Inliners International Forums General Discussion Engines 250 chev sounds like rod knock. Timing gears?

Rebuilding a basket case 250 Chev.
Fired up in stand, sounds like a rod knock.
So I tear it down, rods about .004 to .006, journals all look good just worn down to the copper.
So I tighten the bearings up to .002 to .003, figure it's good.
Fire it up, SAME NOISE. Bang-bang-bang one per crank rev.
Pull the fuel pump & belts, same noise.

Pull all the rods, piston pins all tight, all looks good.
Soin the crank all quiet. Spins easy.
Add the cam & spin it over with spinner wrench: THERE IT IS.
Either the cam gear or retainer plate or crank-cam gear mesh is making the noise, once per crank revolution.
Aluminum cam gear, steel crank gear, looks all factory.

Anybody ever hear a noise like that? What is it?