There's too much emphasis placed on bore condition. You can have all kinds of patterns, wear, gouges, scores and problems with the bore - and the engine will still run reasonably well. But the major weakness of IC engines is poppet valves.
95% of your engines problems will come back to valve sealing and seating and valve head condition. Valves are the most heavily worked part of any IC engine.
Sleeve valves and porting really are a much more durable arrangement, but the drive mechanism and clearances are critical areas, and they can't handle high RPM's. In tests of the early sleeve valve car engines in the late 1920's, the sleeve valve engines were still reliable, and still producing 99% of their power output after 80,000-100,000 miles - unlike their poppet valve cousins, which were suffering serious power losses and valve sealing problems, in as little as 40,000 miles.
I would have liked to have seen the rotary valve head become more developed and widespread, but inertia and lack of funding, often stopped many good ideas. The Deane Rotary Valve, an extremely promising Australian invention by three Aussie engineers, was proven to work, and be exceptionally efficient and reliable, when tested on a motorcycle engine - but it failed to gain financial backing, and fell by the wayside, as with many good design ideas.
Rotary-Valve Internal Combustion Engines.
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Douglas Self, rotary valve engines, Minerva, Aspin valve, Cross valve, Froede valve, Wankel valve, Mellors Rotary Valve