No spark (distributor question)

Hi all, Well my TO-20 (Ferguson) tractor doesn't have any spark.
AFAICT it's either the coil or the distributor that is bad.
Distributor is Delco-Remy 1111722. I don't totally understand how
the distributor works. There are two connections to it. One
from the HV coil. And the other connects the low voltage coil to
ground (negative) The distributor is off the tractor and when I
spin the rotor, I don't see any connection between the low voltage
coil input and ground. (case of distributor.) Should I see a
closed connection at some point as I spin the rotor?
(I'm measuring with a DMM ohmmeter.) Or does this also have some
sort of spark gap?
Thanks.
George H.
(Oh and how the bleep do I get this distributor apart?)
Reply to
ggherold
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Never mind.. got it apart.. bad contacts on low voltage side... off to Java Farm Supply. GH
Reply to
ggherold
Never mind.. got it apart.. bad contacts on low voltage side... off to Java Farm Supply. GH
If the points went bad it's a good idea to replace the condenser (capacitor) as well.
Reply to
Jim Wilkins
The points are likely shot.
See
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Reply to
Clare Snyder
Decent, generic diagram for a distributor, coil, spark plugs here:
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You'll need to set the gap for the points after replacing or moving them around...
Reply to
Leon Fisk
Hey, thanks all. The local farm supply had a rebuild kit with points, (and 20 mil gap tool) capacitor, rotor and four new spark plugs for $20.
Any hints on setting the timing? I made some marks on the distributor before taking it off... but I've never adjusted the timing. (And I've had the tractor for going on 20 years.)
George H.
Reply to
ggherold
Hey, thanks all. The local farm supply had a rebuild kit with points, (and 20 mil gap tool) capacitor, rotor and four new spark plugs for $20.
Any hints on setting the timing? I made some marks on the distributor before taking it off... but I've never adjusted the timing. (And I've had the tractor for going on 20 years.)
George H. ================================
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Reply to
Jim Wilkins
Thanks Jim, I've only got the "Dealer Shop Manual".
George H.
Reply to
ggherold
Hmm looks like I need to find which neighbor has a timing light and wants a beer. :^)
GH
Reply to
ggherold
  Or you can set the timing marks where it's supposed to be timed and use a test light as you slowly advance the dist until the points open and the light comes on . Static timing can get you very very close ... just be sure the points are properly gapped before you try to time it .
Reply to
Terry Coombs
If you were ACCURATE and marked it properly, and the timing was correct to start with, the timing should be good. You cantime with a timing light or you can "static time"
see:
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Reply to
Clare Snyder
No timing light required. a test light is helpful to static time but I've done it for decades just watching for the spark. When the points open, you get spark. If you can't see or hear the spark and don't have a test light just grab the coil wire.
Reply to
Clare Snyder
But put the screwdriver down first.
Put the screwdriver down first.
Reply to
wws
Oh.. I was watching some Aussie guy fix up a Ferg, and he set the timing at 'DC' so to speak. I guess I'm confused about which side of the low voltage points opening- closing- opening - cycle I'm setting 'zero' by. So if I'm getting this right, I want to set 'zero' at the position where the points have been closed and then open up.. (it's my job to get the engine spin direction correct.) That's the point (position) where the spark happens... (Huh. I never understood all this before... thanks.)
George H. (in engine/ flywheel cycle) where th
Reply to
ggherold
OK thanks. Me and the boy will go F around with it as soon as it stops blowing and snowing here. I found a timing light in the 'tool' bus. (The tool bus is an old school bus left here by the previous owner and full of all sorts of junk... useful stuff.)
George H.
Reply to
ggherold
Yeah thanks. But I'm certainly not grabbin' any a 'dem wires. I would have gone out today, but it was blowing and snowing here.
Reply to
ggherold
When the points open the light goes out at least if you have the test lamp wired between the dizzy and the coil low tension side to show when the points are conducting. Your post about the Aussie guy is correct regarding the way the points operate, I've used static timing many times for initial set-up on cars.
Reply to
David Billington
When the points open the light goes out at least if you have the test lamp wired between the dizzy and the coil low tension side to show when the points are conducting. Your post about the Aussie guy is correct regarding the way the points operate, I've used static timing many times for initial set-up on cars.
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If the test lamp is in series between the coil and breaker points it will go out when the points open and interrupt the coil current, which is when the spark jumps.
However I connected the lamp across (in parallel with) the points so the light turns on when they open, and I didn't need to disconnect the coil wire or disturb the points or distributor position by reconnecting it after properly setting them.
The coil is a large inductor which converts the energy of current flowing through it into a magnetic field. When the strength of this field increases or decreases it acts like a generator that opposes the change in current, causing the current to appear to have inertia. Current increases fairly slowly when 12V is applied across the coil by closing the points, and it tries very hard to continue flowing when the points open to break it.
in the old low-tension (low-voltage) ignition system the points were inside the combustion chamber. When the points opened the current would continue between them as a spark, like arc welding, which fired the cylinder.
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've burned through too much of my daily internet ration looking for an image of the early Daimler igniter which IIRC really was pointed, thus the term.
Separating the switching and spark gap functions made both more reliable. The high tension system you have uses a coil with two windings, a transformer.
The low voltage or primary winding is matched to the battery voltage and current, and the high voltage or secondary winding of many more turns of finer wire is optimized to create a high voltage, low current spark across the spark plug. Otherwise it operates like the simpler low tension system whose concept may be easier to understand.
When the points close the current and magnetic field build up during the "dwell" time, which is part of the distributor shaft cam profile. The grease in the ignition kit goes on this cam. When the points open the field tries to keep the current flowing through both windings, and succeeds through the spark plug gap, where the arc current rapidly depletes the magnetic field's stored energy. The condenser (mostly) absorbs the current that would have sparked across and eroded the points.
Then the condenser returns its stored electric charge to the coil, and along with other inherently capacitive elements of the system causes the coil voltage and current to oscillate and create radio and TV interference. The cure is energy-absorbing resistance built into spark plugs with an R in their designation.
If the gas vapor all ignited instantly it could be fired at piston Top Dead Center, but since it doesn't (and shouldn't) the spark occurs before TDC to give the flame time to spread. The timing mark is when/where the plug should fire at idle speed. As the engine speeds up the centrifugal advance mechanism rotates the breaker point mounting plate to make the spark occur about the same length of time before TDC, so a strobe timing light shows the marks appearing to move on the flywheel.
If the distributor has a vacuum advance its purpose is to advance the spark further when the engine is at speed but lightly loaded, just cruising down the highway. This improves fuel economy. Modern engines achieve the same effect by advancing ignition timing until they sense the loud onset of preignition ( knock), then backing it off a bit.
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When I entered the automotive electronics business in 1973 the above had until recently been all the electricity an automotive engineer had to know, since they bought radios from elsewhere. The new engineers Detroit quickly hired weren't familiar with the many non-theoretical aspects of electrical engineering such as component tolerance and corrosion of exposed contacts and the rushed designs of 1974 plainly showed it, though they learned fast. Some of what they introduced was taken from chemical lab instruments or military aircraft, but those were much too complex and expensive to use as-is. I had to learn fast myself in order to build the factory test stations for the new electronics they were introducing like ABS.
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Fortunately I had studied material science, combustion chemistry, thermocouples, hot wire mass air flow sensors etc in college.
Reply to
Jim Wilkins
If the gas vapor all ignited instantly it could be fired at piston Top Dead Center, but since it doesn't (and shouldn't) the spark occurs before TDC to give the flame time to spread....
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Here's a good description;
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I've seen a mechanic set timing by manually rotating the distributor until he liked the sound of the exhaust. I set it by the book, but tune old carbs by idle speed, throttle response and the smell of the exhaust.
Reply to
Jim Wilkins
Wow! OK more than I can digest. But thanks. I did finally understand how my distributor works. So thanks for that too. In the end I just put it back together. Set the rotor at ~ the right place. (I took a picture), checked for spark. A yup. And advanced the dist. til it started. The timing light worked and the 'old girl' started at 30 deg. I set it for the recommended 7-8 deg. And then cranked up the engine rpm. I didn't see any advancement of the timing. She seemed to run OK between 30 and 7 deg and I set it for 15. (?)
So let me ask a related question. The plugs are always getting fouled (black fried gunk) on this tractor and I clean 'em with kerosene. Could I maybe fix that some with better timing? Though it does other things this tractor spends most of it's life dragging a mower deck around the 'estate' (The mower deck is called an estate groomer in the manual. :^) Sorta medium rpm <2k, 1st or 2nd gear (depending on grass) the grass is a heavy load on the pto/engine.
George H. (did you guys do anything actively to reduce the political crap on this site/net? or was it natural?)
Reply to
ggherold

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