Keith E.,
Thanks man. I'm brainwashed from being in the engine industry for 28 years. Just call me motor mouth.
Wyatt C.,
Preload force for stock Kohler K-series (large)
valve springs is 25 lbf valve seated, 50 lbf valve fully opened at .312 lift. Spring constant is 81.4 lbf/in.
On your bearing dilemma, I think your SKF contact is in error. A 6308-C3 is the correct ball main bearing for your engine. Motion Industries numbers are all correct. As the majority of ball bearings used are C3's some manufacturers drop this and only use a different spec (C1, C5, etc) when this internal clearance, or "precision" is called for. Bottom line, believe Motion Industries.
Ball main bearing inner races should always have a slight interference fit with the shaft to prevent rotation or "creep". Otherwise fretting corrosion takes place between shaft and race. It produces that red stuff (iron oxide) that you see sometimes when you remove a bearing from shaft. Interference should only be around .0002 to .0005. Coat the shaft with high pressure grease or STP and you'll be amazed at how easy they slide on, once you get them started. Once together, drive the crankshaft to one side using a plastic or Compothane hammer, then measure clearances between inner race and crank shoulder. This is shown in the manual.