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Technical 51 Flathead V8 no spark

Discussion in 'The Hokey Ass Message Board' started by 51flatheadV8, May 24, 2021.

  1. 51flatheadV8
    Joined: May 24, 2021
    Posts: 12

    51flatheadV8

    Hello all, I have no spark to my distributor or points on my 51 Flathead V8. It has been converted to 12V with a Negative ground. I am running a 12 volt coil with a built in resistor to bring down the power to my points as they are still 6 volt points. The only time I can get power to the points is the initial push of the starter button. Any help?
     
  2. gary macdonald
    Joined: Jan 18, 2021
    Posts: 107

    gary macdonald
    Member

    You need to check the wiring on the solenoid. You should have 12 v keyed at the switch to the coil . With the key in the on , not crank , you need to have 12 v at the coil . Check for other fuses or circuit breakers that could of been used originally. Does your solenoid have 2 little studs and 2 large ?
     
  3. 51flatheadV8
    Joined: May 24, 2021
    Posts: 12

    51flatheadV8

    There are no fuses on the truck, there are 2 large studs and 1 little stud.
     
  4. 51flatheadV8
    Joined: May 24, 2021
    Posts: 12

    51flatheadV8

    I get 12V to the coil. I don’t get spark between the points with a screwdriver but they are brand new as well as a brand new condenser.
     

  5. Glenn Thoreson
    Joined: Aug 13, 2010
    Posts: 211

    Glenn Thoreson
    Member
    from SW Wyoming

    Did you change the starter solenoid when you converted to 12 volts? The '56 and up solenoid does not wire up the same as the old 6 volt variety. The 6 volt coil uses one wire to activate the solenoid. this wire grounds at the button to activate. The 12 volt variety uses a 12 volt wire from a two wire push button to activate. Or, you will need a different modern ignition switch with a "start" position. The modern solenoid has two small posts on it. One activates the solenoid (starter) and the other sends 12 volts directly to the coil, bypassing the resistor for easier starting. That wire cuts out when you let go of the key and the resistor takes over. Not as complicated as it sounds. Hope this helps.
     
  6. rpu28
    Joined: Jan 17, 2006
    Posts: 153

    rpu28
    Member
    from Austin

    "The only time I can get power to the points is the initial push of the starter button."

    "I get 12V to the coil. I don’t get spark between the points with a screwdriver but they are brand new as well as a brand new condenser."

    I'm not sure those two statements are consistent. You get 12V to the coil all the time (when the ignition is turned on?), but voltage to the points only when the starter switch is pushed?

    Have you checked to see if you are getting spark when the starter button is pushed?
     
  7. 51flatheadV8
    Joined: May 24, 2021
    Posts: 12

    51flatheadV8

    I replaced it with a 12v solenoid. There are 2 large posts and 1 small post. I hooked the new solenoid up exactly how the old one was hooked up.

    I only get a small spark the moment the truck rolls over but then nothing
     
  8. Doublepumper
    Joined: Jun 26, 2016
    Posts: 1,053

    Doublepumper
    Member

    Trying to understand.
    You have 12 volts at the coil with the ignition switch on but, loose power to the coil when pushing the start button?
    If that is the case, it's possible the ignition switch has bad/dirty contacts and is loosing voltage to the coil under the higher current draw from the sol./starter.
     
    clem likes this.
  9. 51flatheadV8
    Joined: May 24, 2021
    Posts: 12

    51flatheadV8

    No. I always have power at the coil. I don’t lose power to the coil I just don’t have spark at the points. I’m trying to get spark at the points and I’m unsure why there is no spark
     
  10. Doublepumper
    Joined: Jun 26, 2016
    Posts: 1,053

    Doublepumper
    Member

    Pull the dist. cap and check for frayed/grounded wiring inside the dist.
    You stated you have a coil with a built in resistor. Did you jumper out/remove the original resistor?
     
  11. Diavolo
    Joined: Apr 1, 2009
    Posts: 815

    Diavolo
    Member

    I came to say this. If the ground wire is original, the insulation is shot. It takes about an hour to pull the distributor, run a new ground and replace it.
     
  12. 51flatheadV8
    Joined: May 24, 2021
    Posts: 12

    51flatheadV8

    There wasn’t a resistor on the truck because it was a 6 volt system. The only reason I got the coil with the resistor is because of the conversion to 12 volts so I could keep the 6 volt points. I don’t see any frayed wiring inside the distributor.
     
  13. Mr48chev
    Joined: Dec 28, 2007
    Posts: 29,541

    Mr48chev
    ALLIANCE MEMBER

    Either you don't have the points adjusted right or you don't have the connections on the points in the correct spots and the lead to the points is grounded all the time.
    This 51 Chevy six cylinder but the directions are the same on all rigs with points.
    you bump the distributor around so that the rubbing block on the points is right on the tip of on of the distributor cam lobes (blue arrow) then you adjust the point gap (red arrow).
    If you set the gap with the rubbing block on the flat of the distributor cam the points will be open. If you didn't gap them at all there is a chance they never open.

    On the flathead distributor it isn't hard to get the connection at the points where the strap from the points, the lead from the condenser and the lead from the coil wire all connect out of order so it either grounds out or there is no connection. Did that on my 51 Merc the first time I changed the points and gave my auto shop teacher a big laugh.


    [​IMG]
     
  14. 51flatheadV8
    Joined: May 24, 2021
    Posts: 12

    51flatheadV8

    The gap setting should be .015 right?
     
  15. F-ONE
    Joined: Mar 27, 2008
    Posts: 2,828

    F-ONE
    Member
    from Alabama

    Correct.
     
  16. 51flatheadV8
    Joined: May 24, 2021
    Posts: 12

    51flatheadV8

    I’m going to check this again tomorrow but I’m certain that’s what it is
     
  17. Bad cap or rotor ? Just a guess but I thought I read you have a spark at the points...Bad starter button ? Run a jumper from the battery to the coil - like a hot wire - to see if it cranks up.
     
  18. 51flatheadV8
    Joined: May 24, 2021
    Posts: 12

    51flatheadV8

    Cap is new. I don’t think the starter button is bad because it rolls the engine over. Engine sounds great rolling over but it won’t fire. It’s not getting spark and I don’t know why. The engine has been freshly machined and boared 30 over. New pistons, rings, everything. Getting fuel, has compression, but won’t fire.
     
  19. jaracer
    Joined: Oct 4, 2008
    Posts: 1,099

    jaracer
    Member

    I would like to know a couple of voltages during cranking. The first is the voltage at the negative coil terminal. If it goes to near zero and stays there, you have a short in the lead going to the points.

    If it stays at battery voltage, you have an open circuit somewhere between the coil, points and ground.
    Check the voltage at the point connection while cranking. If it is near zero, the open is between the point connection and the coil.

    If it stays at battery voltage, the problem is the ground to the distributor. You can check that by reading the voltage at the breaker plate that the points are screwed to. Positive voltmeter lead to the plate and the negative lead to a known good ground. The negative battery post is preferred. If it goes to battery voltage while cranking, the distributor has a poor ground.

    All these tests assume you do have battery voltage at the positive lead of the coil while cranking.
     
    ottoman likes this.
  20. F-ONE
    Joined: Mar 27, 2008
    Posts: 2,828

    F-ONE
    Member
    from Alabama

  21. Flathead Dave
    Joined: Mar 21, 2014
    Posts: 3,386

    Flathead Dave
    ALLIANCE MEMBER
    from So. Cal.

  22. 51flatheadV8
    Joined: May 24, 2021
    Posts: 12

    51flatheadV8

    With the key on, I have 11.9 volts to the + coil. Also with the key on I have 2.0 volts to the - coil. When the starter button is pushed, I have 6.1 volts to the - coil. Keep in mind the coil has a built in resistor as I still have 6 volt points.
     
  23. Doublepumper
    Joined: Jun 26, 2016
    Posts: 1,053

    Doublepumper
    Member

    Check voltage on the coil primary (+), while pushing the start button and see what the voltage is.
     
  24. jaracer
    Joined: Oct 4, 2008
    Posts: 1,099

    jaracer
    Member

    The coil is the only consumer in the primary circuit. You should drop your full 11.9 volts across the coil with coil - going to ground.

    Is that 2.0 volts with the points closed? That should be close to zero. It should go up to 11.9 if you open the points. The points take the negative side of the coil to ground meaning that the voltage at the negative side should be no more than about 0.2 volts points closed, less is better. (eg. 0.1 volt, 0.08 volts, etc.)

    Measure the voltage at the connection on the points with them closed. It should be 0.2 volts or less. If it is, you have high resistance in the primary wire to the points.

    If it is still close to 2.0 volts, the problem is either the points themselves or the ground for the distributor.

    If you read close to 2.0 volts at the point connection, move your positive voltmeter lead to the distributor plate the points are connected to. If it drops to 0.2 volts or less, the problem is the points themselves. If it still reads close to 2.0 volts it is the distributor or breaker plate ground.

    Okay, 6.1 volts with the engine cranking may be okay as the spinning distributor make the point a sort of variable resistor.
     
  25. Ralphies54
    Joined: Dec 18, 2009
    Posts: 749

    Ralphies54
    Member

    I don't think the points care if they see 6 or 12 volts, try a regular 12 v coil and see what happens!!
     
    Hotrodmyk likes this.
  26. Points don't care what voltage the car is. Do this quick and dirty test. Disconnect the wire going to the distributer and tap it rapidly to ground. Do you get a spark from the coil? (secondary wire that goes to cap). If so, the problem is in the distributer. See @jaracer post above.
     
  27. Mr48chev
    Joined: Dec 28, 2007
    Posts: 29,541

    Mr48chev
    ALLIANCE MEMBER

    In the simplest terms the points are the switch for the coil's primary circuit.
    When the points are closed the primary winding builds up a magnetic field in the coil.
    When the points open that magnetic field collapses and that creates the high voltage in the secondary winding and core that sends the spark to the spark plug.

    When the points open the power that went through the primary winding in the coil goes to ground though the condenser so that the spark doesn't jump the points trying to go to ground.

    If you have power to the coil when cranking and power through the coil the issue is inside the distributor.
    Points not adjusted as I said earlier. I've seen that several times when getting called to look at a car that someone tried to work on and then had a no start. Usually they set the points on the flat and they open more rather than close when the distributor cam turns. .014 to .016 gap / 28 degrees dwell angle if you have a meter.
    Wires on points not in the right place or connection through the distributor body grounded. This is what I did when I was 16 and mine wouldn't start.
     
  28. 51flatheadV8
    Joined: May 24, 2021
    Posts: 12

    51flatheadV8

    Tried this before and it burnt the points.
     
  29. 51flatheadV8
    Joined: May 24, 2021
    Posts: 12

    51flatheadV8

    When cranking the engine I only get 9 volts to the + coil. I don’t think that’s enough to start it.
     
  30. Doublepumper
    Joined: Jun 26, 2016
    Posts: 1,053

    Doublepumper
    Member

    Probably not enough voltage, especially with the coil having an internal resistor.
    Check the wire connections back to the ignition switch and all the ground connections.

    The yellow wire on the back of the ignition switch, is the power wire and comes from the load side of the circuit breaker. Check for a voltage drop at either one of those points. If voltage is where it should be, the problem is either the ign. switch or the wiring from the switch to the coil.
     

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