028 Super AV Muffler Mod

[Benwa]

Vincent, I may port the cylinder in the near future. How will that affect the timing?

Also when you file the flywheel key -

1. If the key is positioned straight up, do you file the left side of the crescent key
2. When filing the key, I assume you only file that portion which sits above the shaft of the crankshaft
3. What is the best way to hold the key while filing

Danny

Port work effects port timing. Flywheel advance effects ignition timing. If a saw (like the 028) likes a bump in ignition timing when stock, it'll surely benefit from the same when ported. You also usually pick up a fair amount of throttle response off idle, with an ignition timing advance. Some saws don't like an advance in ignition timing, but they're usually far and few between.

1. If the key is straight up & you're looking at the end of the crankshaft (on the flywheel side), you would remove material from the right side of the key. You want the flywheel to move counter clockwise, which will advance it.
2. That is correct, you need the key to still fit snug in the crankshaft.
3. Clamp it with a pair of vise grips. I use the witness line on the key where it sits in the crankshaft. Somewhere around the half way up the key. I clamp it with the tip of the vice grips at this line. It gives you a flat line/guide to file against. You can then clamp the vise grips in your bench vise to hold while you file.

 

[VincentFR]

All my older Stihl saws (024/028/038) responds well to a timing advance. There are not ported just stock saw with muffler mods / base gasket delete (with a safe squish) / ports smoothed.
I read a lot of threads about porting 028 and 038 (here and on the other site). All the ported 028/038 have a 0.020" or more timing advance.

Theory about timing advance :
If the spark fire sooner the air/fuel mixture have more time to burn and can make more power.
But if you advance the timing too far you will have pre-ignition (burbeling) and lose power.

 

[VincentFR]

https://www.arboristsite.com/threads/porting-an-028-super.270227/

 

[wdoc]

I’ve contemplated the muffler and timing mods for my 028S. The saw has good power but there are times that it could use a bit more. Mine has never required disassembly so I’ve not gotten to it…yet.
I’ve done key offset advance/retard on other engines over the years but used an offset key that allowed no movement between the 2 parts.
I’ve seen no offset keys for this application.
Has anyone seen the timing drift due to flywheel movement or is the crank taper enough to keep it secure?

 

[Benwa]

I’ve contemplated the muffler and timing mods for my 028S. The saw has good power but there are times that it could use a bit more. Mine has never required disassembly so I’ve not gotten to it…yet.
I’ve done key offset advance/retard on other engines over the years but used an offset key that allowed no movement between the 2 parts.
I’ve seen no offset keys for this application.
Has anyone seen the timing drift due to flywheel movement or is the crank taper enough to keep it secure?

I haven't personally, I'm sure others will chime in. The crankshaft taper is what holds the flywheel. The key is purely for timing alignment. I've had saws where I ran the flywheel with no key at all, without issue. If you have flywheel "drift" like you mentioned, then something isn’t right. Having a properly clean crankshaft and flywheel is a must in my eyes.