Just had new enging built. I notice that the air pump belt was sliping, so I tighened up from the altenater. Right after that, the screws in the water pump pully backed out. I tightened them up, broke one off tring. is this common?

 

My mechanic lock tights them on customers cars . His custom pully , his son made and one for Rotorbrain s car ,he uses 8mm diameter button head allen bolts . Strong and good looking .

 

8mm x 1.25 or 6mm x 1.0mm?

 

try a bit of thread locking compound.