Ignition Module Rises from the Dead

[Wood Doctor]

No Joke. It happened Tuesday. I was rebuilding the engine on a vintage Stihl 084, installing a new piston and ring assembly. After getting it all back together again, it would not start and there was no spark--not even a trace. I thought, "Dad burn it, another $150 part to order."

Then I took some action. I removed the pull cord cover and checked all the connections for continuity. OK. Then I ran the two typical resistance tests. A little low but seemed OK. Hmmm..., it should have all worked.

Things were a little dirty inside, so I removed the ignition module and gave it a good cleaning all over. Then I cleaned up the entire outside perimeter of the flywheel, polishing it with a soft cloth. I reassembled all, and checked again for a spark. Gadzooks! the plug suddenly responded.

I put the plug back in, and tried starting the engine once more. It popped and fired as if it were brand new. So far, the owner has cut a truckload of wood without incident and loves his rebuilt saw. I'm reporting this because I've never had it occur before. Usually when those ignition coils are dead, they stay dead. This one arose from the dead. Anybody else run into this or have any idea what I did to save it?

 

[Jacob J.]

I've saved a few by changing the lamination, but this is the first time I've heard of just cleaning one and getting spark back. Was yours one with a separate trigger unit?

 

[trophyhunter]

Yea, the module itself was likely just dandy -you fixed whatever was providing a path to ground and killing it when you went through it.

Never seen one that was near death or dead come back 100%.

 

[Wood Doctor]

No Trigger Unit

I've saved a few by changing the lamination, but this is the first time I've heard of just cleaning one and getting spark back. Was yours one with a separate trigger unit?

No. The Pic in the manual shows that separate trigger unit, but mine didn't have one. Wires went straight to the plug and the controls.

This saw was resting on a garage floor for about a year, maybe even on dry dirt. It looked like a mouse had climbed into the area around the controls under the carb and hibernated there after packing it tight with corn kernals and mud. I had a heckuva time cleaning that out also.

One thing for sure, these old 084s have power they don't really know what to do with, especially when rebuilt. Trying to turn it over without the decomp pressed in was almost impossible with new rings and a new piston. opcorn: