I have a e-type s2 coupe from 1969.

My engine started making a loud rattling/knocking noise. Its a terrible sound that forced me to stop the car. The sound starts on higher rev's 2000-3000 rpm, not on idle.

The sound comes from the middle of the engine, the cam followers or camshaft does not show evidence of wear.

If I remove spark plug wire cylinder 3 the sound disappears, removing any other spark plug wire does not make any difference.

Can anybody help me on how to determine to the problem.

Thanks, best regards,

 

As expected, the big end of cylinder 3 is completely wasted.
See this on youtube:
Engine running: MVI 3691 - YouTube
Big end play: Jaguar XK 4.2 big end RIP - YouTube