we found that we can now hook up the vacuum advance without having the car stall (see http://www.forabodiesonly.com/mopar/showthread.php?t=203029). But the vacuum advance adds about 28 degrees, so we'll be looking for a can with less advance. Didn't have a chance to take the car out for a drive today, we'll do that tomorrow. Definitely better......thanks everyone..!!!
       
    • 67Dart273

      67Dart273 FABO Gold Member FABO Gold Member

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      hey, like COOL, man!!
       
    • KitCarlson

      KitCarlson Well-Known Member

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      Sorry, I missed in your other post. Your distributor picture is worth 1000 words. I give you an A+ for updating the post.

      The 28 degrees adder seems about 2x, the norm.
       
    • TrailBeast

      TrailBeast Slightly Twisted Member

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      Just a note on what I exerienced.
      The HEI ignition seemed to advance my timing due to the fuel igniting faster I guess, because I had a WOT ping that was not there before the change.
      My base timing was still the same 14 degrees so I disconnected the vac advance completely and between the base timing and the weighted advance the total timing is just about 2 degrees before the ping at WOT.
      (If I set the base timing at 16 it gets the wide open ping again) and I know for sure it's not running too lean causing the ping.


      This is at 5,500 feet elevation on 89 gas.
       
    • Reddartowner

      Reddartowner UCF Alumni....Go Knights!

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      Actually, my guess would be not that your timing changed, but that the improved combustion from the HEI upgrade probably increased the strength of the combustion pressure wave, which increases peak cylinder pressure. Too high a peak cylinder pressure and you get detonation, i.e., ping. So you might need to dial in a couple degrees less advance.....
       
    • 67Dart273

      67Dart273 FABO Gold Member FABO Gold Member

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      If and when I get my distributor machine back together, I'll have to attempt to check this out. It "could be" that the electronics of the two boxes differ enough that the HEI and Mopar box trigger at enough differential of the incoming pulse that the timing actually IS different.
       
    • KitCarlson

      KitCarlson Well-Known Member

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      There are likely a differences in VR interfaces, comparing GM to Mopar. The trigger level varies some with the VR sensor resistance. It is a component of the bias circuit for the VR sensing interface. The tolerance in the VR sensor (pickup coil) resistance is typically large, so timing varies some with particular sensors. Also the sensor technology is different between GM and Mopar, while there are similarities, the interface may not be optimized.

      I use a specialized VR interface chip and optimize circuit resistor values to match VR sensor to optimize sensor performance. At the present time I do not have a GM nor Mopar box for comparison. VR sensing technology at best is not perfect, it is cheap and common.

      I like Hall gear tooth sensing better. Hall sensing with magnets varies with magnet irregularities. Example Pertronics. Huge efforts to match individual magnet strength and position for consistent trigger..

      With correct phase of the pickup, the trigger occurs in the level above the zero transition where the signal rapidly changes from - to +. Because the transition slope is great, the timing variation will be slight, however it will vary some with RPM. It varies with RPM because the VR signal increases with RPM and the changes slightly the trigger point because the trigger threshold is a fixed voltage, not position. Timing will advance slightly with RPM due to the VR sensing.

      When the VR pickup is incorrectly wired, the trigger point happens between the reluctor teeth, not half way, but at the threshold. Because the transition is slow (flux is nearly constant) the trigger point will be inconsistent. It will be based greatly on noise, RPM, and mechanical variations. The rotor phase is off enough for significant problems in spark distribution.

      I tried to use MS Paint to copy and flip the VR signal in my post, then add the change in trigger point based on the thresholds. I ended up with a mess, so did not want to post. Some might be able to do the mental recreation, and visualize the timing and hysteresis differences with flipped signal. The hysteresis related time significantly increases, this may also result in undesirable change in dwell control, and might rev limit. Hysteresis is the the negative change from the trigger lever, that resets the trigger output.
       
    • Darter6

      Darter6 Well-Known Member

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      Reddartowner,In your post #17 you may find that your Vac can on you distributor is adjustable to set total vac advance. You insert a small allen wrench(I'm sorry I don't remember the correct size)thru the port opening to adjust.It has been a long time but did this on a 74 318 to cure pinging.
       
    • Reddartowner

      Reddartowner UCF Alumni....Go Knights!

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      The vac can on the distributor is adjustable. We have already put 3 turns CCW into it, but with 20 inches of vacuum at idle, it still adds about 28 degrees. How many turns CCW can we go before the adjustment runs out ?
       
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