The fitting of oil seals to the inlet valve guides of earlier cylinder heads is a common practice. Nevertheless, details of the necessary changes are not widely known even amongst Jaguar professionals.

The inlet valve itself is not affected by this upgrade. The most obvious change is the fitting of the later style inlet valve guides which have an external groove near their upper end to retain the seals. The other necessary changes are as follows:

· Use the later Valve Spring Retainer which is 0.530” high whereas the early retainer is 0.630” high. The part number of both retainers is C27480.

· Use the later Valve Spring Collets which are 0.345” high whereas the early collets are 0.438” high. The part number of both collets is C27482.

Unless these changes are made, the higher old-style valve spring retainer will contact the top of the oil seal.

· The later valve spring seat is shallower than the early valve spring seat, but either may be used.

· The later tappet is shorter (0.843”) than the early tappet (1.00”), but either may be used. The early tappet has the advantage of giving a greater bearing area in the guide at the expense of being a few grams heavier than its later replacement.