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Kickback starting my BN with a mag

N

NormS

Member
I have a 48 BN that has mag ignition. In the summer the engine starts fine, occasionally however, it will kick back when starting it but it always starts. When it gets cold however, this tractor is almost impossible to start because it kicks back so severely. Even with my 12V conversion many times it will simply not start, it just continues to kick back on every cylinder. I"ve checked the timing many times, the mag is impulsing right on TDC, I"ve even made the adjustment slot longer so that I could retard it more, still does the same thing. I"m considering converting to distributor ignition to solve this problem if I can"t figure it out. Any ideas would be welcome.

Thanks

Norm
 
Are you sure it is at TDC? Have you found the marks on the flywheel? Maybe the 12volts are turning it so fast that the impulse isn't catching.
 
Yes, I'm sure I have the mark on the FW, I've cleaned it up and marked it with yellow crayon. It even kicks back if I use the crank, a very uncomfortable thing!

Norm
 
Well, if it kicks back it has to be firing before TDC. If you can't retard it by turning the mag, I would guess the gears ( governor to cam)are not timed right.
 
i've run across flywheels with multiple marks...pull all your spark plugs and stick a pencil in #1 plug hole and SLOWLY rotate engine using fan while watching pencil...it will rise out of plug hole and then start to drop...turn fan back and forth till you have it at the top of pencils travel...then check your mark on flywheel...then pull cap off mag and make sure rotor button is pointing at #1 plug wire or at the plug wire 180* across...there are 2 TDC's on a 4 stroke engine...the valves on #1 should be closed when 1 piston is at TDC and rotor button is pointed exactly at #1 plug wire on cap.
 

You said you conv.to 12 volts did you change the starter if not it is turning the engine to fast and the mag impules will not work, ie fires to early
 
I agree with Teddy. If it kicks back thats because shes firing BEFORE TDC, if its a JD BN and iffffffff the flywheels on the right crank spline and ifffffffff cam to cranks in time and ifffffffffffffffff cam to govenor is in time, when the left pistons at TDC the flywheel slot is flat horizintal fore n aft and the open female slot in govenor shaft end (where mag mates) is also flat horizontal fore n aft. if notttttttt one of those above mentioned or more are out of time. To avoid kickbak she has to snap n fire at TDC but if before shes gonna bite you.

If its NOT a Deere BN ignore this other then shes still firinG BEFORE TDC

If????? it still does it even at hand crank RPm thats NOT due to a starter spinning it so fast the impulse isnt working. i.e. I doubt youre cranking it faster then 250 RPM. If its a 6 volt starter and a 12 volt battery she may be turning fast enough that the impulse isnt working in which case she will fire at like 25 BTDC AND KICK BACKKKKKKKKKKKK

BUTTTTTTT in winter she cranks slower then summer and you indicate its more a cold thing so that kinda shoots that theory out some

John T
 
I agree with Teddy. If it kicks back thats because shes firing BEFORE TDC, if its a JD BN and iffffffff the flywheels on the right crank spline and ifffffffff cam to cranks in time and ifffffffffffffffff cam to govenor is in time, when the left pistons at TDC the flywheel slot is flat horizintal fore n aft and the open female slot in govenor shaft end (where mag mates) is also flat horizontal fore n aft. if notttttttt one of those above mentioned or more are out of time. To avoid kickbak she has to snap n fire at TDC but if before shes gonna bite you.

If its NOT a Deere BN ignore this other then shes still firinG BEFORE TDC

If????? it still does it even at hand crank RPm thats NOT due to a starter spinning it so fast the impulse isnt working. i.e. I doubt youre cranking it faster then 250 RPM. If its a 6 volt starter and a 12 volt battery she may be turning fast enough that the impulse isnt working in which case she will fire at like 25 BTDC AND KICK BACKKKKKKKKKKKK

BUTTTTTTT in winter she cranks slower then summer and you indicate its more a cold thing so that kinda shoots that theory out some

John T
 
If you can't get it to fire AT (or just after) TDC and are at the end of the adjustment slot, the governor/mag drive is not correctly timed to the camshaft.
 
OK, let me add a bit of additional info. This is a Farmall BN (sorry, I didn"t know there was a JD BN!). I overhauled this engine myself three years ago and whil anything is possible, I am confident that I aligned the gears correctly when reassembling - however, anything is possible and it could be off a tooth. As for checking the marks, I have put a screwdriver in cly #1 and verified that I have the TDC mark on the flywheel and when I check the timing, the mag trips right at TDC.

As I stated earlier, the problem is much much worse in winter, and happens when I use the starter or when I hand crank. It"s almost as if the mag trips earlier the colder it gets. The tractor runs excellent otherwise.

Thanks guys for all your input.

Norm
 
You are off base so how does it fire when it is running. The 12v will not make it turn too fast to make it start. Just how many have you worked on and made them start.
 
It's possible the impulse mechanism is "gummy" and sticks in the no impulse/advanced timing position when temps get cooler.

That would definitely explain the kickback when using the starter, but at hand cranking speeds it would take a GOOD mag to make enough spark to fire the engine WITHOUT the impulse functioning!
 
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