Author Topic: Stihl 042 ignition timing with no flywheel keys!  (Read 257 times)

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Offline imquattro

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Stihl 042 ignition timing with no flywheel keys!
« on: October 30, 2017, 09:01:14 pm »
Working on the two 042 saws. Current symptom: weak under load (addressed case leaks, compression 150+, carbs working fine, fuel lines and intake boots good).
Neither have flywheel keys and both were not timed properly.
Timing should be 2.5mm BTDC according to: http://www.acresinternet.com//8ea47c2d0942227788256ba20048
>>>>Question:<<<<
Where does 2.5mm put it in degrees? Where is that measured? at the outer edge of the flywheel/case or at the coil? There are no marks on the case or flywheel. When the keyway and flywheel are lined up they are pointing directly at the center of the coil -seems odd.
Whats a good rule of thumb for these? 25+ degrees advance when running right?

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Offline Cut4fun .

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Re: Stihl 042 ignition timing with no flywheel keys!
« Reply #1 on: October 30, 2017, 09:23:12 pm »
@Al Smith I was thinking you knew about these.

Nate your link not working. Thinking it was this one. http://www.acresinternet.com/cscc.nsf/ed1d619968136da688256af40002b8f7/8ea47c2d0942227788256ba2004878e7?OpenDocument
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Offline imquattro

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Re: Stihl 042 ignition timing with no flywheel keys!
« Reply #2 on: October 30, 2017, 09:59:53 pm »
Yep, that link looked funky!
Thanks Kevin!

Offline breese

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Re: Stihl 042 ignition timing with no flywheel keys!
« Reply #3 on: October 31, 2017, 05:46:33 am »

Where does 2.5mm put it in degrees? Where is that measured? at the outer edge of the flywheel/case or at the coil? There are no marks on the case or flywheel. When the keyway and flywheel are lined up they are pointing directly at the center of the coil -seems odd.
Whats a good rule of thumb for these? 25+ degrees advance when running right?

The 2.5mm = 0.098 inches before TDC so that equates to the Piston location.
When the key is used for the flywheel, it will align the coils Fire sensor to align with the sensor on the flywheel.
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Offline Al Smith

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Re: Stihl 042 ignition timing with no flywheel keys!
« Reply #4 on: November 02, 2017, 06:30:13 am »
FWIW the 042 and 048 ignitions are self advancing or at least the SEM type are .I'm not sure about the Bosc .
How it works is a long drawn out affair to explain .
I have 2 048's and one 042 but frankly speaking although I have both ignition types I'm not certain which has which .
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