[Wbulk]

Andronikos, good pictures and video. It would appear you have some engine design parts compatabiliy and possible clearance issues. David is right, you need to contact the engine builder. With these engines they can vary greatly depending on who built them. There is a great number of performance parts that if selected correctly and with clearances checked work great. But if wrong parts are selected, and are not compatable bad things happen. Just buying performance parts and bolting them together does not make a reliable performance engine.

The studs that were broken are called rocker arm studs. That is the pivot point between the push rod and the valve stem and is where the valve lifter pre-load is adjusted.

Since you have two rocker studs that broke this is not a fluke issue with a defective part that broke. This may be beyond your capabilities at this point. Reading books about stock engines will give you the basic concepts but with performance parts the engineering is changed and the clearances are critical.

Just to get an idea of any clearance issues I would put a wrench on the crankshaft bolt and turn the engine over very slowly while watching one of the rocker arms to see how close it comes to the valve retainer. The retainer is the round disc that is on the top of the valve spring. Also look at the valve retainers on the ones with the broken studs. Can you see any contact points ? I wouldn't go any further until you contact the engine builder and see where that goes. Then if that doesn't work out you might take the below steps.

It just might be possible someone tightened the valves all the way down thinking they were like stock valves, bottoming them in the lifter bores and causing the studs to break. You can check this by cheking the adjustment on one of the other rockers.

You can do this by turning the engine over in the direction of travel with a wrench slowly and watching one exhaust valve. With the exhaust valve down turn the engine over until it's push rod and rocker starts to move up. This puts the intake on the base circle of the cam. Then on the same cylinder intake valve slowly loosen the adjusting nut until the push rod just has "any" up and down play in it. You may tell by trying to spin the push rod with you fingers. When you get to the exact point it will free up and spin freely with you fingers. I would go real slow maybe turning a 1/8 of a turn and then check it. Keep doing that until you have play. It should be about 1/2 a turn until you have play. Those rockers most likely have locks with an allen screw that you have to loosen to turn the adjusting nut. If you have a full turn or more until it loosens you have a problem.

If by some off chance someone tightened these all the way down that could explain what happened. My opinion!

Wayne