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8N No spark

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AJH8N

12-02-2007 13:33:11




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I have a 48 8N. I have been tring to get this thing fired up for some time now. I have no spark at the spark plugs. This tractor has 6 volts positive ground and a front mount dist.
I have 6.25 volts at the key switch, both sides of the resistor and around 6 volts going to the ignition coil with key switch on. I removed the dist. from the tractor and placed it in the vise with the ciol on top. I ran 6 volts from a battery charger to the top of the coil and grounded the dist. Hand spun the dist and have strong blue spark when the points open and close(with the cap off) When I put it back in the tractor I have no spark at the plug wires. Can anybody tell me what I"m doing wrong?

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BillM (OH)

12-02-2007 16:45:30




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 Re: 8N No spark in reply to AJH8N, 12-02-2007 13:33:11  
Try jumper from battery to top of coil and see if it'll start/spark at the plugs - short time only to prevent coil cook. If yes, your problem is between battery and coil - suspect ignition switch, bad wire, resistor, etc. If no, your problem is likely on the high tension side - distributor cap/rotor, etc.
Stick with it, you'll find it eventually.....



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Bruce (VA)

12-02-2007 14:24:45




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 Re: 8N No spark in reply to AJH8N, 12-02-2007 13:33:11  
Getting the coil pigtail to make contact after it's on the distributor is critical as JMOR says. Put the coil on the distributor, look at the contact, & then test it for continuity w/ a meter. You can put the distributor back on the engine w/ the coil on it if you loosen the fan belt & hold your mouth just right. That way, you are 100% certain you do not have a pigtail connection problem. The other possible problem is that the condenser wire is grounding against the body of the distributor. (BTDT) Again, good eyes or a continuity check w/ a meter will resolve that. Lastly, don't forget that new points often come out of the box w/ corrosion, or you could have had grease on your feeler gauge. Run a new dollar bill or a brown paper bag through them to "dress" them.

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JMOR

12-02-2007 14:44:32




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 Re: 8N No spark in reply to Bruce (VA), 12-02-2007 14:24:45  
Bruce, I was recently adjusting the timing on a front mount and at the extreme of the adjuster, the pig tail lost contact with the screw. So, as you and others have said there isn't a lot of room for error here. In my case I lost contact, but while sorting that out, I observed that it is just about as likely that the pig tail short to the distr housing at the extreme of adjustment range. Some say center the adjust and live with it..... ..maybe there is a reason.

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JMOR

12-02-2007 13:48:30




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 Re: 8N No spark in reply to AJH8N, 12-02-2007 13:33:11  
Several things come to mind.
Placement of coil is fairly critical on front mounts, in order to get the pig tail spring that connects to points to make contact and for the High Voltage tab to contact the distributor cap contact. If, for example, while on the bench, you skipped the coil to distr gasket, that gives a little more travel downward by coil for the spring to touch the concave screw leading to points.
The rotor could have insulator material breakdown, thereby putting the HV spark to ground via distr shaft.
Likewise the cap could have insulator breakdown. Occasionally, a very careful eye can see a carbon like trace where the HV make a track across or thru the insulating material.

From what you said, coil makes spark, it is just not finishing the path from coil, thru HV tab to cap, thru rotor, back to cap thru wires to plugs.

So there are the items to look at: HV tab, cap, rotor, wires.

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AJH8N

12-02-2007 14:05:00




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 Re: 8N No spark in reply to JMOR, 12-02-2007 13:48:30  
I did have the gasket between the dist. and coil when bench testing, and did stretch the pig tail on the coil before putting it back on the tractor. I pulled the HV tab down to make sure it was contacting the cap The cap and rotor are only about a year old but I will take them back off and inspect them for carbon> the plug wires were also changed out last year. I just put in a new set of AL437 plugs.

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JMOR

12-02-2007 14:19:24




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 Re: 8N No spark in reply to AJH8N, 12-02-2007 14:05:00  
I re-read your post. You said you have 6 v at both sides of resistor & at key switch. Well, that's to be expected when points are open, BUT you should also check when points are closed. Bump with starter or rock tractor in gear enough to get points closed. Should see ammeter show a little, ~3 amp discharge. At this time should still have ~ 6 at key sw & input to resistor, but only about 1/2 that at coil side of resistor and top of coil. Now you know you have coil current.

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AJH8N

12-02-2007 15:27:48




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 Re: 8N No spark in reply to JMOR, 12-02-2007 14:19:24  
JMOR,
I checked the voltage at the resistor with the key on as I bumped the starter. On the coil side of the resistor the voltage would stay at about 6.3v after I bumped the starter 6-7 times I found a spot where the voltage was about .25 volts. I bumped the starter again and it jumped back up to 6.3 volts and after 6-7 more bumps It would find a spot and drop to .25v? The amp meter on the tractor used to show some - movement when I would turn the key switch on but now it does nothing, even when I bumped the starter. When I check the resistor with my multimeter set for amps I got .38 amps on both sides of the resistor? (I'm a rookie with the multimeter) How else can I tell if I have the right current to my coil. I have a new battery (6v) and I thought I had problems with the starter so I took it to the shop and they said it checked out. The old guy at the starter shop was pushing me to go 12v and took what was a good 6 volt starter selaniod(s?) and replaced it with a 4 post 12v selaniod that he said would work with 6v until I swap to 12v (I never told him to do that) Could that 12v selaniod be drawing to much juice? I'm lost.

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JMOR

12-02-2007 15:42:38




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 Re: 8N No spark in reply to AJH8N, 12-02-2007 15:27:48  
0.25v at coil side of resistor is way too small. I would look for a bad connection along the batt, key sw, resistor, wiring to coil. Possibly resistor is open or gone to very high resistance. Just to try & pin point the problem, jumper the resistor (in to out) and try starting. Don't bypass resistor more that maybe 30 seconds or you might over-current coil & damage it. If that doesn't work, try a home-run & jumper all the way from battery to coil (again keep the time short).

If the solenoid is making the starter run, I wouldn't be concerned about it.

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AJH8Nw

12-03-2007 06:16:38




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 Re: 8N No spark in reply to JMOR, 12-02-2007 15:42:38  
JMOR,
I tried the jumper wire from the battery to the coil and then I got spark to the plugs but when I remove it nothing. What does that tell me I need to check next? Does it mean I have a problem in the dist.?



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JMOR

12-03-2007 06:53:50




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 Re: 8N No spark in reply to AJH8Nw, 12-03-2007 06:16:38  
No, not distributor. It means you are losing the current (suffering a voltage drop) somewhere up stream of the coil. The places to look as I mentioned before are: resistor, key switch, wire between key & resistor, wire from key sw to solenoid's batt terminal(where everything except starter gets power).See the diagram (green path).
Turn on key, rock to get points closed (you did that before) and when voltmeter connected from top of coil to ground shows the 0.25v (if repeatable) or some other low voltage, then start working your way up stream, one step at a time. 1) voltage from resistor output terminal (the one going to coil). If it is vary nearly the same voltage as at coil, then that connection is ok. Next: 2) voltage at input side of resistor (should be very nearly full battery voltage or 6 v (if it is, then we have found a bad resistor or dirty connections to resistor (remove, clean, reconnect, re-measure), If the voltage in step #2 is NOT 6v but something very low, then the problem is further up stream toward the battery ( next step is Key Sw) 3)Key on, measure voltage at output of key sw and at input to key sw...should be very nearly identical at 6v, if not then bad key switch. If you have very low voltage at both in & out of key sw, then look still further upstream. 4) Trace wire from key input 3rd terminal on resistor terminal block, measure voltage, next, ammeter, measure IN & Out ammeter terminals (if no ammeter terminals & wire just passes thru loop on back of ammeter, skip ammeter measurements)then to solenoid battery terminal and measure voltage on that wire terminal, if 6v, then the wire in question or it's terminals are the problem, if still very low voltage at that point, then the only thing left in the path is the battery cable, but since starter motor run, it is not likely. OK, now you should see where the voltage disappears as you traversed the path point by point. In which ever item/component it was lost, temporarily jumper that item & try starting. Items were several wires, resistor, key, terminal block, ammeter, etc.

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AJH8Nw

12-03-2007 07:02:36




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 Re: 8N No spark in reply to JMOR, 12-03-2007 06:53:50  
Thanks again, when I get home I will trace it backwards like you described and try to find the culprit.



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AJH8N

12-02-2007 16:17:15




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 Re: 8N No spark in reply to JMOR, 12-02-2007 15:42:38  
JMOR,

I am trying to figure out how the points position affects the voltage on the coil side of the resistor? I am new at this tractor thing and I appreciate your help. I will try the temp. jumper to the coil and see if it gives me spark.



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JMOR

12-02-2007 16:51:57




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 Re: 8N No spark in reply to AJH8N, 12-02-2007 16:17:15  
See circuit diagram posted earlier. When points are open, nothing is happening. No current flow, no voltage drop. When points close, the circuit is closed so that a round trip path is created for the current (battery, thru green wires, to coil, thru coil's pigtail, points, and back thru metal structure of tractor to positive side of battery (full round trip). It started out at 6v neg and a little voltage is dropped (lost) in every element that the current flows thru, only a few tenths in wires, terminals, switched, with th majority of the 6v appearing (dropped/lost) across the resistor & coil, such that by the time current has traveled all the way back to the battery pos terminal, the whole battery voltage has been dropped/lost. You start out at the hose bib with maybe 60 pounds per square inch of water pressure, by the time the water (current) passes thru the hose, fittings, nozzle and winds up on the ground, all the 60 has been dropped/lost and the puddle on the ground is zero PSI (gauge). If you capped the end of hose so there was no flow, it would still be 60 # at end of hose. If points are open such there is no flow, then still 6v at end of path at open point contact.
Elementary my dear Watson!
HTH

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JMOR

12-02-2007 16:10:16




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 Re: 8N No spark, also.... in reply to JMOR, 12-02-2007 15:42:38  
third party image

I don't know how/where you had the meter connected fro this: "When I check the resistor with my multimeter set for amps I got .38 amps on both sides of the resistor? "

However, in order to obtain an ampere reading, the current must flow THRU the meter, i.e., the wire who's current is of interest must be opened and the meter inserted INTO the circuit. Nothing can be in parallel with the ammeter. See picture...current flows in green path to coil. Opportune points to insert ammeter are circles with "A" in them or anywhere in the green path.

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