# Stihl Ignition Module Air Gap...



## Nicholas (Jun 12, 2005)

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


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## NWCS (Jun 12, 2005)

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!


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## Stihl #1 (Jun 12, 2005)

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.


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## Al Smith (Jun 12, 2005)

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.


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## Bill G (Jun 13, 2005)

Al Smith said:


> 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.




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


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## Nicholas (Jun 14, 2005)

Thank you for the information everyone. I appreciate it.

Nick Gajewski


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## Al Smith (Jun 14, 2005)

Bill G said:


> 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


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.


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## JP56 (Dec 16, 2018)

Bill G said:


> 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



CORRECTION: According to the service manual for the 029/039/290/310/390, the air gap specs for the module are 0.15 - 0.3mm.

Just a side note: I have a BR380 blower which has the same air gap specs, that was a bear to start from day 1. I finally found an article about it where the problem seemed to be an improperly gaped module, and the article also stated that the modules in this blower sometimes take 2 or 3 shot to get it gaped and locked down properly because for some reason on this blower the module tends to shift out at one end when you tighten down the screws . Anyway, I took it apart and sure enough it was set crooked. I found a thread exactly like this one where there were various gap sizes mentioned, so I just took a piece of paper from my printer, cut a strip off, folded it in 1/2, put it between the legs and the flywheel and tightened the module down. Was surprised to see the one end of the module walk it's way out away from the flywheel when I tightened it down, so on the second try I simply squeezed the module against the flywheel as I tightened it down again(as opposed to just holding it down by pushing down against the case). Worked perfect and starts on no more than 2 pulls every time on a cold start and on 1 if shutting it down then starting it back up during use. At the time, I couldn't find my caliper/micrometer, so I really don't know what the exact gap it, but I have had no problems at all since I set it this way. I am currently rebuilding my MS290 saw now so plan on doing that the same way.


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## Jasonrkba (Dec 16, 2018)

Business card.


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## ray benson (Dec 17, 2018)

JP56 said:


> According to the service manual for the 029/039/290/310/390, the air gap specs for the module are 0.15in, or 0.3mm.


Take another look at the service manual gap setting, it says

It should be 0.15 - 0.3 mm
(0.006 - 0.012").


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## pioneerguy600 (Dec 17, 2018)

Regular card stock business cards average around .010 and have become the most used gauge for setting air gap, set the gap at the magnets on the flywheel as they sit higher than the rest of the wheel. The magnets will pull the module tight to the card, after torquing down the holding screws rotate the flywheel counterclockwise and the card comes out easily.


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## HarleyT (Dec 17, 2018)

Al Smith???????


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## pioneerguy600 (Dec 17, 2018)

HarleyT said:


> Al Smith???????



I know of him, what`s your question again?


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## Ax-man (Dec 17, 2018)

Al is a good guy , knew his way around a saw. I think he got banned from the site or just lost interest in being here. I am not sure what happened. The forum these days is pretty tame compared to the way it was when I first came here . Things would get pretty intense between some of the members.


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## JP56 (Dec 17, 2018)

ray benson said:


> Take another look at the service manual gap setting, it says
> 
> It should be 0.15 - 0.3 mm
> (0.006 - 0.012").


Thnks Ray, that's what happens when you use your manual w dirty hands & don't put your cheaters on!


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## HarleyT (Dec 17, 2018)

I am arguing politics with him right now on Facebook!


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## Ax-man (Dec 17, 2018)

Glad to see he is still around. I see he still posts on some of the other forums that have a chainsaw section.


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## HarleyT (Dec 17, 2018)

He is on Facebook, just search al smith lima ohio,

he spends his days hating Trump!!!


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## Huntaholic (Dec 17, 2018)

Oh come on Harley, we can do better than that!  Feeler gauges? Stihl gauges? GEEZ! Whats up with this place???? Just use a friggin business card placed between the magnets and the flywheel, tighten it down and be done with it!


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## HarleyT (Dec 17, 2018)

Yeah, I kept out of all of that.
I think the O.P. has problems elsewhere, if he thinks that the gap has anything to do with his saw problem.....


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## shona13 (Jun 17, 2020)

Huntaholic said:


> Oh come on Harley, we can do better than that!  Feeler gauges? Stihl gauges? GEEZ! Whats up with this place???? Just use a friggin business card placed between the magnets and the flywheel, tighten it down and be done with it!


I normally use a business card but in the past I have had chainsaws that were hard to start and after bringing the air gap down the saws start better,just my two bobs worth.
Stay safe.


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## HarleyT (Jun 18, 2020)

Huntaholic said:


> Oh come on Harley, we can do better than that!  Feeler gauges? Stihl gauges? GEEZ! Whats up with this place???? Just use a friggin business card placed between the magnets and the flywheel, tighten it down and be done with it!


Now that it is 2020, we now refer to them as "feelings" gauges......


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## shona13 (Jun 18, 2020)

HarleyT said:


> Now that it is 2020, we now refer to them as "feelings" gauges......


Rrrright !


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