|The MGA With An Attitude
HEATER VALVE MOUNTING - Bolts or Studs? - HR-103
Heater control valve mounted with hex head bolts or with studs and nuts
The MGA heater valve was originally mounted with a pair of threaded studs, lockwashers and hex nuts. The tapped holes in the head are rather shallow, so if you use hex head bolts they need to be cut to exactly the right length for best thread engagement without bottoming out. It is a bit tricky getting the length right, and then you have special non-stock bolts, so if you lose or damage them you start over to make new ones.
Better to use studs and nuts, and easier too. The stud needs to be 1/4-28 fine threaded and wants to be 7/8 inch long for neatness and originality (but off the shelf 1 inch long will work). You can start with a long 1/4-28 bolt, use a threading die to extend the thread to an inch long, saw it to length and grind off the burrs. It should screw in easily with fingers, if not use a tap to clean out the hole. Double nut the full thread stud to screw it with a wrench just tight enough to jam the thread at bottom so it stays put. You only need to do it once in your life, and it's good for the life of the cylinder head. These side studs can even be left in place during machine work for a valve job.