Sorry I didn't explain properly, in the centre of the crank pulley is a large bolt very unlike to have come loose but maybe worth a check.
Thanks for letting me know it's chain driven cam shaft.
Have you had a listen to other identical engines in other identical cars?
Could the noise be a normal noise?
How long have you had car?
How many miles you driven in it?
Has it been serviced properly all is life? Service history?

Try not to get too frustrated you are doing all the right things, well done.

What is the star shape bolt in the middle of the crankshaft for

Holding things to the crankshaft .
Is it loose?

Not checked it will try that if I go the wrong way will I do any damage !

No
just check it's obviously not loose.
Please answer the other questions , trying to help.

Sorry service history yes done about 500 miles in it not listened to any cats like this do no anyone with one .

Sorry have not listened to any cars like this so would not no what they sound like