Old stock production engines with tapered bore

Bought a couple of decently used red postage stamp backplate reedies with thin wall No.1 cylinders over the past 2 years off of feebay. They must have served their prior owners  until their host COX planes were damaged beyond repair, and then have been sitting around for decades in drawers..all have very good compression, and when equipped with a turbo plug adaptor head, turn the COX 5x3 safety tip black propeller 21k on the bench when fed with 20% nitro in the fuel..

Based on their component details I traced them back to the mid 60-s with the help of COX Engine Handbook of Dan Sitter.

When dismantling them on arrival from the seller for a check and clean up, most turn out to have tapered bore with the piston moving up to the TDC only...hmmm... A nice surprise and makes me wonder, how come, when only old stock TeeDees were known to have tapered bore.......???

This one just joined the fleet, was a piece of gunk on arrival,




...and was given the right cleaning, additional parts and care it deserves.