Chainsaw Repair

I've only been around and observed four of these saws. I have a 2 port 026 from 1991 and it is 42mm. I have a four port 026 that is from more like the millennium era. It could be probable that there is a intermediate combination?

The saw in the picture a couple posts above may have started out as a 1991 025. I'm essentially the second owner. But observing after having it completely apart - due to wear and tear of use over the years, the only thing 1991 left about it is the crank and cylinder. The covers are from a 025 but not a 1991 025. The rest of the parts are from a 2013 MS250. The crank is unusual in that it has rollers on the big end of the rod rather than a caged needle bearing. The smallest saw of this family had a single counterweight crank with rollers for bearings on the big end in the beginning. Also the rod is a billet style rod. It is not a forged I-beam.

Since the picture was taken I've had to replace the starter cover because the pulley post in the cover was a smaller diameter than current production. It now has a 2013 MS250 starter cover. The new MS250 parts were no more expensive than buying used 026 parts from Ebay.