If my engine I'd first pull the cylinder off, and inspect the head, gasket, rings and wrist pin bearing. Then inspect the crankshaft/camshaft bearings (rotate crankshaft at the magneto nut), if it feels like a bearing, go ahead and open the case. Weather crankshaft or camshaft bearings, the case needs to be split.
[/QUOTE]In your opinion are the stock bearings high failure points?[/QUOTE]
I personally have never had a bearing of any sort fail on 6 engines, BUT there are other members that have had, numerous.
Chinese HT breakdown pictures by Ron-Becker - Photobucket