Oscillators Question

[Gdavis5000]

I'm about to make my first engine, a small oscillator. Simple enough, but is there a rule of thumb about the clearance when the piston is at top dead center? Obviously it can't hit the top of the cylinder, but how close? Does anyone know of an available book dealing with such simple questions?
Isn't it great to have this BB? Thanx Clover
George

[PolskiFran]

I don't know if there is any rule of thumb, but the closer to the cyl. head the less steam is needed to fill the space. Make sure the ports are above the piston so the piston does'nt block the passage.
When I designed my two small oscillators I made the clearance at least the diameter of the ports.
Frank