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.

Addendum: 8/15/2:
An era of confusion may be coming to a solution, nd I may have been mistaken about the threaded studs when this article first appeared in2006.

In 2020 I added the Part Numbers tech section to this web site. It contains all of the part numbers used in all MGA models, as gleaned from multiple issues of the Service Parts List. One reveal then is that none of the SPL mention any threaded studs for attaching the heater valve. The base models show 1/4-28-UNF x 1/2" long hex head screws attaching a blanking plate (with a paper gasket). When the optional heater is installed, the blanking plate changes to a water valve with flanged mounting feet, and the screws need to be longer.The SPL then calls for one screw 3/4" long, and one screw 7/8" long. Difference is, the bottom screw is carrying a spring clip that will hold the thermometer signal pipe, and the clip needs the longer screw. Now talking about three different length crews. If you change these hex head screws to studs with hex nuts, the new threaded studs need to be a little longer, like 1" to 1-1/8" long to accept the clip, lockwashers and hex nuts. But I still think it is good to use threaded studs, as it makes assembly easier, and the stud length does not need to change for adding or deleting a heater.

Picture at right is the clip that goes on the lower stud to secure the thermometer signal pipe. This started out as two pieces, a BHA4081 clip with one bolt hole, and a AHH5802 Bracket (clip retainer) with two holes, held together with a screw and nut. Part way through MGA 1500 production it changed to a BHA4081K single two-piece clip, permanently assembled, as shown at right. If you need a clip now, do buy the later model clip (as the early model parts may not be available).