WIFI/BT Inspection borescope.
2.0mb Depstech borescope, cheap amazon one with an adjustable light on the tip and a few little end fittings (hook, 90 degree mirror, ?) is about $15. minimum focus is about 2" but you can put a lens from a laser pointer on the end and get that tuned to probably 0. These are probably just webcams on a shaft, not real precise but they do get into things. could ID 273-4 pistons in the bore in a heartbeat.
2.0mb Depstech borescope, cheap amazon one with an adjustable light on the tip and a few little end fittings (hook, 90 degree mirror, ?) is about $15. minimum focus is about 2" but you can put a lens from a laser pointer on the end and get that tuned to probably 0. These are probably just webcams on a shaft, not real precise but they do get into things. could ID 273-4 pistons in the bore in a heartbeat.
