On the 660's the as delivered bearing and seals held up fine. I had a crank failure but really not sure if it was the crank or another victim of another brand of Aftermarket cylinders, not FT's btw. And the only failure of the 660cases came from accelerated corrosion, not a running , material, or geometry related issue. So a lot of money is spent on those 660 that really doesn't have to happen for the 13'000 rpm "no load" work saw builds in my humble opinion. Add RPM's... Most of my builds like to sit "no load" ( for reference tuning , not in the cut ) around 13500 and I still am comfortably in their reliability zone apparently as none have failed. Typically massaged intake filter holder, muffler mods, massaged lower transfers, compression around 180-185 and some with finger ports, all survived so far. Go further than that type of build, a better crank would make sense possibly.
On the 372's. I rattled one apart with an OEM crank as well. It has nothing to do with the AM bearings. The AM cranks with that "slot" in the connecting rod are simply not up to the task of a leaned on 372 build. Especially ones with heavier than 50mm OE pistons. So Xt's builds on those are hand grenades in my opinion for real work. Cases too are not up to the task but the bearings are surprisingly tough, in fact I have never seen a Farmertec bearing fail in any build from 2014 to now. As I said, every leaned on 372 class build I did on the Aftermarket cases, every one had the pto bearing pocket open up. Again that's not a bearing failure in fact in one instance I pulled the bearings out and reused them for kicks in a saw build on OEM cases.....its still out there making chips. So in my most humble opinion for most hobby even work saw builds, expensive bearing and seal options on Farmertec 660 or 372 builds are a waste of money unless other factors intrude like high RPM's. Subbing in a better crank makes sense on 660's if your build is going to be a higher RPM than the 13K "test no load" setup. Twist them past 13500 and a better crank probably is required. AND leaned on 372 build starting from and AM source, and a better set of cases and crank is almost mandatory. Used OEM is way better than a new Chicom 372 bottom end anything. I don't have any experience on the 440's and limited on 361 & 360's.
