Chainsaw Repair

I couldn't list them all but the motors stayed pretty much the same. Bar studs were changed from 5/16 to 3/8, the 5400's added a hand guard to the rear handle.
The starters were upgraded for durability and 10-24 fasteners for the starter housing to case were changed to 1/4 - 20. At some point early on a rib was added to the front of the case for durability and the top cover fastening was changed from a captive nut with locating pins to three screws. That was likely for a cost savings. The starter housing was changed, I believe by adding a stud to anchor the recoil spring.
The 8500 had a different air filter system.

The power stayed the same as I guess that was very difficult to improve on.
I couldn't agree more as to how powerful and innovative these saws were when they were introduced.