This is the 064 that exploded in my hands at 14,000 RPMs. I rebuilt it with a new crankcase, a new 13-pin big-end bearing 066 crank, a KS 064 cylinder, and a new Stihl piston. I took .037" out of the squishband and set the squish at .019". It has a modded muffler and DP cover. This cylinder has NO PORTING. It's amazing how well this saw runs. It tunes out to 14K and has a powerband from 9,000-12,500 RPMs. I'll be going back in a porting this saw at a later time.