True top dead and valve to piston clearance

When you identify the true top dead centre on both side of the cranks..for example 12btdc and 12atdc then when you set up the camtimming you move the crank to zero...........then start doing the valve open and closing event..........Also can you use a borescope or inside camera to check piston to valve clearance........... many thanks ron

Normally you'd do the check during the dry/dummy build using one or two traditional methods, but a borescope is so cheap nowadays, it could be a good way to double/triple check if you have access.

Where it may be useful is if one wants to swing the cam' timing a little and wants to check without pulling the engine down - it's a good idea to check the clearances a little either way during the dummy build, but sometimes one doesn't think about it.

Other times that would be good id with OHV engines when the rocker ratio is changed, or any engine where a camshaft is changed.