D2 S8 - Big end gone?

[RICKY D]

Evening guys,

Just popped out to the shops and as I was heading back I opened the window because I thought I heard a rattling around. I nearly cried when I heard what sounds like the big end rattling away. It seems to increase and get louder with revs from what I can hear but the car doesn't seem to vibrate or be down on power.

I know this is difficult to diagnose without a video, but I'm not going to sleep tonight if I think its kaput! Its very cold and dark here but I had a real quick listen under the car and if anything it sounds like its coming from the behind the engine, more towards where the exhaust joins from the two banks to one.

Is there any chance others have had this and it turned out to be something simple like an exhaust clamp maybe?

Any help appreciated.

Cheers
Rich

[HPsauce]

More likely one of the catalysts, they can make a hell of a racket!

[MikkiJayne]

Are you sure its not the cam chain tensioners rattling? They have a service life of ~100K in all the engines I've seen so far.

Also, if its down the back under the tunnel its more likely to be a hear shield. There are a couple bolted to the engine which could rattle with rpm, and also a few on the tunnel which can come loose when the steel fasteners corrode away the aluminium studs they're fixed to.

It could also be a catalytic converter matrix come loose and rattling around in the housing.

I would be astounded if the bearings had worn out in one of these engines unless it had been run out of oil at some point. They are properly tough engines in that regard - even >200K examples I've dismantled are still within tolerances. Big end bearings wouldn't even be on my list of things to look at for engine rattles tbh.

[RICKY D]

Really? Could it be the internals breaking up then? It sounds terrible - really like the engine is on its way out.

[RICKY D]

You've both given me some comfort for now - thanks!

It's definitely not the tensioners. I hear them briefly on start up on cold morning and they sound different. They are on my long term list of things to replace as my mileage is just over 130k now.

[MikkiJayne]

Yeah the cats are a known problem. A forum member recently sent theirs to Germany to have new insides fitted. Can't remember who though, but there is a thread about it. Not cheap, but less than brand new ones!

Are you familiar with the concept of a 'listening stick'? Get a large screwdriver and stick the handle end to your ear, and then poke the other end around the engine. It works like a stethoscope and amplifies the sounds in the area in which it is poked. Its very easy to hear valvetrain noise like that (ie the cam tensioners). You'll hear straight away if its big ends that way too - touch it on the block where the engine number is at the front.

Edit - I'm taking far too long typing replies tonight

[HPsauce]

My nearside Cat was failing when I bought the car, factored into the price.
It never failed an MOT but I replaced it eventually, by which time there was just one medium lump of ceramic substrate rattling around inside, making a very loud noise but doing nothing.
The rest had blown out the back as powder

Get a skilled mechanic to have a listen , they'll soon tell you what it is.

Adrian_E had his cats done in Germany, then sold his FE!

[Adrian E]

Yep, was me that had cats refurbished. Much cheaper long term than replacing one from Audi (Audi price is £950ish EACH!)

There's a thread on here with the details IF it turns out to be that

[Goran]

My cats were rattling terribly just last year, sounded really awful and loud. When I had them removed for new ones I could see why, one huge chunk was lose and rattling away. The noise varied with revs.
Get under there with the engine running maybe you will be able to locate the noise as the cats. If you really want to make sure disconnect the cats, although that would be a pain to do as the drivers side cat is welded to the downpipe. Thanks Audi for another helpful design 'feature'
The stock ones are made using ceramic honeycomb, not very durable.

[Pug]

You can get aftermarket cats much cheaper. Be careful on the number of cells, as if they aren't 'capable' enough it can flag the EML.

Bottom end failure tends to sound a bit more 'pneumatic drill' digging up a pavement sound. You'd probably notice oil consumption and other issues for it to be that. But like everyone has said, either one of the tensioners or one or both of the cats.