Breaker Point Operation

[turtle1173]

Hi all,<br /><br /> This is on a distributor driven 3 Cyl. 85HP Chrysler 1972, model #: 857HD.<br /><br /> I'm trying to understand "how" the distributor works and the purpose of points. Let me run this by you all and tell me if this is right.<br /><br /> When the Ignition is on, 12 volts DC go from the battery to the CD Module. In the module it is turned into AC Current, stepped up to approx. 240 volts and then converted back into DC current and stored. That current is then ready to be jolted into the coil when an electronic switch is activated. Is that correct??<br /><br /> OK, the lead that goes from the CD module to the distributor has 12 volts DC going through it. It goes through the distributor and directly to the backside of the point set. OK, here's where I get a little fuzzy. When the points are closed, should the entire point set register at 12 volts? Does the current go anywhere else or does it stop at the point set? Now when the points open, that's supposed to trigger the electronic switch in the CD module to release the voltage to the coil. The voltage then is stepped up inside the coil and goes through the lead back to the distributor where it is then distributed to each cylinder. Is that right?<br /><br /> My "current" problem (no pun intended) is that I'm getting 12 volts to the back of the point set but I'm not getting any spark to the plugs. I also cant register 12 volts on the cam side of the points, when its closed. My theory is that perhaps the points are bad and the 12 volts are grounding out. The point set looks good but I don't know how the tips are supposed to look. I can hear it snapping inside. Any suggestions??<br /><br />Thanks,<br /><br />Shane

 

[rwise]

Re: Breaker Point Operation

turtle1173<br />12 VDC to the "open" points sounds good. 0 VDC to the "closed" points is also good as they complete the circut sending a pulse through the system to be amplified. The surface of the contacts should be flat and clean.<br />Richard

 

[dkondelik]

Re: Breaker Point Operation

mornin' turtle,<br /><br />so sorry. don't know your set up but i do think i know this about points.<br /><br />they are just a "current switch". usually used to "break" current flow in an inductance path (frequently the primary (low side) of a transformer (coil)). the di/dt (change in current with respect to time) in an inductor (primary of coil in this case) will induce a voltage proportional to the initial current & the inductance of the coil. as "dt" approcahes 0, the resulting voltage increases as in di/dt = V = di/0. ignoring losses and interwinding capacitance, the primary voltage is coupled to the secondary voltage by the "turns ratio" of the transformer "secondary"/"primary" windings. in an "ideal" world, the "secondary" voltage would approach infinity. this would surely be enough for a spark plug.<br /><br />don't know if this helps but it's 'bout all i can offer on the subject.<br /><br />surely one of the Chrysler guys can clear things up for you.<br /><br />Good Luck

 

[turtle1173]

Re: Breaker Point Operation

Thanks for the quick response. Whether the points are open or closed I get 12 volts on the one side only. Is that the way it is supposed to be then?<br /><br /> Does a clean point mean shiny?<br /><br />Thanks,<br /><br />Shane

 

[rwise]

Re: Breaker Point Operation

when the points are closed you should get zero volts at the points as they complete the circut to ground. I have used a doller bill to clean points, just get them closed, gently pull them open, slide the bill between them, let them close on the bill, pull it out, if it comes out dirty then repete using a new spot of the bill.

 

[turtle1173]

Re: Breaker Point Operation

So if I get 12 volts constantly, does that show that the points are bad or could it be a problem with the module??<br /><br />Shane

 

[dkondelik]

Re: Breaker Point Operation

i belive that in most instances the circuit is as follows:<br /><br />V(battery or magneto) -> Coil(low side+), through coil to low side-, to fixed side of points. cam side of points to ground.<br /><br />So, when points are open, 12V at fixed side of points (under dc contions). when point are closed, both sides of points should be at ground.

 

[rwise]

Re: Breaker Point Operation

with the power removed from the points use an ohm meter and you should get a very near "0" reading on the lowest ohm scale

 

[turtle1173]

Re: Breaker Point Operation

Is that with putting one lead on one side and the other lead on the other side? (I'm not the best with electronics) I'm assuming that this is done with the points open?? What will it show if it's bad?<br /><br />Thanks,<br /><br />Shane

 

[rwise]

Re: Breaker Point Operation

with the points closed, from one side to the other, also I edited one of my posts to add a cleaning procedure

 

[dkondelik]

Re: Breaker Point Operation

that'll confirm the continuity of the points. once confirmed, you night want to put the black lead on the block to confirm integrity of the circuit to ground.

 

[turtle1173]

Re: Breaker Point Operation

Thanks Rwise.<br /><br />Klondike, could you explain putting the black lead on the block to confirm the integrity of the circuit to ground. How would I do this exaclty? Remember, I'm very uneasy with electronics <br /><br />Thanks again<br /><br />Shane

 

[rwise]

Re: Breaker Point Operation

turtle1173 klondike7 I'm out of time got to go, good luck turtle, I'll check back later<br />Richard

 

[turtle1173]

Re: Breaker Point Operation

Success!! Yesterday, I had the cap off with the ignition on and was checking the voltage at the points. I could hear it "snapping" even though I couldn't see a spark. Anyway, I decided to check the spark again with everything put back together except I took the wire out of the coil and put my spark tester in it and grounded it to the powerhead. When I turned the flywheel there was that beautiful blue spark! I squired some fuel into each carb and she started right up. I was so excited, I felt like screaming <br /><br /> Anyway, this is the first time I've had her started. She sat up indoors for 10 years and I got this engine about a month ago. I've got the carbs clean and the fuel pump replaced. I can't wait to change the impeller tomorrow and take her down to the river and run her (on the trailer).<br /><br />Thanks a bunch everyone!<br /><br />Shane