Ignition question

Discussion in 'General Engine Discussion' started by deverett, Jun 30, 2019.

Help Support HMEM by donating:

  1. Jun 30, 2019 #1

    deverett

    deverett

    deverett

    deverett HMEM Supporter

    Joined:
    Sep 6, 2007
    Messages:
    1,095
    Likes Received:
    214
    Occupation:
    Retired
    Location:
    Skibbereen, West Cork
    Ignition on an old-time model 4 stroke engine with simple points.

    I get a spark at the plug when the points close but also get a spark at the points at the same time.
    I understood that sparking at the points was due to a bad condenser, but I've tried 3 different New condensers with no change.

    I've checked the wiring and all seems OK, so what could be the trouble?

    Changing to Hall effect or other electronic ignition is not an option for this engine.


    Dave
    The Emerald Isle
     
  2. Jun 30, 2019 #2

    Gordon

    Gordon

    Gordon

    Well-Known Member

    Joined:
    Jan 4, 2011
    Messages:
    566
    Likes Received:
    66
    Make sure that the points are clean and aligned properly,
     
  3. Jun 30, 2019 #3

    stevehuckss396

    stevehuckss396

    stevehuckss396

    Model Engineer Project of the Month Winner HMEM Supporter

    Joined:
    Nov 19, 2008
    Messages:
    4,067
    Likes Received:
    1,007
    Gender:
    Male
    Occupation:
    Construction
    Location:
    Sterling Heights, MI
    Sorry I can't help but that is the function of the condenser to suppress the arc on closing and save the points from pitting. Points are on the negative side of the coil with the condenser?

    I got nothing!
     
  4. Jun 30, 2019 #4

    deverett

    deverett

    deverett

    deverett HMEM Supporter

    Joined:
    Sep 6, 2007
    Messages:
    1,095
    Likes Received:
    214
    Occupation:
    Retired
    Location:
    Skibbereen, West Cork
    I think Gordon may be onto the right track. I looked at the points alignment and they were a bit out. Haven't had the opportunity to reset them, but that will be the first line of attack.
    I will also double check the coil polarity with the points - and the remaining parts of the circuit. You never know!

    Thanks to both replies.

    Dave
    The Emerald Isle
     
  5. Jul 1, 2019 #5

    BaronJ

    BaronJ

    BaronJ

    Grumpy Old Git.

    Joined:
    Dec 6, 2013
    Messages:
    748
    Likes Received:
    274
    Gender:
    Male
    Occupation:
    Retired.
    Location:
    North Yorkshire
    The condenser also forms a tuned circuit with the coil, but you may still get a tiny spark at the points. Usually not enough to cause rapid damage. Search "Kettering Ignition"
     
  6. Jul 1, 2019 #6

    retailer

    retailer

    retailer

    Junior Member

    Joined:
    Oct 14, 2011
    Messages:
    110
    Likes Received:
    40
    If it is just a conventional points and coil then I would have thought that the plug would spark when the points open - that is when the magnetic field in the coil collapses, as others have mentioned a you may get a small spark at the points - what sort of coil and what voltage are you running, if it is a car coil on 12v then it may be a coil designed for a ballast resistor.
     
  7. Jul 1, 2019 #7

    Chuck Leininger

    Chuck Leininger

    Chuck Leininger

    New Member

    Joined:
    Apr 4, 2019
    Messages:
    1
    Likes Received:
    0
    Gender:
    Male
    Location:
    Ridgefield Washington
    Add a ballast resister before the coil to lower the voltage to 6V before reaching the coil. Many older applications
    Used a jumper wire in the cranking circuits to supply full voltage for starting and back to 6V to run on.
    Assuming here that your condenser is good.
     
  8. Jul 1, 2019 #8

    WOB

    WOB

    WOB

    Well-Known Member

    Joined:
    Sep 12, 2013
    Messages:
    155
    Likes Received:
    31
    The function of the capacitor( condenser) is to suppress the arc when the points open. There should be no arc at the points when they close unless they are bouncing.

    Points are a lousy switch for an inductive DC circuit. They open relatively slowly and only a small gap. Without the cap. the back emf from the coil would cause an arc that would wear out the points in short order and reduce the coil output greatly. Unfortunately, the cap also absorbs some of the energy in the coil thus reducing the output to the plugs slightly. But it is necessary to get a clean and rapid primary current cut-off as is required to get a coil to work properly. The loss in the cap is tiny compared to the gain in coil output.

    Transistor switch ignitions don't need the cap. and thus allow max. coil output and nothing mechanical to wear out.

    WOB
     
  9. Jul 1, 2019 #9

    canadianhorsepower

    canadianhorsepower

    canadianhorsepower

    Well-Known Member HMEM Supporter

    Joined:
    Oct 22, 2011
    Messages:
    1,671
    Likes Received:
    320
    Basically the function of a condenser in a coil ignition circuit is to reduce (not eliminate) the spark at the contact points as they open in the distributor and thus minimise burning and pitting of the points. Arcing is caused by the effect of self induction in the coil as the points interrupt the flow of current.

    in other words , if you get rid of the spark at the contact point, you will also get rid of the spark at the plug.
    that is the reason why you need to replace contact point at some time
     
  10. Jul 1, 2019 #10

    Andy Munns

    Andy Munns

    Andy Munns

    Member

    Joined:
    Feb 7, 2019
    Messages:
    8
    Likes Received:
    0
    Gender:
    Male
    Location:
    Australia
    Car club members today with older vehicles suffering from ignition woes often have to get their vehicles towed as young roadside assistance techos don't know about points ignition. Set gap to specs (often 0.015" or a business card.) Clean points after with folded strip of abrasive paper - never emery as it contains oil. I then clean points a last time with a business card or similar. Spark at points is normal and expected if all is well - Also proves earth connection OK. Check coil is OK by testing for spark at coil HT lead - Should jump 1/4". Then test spark plug. You can cross test your spark plug on a working engine like your lawn mower. If your coil is a non-original selection, the parts number should not contain "R" for a simple non resistor system (These were used for electric start engines where the loss of volts into starter motor is compensated by bridging the bypass resistor and giving coil as much volts as possible during start.) A ballast resistor coil probably works fine at 12 volts for a short time but soon overheats on a steady 12 volt diet.
     
  11. Jul 2, 2019 #11

    johnmcc69

    johnmcc69

    johnmcc69

    Well-Known Member

    Joined:
    Dec 5, 2011
    Messages:
    234
    Likes Received:
    33
    Personally, I would love to see a separate thread on ignition & ignition based problems. I'm by far no electricity kind of guy, but have had my fair share of chasing down ignition problems on old cars, tractors, ETC.
    lots of good info on the net, but hard for a casual troubleshooter to interpret.
    I would be interested in knowing the basic principles & what to check. How do I check a condenser with my meter? What's the difference between a condenser & a capacitor? How do you check an ignition coil? How much resistance does a ballast resistor "resist"? Questions like these...

    Sorry Dave that I can't help with your problem, but your query got me thinking. Some good "points" brought up here in the responses though & I would like to learn a little more.

    John
     
  12. Jul 2, 2019 #12

    bluejets

    bluejets

    bluejets

    Well-Known Member

    Joined:
    Apr 22, 2014
    Messages:
    136
    Likes Received:
    50
    Not abnormal at all for points to have a small spark when they close the circuit, same as any switch but more-so with an inductive coil as a load.
    The condensor is the same as a capacitor, just depends on which side of which ocean you reside.
    Testing capacitors is done with a .......yes, capacitor test meter.
    Purpose of the condensor is to allow a path for the current flow during the period of the collapsing field of the coil. Without it, nothing works as expected.
    As someone already mentioned, spark at the plug occurs when the points open.
    Balast resistor...no need. They are used in automotive with a 12v system and an 8v ignition coil.
    Purpose is to run the coil on 12v at startup and via the resistor at normal run time to give more "start up spark".
    Nothing wrong with using points, my 1978 Celica has done 1/2 million kilometers on points with very little maintenance required.
    The problem associated with a tutorial on how to test a coil is, there are many and varied types.
    So pointless really unless one has a complete understanding of every type available and know how to recognise which one you have in your hand at any given time.
     
  13. Jul 2, 2019 #13

    WOB

    WOB

    WOB

    Well-Known Member

    Joined:
    Sep 12, 2013
    Messages:
    155
    Likes Received:
    31
    A capacitor ( or condenser) can be tested with a analog VOM ( volt-ohm meter) to determine whether it is shorted or open but not for capacitance value. Set the VOM to resistance test somewhere near the middle of the range. Momentarily short the cap to remove any residual charge. Connect one meter probe to a one cap. terminal. While watching the meter needle, connect the other probe. The meter should dip toward zero and then move back towards full scale smoothly and fairly rapidly. The momentary dip shows current flow into the cap and then as the cap voltage rises and the current goes down, the meter will indicate rising resistance to infinity as the cap charges up to the meter's probe open circuit voltage. If no rise to infinity, the cap is not good and is internally shorted out. If no dip on initial connection, the cap is open internally and is not good.

    I suggest you get a variety of caps and test them to get an idea of the meter's behavior with different cap values and meter resistance range selections. This test does not work well with a digital VOM because of the problem of interpreting a changing value with a digital meter.

    Electrolytic cap testing is problematic because they are polarity sensitive and there is no standard for VOM resistance probe polarity. Old style VOM usually had the black probe positive and the red probe negative when resistance testing but probe polarity for voltage testing was reversed for DC voltage/current testing. The only way to know for sure is to check a VOM resistance probe polarity with another VOM set on DC voltage.

    Ignition caps are never electrolytic, so you really don't need to be concerned about testing that type unless you are working on power supplies.
    If cap testing is ongoing for you, there are lots of cheap import cap testers out there that take all the guess work out of testing.

    WOB
     
  14. Jul 2, 2019 #14

    bluejets

    bluejets

    bluejets

    Well-Known Member

    Joined:
    Apr 22, 2014
    Messages:
    136
    Likes Received:
    50
    In addition, make certain any capacitor is discharged before testing.
    A charged capacitor can wreck a test meter and it can also give a nasty shock if you happen to wrap your fingers around the contacts.
    I have a general use discharge resistor on my test bench with a lead soldered to each end.
    Primarily for when working on SMPS ( power supply units) but same thing can be used for any cap.
    Size is 1K5 ohm and 2W.
    Don't be tempted to short out a cap even though it may be rather spectacular and frighten hell out of the cat.
    It can do damage to cap.
     
  15. Jul 2, 2019 #15

    canadianhorsepower

    canadianhorsepower

    canadianhorsepower

    Well-Known Member HMEM Supporter

    Joined:
    Oct 22, 2011
    Messages:
    1,671
    Likes Received:
    320
    Can't believe how much BS can go into answer , HOLY MACARONI, it is normal to have a spark , get off all those theories,
    It' IT' NORMAL , let the spark be......................
     
    doc1955 likes this.
  16. Jul 3, 2019 #16

    bluejets

    bluejets

    bluejets

    Well-Known Member

    Joined:
    Apr 22, 2014
    Messages:
    136
    Likes Received:
    50
    Ease up bloke, you're not the only one in this forum and each is entitled to have a say.
     
    XD351 likes this.
  17. Jul 3, 2019 #17

    XD351

    XD351

    XD351

    Well-Known Member HMEM Supporter

    Joined:
    Feb 17, 2015
    Messages:
    323
    Likes Received:
    66
    I agree 100%
    If it throws a healthy spark , the timing is right and the engine fires up there is little to be concerned about .
    If it were arcing across the points ( big fat blue spark ) i would be more worried as that will kill the points very quickly . I remember when i was a kid you could buy clear distributor caps and it was a source of amusement watching the rotor button wiz around and you could see the faint orange spark on the points when it got dark enough to do so .
     
  18. Jul 3, 2019 #18

    doc1955

    doc1955

    doc1955

    Gone

    Joined:
    Aug 27, 2009
    Messages:
    1,090
    Likes Received:
    67
    Occupation:
    Retired Former Tool Design Engineer
    I too totally 110% agree it's normal. Only way to get away from it is to go to an electronic ignition with a cap discharge. And yes others are entitled to have a say trouble is you need to be careful not to be led astray. The cap is only there to lessen the spark not totally get rid of it.
     
    XD351 likes this.
  19. Jul 3, 2019 #19

    deverett

    deverett

    deverett

    deverett HMEM Supporter

    Joined:
    Sep 6, 2007
    Messages:
    1,095
    Likes Received:
    214
    Occupation:
    Retired
    Location:
    Skibbereen, West Cork
    Well, lots of interesting replies!
    I've reset the points and get 15 thou gap when they are open.
    Looking at the points there are signs that the contact area was not over the full width of the contacts. I've run a points file through the closed points to ensure there is no peak from burning and hopefully they are now parallel when closed.
    Still get sparking when the engine is turned over; I didn't realise that sparking at the points was to be expected. So maybe I will leave well alone, except maybe to try a ballast resistor. to see if that makes any difference.

    Dave
    The Emerald Isle
     
  20. Jul 3, 2019 #20

    stevehuckss396

    stevehuckss396

    stevehuckss396

    Model Engineer Project of the Month Winner HMEM Supporter

    Joined:
    Nov 19, 2008
    Messages:
    4,067
    Likes Received:
    1,007
    Gender:
    Male
    Occupation:
    Construction
    Location:
    Sterling Heights, MI
    Yes I stand corrected. The condenser is supposed to "greatly reduce" the arcing across the points but won't completely eliminate it. Auto shop was 1980.
     
    doc1955 likes this.

Share This Page