Ignition Coil (module) Resserection

[Jiles]

I cannot take credit for this because I didn't discover it.  I guess I just thought it was well known. Might be that that person is a member here and can elaborate more:
I bought a Makita DPC7311 Concrete Saw that wouldn't run. I found the ignition coil was bad and was shocked to discover it cost $145.00 new. In several weeks, I did not find a used one, so I bought a "junk" saw with hopes of receiving a good coil.
Not to be--that coil was bad also, so I kept looking.
Then I read an old post, in another forum, describing how to SOMETIMES Revive a defective coil.
Of course this will not work everytime because if the coil is "fried" ---it won't.
His suggestion was to remove the spark plug and also to lubricate the cylinder wall, and make sure the clearance between the flywheel and coil is correct---app. 012. Proceed to spin the flywheel with an electric drill, at about 2,000 rpm, being sure rotation is in the right direction. C/C in most cases. Flywheel may have to be spun for a length of time but I had results within a few seconds from a DEAD coil. Be aware that you will be loosening the flywheel nut by rotating counter clock wise.
I am fortinate  that I have a Lathe and it is a simple matter to set the components up and run the procedure.
As I stated, I had TWO dead coils and this worked on both and the saw has continued to work.
These modern day coils are complicated because many change the engine timing and also limit the maximum rpm.
Much better then a point type ignition because at 13,000 rpm there would be "floating" and other problems.

[AdkStihl]

 

How does this revive a dead coil?

[Jiles]

I have no idea---I just know that it has worked for me, as well as the original poster that discovered it. The first one that I set up in my lathe was completely dead. No spark at all, checked with a new spark plug. I stood there and watched the coil come back to life in app. thirty seconds.
I would like for someone to inform me as to how an ignition coil advances the ignition??? I am only familiar with vacuum advance or computerized ignition systems.
These modules must be computerized??

[joe_indi]

How does this revive a dead coil?

How this possibly could revive a coil might be something similar that is used to revive dead Nicad cells.
In most cases it is not the winding in the coil that goes bad, it is the silicon content, such as the thyristor and stuff.
These go bad by way of a short inside .
In the case of Nicad cells they went bad because of a short(circuit) inside. The remedy was to 'electrocute' the cell using a very high momentary charge that would break the short circuit.This was achieved by using a high value capacitor for delivering that charge.
In the present case the spinning in reverse would cause a reverse flow of current. I know its AC current but the pulses would be reversed and could 'beat' down that short in the Thyristor or other components inside.
That is what I would think happens until somebody gives another explanation.
Joe

[Jiles]

The flywheel is not spun in reverse--it is rotated in the run direction. I am sure that would make a difference.

[AdkStihl]

I have no idea---I just know that it has worked for me, as well as the original poster that discovered it. The first one that I set up in my lathe was completely dead. No spark at all, checked with a new spark plug. I stood there and watched the coil come back to life in app. thirty seconds.
I would like for someone to inform me as to how an ignition coil advances the ignition??? I am only familiar with vacuum advance or computerized ignition systems.
These modules must be computerized??

taken from a STIHL shop manual:

Ignition timing is fixed and is not
adjustable.
Since there is no mechanical wear in
these systems, ignition timing cannot
get out of adjustment. However, an
internal fault in the circuit can alter the
switching point in such a way that a
spark test will still show the system to
be in order although timing is outside
the permissible tolerance. This will
impair engine starting and running
behavior.


EDIT: the only way I know how to advance timing on a saw is
          to advance the flywheel by filing the woodruff key. 5* is a magic number

[Al_Smith]

Well again my 2 cents worth .All mags work the same the only difference being the way they are triggered .

With points they act like a switch .A solid state works with a type of transister which in effect is a switch .

Some solid state ignitions can self advance and some cannot .

As far as winding one up to kind of regenerate  them probabley  it would work.  The faster the magnets pass the coil lamenations the more voltage it generates  .Up to a point is reached termed coil saturation at which time the max voltage will go no higher .

I think on a normal pull start the speed has to equate to something like the equal of 400 to 600 rpm of relative speed .Winding one up with a drill motor obviously would generate a higher voltage and probabley have same effect as what they used to do with a big coil and a batterry on antique coils of old tractors .

I forget the exact term but in theory it caused a little residual magnetism in the lamenations .Which it would be my guess this winding the thing up would probabley do also .

Now as far as the points bouncing ,perhaps but it's never happened to me .Just as general information I have a souped up 70 cc McCulloch with points that will turn 15,600 WOT and it never has missed a beat .

[bandmiller2]

I think Al hit upon it,building up the residual magnetism by spinning at a higher speed.Many times the problem with generators is they loose that residual magnetism and won't build voltage. Has anyone here ever built a module test stand,a motor driven flywheel and a place to fasten modules close to it. Frank C.

[Jiles]

"Has anyone here ever built a module test stand,a motor driven flywheel and a place to fasten modules close to it."

I think my  lathe set up would be close??

[bandmiller2]

It would be easy enough to cut the female end off a cheap 3/8" drive extension and chuck it in a drill motor to fast spin a saw with a socket on the flywheel nut.Remove the plug and lay it on the metal head.Don't use anything impact I've seen a guy wring off the nut with one. Frank C.

[Al_Smith]

Problem is you are spinning it in a direction you can unscrew the flywheel nut .I tried that on an old Homelite that spent a decade living under a pine tree near Meadville Pa .The dang flywheel must have circled the garage about 3 times before it fell out of orbit . :D

You got no where to run and no where to hid .

[sharkey]

I can tell you from working on mowers that baking a coil on low heat in an oven will sometimes bring it back.  I learned this from working on Lawnboys.  Apparently they had a run of bad ignitions where the capacitor or silicon switching/timing electronics would fail.  We would put them into a toaster oven on 200f for an hour.  Most all would work after this.  Some would last a season some would last many years.     

[Al_Smith]

I have warmed up points type coils from saws and old Wico coils  from old tractor magnetos  with success several times .I've never tried it with an encapsulated solid state coil .

With a solid state triggered modual I doubt it's the actual coil that goes bad but most likely the solid state trigger circuitry .Which for all intents because it's encapsulated is not repairable .

[Real1shepherd]

I'd like to revive this thread if there is any interest. On the AS forum a EE has figured out how to revive a dead SEMS module on a 056. Apparently, most of these modules fail because of a bad Bosch pulse capacitor. He figured out where to melt and scrape away the 'potting', cut a trace on the circuit board, attach a wire and mount an external pulse capacitor inside the flywheel well of the saw. Run your new wire to one lead on the pulse capacitor and the other lead to a good ground.

I think many if not most of these SEMS modules are made in the same way and this 'fix' will apply to many other saws....Husky etc. People have been throwing these modules in the trash for decades....now it's time to start repairing them. The pulse capacitors are usually available on eBay and are poly caps with certain specs, obviously. I have two, but no dead saw modules.

We just need folks willing to experiment...I think we're on to something epic here.

Kevin

[dougand3]

Working on a Mac Timber Bear 55cc. No spark. Resistance is 890 ohms and I THINK it should be 2000-4000 ohms. Does spinning or heating sound it may revive coil? Which to try first?

[TLahti]

Hi Jiles:
  When you are spinning the flywheel, do you have a grounded spark plug attached to the coil wire?
  I would assume you did.
So, you show no spark at the plug at first, then after 30 seconds, you saw good spark at the plug?
   I have seen some bad coils show weak intermittent spark when hand cranking.
  TL

[dougand3]

I worked on coil:
Tried spinning at 2k-2.5k RPM for 3  mins or so = no joy.
Heated in toaster oven at 200* for 2 hours = joy. Good spark now.
Puzzled at resistance, tho...it moved form 890 ohms to 920 ohms...but it has stable, bright spark.

[Al_Smith]

My father had a walk behind garden tractor that is now as old as I am and I'm pushing  70 .He only used it about 3 hours a year to seed the garden .Dang thing would never start the first time out .He would belt it up to an old  reel type lawn  mower and spin that thing full throttle ,by golly it would fire up then .

I used that mower engine on a mini bike built from a bicycle frame when I was 14 years .24 MPH,not bad for a kid .Over 100 miles per gallon also . Held 7 cents worth of gasoline at 28 cents per gallon . 8)

[joe_indi]

Just a thought, would compressed air through the plug hole or inlet serve to spin the crank instead of the drill?

[dougand3]

I'd think compressed air would be tough - how much compression would you need to bottom out piston? And losing compression when piston drops below exhaust port. Seems like it'd have to be pulsed compression, like fuel/air explosion, to let piston come back to TDC.
The drill is real easy. Variable speed with speed set low. Gradual throttle up. I felt no hint of flywheel nut loosening. Less load with plug out, too.

[Ljohnsaw]

Interesting thread.  I recall reading something about revitalizing a generator stator or something and Kbietz comes to mind ;)  He's got it all and done it all, so it seems!  There was something about hooking the coil up to a battery to impart some residual magnetization.  I think it might have been the old thread where Jeff got his two tractors...

I've worked on a number of small engines and I seriously doubt that using a drill to spin a crank without a plug installed will loosen a flywheel nut!  Most times on a lawnmower, I had to use a breaker bar with a cheater pipe and something big on the blade to budge those nuts.

[Al_Smith]

Okay another example .In my shed resides an Echo  weed wacker that for some reason one of the magnets in the flywheel looses magnetism.It"s  a three magnet type .

I've taken a rare earth type magnet and stroked the offending magnet and got the thing to fire .It would last a season but again loose strength for some reason .I never knew  out why .So it might not be the coil itself might be the magnets .

Yes by the way you can spin the nut right off the flywheel trying to start one with a drill motor .It's a right hand threaded nut but the engine needs to spin counter clockwise to start .If it ran the other direction the chain would run backwards .

As far as the offending Echo .I haven't tried in it a while .Lost my patience and bought a brand new Stihl . Out of character  for me but it starts every time .Something to be said for that . ;D

[Kbeitz]

Interesting thread.  I recall reading something about revitalizing a generator stator or something and Kbietz comes to mind ;)  He's got it all and done it all, so it seems!  There was something about hooking the coil up to a battery to impart some residual magnetization.  I think it might have been the old thread where Jeff got his two tractors...

I've worked on a number of small engines and I seriously doubt that using a drill to spin a crank without a plug installed will loosen a flywheel nut!  Most times on a lawnmower, I had to use a breaker bar with a cheater pipe and something big on the blade to budge those nuts.

Oh yes a drill will loosen a flywheel nut. I've had it happen many times.
Another problem is if it tightens up you can split the flywheel.
I have had that happen to. I also had the crank snap off when the
engine miss fired with the drill on the nut. Now I put one of these
between my drill and the nut.



 

[Al_Smith]

I think where people get confused comparing a saw engine with a mower engine is the fact they counter rotate with respect to the flywheel .A four cycle starts by clockwise rotation if you stop and thing about it .An automotive engine is the same way .A counter rotating marine engine has the timing gears and thus the oil pump drive,distributor gearing etc machined for opposite rotation,parts do not interchange.

I suppose for testing with the plug out you could wind one up with a drill motor though .As I said before it's not a good plan to attempt to start a saw engine with that method .If you do wear a football helmet and a suit of armor because a loose flywheel might get you  .You'll only do it once I'll bet .

[Ljohnsaw]

I think this discussion has gone a little sideways :-\  The OP was talking about spinning the flywheel WITHOUT a spark plug to recondition the mag.  Without compression or any other resistance, there is no way a drill (not talking impact driver) is going to remove or tighten the nut that is properly attached to the engine.

However, I would NEVER attempt to do that with a plug in/trying to start the engine with a drill.  A backfire or something else could cause problems to the engine or you!  Not saying it will, but why risk it.

[Kbeitz]

I think this discussion has gone a little sideways :-\  The OP was talking about spinning the flywheel WITHOUT a spark plug to recondition the mag.  Without compression or any other resistance, there is no way a drill (not talking impact driver) is going to remove or tighten the nut that is properly attached to the engine.

However, I would NEVER attempt to do that with a plug in/trying to start the engine with a drill.  A backfire or something else could cause problems to the engine or you!  Not saying it will, but why risk it.

Sorry but I have to disagree with you 100%.
Over my lifetime I have collected over 3000 small gas engines.
Many many time I have used a drill to spin the flywheel to
start or just to work on my engines. I've had the nut come off
many times with the drill and I know that it was on tight before
I started. When a engine tries to start it will kick back on the drill
and act just like an impact drill.



 

[Ljohnsaw]

Kbietz,
I'm not going to argue with you - yes, if a plug is present, not a good idea to spin with a plug.  BUT, the OP was saying to spin WITHOUT the plug.  No compression, no spark, no way to fire.

Continue on...

[Al_Smith]

On a mower engine as I said the rotation is clockwise .If you use a rachet mechanism it's no big deal to spin one up ,I've done that.

Fact of the matter is when we at one time "hot tested" automotive engines at work (Ford Motor ) we used an air motor to wind them up using the bolt head on the crankshaft that holds the vibration dampener on .Every so often if the engine was miss timed it would snap the bolt but that was very rare .

Another piece of data from decades ago in the era of two cycle karting .Because of the high compression the engines were next to impossible to spin over by hand .They mounted a starter puller in place of a recoil starter and used a long shafted Ford starter to wind them up using a v-belt .However using that system the strain was not on the crankshaft nut but rather on the flywheel because of the way it was made .Trivia---

[Kbeitz]

We used a long shafted Ford starter to wind them up using a V shaped
rubber block on the end of the starter that fit into the rope starting cone.
That was the good old days.

[Al_Smith]

 :D Oh we do wander off sometimes but it's interesting some of the methods mentioned .

I have a D4 Cat the mag had problems .I used the points from the mag to fire two 12 coils from a Ford to fire both plugs at the same time and wound  the pony motor up with a Ford starter .It worked but I later found an open wire in  the mag coil and fixed it .After that and as far as I know now it would start rather easily with the rope .That model,1942 did not have an electric starter  only a rope .---never tell a junk yard dawg anything is impossible .---- 8)

[Kbeitz]

All this talk about coils I thought I would bring this up.
Many years ago I found something at our junkyard and
I had no idea at the time what it was. Later I found it to
be a coil tester. No one has ever seen one like it and I
have even posted it many places on the internet. so
maybe I got the only one. It sure works good but you
really got to watch what your doing or it will knock you
on your butt.