1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

Distributor tester

Discussion in 'Fuel System & Electrics' started by saabman, Oct 13, 2016.

  1. saabman

    saabman Well-Known Member

    Messages:
    4,864
    Location:
    Goulburn
    Well I bought the latest VWMA Mag to read the article on the dizzies and well was somewhat disappointed. Not what I was expecting so A started thinking about dizzies and how they worked and advance curves etc and thought what I really needed was a dizzy tester. Something that would empirically test and map the performance of a given distributor. Given I've got a few dizzies lying around and I know at least one of them is shagged it would be nice to make it good again.

    Soooo I'm thinking about haveing a go at makeing a tester something that would allow me to repeatedly read the advance for a given rpm and also a given vacuum as well.

    Today I had to sit through a 4 hour mandatory training session at work on a particular irrelevant topic during a break I grabbed a pad of paper and pen and started noting down some ideas etc on how I could put one together. A quick google showed on different automotive forums a few other people expressing a desire to build one and the usuall response was "just buy and old Sun unit" and there was some reference to a wooden unit in a popular mechanics magazine from around the time of Noah and not much else.

    As old Sun units are few and far between I figured it can't be that hard to knock up a modern version.

    I've got some ideas as to how to do it and do it cheap and easily with high accuracy but want to put it out to those that know what features such a device should have.

    Some critical parameters I'm thinking of are.
    RPM
    Advance at any specified rpm
    Advance at specified vacuum

    What do others think is there other things that would good - determining dwell perhaps or amount of points bounce, consistency of advance between cylinders?
     
    cbus likes this.
  2. grumble

    grumble Well-Known Member

    Messages:
    1,222
    Location:
    Taree
    From memory most of these were in the VW factory workshop manual,there is probably a picture of the unit. If I have a few spare minutes sometime I will have a look at what i have in my stash.
     
  3. saabman

    saabman Well-Known Member

    Messages:
    4,864
    Location:
    Goulburn
    It would be interesting to see what parameters the professional units measure.
     
  4. rstucke

    rstucke Well-Known Member

    Messages:
    1,464
    Location:
    Wamberal NSW AUS
    I'm half way to building one. Use to use one while I was employed (retired now) and can't find a second hand one for love or money(Sun, Blackhawk Vane etc.)
    Just not quite up to it in my rebuild at the moment but I have the makings. Will post when done.
     
  5. kool_kombi 79

    kool_kombi 79 Well-Known Member

    Messages:
    380
    Location:
    Brisbane
    I have made one, seems to work ok, fantastic for setting points dwell.

    dwell
    rpm
    spark (to check miss fire)
    vacuum for vac advance
    lots of time
    lots of patience.
     
  6. saabman

    saabman Well-Known Member

    Messages:
    4,864
    Location:
    Goulburn
    This great that other have been thinking about / building something

    I'm thinking of having a display that will show RPM and advance to start with.

    And usesing a drill to spin the dizzy up - I'm not sure how that will go as I was thinking of taking it out to 8000 rpm (engine speed) which is 4000rpm dizzy speed I don't think my drill goes that fast - might need to find a faster motor.

    I'm thinking of using a hall sensor on the drive shaft to determine RPM

    Simple matter of detect when the sensor is triggered than time how long till its triggered again. RPM =120x 1/time

    Timing will be determined by recording the time the points open and subtracting the next RPM pulse time.

    At 8000 RPM the dizzy takes 15mS per revolution that's about 41uS per degree.

    At 7.5deg Btdc that's a whopping 312uS between the points opening and TDC been detecting so tonnes of time.

    Dwell might be a bit tricker as it's only in the order of a deg or 2 so 50 to 100uS that will be tight but should work.

    Kool-kombi how did you monitor the spark? Was that a measured parameter or a visual observation?
     
  7. kool_kombi 79

    kool_kombi 79 Well-Known Member

    Messages:
    380
    Location:
    Brisbane
    I made mine to replicate the engine set up as much as possible, tried to keep as much electronics out of the build as possible, the plugs are set up on a bar so I can see them spark.
     
  8. Andy.

    Andy. Active Member

    Messages:
    520
    Location:
    Brisbane
  9. saabman

    saabman Well-Known Member

    Messages:
    4,864
    Location:
    Goulburn
    Some good reading there Andy - thanks for that.

    I didn't get to play with dizzies today- spent the day removing rust :(
     
  10. saabman

    saabman Well-Known Member

    Messages:
    4,864
    Location:
    Goulburn
    After some good reading Ive decided to keep it simple to start with and just get the basic parameters.

    RPM
    Mechanical Advance

    Ill add automated vacuum advance monitoring later.
     
    Mordred likes this.
  11. ttmck

    ttmck Super Moderator Staff Member

    Messages:
    2,769
    Location:
    Hallett Cove STH AUS
    last time I used a distributor graph was some 10 years ago on a turbo motor , but alas they are around if you look hard enough just wait for your TAFE college to close down and pounce come auction time but I would just leave it alone unless you were doing a turbo engine hence you don't need to much primary opening on the springs due to pinging or detonation and certainly next to no advance on the secondary side distributors set from factory are good for common street performance main thing is make sure the base plate is not seized and the timing does actually advance lube the springs and weights inside if the dwell meter alters that means you have a worn shaft
     
  12. saabman

    saabman Well-Known Member

    Messages:
    4,864
    Location:
    Goulburn
    Our Tafe closed down everything but ESL courses a few years ago so no chance of finding something there.

    The main reason I'm looking at making one is to confirm the correct operation of the dizzys I have and likely to acquire. I've been stung a few times lately with no advance/ erratic advance and just the plain wrong advance.

    With the marvel of modern electronics been so cheap it should be fairly simple to make a reasonably sophisticated tester for only a few bucks.
     

Share This Page