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Stihl Ignition Module Air Gap...

Discussion in 'Chainsaw' started by Nicholas, Jun 12, 2005.

  1. Nicholas

    Nicholas ArboristSite Operative

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    Good morning everyone,

    I have a question regarding the ignition module on my 038 magnum II. According the the shop manual I have, a person is supposed to insert the Stihl setting gage (which I have) between the ignition module and the flywheel magnets. Next, a person is suppose to push the ignition module against the setting gage, and flywheel magnets while torquing the torx screws to 9 newton meters. Next, the shop manual says to remove the setting gage, and measure the resulting air gap which is 0.008" - 0.012". Sounds easy enough.

    Here's the problem, the stihl setting gage seems to set the air gap too tight, like 0.004" measured between the ignition module arms and the flywheel magnets using a feeler gage set. It seems as though the center coil pick up on the ignition module has a wider air gap.

    Now my question, what is the proper way to measure an ignition module air gap? Shall a person measure the gap between the flywheel magnets and the ignition module arms? or Shall a person measure the air gap between the center coil pick up and the flywheel magnets. Please enlighten me, I am a bit confused

    Any help would be greatly appreciated.

    Thanks,

    Nicholas Gajewski
     
  2. NWCS

    NWCS Addicted to ArboristSite

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    i used a very cheap and quick method to get the air gap. i use a thin match book under the arms of the module, after tightening spin the engine a few times and check for any contact, if there is a high spot i re-gap at that high spot. sometimes a thicker item is needed, just grab an envelope or sometimes even a napkin. crude but does work!
     
  3. Stihl #1

    Stihl #1 ArboristSite Operative

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    I agree, the manual is a bit confusing. The intent I think is to verify that the clearance is not too great. The setting, or gap, is necessary, as the pole shoes in the flywheel should not hit the legs of the armature, resulting in damage. If you ever see this kind of damage, either the ignition module (coil) is loose or wasn't set correctly, or the crankshaft bearing has failed, and allowed the magnetism to take up the slack in the bearing and pull the flywheel into the armature legs. The gap is critical. If too wide, timing can be off, and voltage will be weak, as the magnetic energy falls off rapidly as the gap is increased. The magnetic lines of flux travel through the armature as the flywheel spins by and induce voltage in the primary windings. Lots of physics going on here, and at 12000 RPM the plug is firing 200 times a second, so timing is critical, whether the ignition is being switched by points or with a transistor, which is why the manual is asking you to verify the gap. I measured a new setting gauge and it is .008", so the gauge should be all you need. Otherwise, just use a feeler gauge in the first place, and be sure both legs of the armature are set correctly.
     
  4. Al Smith

    Al Smith Banned

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    A neat little trick.A piece of printer paper is abot.002" thus 4 would be about .008".A bio degradable feeler gauge,what a novel idea. :)
     
  5. Bill G

    Bill G Addicted to ArboristSite

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    Al nailed it. I always though a sheet of standard paper was .003 but I will not argue .001 with a tool and die maker. I have always used a folded over sheet of paper and let the magnet set the gap.

    Bill
     
  6. Nicholas

    Nicholas ArboristSite Operative

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    Thank you for the information everyone. I appreciate it.

    Nick Gajewski
     
  7. Al Smith

    Al Smith Banned

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    I always wanted to be a tool and die maker,but that part is self taught,with a little help.My great grandfather,grandfather,and father,were tool makers.For heavens sake,I ended up as an electrician. :dizzy:
     

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