I'd be very worried if the cam timing was out and the engine run for exactly this reason. The K-series is not a no-impact engine design, meaning that the valves can strike the piston heads if the timing is not correct. If a valve (or valves) have struck the piston face and bent as Nodge suggests, then they risk disintegration and complete engine failure at a later date.
If you have access to an endoscope, you can look down the spark plug holes and see whether there is any evidence of valve/piston contact. Otherwise, it would be sensible to lift the head to inspect carefully. If there has been piston/valve contact, I'd replace all the valves as a matter of course. I'd probably angst over the pistons too, but if low speed impacts and little obvious damage, I'd leave them but worry...
Pinking is premature air/fuel detonation that can occur when there is too much ignition advance, too lean a fuel/air mixture, fuel with too low an octane rating etc.