Hello,

I've been working through timing chain noise on my XJR6 for the last few years with mixed results. The following bullet points summarize my efforts so far and their results:

- Bought car in 2021 with 43k mi and typical engine rattle under load at 1500-2000 rpm
- Replaced upper timing chain tensioner, no change.
- Replaced timing chain guides (and head gasket after I damaged the overhang when refitting the timing cover), improved rattle but still there.
- Gave the car to a British car specialist to have the primary tensioner itself replaced and the supercharger rebuilt. Shop was out of their depth with this job, car came back with massive coolant and oil leaks. Engine noise while running is mostly cured, but now makes an awful rattle on cold start.
- I removed the timing cover, fired off the primary tensioner, replaced the oil seals, tightened down the coolant hose clamps. Car no longer has massive leaks, but still makes awful rattle on cold start.
- Replaced the upper tensioner again, ensuring that the tensioner is assembled according to the attached write-up, car still rattles loudly on cold start.
- Replaced engine oil with Castrol 10W-40 Semi-Synthetic and OEM oil filter. Car still rattles loudly on cold start. Car runs nicely with good power, however there is a faint tick that I am assuming is an exhaust leak which has been present since I replaced the head gasket. I plan on attempting to remedy this with new 'donut' gaskets on the downpipes, but I am prioritizing solving the cold start noise at this point.

I am avoiding driving the car as I troubleshoot this issue. Since the oil seems to be bleeding down as the car sits, the engine takes 7-10 seconds before the oil pressure builds, I'd like to avoid wearing out the bearings with too many unnecessary startups. After these few seconds, the upper tensioner builds pressure (I'm assuming), and the awful rattle occurs. From then on, the oil pressure gauge remains steady at the center of the gauge as long as the engine is running.

I've searched the forums for causes of bleed down on the AJ16 engine and haven't found anything I haven't tried so I wanted to make a post and see if anyone has heard of a similar issue on vehicles fitted with the AJ6/AJ16 engine.

Thank you!
Michael