Stihl Ignition Adjustment

[Vintage Engine Repairs]

Hi Gents,

I had an interesting discovery this morning that I wanted to share!

The manual says that if one of the 3 settings (magnet edge gap, points gap or timing) is correct, the other two should be too.

Anyway:

So I set the points gap to .4mm and figured it will be ok for now while I focused on other aspects of the saw.

Put it back together and noticed there was terribly weak spark.

adjusted the points to .33 figuring that the anvil of the points is worn.
Got bright blue spark.

Now a few days later I got up early before work to finish the ignition setup.

I checked the magnet edge gap and It was 7.6mm should be between 4-6mm.

Therefore out of interest I tested spark strength - 3.18mm

I took the flywheel off to check points gap, opened slightly from .33 - . 38 to give a smaller edge gap.

I put the flywheel back on, but noticed a few degrees slop between that and the key.

I then decided to take the key from my other 020 and checked width - same width.

Therefore, figuring that I needed to reduce the magnet edge gap anyway, I adjusted the flywheel all the way to take up the slop and get a smaller edge gap.

Checked everything again, edge gap was now 5.5mm, which is perfect.

Put it back together and tested spark strength - it went up to 8.3mm!!

In summary:

Edge gap setting parameter: 4-6mm

Edge gap before:7.6mm gave spark 3.18mm

adjusted flywheel position and points.

Edge gap after: 5.5mm gave a spark of 8.3mm


The long and short of the lesson I learnt - don’t overlook any of the details and think “well it sparks, it’s fine” because in reality all the 1%’s make a big difference and in this case nearly 3x the strength of the spark!

Warm regards, Tom

 

[RED-85-Z51]

Me: so glad i dont own anything with points anymore[emoji23]

Sent from my LM-G820 using Tapatalk

 

[frank_]

the points gap is critical for the dwell angle tom
if the gap is too big the points are,nt closed for long enough for the coil to energise fully (dwell too short)

 

[Mad Professor]

What saw are you working on?

 

[Vintage Engine Repairs]

What saw are you working on?

020 av mate

 

[Mad Professor]

020 av mate

Does the coil have a common screw with the points? I can't understand why coil gap would effect timing/point gap.

But I've not wrenched on of those.

 

[Vintage Engine Repairs]

Does the coil have a common screw with the points? I can't understand why coil gap would effect timing/point gap.

But I've not wrenched on of those.

Hey, it’s not magneto air gap, its edge gap - the distance between the trailing edge of the north pole magnet and the magneto pickup at the point that the points open and the magnetic field around the primary coil collapses. From what I have been reading, too small of a gap causes running / miss firing issues and too large the spark is too weak.

when I have time, I’ll test it myself to learn what to look for in future issues / diagnosis - for now, I just set it all to spec.

 

[Vintage Engine Repairs]

Me: so glad i dont own anything with points anymore[emoji23]

Sent from my LM-G820 using Tapatalk

Haha I enjoy the challenge, but I can’t see any advantage of points and condensers!

Replacing them is surprisingly expensive too!

 

[Vintage Engine Repairs]

Can someone please confirm something for me. The reason for the weak spark when the edge gap is too large is because there won’t be efficient charge in the primary windings before the points open as it’s the change in magnetic field that causes the primary windings to charge?

What I don’t quite understand though is If the gap is too small and the magnetic field collapses after the points open why that would be an issue because they stay open for a good 135 degrees? My presumption is it’s ignition timing rather than the energy of the spark?

Thanks for the advice in advance.

 

[Vintage Engine Repairs]

Done! if I could get the seals and bearings I’d do a full paint job on it too

 

[frank_]

you could try setting them with a dwell meter tom

 

[buzz sawyer]

Can someone please confirm something for me. The reason for the weak spark when the edge gap is too large is because there won’t be efficient charge in the primary windings before the points open as it’s the change in magnetic field that causes the primary windings to charge?

What I don’t quite understand though is If the gap is too small and the magnetic field collapses after the points open why that would be an issue because they stay open for a good 135 degrees? My presumption is it’s ignition timing rather than the energy of the spark?

Thanks for the advice in advance.

The field intensity through the primary windings is proportional to the proximity of the flywheel magnets as they pass by the coil and by the speed at which they pass. Closer gap and/or faster speed = higher induced voltage. Since the field can only build when the points are closed and drops when the points open, the timing of the ignition points is also critical. So yes imo, if gap is too wide or the ignition points timing is off slightly, it would affect spark intensity - more so at slower speeds. Strength of the flywheel magnets will also play a part.

 

[HarleyT]

I try not to "dwell" on things like this.........

 

[Vintage Engine Repairs]

I try not to "dwell" on things like this.........

I wish I could “condense” my question and get to the “point” quicker.

 

[buzz sawyer]

I try not to "dwell" on things like this.........

I like your angle on this.

 

[Old2stroke]

The points gap specified by the manufacturer is designed to open the points when the primary current is at it's maximum, the timing can be varied by changing the points gap, a wider gap will advance the timing and a smaller gap will retard it but if you stray too far either side of optimum, the primary current will be less when the points open and thus a weaker spark. The magnetic edge gap can only be changed by moving the coil and most saws don't have slotted holes to enable this but if yours has adjustment it can be done but might be tricky to get it to the right specs.

 

[Be Stihl]

My mind just doesn’t have the “capacitance” for these type problems anymore.


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[trains]

My mind just doesn’t have the “capacitance” for these type problems anymore.


Sent from my iPhone using Tapatalk

Your Point being ?

 

[Vintage Engine Repairs]

The magnetic edge gap can only be changed by moving the coil

I have seen many (non chainsaw) engines with a built in lever to adjust advance or retard, but stihl recommend adjusting the edge gap via the points gap, giving preferential treatment to the edge gap even if the other two variables are slightly out of spec.

 

[buzz sawyer]

Found this. Seems to make sense.
https://www.manualslib.com/manual/1040630/Stihl-009.html?page=34