Avoiding Head Gasket Failure

Leaking or blown head gaskets are a common problem with British sports cars engines – particularly with BMC A-series (Spridget) and B-series (MGAs and MGBs). The problem arises from many different causes, such as the mating surfaces of the cylinder head and block being warped, the cylinder head studs stretching, or the gradual deterioration of the head gasket. The symptoms can range from a minor weeping of coolant from between the joint of the head and block, to chronic overheating and loss of power. But fear not, there are steps you can take to avert these problems.

The first thing to do is to check that the head and block laces are perfectly flat, smooth and clean. It is easy to check for warping using a straightedge, and a single-edge razor blade and putty knife will remove any residue or old gasket material. Block surfaces seldom warp, (but they can!) and cylinder heads often do. If either of these surfaces are not as above described, it is time to visit your local machine shop to have them rectified. Your cylinder head studs live a hard life; it is their job to retain the cylinder head and gasket tight to the block against combustion pressures of several thousand pounds per square inch! It is not the friction between the head nuts and cylinder head that holds the head on. hut rather the elastic tension of the cylinder head studs stretching a few thousandths of an inch, that holds everything together. After many years of use, these cylinder head studs and loose their elasticity, resulting in the head no longer being held firmly against the block. If you try to retighten them, they only stretch more.

So the next time you have the cylinder head off, think about replacing the studs either with stock or high performance cylinder stud replacements. Whether you choose the stock or premium studs, before you install them in their threaded holes, it is a good idea to run a tap down the threads in the holes to remove any rust or sediment. Then take a s/a”machinist’s countersink bit in a electric drill (go slowly!) and counter sink all the stud holes in the top of the block so that 1/16th of an inch all the way around. This will prevent the stud from pulling up the metal immediately surrounding the hole, and forming a burr or ridge that will actually lilt the head and gasket away from the block, ruining the seal.

Always install a new head gasket, again choosing from stock or competition, and using some sort of gasket cement – never install one dry! While the metal flame rings on the gasket will seal the combustion chambers, the water and oil passages don’t have them and need something to help them seal and prevent the fluids from eventually deteriorating the gasket. Put a head gasket In dry. and It will only be a matter of time before coolant and oil Is weeping down the side of the block; that’s why I recommend using a gasket cement such as Permatex Hy-Tack, Coppercote or Hylomar, all of which are available commercially.

When retorquing the cylinder head nuts, be sure to follow the recommended sequence and torque specs as called by the manufactuer. If your manual says to torque your head to 55 foot-pounds, instead of starting at 55, start at 35 and go through the tightening order, then go through the sequence again at 45, then finally at 55. This way you will gradually increase the load on all parts evenly and assure yourself of a good seal. While many modern engines and head gaskets do not require retorquing, our trusty British engines do, so retorque your head nuts within 500 miles, “…and remember what the Doormouse said… Keep your head!”

(My apologies to Grace Slick and the Jefferson Airplane.)

By Ben Trovato, Santa Barbara, CA