lawn mower IGN coils

[dacflyer]

i work on mowers a lot, and from a rare time to time i get a bad coil, these coils are magneeto type with built in internal electronics.
some flywheels have 2-3 magnets in them, whenthe magnets fly by, they create the power needed to fire the coil.
its all self contained. nothing to adjust or change, but the whole coil itself.
you cannot even test the coils accuratly because of the internals..

anyone ever made or built a coil tester with a timeing circuit of sorts with magnetic coils to simulate the flywheel magnets flying by the coil

the coil looks like a open ended e-core. with a small metal pad that is the sensor for the fireing of the electronic ign inside, i am thinking that it senses the magnetic flux to trigger itself when to fire after it has enough charge in it,.or something like that..
any info is appreciated. just holding the coil in your hand and swinging a magnet by, near it does not seem to do the trick. Hmmm,,,

[MrAl]

Hi,


How about mounting some magnets to a disk and disk to a motor and hold the disk close to the
open end of the coil. As the magnets spin they will generate a voltage which can then be
measured and compared to previous readings. Ultimately the output could be viewed on
an oscilloscope.
The disk would be made from several magnets, where the poles are made to alternate.
That is, one magnet is mounted with the N face outwards, the next magnet is mounted
with the S face outwards, then N, then S, etc., repeating to fill up the circumference
of the disk.
Alternately two magnets mounted to a shaft, the two N's in one direction and the two
S's in the other.
You'll also need some way to set up the test so that the coil end is always the same
distance from the test disk magnet ends in order to get repeatability in the readings.
Perhaps mount the coil to be tested and have the disk/motor on a sliding platform
and measure the distance between the coil end and one of the magnets with a
feeler gauge.

If not using a scope probably a peak reading would be second choice.

[kheston]

I wonder if pulsing a big electromagnet in close proximity to the coil would do the trick? If it did, It would be less dangerous than spinning something would be.

[MrAl]

Hi,


I have to agree that an electromagnetic solution would be a bit better, although not as realistic.
The coil could be mounted close to the ignition coil to be tested. The input to the generator
coil could be controlled with a transistor bridge.

[dacflyer]

the coil idea sounds better to me than the spinning magnets..
was thinking something like 2 coils, possibly something like a center tapped fashion. ct being ground, and +- on the ends, and maybe somehting of a push pull vareity ?? just cannot think what to use as a driver...

[goingjag]

Hope I'm not being redundent to your own knowledge as I only dabble in these. My experience has been with clean magnets on the flywheel, and clean coil surfaces, and a coil adjusted close enough to the flywheel, I can simply rotate the flywheel back and forth while holding the plug wire and that gives me a good enough "hello" to tell me the coil is working. It's nowhere near what will be put out by a rope pull, but my rationale has been if I can feel a tingle with just a hand sweep of the flywheel, then the coil is good. Obviously the plug has to be removed so you can get a nice easy hand swing back and forth.

If you have been used to working with older model mowers, I found out the hard way that somewhere along the way mower makers realized they could make the flywheels much lighter (read cheaper) by making the blade a part of the flywheel speed mechanism using it's weight. In other words, if you don't have a blade mounted or the correct blade mounted on the mower, the timing of the spark seems to be out of sync. Some mowers will act like they have no spark, spraying some starter fluid can get you a nice arm wrenching backfire .

On older mowers that still have points under the flywheel cover, I will replace them with the newer electronic modules that can't be fouled by oil sneaking in. Bottom line, clean/electronic "points", clean flywheel, clean/adjusted coil equals a jolt to the hand unless a wire is broken or shorted in the ignition/shut off mechanism or as you point out very very very rarely the coil has been cooked.

Good luck.

[CeaSaR]

My experience w/small engines has been with the point variety. As long as the plug sparked,
the coil was good. Hand cranking/spinning was usually enough to see a spark with the plug
pulled and resting against a decent ground.

Funny you should mention electronic ignition. My old B&S used points and I would gap them
every year or two. If the flywheel key would shear, even the tiniest bit, the engine would
run rough or not at all (shear key sets the timing). Obviously I would check them when I had
to replace the shear key also. I got tired of setting the gap so I bought a B&S drop in electronic
module that replaced the condenser, effectively turning the points into a low voltage switch.
The thing worked great for a couple of years, but then started dying on me. Switched back to
the original configuration and never looked back.

Yes, you should always clean the flywheel and coil ends in addition to checking for corrosion
or rust at any and all mounting or electrical contacts. Your coil should have a slight bit of play
in the mounts to allow for gapping to the flywheel. Lastly, always inspect the plug for burn quality
and to make sure they have not fouled or grounded the tip. Keep them clean, lubed and adjusted,
and a small engine should outlive any deck or frame they are mounted in/on.

CeaSaR

[dacflyer]

i been working with small engines over 25 yrs now,, had lots of exp.
the suspect coil would fire, but it only fired as if the timing was off.. it only backfired thru the carb, indicating oo much pre-ignition.. i replaced it with another coil, and the motor fired right up.
i noticed that the replacement coil fired more spark than the other coil.

and as with the electronic coils, i really do not care for them unless the top crank has some wear to the point that the points style cannot keep the points gapped.
the other reason i do not like them, is they will not fire well unless they get a good pull.. with points style i loved them, because the engine would fire and or run at lower rpms,

but anyway i know for sure that the 1st coil was bad, even tho it did spark. just for giggles, i put the old one back on.. same thing..so back with the replacement one and it fires right up!

[CeaSaR]

Sometimes the replacement method is the quickest, as long as you have a
Known Good Part.

CeaSaR

[Lenp]

In a post long ago I mentioned coil ringing with an 'o' scope. I'll bet that would tell something that a meter wouldn't!

The problem I've had is mice chewing the HV wire right at the coil! Many Kohler coils can be repaired if you use a Dremel to clean the bad wire from inside the HV well. There's a pin in the middle so be careful. Square cut the new wire, coat the jacket with adhesive and push it all the way back into the well. 2+years and still sparking!

Len

[Robert Reed]

Ceasar
Interesting you should mention that about the flywheel key. Ages ago, that key was steel and when an obstruction was hit hard enough to stop the mower dead in its tracks, it generally would bend the crankshaft due to the fact that the flywheel still kept moving ( a very small amount of rotation) after the blade was dead stopped. This put a twisting torque on the crank at opposite ends and did its dirty deed.
Some years after that ,one of the design engineers came up with the aluminum key. This would break away due to that torque and releive damage that would be done to the crank. My first experience with the 'new' key and the first time I hit a rock and stalled the mower, I could not restart it. It took many hours of trouble shooting to locate the culprit which was as you discussed- a bent but not sheared aluminum key.
This has happenened several times since then over the years and the first thing I look for in this situation is a bent key (or sheared key). In all instances, I have to remove the flywheel to examine the key as the damage to the key is so slight I cant see it with the flywheel still attached. All of these damaged keys had only a slight bend in them which is more of an offset and only by maybe 0.50" of an inch. The only thing occurring here is that the timng is thrown off slightly and preventing restarting. I am still amazed that this slight offset in angular rotation can completely kill the engine.

[CeaSaR]

Robert,
That's exactly why they went to aluminum. Keys are a heck of a lot cheaper than
a crank and any associated other parts that may have been damaged. I think you
missed a "0" there, 0.050", as 0.50" would be a completely sheared key.

LenP,
I vaguely remember that post, year and a half ago, maybe two?
Aren't mice a real b*t*h when it comes to rubber coatings? Good thing to know
about the Kohler's coil.

Dac,
Maybe you could use one of those little neon bulbs (NE02?) connected to the
coil wire to test them with a spare flywheel (from an old junker - gotta be zillions
around) in a jig. Hand speed ought to be enough to light one up. Bad coils would
show as weak to non-existent lighting. Sort of like an old AC outlet tester.

CeaSaR

[MrAl]

i been working with small engines over 25 yrs now,, had lots of exp.
the suspect coil would fire, but it only fired as if the timing was off.. it only backfired thru the carb, indicating oo much pre-ignition.. i replaced it with another coil, and the motor fired right up.
i noticed that the replacement coil fired more spark than the other coil.

and as with the electronic coils, i really do not care for them unless the top crank has some wear to the point that the points style cannot keep the points gapped.
the other reason i do not like them, is they will not fire well unless they get a good pull.. with points style i loved them, because the engine would fire and or run at lower rpms,

but anyway i know for sure that the 1st coil was bad, even tho it did spark. just for giggles, i put the old one back on.. same thing..so back with the replacement one and it fires right up!

Hi again,


Ok, what this means is that some form of calibration would be needed regardless of the test technique used (mechanical or electrical).
You'd have to take some measurements and determine some go/no go criteria.

If you use the spinning magnets, you most likely would set it up to be the same diameter as the flywheel, with the
same magnets, and with a variable speed motor where you could find out what speed makes the coil under test
work the way it should.
If you use the driven coil technique, you would have to do the same only you would vary the frequency of the pulses
but you'd also have to determine the pulse amplitude too.

To drive a center tapped coil you would connect the center tap to +Vcc and drive the two coil leads with MOSFETs
that switch to ground. There are issues that come up with this technique too though, such as spikes and current
ratcheting. To clamp the spikes you need snubber circuits. To stop the current ratcheting you need enough series
resistance (without too much) and accurate pulse widths that sometimes have to be fine tuned with a special kind
of feedback circuit, although sometimes for low power like this you can get away with a simple self oscillating
'converter' type circuit although adjustment might not be as easy.

Either way is going to require some calibration.

[Joseph]

My Central Park mower with the electronic Briggs and Stratton coil assembly one day would no longer start. Examination of the coil revealed a crack in the plastic over the winding. I've seen flyback transformers on TV sets fail after such cracks have formed.

[dacflyer]

well like i said, this coil i had was fireing, just not at the right time for some reason..
and yes the flywheel key is good..
weirdest problem i ever had..

LENP >> these coils are not possible to ring because they have the electronic modual in them, and everything is sealed except for the HV wire and the kill switch connection.

now the old coils that had points, you could ring them easily.
self contained ones,, forget it..