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I could be reading it incorrectly, but below is a screen shot from the Stihl 021/023/025 Service Manual. Page 3. Under all four variations (021/021L/023/025) it shows a 32mm stroke. Oddly, it does say 28mm immediately adjacent to the word "Stroke", so perhaps the manual is misprinted?

upload_2015-2-22_21-26-31.png
 
I think his spreadsheet may be wrong....

If you look there is nothing in the 020 modern column. Looks like he may be a bit messed up.


I've actually been to Bill's shop before, when I lived in Chautauqua County, he was just over in Cattaraugus County, NY. Durn nice guy.

MediaCat also states that the cranks are the same and the cylinders are interchangeable throughout the whole series.
 
Ummm.

Don't think so.

023/025 share crank.

021 shorter stroke.
That's why I said "don't think so". I always avoided the 021 thinking I couldn't put an 025 top on it.

When I looked at the pics in the service manual, the 021 crank had one counterweight only, whereas the 023/025 had 2. I think a caged and non caged bearing crank existed for all and may be the variation I saw.

I could be wrong on this too. Seems to be a lot of variation here.

So I guess if it's a smaller stroke, it's got a longer connecting rod or a taller piston to fit into the same jug as an 023.

It would be interesting to hear from a member that's swapped jugs on these models.
 
I could be reading it incorrectly, but below is a screen shot from the Stihl 021/023/025 Service Manual. Page 3. Under all four variations (021/021L/023/025) it shows a 32mm stroke. Oddly, it does say 28mm immediately adjacent to the word "Stroke", so perhaps the manual is misprinted?

View attachment 406338
That whole things confusing. Lists same bore and stroke with different displacements.

I know 100% that an old 025 is 42mm, newer and ms250 42.5. Also 100% that a 025 P&C works on a 023. Now, I am questioning whether or not the 023 crank I used in my last 025 build is actually a shorter stroke with a long connecting rod. The squish is normal in the motor.
 
http://bricomeca.free.fr/Stihl/piece_021_023_025.pdf

This service manual lists the 021 crank as PN 030 411 and the 023/025 crank as 030 400.

Page 55 of this owners manual shows the stroke to be shorter in the 021

http://www.stihlusa.com/WebContent/CMSFileLibrary/instructionmanuals/STIHL_MS021023025.pdf

So I guess it's conceivable that an 023 jug , or a cheaper and more available 025 head may fit and just be a shorter stroke motor. That is if the piston height or the con rod compensates.

THOROUGHLY CONFUSING.

To the OP, look on eBay for an 021 or 023 P&C. There typically really cheap and OEM. Everyone wants to use the 025 bore.
 
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