Jump guard

Why you need a jump guard. Watch how the two chain guards jump in time with a loud clonk. The profile of the cams makes the camshaft momentarily try to run ahead of the crankshaft. This slackens the bottom run of the chain and it tries to jump ahead by one tooth on the small crankshaft sprocket.
This is the latest 1300 engine and cam chain tensioner. Often rattles on start up after standing a while. This slow cranking of the engine shows what that rattle is until the oil pressure reaches the tensioner.

[@user-jo3hk5pu1v]

What is the reason for this work? What's broken? Was there a knock at idle?