8N doesn't sustain spark

Windancer

New User
On again off again problem for a couple of years. Doesn't start. Went thru carb. Narrowed down to no spark. Trouble shot the ignition system many times.
Changed and rechecked coil, condenser, points, ground etc. etc. New coil today. 12.8-9Vs at switch, upstream of ballast resistor. 9+ volts downstream of
ballast resistor to coil terminal. Checked grounds, checked continuity open/close points. After new coil, today it started right up, adequate visual spark
on spark plug wire aux jumper device. Sparked and ran good for about three minutes then died. No spark. I'm at the end of my knowledge, experience and abilities.
 
Hi Windancer, welcome to the forum. So, you've been fighting this for a couple of years now. Intermittent troubles are difficult. Two questions to start off.
1. Do you still have 9 volts at the top of the coil?
2. Have you tried bypassing the ignitions switch?
One other thing, it's obviously a 12 volt conversion, are you using a 12 volt coil?
 
(quoted from post at 15:15:05 08/19/22) On again off again problem for a couple of years. Doesn't start. Went thru carb. Narrowed down to no spark. Trouble shot the ignition system many times.
Changed and rechecked coil, condenser, points, ground etc. etc. New coil today. 12.8-9Vs at switch, upstream of ballast resistor. 9+ volts downstream of
ballast resistor to coil terminal. Checked grounds, checked continuity open/close points. After new coil, today it started right up, adequate visual spark
on spark plug wire aux jumper device. Sparked and ran good for about three minutes then died. No spark. I'm at the end of my knowledge, experience and abilities.
lmost 4 volts across ballast res sounds high. What is coil primary resistance? What is resistance of ballast res? Is ballast resistor white ceramic or the factory wire wound with 3 terminals & 2 mounting screws?

This post was edited by JMOR on 08/19/2022 at 01:55 pm.
 
Will double check voltage at top of coil (Maybe tomorrow. Frustrated enough today). I think I might have previously bypassed the ballast resistor.
Coil is new from Steiner 12V (probably for Asia) It's my second coil now. Last year when wouldn't run I put the coil that came with tractor. It ran.
I will consider bypassing the key switch. Thanks
 
JMOR: Will check resistance in coil and ballast resistor (tomorrow) . I could bypass ballast resistor and send 12V to coil post, yes?
 
Look like this? yes/no? You can temporarily bypass resistor, but if you leave it bypassed long at all, the current will be so high as to damage the front mount coil. OK for a few moments for a trial start. Greatest danger to coil is bypassed res and leaving key on , points closed (not running or cranking).
o9LCKsS.jpg
 
(quoted from post at 17:34:56 08/19/22) Sorry but what is 12250?
t is the ballast resistor assy/terminal block pictured. I never remember the prefix & suffix for the earlier & later units , so just call them all 12250. One is A8NN12250B.
Only difference in the years is mounting hole differences.
 
OK, this might get long and loud. We know you have an early 8N with the front mount distributor. You also indicate using a 12V system, but, just because your battery is 12V don't assume you are wired correctly for it. So, was the distributor rebuilt, tested, and mounted correctly? If mounting gets forced down 180 DEG off, at power up it will bust the aluminum base and render it scrap metal. At that point it may try to fire up but will have issues trying. You'll need a new base, but can pull out old guts and reuse or swap out with another good, full base. Next, ...New coil today... Did old one test bad STATIC? 6V unit, VOM set to OHMS, pigtail to terminal post should be about 1.5 OHMS. Did you test the new coil to ensure it is a 12V unit? Don't assume. Next: OEM BALLAST RESISTOR, Assembly p/n A8NN-12250 includes mounting block and screws, about $30, or you can just get the resistor unit, p/n 9N-12250, about $6, and replace if insulated mounting block is OK. Mounting screws are different for the 9N/2N and the 8N, but the resistor is the same. I think nowadays they offer a kit that will fit all models. But, don't just start buying new parts and replacing without testing first. Next: 6V and 12V Coil. The front mount system requires the Ballast Resistor as shown regardless if 6V or 12V is used. If you choose to use 12V and keep your 6V coil, then you need to add an inline 1-OHM resistor to the coil circuit as shown. You can delete then extra resistor simply by replacing the 6V coil with a 12V coil. Next: WIRING. Verification required. Get the wiring diagrams and begin tracing the wiring. First, I advise to disconnect the battery and the lights, if any are used. Lighting kits were never a factory feature, only a dealer optional accessory, and many guys wire them wrong. You will use your VOM set to CONTINUITY for testing the wiring. Do not use an Idiot Test Light. Also do not use wire color codes to ID/Trace wires. Colors do not conduct electrons. Chances are your original wiring harness has been replaced. Many new aftermarket harnesses are cheap, vinyl covered ones, and most are not color coded as the OEM. There are OEM exact-as-original wiring harnesses available, but always use a VOM anyway. Next: Preliminary Testing. Once wiring and distributor are verified to be correct, perform a simple test at the coil. You can connect the battery, but do not activate ignition switch. Set VOM to VDC. Take a reading of battery voltage and note it. Then place one probe of VOM on the left terminal of Ballast Resistor viewing from behind dash. Place the 2nd probe anywhere on metal ground. Turn key ON but DO NOT press stat pushbutton and activate engine. Reading should be battery voltage with points open, half that with points closed. The Resistor LH terminal is the coil wire. You are testing to see if you are getting power to the resistor. Now repeat method only place 2nd probe on the top of the lone terminal post where the coil wire connected to the previous LH resistor terminal. Got power, same reading? No? Problem is most likely in the distributor and points. Its time to R&R the distributor. Now before you start troubleshooting the electrical system, if the carb is working fine, leave it alone. If carb has issues, I advise to perform the Fuel Flow Test first with a cold engine. If carb passes, leave it. If it fails, start with the usual fuel flow tests, then if problem not solved, time to rebuild the OEM M/S unit or swap it out with one already rebuilt but there is no need to go buy a newer Cheena made junker one. When doing a carb rebuild, set adjustment settings to specs as outlined in the Manuals. Many non-starting issues are blamed on fuel and end up being an electrical issue and vice versa. Most turn out to be an electrical issue due to incorrect wiring regardless if a 6V or a 12V setup. Incorrect 12V switch over jobs are a big culprit and incorrect lighting attribute to the problem. There is nothing wrong with using the OEM 6V/POS GRN system and likewise, there is nothing wrong with using a 12V/NEG GRN setup as long as you understand each and if they are wired correctly. Avoid just switching from 6V to 12V if a non-starting issue occurs and you think or someone else has told you to go to 12V without first diagnosing the problem. If it isnt running on 6V, what makes you think it will on 12V? I wont even discuss EI here. Whichever electrical system you choose, do it right and for all the right reasons. On 12V you will have faster starting which helps with a worn engine and in cold weather. You will also have brighter lights on 12V and can run your 8-TRACK player and other 12V equipment like a sprayer as well. Finally, whether using 6V with a GEN and a VR or using 12V with and ALT and NO VR, you must use a fan belt tensioning device otherwise you will never charge the battery.


HOW TO SET TIMING ON THE FRONT MOUNT UNIT:
nM5tfJNh.jpg

RESULTS WHEN UNIT IS MOUNTED 180 DEG OFF:
fqKAmFuh.jpg
UwHSwizh.jpg

FORD 8N-SERIES TRACTOR OEM 6V/POS GRN WIRING PICTOGRAM:
TBC19a5h.jpg

*PICTOGRAMS courtesy of JMOR

12 VOLT SWITCH OUT WIRING:
noSTej6l.jpg
xQ2ojiTl.jpg
2KkQjBal.jpg

AFTERMARKET EXTERNAL 1-OHM CERAMIC RESISTOR REQUIRED WHEN USING A 6V COIL:
XRLi3vSl.jpg



FRONT MOUNT 6V COIL BASIC STATIC TEST:
BCAtemml.jpg
*NOTE - VOM MUST BE SET TO OHMS. FOR A 12V COIL, READING APPROX DOUBLE

FORD OEM BALLAST RESISTOR -USED ONLY WITH FRONT MOUNT DISTRIBUTOR:
swlv82hh.jpg
FIK0D4Ih.jpg

HELP: The LH resistor Terminal Post connects to the COIL Stud Terminal Post as you face the back off dash. OEM Wiring is RED.


FORD TRACTOR FRONT MOUNT DISTRIBUTOR FIRING ORDER; 1,2,4,3 CCW:
Tbt5WvEh.jpg


Breaker Points/Front Mount = .015; Spark Plugs Champion H12 or AUTO-LITE 437 14mm gap at .025-.028; Firing Order: 1, 2, 4, 3 CCW.



FORD 8N TRACTOR ESSENTIAL OWNER/OPERATOR/PARTS/SERVICE MANUALS:
qI9P22kh.jpg

Tim Daley(MI)
 

We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today.

Back
Top