MK I SQTop End 1949-51

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MK I engines are notorious for blowing head gaskets and when they do the temptation is to tighten the head studs to try and seal the joint. Do not do this, as it is most likely that the studs will pull the threads out of the alloy. The principal reason for this problem is that the alloy of the head expands by a far greater amount than the steel of the studs and as it does so, something has to give, firstly the gasket is compressed, and then the head nuts are tightened again as the gasket blows. When the gasket cannot be compressed any more either the studs will stretch or the threads in the aluminium will strip.

The cure! Firstly check the threads by placing a suitable spacer over each in turn and torque a nut up to 20 ft/lbs, if the stud is still in place it is OK but you may prefer to use a proprietary thread insert anyway. The vast majority of heads have already had some kind of thread repair carried out from the ubiquitous ‘Helicoil’ (good) to massively oversize studs (not so good), I have seen up to 9/16” Whitworth used! The best approach to these earlier bodges is to remove them and have some alloy plugs professionally welded in place. The stud holes can be drilled and tapped and standard studs used. We have done so many of these heads that we have had a drilling jig made so that we can accurately position the holes. The studs should be ‘R’ quality, which is a standard high tensile steel, mild steel will stretch too much and harder materials will not stretch enough! Next check that the gasket surfaces are flat, they rarely are in spite of having been skimmed, perhaps several times in the past.

The most important point is to use Otto’s super gaskets. A good quality gasket cement such as Loctite ‘Ultra Copper’ should be used and the head torqued to 12-15 ft/lb initially and no more. The studs should be checked after the first run of the engine but the torque used should be 10-12 ft/lb, thereafter they should be checked several times until they have settled and continue to do so at every service but only to 10-12 ft/lb.

A torque wrench can be used on the nuts between the fins. Using a double ended spanner, place one end on the head nut and a bolt with a nut wound all the way down the thread in the other end of the spanner. Attach the torque wrench to this bolt and apply torque. This does work contrary to expectations, try it out on a nut and bolt in the vice or use a spring balance on the end of a spanner. Full details are available on our website and are included with the Otto gaskets also available printed on paper by request.

The very early heads used ¼” studs and it is doubtful if any of these have survived, later engines used 5/16” studs, these are the ‘early 1949 engines’; the later 1949 engines with an ‘X’ suffix to the engine number and later used a 3/8” Whitworth x 5/16” CEI stud. Any early engine should be converted to this later arrangement.

Early 1949 Head Studs: – (Series A engines without ‘X’ suffix to the engine number)

Late 1949 Onwards Head Studs: – (Series B engines with the ‘X’ suffix in 1949)

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