You are welcome. One thing I forgot to mention is that possibly Ohrndorf specifies his piston/liner annular clearance somewhat related to his own method of making compression rings, although I think those are kind of 2 separate issues. The ring is the principle sealing component, the piston is kind of the carrier. Its not that simple but hopefully you get what I mean. He doesn't use or reference 'heat set' ring making methods like Trimble, but as mentioned, aside from the reduced crown diameter, the annular gap was close to other (commercial) engines I measured. The only other variable is what aluminum alloy they use vs what is more available to us. I discovered after the fact that tensile strength degrade at different rates with elevated operating (combustion) temperature, so the strongest material at room temperature may not be the strongest at operating temp. Luckily I guessed right but was not aware of this factor.
FWIW, this year I treated myself to 2 indicating micrometers encompassing my expected work range (0-25mm & 25-50mm). You can very rapidly & accurately measure many positions of a part, either while still in-situ on a machine or on a work bench. I find the 'analog' needle range deviation display to be visually more useful than digital 0.00000, especially on operations like lapping. So, useful for direct dimensional sizing, or as a comparator to some standard like a gage block or whatever. The floating anvil is what makes this distinctly different than a regular micrometer. Brand new they are very expensive, but many nice used ones can be had on Ebay & such if you are patient. I'm kind of a Mitutoyo fan boy myself, but I came close to buying German Suhl, particularly from this seller. Fortunately for you, seems like majority are metric & closer to your home.
