Stripped Jackshaft Gear in the V12
This 1987 XJS was the topic of discussion on the Jag Lovers Website. The symptoms were that the car would run for a bit and then start pinging, misfire and die. The engine would not restart. Checking the distributor would show that the timing was a cylinder or two off. Correcting this would let the car start right up for a short while until it happened again. Turns out that the front drive gear for the jackshaft was not properly hardened and the teeth had worn off. The other gears had no similar signs of wear. This was verified before taking the front of the motor apart with a scope that would go in the oil filler hole. The picture below tells it all. It also aggravated the situation that the tensioner was snapped and was not holding the chain as tight as it could have been. Mostly sure that the tensioner break was just a coincidence.
The picture below shows a good gear installed.
