Edited on 2013-01-08 10:10:47

Edited on 2013-01-08 10:09:27

In late 1969 and early 1970, Jaguar fitted a "new and improved" timing sprocket adjusting plate to the XK engine (now referred to as "cruciform") which had four raised arms on the backside with fewer teeth to grip the inside of the sprocket rather than the previous adjusting plateÔÇÖs 360?? of teeth. But the ÔÇ£cruciformÔÇØ adjuster plate was found to possibly slip around and cause timing problems (at the least) or the valves could even hit the piston crowns (at the worst).

The solution is to remove the cam covers, unbolt the camshaft sprocket adjusting plates, and examine the backside to determine whether they are ÔÇ£cruciformÔÇØ whether they have rounded off gripping teeth.

If present, replace the ÔÇ£cruciformÔÇØ adjusting plates with the 360?? toothed adjusting plates (part # C30767) if you can find them. Otherwise, replace with the ÔÇ£newÔÇØ camshaft sprockets with slotted bolt holes for making the timing adjustments (part # NBB2549AA used on 3.6 and 4.0L AJ6 engines from 1988 on) which are also becoming more scarce.

Be aware that this ÔÇ£newÔÇØ sprocket uses a different flanged (or washer) head bolt (part # JZS100082) measuring 3/8ÔÇØ x 24 fine thread x 5/8ÔÇØ length which grips the sprocket face in a way that the earlier regular cap head bolt will not. These original Jaguar bolts are also getting difficult to find, but an alternative can be ordered from Fastenal (part # 0148165) which will be ?¥ÔÇØ long. Grind off the extra 1/8ÔÇØ to so that it will not protrude from the back of the sprocket and rub against the cam bearing cap.

Good luck!