********. The BBK engine cannot make 400 BHP without a supercharger or built engine.
The engine has to be stone cold or it might not rattle at all. Make sure the seller doesn't use it on the day you go. You can't miss it - it's a very metallic, clacking rattle. As long as it's under a second, it's not going to fail immediately but at that mileage, at least one guide will be broken so the timing will need doing soon at a cost of a couple of grand.
Chain rattle doesn't automatically equal broken guides or worn adjusters as some very low mileage engines have been know to rattle - some rattle, some don't, but the ones that do should only do it for a very short time at start-up.
JHM have worked on hundreds of S4s and
here's what Jake has to say about the rattle:
I get the feeling that everyone desperately wants this to be the magic fix to all the timing chain issues. However it is not even though I really would like it to be as well. The fact of the matter is that these guides and adjusters fail. Even Audi recognized the guide failure and made an updated guide. If it was a valve failure causing these issues Audi would have made an updated valve years ago. I know this is a crappy situation it is the truth. Broken guides will cause rattling. Worn adjusters will cause rattling (even slightly worn adjusters will. As soon as the hole is bigger than the pin which doesn't take much will cause a rattle. Whether you can hear it or not in the beginnings stages is tough do to other engine noises).
Every engine we have done a timing chain job with over 80k miles has had cracked guides. We even have a display of 6-7 broken guides all in the 80k range in our lobby.
Even slightly worn adjusters will cause a rattle. All it takes is enough room for the pin to move around to cause a rattle which isn't much.
If you're buying an S4 with that mileage you need evidence the timing job has been done or you need to get it a couple of grand under market value so you can do it. I can appreciate that most people don't know about this and a seller will likely tell you to sod off and sell it to the next uninformed individual but that's the way it goes.
Check the B6/B7 S4/RS4 forum on Audizine for technical information about timing and cylinder scoring - if the engine has that it's pretty much junk, I think.
I've been to see cars before and wanted them inspected and the seller was in too much of a rush to wait. That tells me there's something wrong so I if the seller's not accommodating to a serious buyer you're better off giving it a miss.
