While driving into work this morning, my carpool-mate was talking something about taxes to me and I was daydreaming about Cox engines. Caution: the following is personal opinionated info based only on observation, speculation, and poor memory... I may at one time have been concerned over the piston hitting the glowhead at TDC and perhaps this had something to do with using the cyl shims (not head shims [for clarification]). One of the late C/L toys from my youth - I remember as having a metal screen spot welded to the cylinder around the exhaust ports like a spark arrestor? I think this was done to try to prevent fires because liability issues were becoming more prominent in the culture at this time (mid-70's). If you've ever had an alcohol fire on an airplane, they are very difficult to see. Funny things start happening before you realize what's going on. I think the narrow exhaust slits in cylinders showed up shortly thereafter to try to perform the same function(?)

CP, forgive me if a really dumb question but do you separate the conrod from the piston to facilitate shaving it and what is "friction proofing"?