STIHL 028 cylinder interchangeability...038???

[Mad Professor]

Just went to the garage and measured .021 (.53mm ) on both rings. Sounds excessive to me but I don’t know the spec. A leaking PTO seal started this rebuild.


Sent from my iPhone using Tapatalk

New rings should be ~ 0.002" per inch of bore, so those rings were shot.

 

[drf255]

Check your squish with the 028S piston in the 034. Just because the bore and pin are the same, it doesn’t mean it will run well. The compression height and skirt length are not the same, and high compression with no squish area is far from optimal.

 

[glennmac]

Check your squish with the 028S piston in the 034. Just because the bore and pin are the same, it doesn’t mean it will run well. The compression height and skirt length are not the same, and high compression with no squish area is far from optimal.

Yes I should do that while I have the chance. I can say I’ve seen this saw cut it was several years ago. My son says it always ran good.


Sent from my iPhone using Tapatalk

 

[Mad Professor]

Check your squish with the 028S piston in the 034. Just because the bore and pin are the same, it doesn’t mean it will run well. The compression height and skirt length are not the same, and high compression with no squish area is far from optimal.

I'd like to see both pistons side by side and measure up the pistons.

Would also be interesting to install both pistons, check squish, put at TDC, and measure the volume inside the combustion chamber. Like "ccing" a head on a car motor.

Next step would to be look at port timing.......... Too much work for me!

 

[glennmac]

Just checked squish, my solder is 1.6mm , 0.062 inches. IT NEVER TOUCHED! So naturally I removed the base gasket and tried again, still no squish to measure. Looks like I have a nice OEM 028 piston up for grabs. I don’t see any reason to put that back in.


Sent from my iPhone using Tapatalk

 

[drf255]

I know for a fact that the 034 piston has the highest compression height of any 10mm pin non-strato piston. I could be wrong and this may have changed since I did the research.

I have a hot 026 body set up for a 46mm 028S jug that is a 2 piece head. For timing, the 034 piston was all I could find to give me any reasonable numbers, the 028S slug came nowhere close, and my plan was to cut the dome off the slug and weld it flat.

If you want that saw to really run, find a used 034S 48mm oem jug and add a meteor without a base gasket. You’ll be a very happy man.

 

[glennmac]

In case anyone is interested here are the 028 and 034 pistons side by side. Now I can see the squish lacking with the 028. Pretty much everything is different.

Sent from my iPhone using Tapatalk