Chainsaw Repair

This is a topic that interests me - I've been reading that people believe that the case volume can be too small and that this will hurt performance, but I do not see the logic in that.  The swept volume of the case will always be the same on both sides of the piston, so there must always be "enough" volume.  The only thing I can think of is that a full circle crank might block flow to the transfer entrances, but otherwise I can't see the problem with reducing case volume.  It seems like less should always be better.

When drawing mix into the case you can have at best one atmosphere of pressure to push it in, and any extra volume just reduces that pressure differential and makes for less efficient pumping.  When pushing mix up the transfers you can generate much more pressure, but initially must push against the residual combustion pressure in the cylinder.