Jaguar Repair: 1986 XJ6 Engine Tapping Noise, piston speed, oil viscosities

Question
Hi Howard,
I have a tapping noise which sounds like it is coming from the top of the engine. This tapping is only audible on cold starts and disappears after driving about 2 miles. There in no tapping noise on warm starts. The engine only has 52,000 mile on it and does have a stakedown kit installed on the exhaust side valve tappet sleeves. Oil pressure is 30psi at idle and 60psi at cruising. Different oil viscosities have had no effect. Any suggestion?

Answer
Hi Jim,
By "tapping" I take it that it is a light noise. If it were mine I would first use a mechanic's stethoscope to try to narrow the noise down to a smaller area. Then check valve clearance cold and check it again hot to see if you can find anything. Also try to determine if it is piston speed of valve speed. A good method is to put a timing light on the engine and note if the tapping is about the same speed as the flash. Also move the timing light pick-up to different cylinders to see if you can get it to look like the flash of the light is causing the tap. Keep in mind that the light flash is on a cylinder that the valves have been closed for a while and only other cylinders have valve action at that time.
Howard