2006 XJ X350 Super V8 rattling noise from top of engine

So I arrived home with my V8 after a long journey on the autobahn (see my other thread about my new Super V8) and took the car to my favourite workshop yesterday and asked the owner to have a look at the air conditioning that wasn’t working correctly. He told me to start up the car with the bonnet open. We could clearly hear a rattling sound like a bunch of heavy bolts in a metal can that came from the top of the engine. The immediate diagnosis was loose timing chains. This is a 2006 car and folks on the German Forum are sceptical. They’re saying by the time this car was built all the timing chain issues like cheap plastic tensioners etc were fixed and problems here would be extremely rare. They’re assuming it’s the supercharger. I left the car right where it was as I didn’t want to risk driving it any further, which meant calling the wife, asking her to pick me up at the garage and having a bit of explaining to do.
I’m asking for your experience and opinions here. If it is the supercharger (and I’m not ruling out the timing chains), which would be the best way to proceed?
Please tune in,

I suppose for peace of mind you would 1st check the timing chain and tensioners. If you dare to run the engine a stethoscope could help to pinpoint the noise, but probably you don’t want to run the engine at this point.

I also lean towards the supercharger as the source. The most common failure for the supercharger (and matches your symptoms) is a bad supercharger coupling (internal part.)

This link has more information - Eaton’s own website directs to this. How to replace an Eaton Supercharger Coupler - Superchargers Online


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Disconnect the S/C belt and see if the noise is still there.


You can basically rule out the timing chains.The timing chain issues were basically fixed with the latest 4.0, which actually have half of the 4.2 system even though the parts book doesn’t document that. Totally fixed with all 4.2. The superchargers frequently make nasty sounds

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Thanks for your input here everybody, very encouraging.
So the next step is to disconnect the s/c and see if the rattling noise persists.
The mechanic wanted to do that today but didn’t have time in the end. I stopped by at the workshop after work and saw that he had moved the car around. He said it sounded awful this morning and fired it up for me to hear.
When started it sounded like a friggin diesel truck, and once it ran it was fairly smooth but after about 20-30 seconds the rattling set in, so we shut her down again.
I’m hoping it might only be the s/c coupler, but I’m afraid it might be a much larger job.
Quite disappointing.

That sounds more like the coupler than the SC but I can’t hear it from here. The noisy SC tends to be more consistent, not stop and start.

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I stopped by at the workshop again this afternoon and was happy to see that they had been working on my car. The engine cover had been removed as well as the supercharger belt, which was brand new. Apparently someone has been fiddling around here, the s/c belt as well as the belt pully and tensioner were brand spanking new. The engine drive belt had not been replaced and was showing its age and the water pump (or was it the s/c coolant pump?) was just dangling around. Signs of a botched job.
The shop owner started the engine while I was there and it sounded very good to me with no rattling, but he said it sounded very bad when he had started it earlier in the day. He invited me to come back tomorrow morning where he will start it again with a thoroughly cooled down engine. I’ll try to make a cell phone movie, but something’s wrong with my phone’s microphone.
Next task will be to mount an new engine drive belt to see if that changes anything. We’ll see… We’re taking one step at a time here.

Thanks for krrping us in the loop, Chris.

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Another visit at the shop today, where the owner started up my car with a cold engine for me to hear what it sounds like with the s/c removed. With the starter still engaged it sounded to me very much like a diesel egine, and after that, for me at least, it was quite smooth, although the shop owner doesn’t agree. Maybe some wishful thinking from my side.
The following movie was done with my iPhone, but please beware; it currently has some serious microphone issues. Playing the video on my phone the sound was awful, but then I tried it tonight with headphones on my laptop and it was much better. You can hear that the sound drops quite randomly, but I hope it’s good enough to give you all an idea.

Next we will disassemble the s/c to see what the coupler looks like but that probably won’t be earlier than Wednesday.

How about an update, Dave?