Stihl 042 ignition

Mark Klaiber · Jan 1, 2005

Hi, I've got an 042 that seems to have a coil (ignition module) problem. It's an SEM unit. I had it idling to warm it before tuning and it died. I couldn't restart it so I checked the spark- nothing. Let it cool and checked spark again - good spark. Started it and it died again. I'm guessing from what I've read in the archives that this is a faulty coil that fails when warm. I'd bet there are alot of dead 042s and 048s out there due to the crankcase gaskets failing. Anybody know where I might try for a coil? I have an 038 super and though the ignition is different it looks like they might interchange. The mount screws are the same and it looks like the legs of the coil would land in the same place. Anyone ever tried this swap? This is a low hour saw and it would be nice to put it back in service.

stihltech · Jan 1, 2005

042

Just happen to have some of those. Email me with some more info.

Mark Klaiber · Jan 2, 2005

Thanks for the reply. I will send an email. I figured you might have an answer

Al Smith · Jan 2, 2005

Right on about the dead ones,from lack of a coil.I had one that would start ok,but would cut out when trying to advance[electronically built into the circuitry of the coil].It about drove me nutty,trying to figure that one.My 2 048's and 1 042,have been a real learning experience for me .Hot little saws,when they run right.

Mark Klaiber · Jan 2, 2005

Yes Al,
When this thing runs it cuts well. A little heavy, definitely not for limbing. It also would stagger on acceleration sometimes before it would quit. I didn't know there was a spark advance in the module design. Ther is no advance in a points and coil setup -- right?

Al Smith · Jan 2, 2005

Here is the SEM unit used on the 042/048 .Sorry about the quality,best I could do.To advance a points type system,the easiest way is to make the points open earlier,sometimes refereed to as "mavericking".Karters,and perhaps saw racers,sometimes used off-set milled flywheels.Both of these methods ,were fixed advance,and not responsive to an "automatic" advance,responsive to engine rpm.

Mark Klaiber · Jan 2, 2005

Thanks Al, I sure hope you solve the problems getting all the info you have posted, it would be a great resource. THYRISTOR ? I couldn't find this in my "Standard Handbook for Electrical Engineers" but the edition I have is 1941. I do love learning and figuring out problems. Re-inventing the wheel.

Al Smith · Jan 2, 2005

Thyristor

A thyristor,is just a generic name for SCR [ silicon controlled rectifier].They have wide spread uses,in electronic circuits.One use is as an electronic switch,as in the SEM module.It's all electronic"gooble-de goop",nice to know,but not entirely necessary.That "it works" is more important than "how it works".For all intents and purposes,"solid state" ignition systems,are non repairable,under normal conditions.

Stihl 042 ignition

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