"I have always believed the the tilting and jamming theory was an incorrect diagnosis for the fracturing tappet problem. A study of the history of the three types of tappets used by the factory shows that the increase in tappet length did not cure the problem, neither did the fitting of the tappet sleeves. The whole idea of the tappet tilting and jamming is just rubbish. There are many overhead camshaft engines and they have never had this problem. Jaguar engines, although sleeved, have tappets only 1 inch long, even shorter than the original MGA tappets. The Triumph Stag runs the tappets directly in the alloy head with no problems. The list goes on.
The tappet fracture problem was only solved by by the addition of Molybdenum to the material of the third type of tappet. This change of material was introduced at engine #2211 as shown in the factory Technical Data Book. The only reason for the very significant chamfer on the third type of tappet was to allow the BMC Service mechanic to determine if the new tappets had been fitted.
Every Twin Cam engine I have seen in Australia has had the third type of tappet fitted at some time early in it's life. I have never heard of a tappet fracture in Australia with or without sleeves. Even though there is no Service Memorandum, the BMC Dealers must have received advice to retrofit the third type of tappet. This was probably because all BMC Dealers in Australia were strictly controlled by the BMC factory in Sydney".
-- Regards, Mick Anderson

Sleeves for tappet bores