dead coil


Old 01-24-10, 05:27 PM
Thread Starter
Join Date: Jun 2005
Location: ontario canada
Posts: 381
dead coil

i have a 4 year old 036 stihl that worked fine 2 weeks sat for 4 day sand wouldn't start...took the kill switch wire off for testing and still no spark...took to my dealer he says coil is coil (costly) my question, what makes a perfectly good coil one day , not work the next? there was no hint of failure like missing when the saw got to operating temp or hard starting or anything??
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Old 01-25-10, 08:14 AM
Join Date: Dec 2009
Location: Kingsport, TN
Posts: 217
While this may not apply to your situation here is what happened to one of my blowers. I was using it one day and all of a sudden it missed a little, then picked up normal speed, then totally quit and would not restart. I pulled the plug and cranked. There was no spark and no tingle when I put my finger in the lead and cranked it.

I disassembled it to see if the magneto had gone bad. I had a spare lying around and was hoping it would fit. It was different. Muttering unprintables to myself, I looked at the clearance between the flywheel and the laminated parts that are cut by the flux of the magnets. Lo and behold, the clearance had increased dramatically, due to vibration I suspect. I loosened the hold down bolts, edged the metal flux cutters (or whatever they are rightfully called) closer to the flywheel, and pulled the starter with my finger in the lead. Given the tingle I got, I decided the ignition was still good.

As I do not know what to set the clearance at, I took two pieces of standard notebook paper and put them between the pickups and the magnets on the flywheel. The pull of the magnets snatched the pickups to the sandwiched paper. I tightened the bolts (loctited them in place), rotated the flywheel to get the paper out, and it has been running ever since.

Might be worth a try unless the service place actually tested the magneto. Maybe they just wanted to sell you one....
Old 01-25-10, 10:32 AM
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Join Date: Jul 2001
Location: USA
Posts: 16,815
To determine if the coil is good or not, unplug the kill wire from it, make sure the air gap between the coil and flywheel is .010 to .014, and use a known good spark plug. Plug the spark plug into the coil wire and make sure the metal end of the plug is touching the metal on the saw. Pull the rope quickly while checking for spark. If none, the coil is bad.
Old 01-25-10, 10:45 AM
Join Date: Dec 2009
Location: Kingsport, TN
Posts: 217
Two sheets of notebook paper have a thickness of about 0.008 inch. Guess I'm was a little close. Well, if I ever have the occasion to take it apart again, I reset it. Dad used to tell me when I was a kid, "Leave well enough alone".
Old 02-06-10, 09:25 AM
Join Date: Feb 2010
Posts: 1
Hi my Stihl Blower had seen about 4 years commercial use then it wouldn't start up last week. My local dealer diagnosed bad coil so ordered new coil and i fit. 4 years seems to be about how long these last. Just before it died i had to toggle the kill switch to switch the blower off. It was an expensive part, about 1/5 the cost of the machine new but for the time being i'm satisfied... Many thanks for your post on setting the distance between the fly wheel and coil otherwise i would've spent all day messing with it.
Old 02-06-10, 10:12 AM
Join Date: Jun 2006
Location: St. Louis
Posts: 2,365
The simplest method I have found for the ignition/flywheel measurement is to use a new business card. Have a good one. Geo
Old 02-08-10, 01:22 PM
Join Date: Jun 2004
Location: South Florida
Posts: 53
I couldn't find my feeler gauges when I needed to replace the magneto on my lawnmower so I cut a strip of steel flashing and curved it to match the flywheel and tightened the mag screws.

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