Chainsaw Repair

Looking forward to pics.  The 6900/7700/8500 has a plastic top cover with separate af cover to go with the different af that Tim mentioned. 

The 4400/4900/5400 and later saws have a longer tank/rear handle casting.  More fuel capacity (and distance between the handlebar and rear handle.............and more weight). 

The plug lead is different on the coil of the 6900/7700/8500 saws. 

The 6900/7700/8500 saw cylinders have a different fin profile than the 1st and 2nd gen saw cylinders.  The bulkhead behind the jug is different to match. 

The 6900/7700/8500 saws have a larger crank PTO snout, with a larger clutch bearing and race and a different clutch drum and hub.

Tim covered the remaining upgrades.  The 3/8 bar studs were phased in during the 4400/4900/5400 production.  There were 2nd gen saws with both stud sizes.  My 4900 had 5/16" studs.