Hi all first post and a desperate one. I have a knocking noise coming from my engine. It kicks in almost like a switch being flicked, halfway up my temperature guage at between 1500rpm and 2000rpm. Prior to this my engine is so quiet I can barely hear it. It started a year ago and below is a list of my attempts to rectify it.
1. Alternator belt changed/pulleys checked - No fault found
2. Alternator bearings replaced - Knackered and replaced but noise still present
3. Tappet clearances checked/adjusted - Engine runs quieter but knocking remains
4. Full service - Spark plug clearances checked during service
5. Oil treatment - oil replaced also coming out clean
6. Big end/conrod bearings replaced - Found to be worn but no damage to crank
7. Oil pump inspected and filter/pickup cleaned out - no blockages and working well oil pump tested in operation oil moving freely around engine.
The timing belt has been done in last 2 years, before anyone asks. Please help I am at my wits end!