Well, I decided to go for it:



I reduced the thickness of the crankshaft at the intake port from 7.69mm to 7.44mm, meaning the intake port will be open ~ 2.9° longer. (the crankshaft diameter is 9.98mm.) Most of the grinding was done on the trailing edge, but per Roelof's recommendation some of it was done on the leading edge as well. I started the job with a Dremel diamond cutting wheel and finished the job with a diamond-coated jeweler's file. I also did a small amount of polishing inside the crankshaft, because I had to go in there anyway to make sure the edges I rounded-off didn't have any burrs still attached.

I haven't found any shims I can use to raise the sleeve, but there is room, so that's something I can try if I don't see any noticeable improvement from the crankshaft porting job.

As I was putting the engine back together, I suddenly remembered there was something I wanted to do the next time I had the engine apart -- open the lowermost area of the swirl-port channels. They were almost completely blocked off at the bottom originally:



The channels are nice and open now. (yes, I made sure to cover the bearings as best I could and then flush them thoroughly afterwards.) When I shine a light down through the sleeve, you can see plenty of light making its way down through the channels, and in through the side of the piston. There shouldn't be any intake-related breathing difficulties with this engine anymore.



I'll try to run it briefly tomorrow if the weather isn't too terrible, just to make sure it still works, but it's way too cold to run it hard so a speed test will have to wait until spring, or at least an unusually warm day this winter.