sounds like you have 50-60k on plugs\coils - these are due for replacement now - so if you do the compression test - replace them. If you want to stay on cheap side - replace the coils only if broken.
Get a 20$ USB snake camera from Amazon - you may not see anything - but it's only 20$
Try to record sound from the serpentine belt area - maybe while it wasn't driven much - it has a flat spot that is responsible for the clicking,

 

Something else to consider is the small vapor canister purge solenoid under the black V8 cover. Not sure when it's supposed to activate or for how long, but that thing can cause a hell of a knocking sound. When I pulled the V8 cover off, the canister was tapping so hard it was literally moving.
I was going to order a new solenoid but the ordeal lasted only minutes and I've not heard it again. It may be normal operation and I was just under the hood when it decided to do what it does. It is enough to give a Cayenne owner a panic attack.

 

The purge valve, PN 948-110-202-01, was replaced at 66k miles. One of the few other repairs I did not list earlier (trying to keep to relevant stuff).

I've already got a fiberoptic snake camera thing, so that's ready to go.

I'll talk to my BIL soon to confirm on all this. It sounds like I should at least get 8 new plugs before taking things all apart.

 

Sounds like solid plan - check on your snake camera if it has some kind of "fisheye" attachment - as you want to see the side of cylinder, not the top of the piston

 

Interesting about the purge valve. Apparently all the 958 CTT's have noisy ones.. and that's normal. The clue that it isn't a scored cylinder is the clacking from the purge valve is most noticeable on cold startup when the system burns off fumes from the purge canister, AND the clack noise isn't directly related to engine speed. The 958 CTT one doesn't have an electrical connection, but it serves the same purpose. FWIW - Mercedes uses the same valve/system on some of their engines, and have built a sound-reducing foam cover to quiet it down. I've thought about looking for one for the CTT.

 

Great info. I would be interested in seeing what the foam cover looks like. Let us know what you come up with.

Cheers,
TomF

 

Add 1.5 300ml bottles of Liqui Moly Cera Tec to the oil. Everything will STFU in about 200-300 miles.

 

Some more results on this engine ...
Repeated the video test, with all panels removed now, with a cold start in ~50-60*F weather.

I can still hear something a little off, near the 5-6 cylinders, in that video, and just listening live, but a mechanics stethoscope on all cylinders (on valve covers, etc.) sounded smooth and uniform between all 8 cylinders.

I tried to get the video equivalent of that toward the end of this video by holding the camera in contact with each cylinder area for a few seconds.

Compression test was very uniform among all 8: 200-195-195-195-195-190-190-195. (so 6 and 7 were 190). All in PSI of course, with the engine cranked until it automatically would stop after about 10 seconds (so uniform). Repeated to confirm numbers, for example #6 at 190 psi was run 3 times with that result.

Borescoping cylinders 5-6-7 (at bottom dead center) showed smooth, reflective cylinder walls, with no hint of scoring. Here are some photos of that, mostly aimed at the cylinder / piston interface. The pistons showed carbon buildup, and then some white spots, where I assume it had flaked off - the useful thing about those were that the white spots would show as reflections on the walls, seemingly confirming a smooth reflective surface there. Also suggests that if there were any scoring, I'd be able to see it. Watching it live (vs. still photos) was a little clearer, and yes, a brighter light and better focus would be nicer. But I don't see anything here that hints at any problems on the cylinder walls.







Spark plugs all looked great (to me at least. any comments?) (these are the OE-spec Bosch FGR-6-KQE (7413) 999-170-218-90, installed by the dealer 56k miles ago when the crate engine was installed. The only thing out of the ordinary is that plug #6 had noticeable oil on the threads (you can see that in the pics). Would that be explained by a slight leak in the valve cover gasket, and nothing to worry about?







The coils (went in with the crate engine too) all were visually perfect. No cracking seen. Interestingly, coils 1-6 were all 948.602.104.03 (330C6 at top), and coils 7-8 were ...05 (211B8). So I guess I was "lucky" to be the one to straddle the version update.

Since there are no running problems, those coils are going back in. But new (same type) plugs will go in when they arrive tomorrow.

The final check will be oil analysis for metals indicating cylinder wear, but to me this all looks good, so I expect to proceed with the purchase.

I was going to do a sound test with the serpentine belt removed as well, but that looks a little more difficult on this engine, and listening carefully for it did not suggest it was the issue, so I plan to skip that one.

And BTW, this is all looking better than I could have expected, so I'm expecting the deal will be done.

Any comments or suggestions on any of this before I button things back up tomorrow?

 

Yes, the oil on the threads of #6 is due to the interior valve cover gasket around the plugs. Very, very common issue on these engines.

The plugs all look good to me for 56k miles. There is a bit of carbon build up, but a reasonable amount. The compression does looks consistent enough. Looks like you have enough information to now know that this engine is in decent health and passing it up due to a very, very slight undistinguishable mechanical noise might not be worth it.

 

I am not expert, but I think it looks good. Compression within 5%
Think about it - this one may be in top 5-10% condition of all 2004 S available, you had great opportunity to check it out. And it will have brand new plugs - I don't think you will be able to find a better one.
But if you doing oil analysis - wait for results.

 

Following up, I did end up getting this 2004 S. Love it so far.

I did a Wix oil analysis, oil changed on 12/28, mailed in a few days later, got the results by email on 1/11. Pretty fast service. Results follow, look good to Wix and to me. Silicon and Aluminum are pretty low as far as I can tell, which I think would have been the main things to look for, right?

Any comments?

 

That's a good looking report, but I'm a little suspect because I don't think Mobil 1 makes any grade of oil that even when fresh has as much Zinc and Phosphorus as you're showing in your used sample.

Wear metals look good though. To get even more info from a UOA request a TAN and TBN.

 

Thanks for the feedback.

I'm pretty certain on the Mobil1 0w40 full synthetic, European Car Formula, in the 5-qt jug, like this:


PO is my brother in law, and he even gave me an extra 1.5 of those 5-qt jugs along with the truck. And I bought and used more of the same for the oil change.

So what could explain the high Zinc and Phosphorus? Swapped sample in the lab (seems unlikely)?

BTW, again this oil was 2216 miles and about 25 months since the last oil change.

EDIT - I looked it up, and Mobil specifies nominal values of 1000 and 1100 ppm for Phosphorus and Zinc, respectively. That's pretty close to my lab results of 1016 and 1118. Close enough for me.

 

My mistake - I looked it up and the European Car Formula of M1 actually has 1000 ppm Phosphorous & 1100 ppm Zinc, so it looks to be a good winter oil choice for when you need 0W-40 as it's the Zinc & Phosphorous that protects from valve train wear. Still a little odd how you ended up with more of it than the oil has originally (see attached PDF - 6th entry down). What's important about UOA is to establish a trend on a vehicle with a specific oil and then look for any changes in the #s for that vehicle. Obviously with a new to you vehicle, you can't look at a trend. I'd look to do 6 month or 5,000 miles on an oil change and then fine tune it from there based on what you see in the analysis results. If you decide to add TAN (Total Acid Number) and TBN (Total Base Number) to your analysis - usually costs extra - what you want to look for is not to let the oil become too acidic. A good rule of thumb is to use an oil change interval where the TAN is still lower than the TBN - if TAN is higher, change the oil at fewer miles.