it is possible valvetrain components are stickin g or binding but that's a stretch ...I'd be wondering if the temper og the pin metal was adequate.. but either way I'd replace timing chain and gear and get a good pin

 

The timimg chain looked almost new when I took it out...

 

in a situation like such if you can see anything obvious there are two choices....put it back together using titanium pin or tear motor apart and inspect all internal components...but before that..I'd pull the dizzy and make sure that the dizzy shaft is not binding and or a possible oil pump binding but you'd think it'd shear the roll pin on the dizzy gear first

 

The only 2 things I can think of is slack in the timming chain or a defective dowel pin. Maybe you have too much preload or too strong of valve springs. I agree witrh mjr, put a new chain and gear set on, a new pin and run it unless you want to tear the engine down....you could have less then 50 bucks into that.