Lost spark again after changing points

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marshall
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Lost spark again after changing points

Postby marshall » Sun Jul 03, 2022 7:05 am

A couple weeks ago you all helped me diagnose a problem with my electrical system. I replaced the points and condensor correctly and the tractor was back in action for a couple hours of mowing. Then a pulley fell off my PTO and I had to deal with it and the tractor sat for 10 days. After fixing the pulley and putting a few new knives on the sickle bar, I try to start it and its a huge struggle. Finally it comes to life and seems to be running OK. I engaged the PTO, the sickle ran for a couple seconds, the engine died. Now it really won't start. I cleaned out the fuel bowl, carb jet, checked that distrib cap is dry. But it only cranks and there's now no hope that it ignites. I checked spark at the plug. No spark. How does this happen...

I'm mystified. Does anyone have ideas of what could be going on here? How could adding the load of the PTO cause the engine to die and no longer spark. Maybe just a coincidence?

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Re: Lost spark again after changing points

Postby Mht » Sun Jul 03, 2022 7:15 am

I would revisit the points. Maybe they were not tightened well and they moved or wire to coil or condensor came loose. It’s possible the new condensor failed and the points burned. Easy to check and always the first thing I check in a no fire situation

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Re: Lost spark again after changing points

Postby tst » Sun Jul 03, 2022 8:33 am

check point gap 1st

Eugene
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Re: Lost spark again after changing points

Postby Eugene » Sun Jul 03, 2022 8:50 am

And then, points open, check for battery voltage at terminal on side of distributor. Disconnected wire?

Wrong information. Original poster indicated a magneto after my post.
Last edited by Eugene on Sun Jul 03, 2022 2:18 pm, edited 1 time in total.
I have an excuse. CRS.

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Re: Lost spark again after changing points

Postby Jackman » Sun Jul 03, 2022 8:58 am

And wipe points clean with a piece of light cardboard (like old match book cover)

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Re: Lost spark again after changing points

Postby Waif » Sun Jul 03, 2022 10:12 am

You killed it under load.
Highest stress on components.
A weak spot failed. Or weak circuit / system.

After reviewing and knowing your ignition is clean and to specs as mentioned , check air and fuel balance.
Conking out under load with vacuum involved can continue the draw. Be sure air cleaner and throttle plate both work right.

Heat is hard on magneto coils if that is what you're running.
Fan and radiator need to be working right and heat able to dissipate. Every time I conk out the 48's coil , it is under load and running hot.
It'll sputter out and don't bother trying to restart it if it doesn't fire up in a few seconds. It'll need to set until cooled off.
And yes I've replaced the coil.
Only to heat the replacement up under heavy load in the summer heat till one day it too conked out.
A hand placed on it hints of it being roughly well above 120 degrees. Hotter than electric motors tend to average anyways.

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Re: Lost spark again after changing points

Postby marshall » Sun Jul 03, 2022 12:26 pm

I took off the magneto cover and everything seems in order. I used some fine sandpaper on the points and then cleaned the surface with some absorbent paper so they have to be fine. I decided to try cranking the motor with the magneto cover off so I could observe the points to see what kind of spark I'm getting there. Here's what I'm observing:

1. At best, a tiny spark that is barely perceptible unless I'm looking into the gap at a perfect angle. It doesn't seem like the spark is happening regularly, but this could just be my angle and the fact that its so small. I'm doing this in daylight (with cardboard box helping to block incoming light). Can't even capture it on video.

2. As the engine turns it really looks like the points may be closing to tighter than the gap that I set at 0.013 with the rotor pointing at #1 plug with cam lobe on the high point of the D-shaped shaft. Each time I stop the engine after cranking the point gap is a little different and there have been times where they are closed more than 0.013 from the looks of it. For reference on whether my points were installed correctly, please see: https://marshall62.github.io/cub-point-install/ which I made as a help guide for others who struggle with poor eyesight and fumbling fingers and having to make repairs in the field.

So I don't know what to make of this spark. Is something tiny and white about what one would expect or should there be something larger and more discernible?

As an aside I've set myself further back by cranking the engine with magneto apart, right? I guess I now have to learn how to set the timing on the engine now that I've cranked it with the cover off but maybe this doesn't need to happen until I've located the source of the problem (coil replacement?). Any good step-by-step instruction videos or picture sequences that you can refer me to.

As an alternative to going through the timing setup, based on my photos in the website above, I wonder if I can just rotate the fan until it is exactly like it was when I set the point gap and then reinstall the mag cover with rotor at #1. Seems like there's a 50% chance I get it right based on there being two D-shaped sides on the magneto shaft and maybe I can figure out the particular one that is facing the breaker arm from my shots. Or is this too simplistic a notion?

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Re: Lost spark again after changing points

Postby Dale Finch » Sun Jul 03, 2022 12:55 pm

I just have 2 observations, both from your posted guide:
First, I might be wrong, since I only have battery ignition, but I'm pretty sure the stationary/adjustable point is held in place with ONLY a screw, without a lockwasher. Trying to set that small screw in a slotted hole would be difficult with a lockwasher.

Second, I'm also pretty sure you cannot set the points gap until you have secured both sides of the insulated terminal. Otherwise it would be able to move.

Maybe these two things aren't significant, but just a thought. Good luck!
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Re: Lost spark again after changing points

Postby marshall » Sun Jul 03, 2022 5:22 pm

From looking at the design of that mag shaft with D-shaped cams on both sides, if you gap the points such that the high-point of the D side is in contact with the nub on the breaker arm, then this is the MAXIMUM gap the points will achieve during the cycle. So that is 0.013". As the shaft rotates and the nub slides down the cam, the points narrow. When the nub slips off the cam and the shaft to 1/4 from the D high-point, there is no longer contact between the breaker arm nub and the shaft and the points are closed (in contact). They reopen again to full gap at 1/2 turn from the beginning point when they are again on the high side of the opposite D. Now that there's a little less sun, I do see a spark in that gap. It's small but there. I'm guessing the bigger spark would be found from the coil cable to the center of the distrib cap, right. This would be the high voltage spark that is distributed to the plugs. So maybe this spark at the gap of the points is enough to indicate voltage???

Dale, your second point about setting the gap before I put the nuts on is a good one. Looking at the pics I see a bit of a gap under that insulator so maybe the points aren't gapped right. I'll reset the gap but am not optimistic that I'm going to get it started up from a gap correction.

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Re: Lost spark again after changing points

Postby Glen » Sun Jul 03, 2022 6:40 pm

Hi,
Too bad the engine quit running.

The points should open the same amount on both of the high places of the cam.

Yes, the spark between the points should be a small spark.

By turning the engine many times with the cover over the points off, you have lost the right position that the rotor should point.
Since you have done that, you can check to see if the points open the same amount on both parts of the cam.
Use your feeler gauge, and see if they are open to .013" when on the highest place on both parts of the cam. Turn the engine so the point rubbing block is on 1 highest place, measure the gap, then turn the engine so the rubbing block is on the other highest place, and measure the gap.

If there is a difference, probably the cam has worn slightly.
It's not a problem, unless there is enough wear that the point opening is much too small.

You could write what measurements you find.

Here is info for putting the point cover back on, with the rotor pointing to the right cylinder post on the cap.

You need to figure out where the engine is turned, to put the magneto cover on with the rotor facing to the right cylinder post on the cap.
The engine will not run with the rotor facing the wrong cylinder post.

You need to turn the engine, so it is at number 1 cylinder Top Dead Center, or TDC.
This means it is turned to the place where number 1 cylinder will fire.

Below is a page from the 1949 Cub owner's manual, telling about timing the engine.
Do what paragraph 2 says to find number 1 cylinder TDC.
Use Only paragraph 2, do not change the magneto timing now.

http://farmallcub.com/rudi_cub/www.clea ... age-32.jpg

When you have turned the engine to number 1 cylinder TDC, turn the rotor so it is pointing straight up, and the D shaped hole and shaft should go together. :)

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Re: Lost spark again after changing points

Postby phill_mi » Sun Jul 03, 2022 7:23 pm

I am in the process of doing this for the first time myself (and waiting for parts), but in your photo labeled "insert post in mag..." it looks like the lip on the insulator is on the top, whereas I expected it to be on the bottom to protect against contacting nearby base metal. Regardless the question in my mind is: Are the wires on that post grounding to the case? I would remove the outside "kill" wire temporarily and use a continuity checker or ohm meter to check the bolt to the case of the mag when the points are open. If there is a short look for the cause around that bolt as it has to be insulated from the mag case. As stated the spark at the points should be very small, as that is the low voltage primary circuit of the coil. The big spark should be on the secondary at the output of the coil (or rather at the sparkplug). If you have the "kill" wire removed, make sure you have a path for the secondary to discharge through a spark plug if you turn the mag and get the click. Timing the mag is pretty straight forward but it starts by making sure your #1 is at TDC on a compression stroke. I have the valve cover off so it is pretty easy to tell when #1 is TDC, but putting your hand over the sparkplug hole is the more typical approach.

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Re: Lost spark again after changing points

Postby Glen » Sun Jul 03, 2022 7:55 pm

Hi,
If you need to replace the magneto coil, it is not hard to do.
It is under the cover on top of the magneto.

Below is a listing at TM Tractor for a new magneto coil. You can look at the pic.

http://www.tmtractor.com/new/el/713fp.htm

There is a metal bar through the center of the coil, keep the bar from your coil and reuse it in the new coil. They have said on here that a replacement bar is hard to find.

The cover over the points has to be off to replace the coil. The small wire connects inside the magneto.

Dale said above, and I agree, the screw for the adjustable point doesn't use a lock washer.
The lock washer might make the point move around as you tighten the screw, as the washer compresses.

I don't take the metal post out of the side of the magneto, or a Battery Ignition unit, to change the points. Just loosen the 1 nut inside the unit, and the point and the spring slide out.

I think the nuts on the post in your last picture in your post above are assembled wrong.
The parts manual pic for the magneto doesn't show it too good, but does show on the outside of the unit, like on the Battery Ignition unit there is an insulating washer 1st thing next to the insulation, then going outward, 1 flat washer, then 1 nut. Then the wire, then 1 lockwasher, then 1 nut.

Below are pages from the Cub parts manual of the magneto, if you need them.
You can see the coil in the pic. :)

http://www.farmallcub.info/manuals/cub_ ... 012-22.jpg

http://www.farmallcub.info/manuals/cub_ ... 012-23.jpg
Last edited by Glen on Wed Jul 06, 2022 5:30 pm, edited 1 time in total.

marshall
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Re: Lost spark again after changing points

Postby marshall » Mon Jul 04, 2022 9:17 am

If you need to replace the magneto coil, it is not hard to do.


I replaced it about 3 years ago. With shipping, it's a $70 purchase. Can I test it with a digital multimeter to isolate that the problem is indeed the coil or does one just have to buy a new one periodically and hope that it fixes things?

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Re: Lost spark again after changing points

Postby marshall » Mon Jul 04, 2022 9:23 am

phill_mi wrote:I am in the process of doing this for the first time myself (and waiting for parts), but in your photo labeled "insert post in mag..." it looks like the lip on the insulator is on the top, whereas I expected it to be on the bottom to protect against contacting nearby base metal. Regardless the question in my mind is: Are the wires on that post grounding to the case?


Maybe someone else knows. The reason I use the lip upward is so that, along with the square washer which also has a lip, the two kind of form a sandwich that contain all the other elements so that they can't twist around the shaft. This is especially true of the breaker arm which you want to be aligned correctly.

The plastic insulator on the inside of the magneto and the rubber washer on the outside should isolate all the elements on this post from the magneto case (ground). I wish that insulator was made of a hard rubber because then it would be more tolerant of tightening those nuts on the post. Be very careful at that stage because that insulator cracks if you get too ambitious about getting things really tight.

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Re: Lost spark again after changing points

Postby marshall » Mon Jul 04, 2022 11:31 am

Are the wires on that post grounding to the case? I would remove the outside "kill" wire temporarily and use a continuity checker or ohm meter to check the bolt to the case of the mag when the points are open. If there is a short look for the cause around that bolt as it has to be insulated from the mag case.


I used my ohmmeter. The post is definitely isolated from the case. Put on an extra rubber washer on the outside to be certain.

NB: You can't do this test with the coil or condensor attached to the post b/c those are attached to the case.


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