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Hi Guys

I need some assistance with an issue, and really hope your knowledge can help out here...

I recently bought a cheap C5 RS6 as spares repairs. I only bought it as it was cheap, and I have a friend who breaks Audi's and I can offload it to him if I get stuck. So if it's a terminal issue, then not the end of the World - but I have a good feeling that it's far from terminal TBH...

Basically, when you start the car it fires up as normal. Sounds great, ticking over lovely etc. This continues for around a minute approximately, until the revs drop to their normal 'resting' level (revs are higher for the first minute approx when you start the engine, and then drop to the normal level - this is normal in all cars I believe). When the revs drop to their 'normal' idling level the engine develops a rattling noise.

The noise starts literally immediately as the revs drop to their resting level, and there is zero rattle when it revs high for the first minute or so.

Now, shoving my head around the engine bay it's clear that the noise is coming from the top end of the engine (phew!). It seems to be towards the back, but hard to discern left or right. It's a pretty constant rattling.

Does anyone have any idea what could be causing this rattle, and the reason why it become apparent only when the revs drop?

Any helps and idea's most welcome!!!

Sounds like the cam chain tensioners. Common problem.

Thank for the reply.

Are those located on the end of the cam rods themselves? Are they expensive/easy to replace?

And any idea why it only starts when the revs drop to normal idle speed?

I believe the left one (as you are standing in front of the car) is the one at the back of the engine, and typically its the side that has that damn water pipe in the way of accessing the cam cover. The chains / tensioners are for linking the intake and exhaust cams just in case you didnt know.

They are expensive if you get them from Audi - think they were £500 a side. There are cheaper ones on ebay etc.

They are sprung to take the tension but are also oil fed so could be at lower revs, it's not getting the pressure to overcome the shortcomings of the internal spring. It might be the variable timing as well helping out with stopping the rattle.

From what I have read on the internet, the rattle will increase the wear on the pads which will eventually fail (used to be a big issue on my R56 mini)

Thank you for the input, much appreciated!

I've taken a look on eBay and non-genuine are around £210 a pair from decent looking sellers, so not too bad.

But are they a pig to change? I assume it's not engine out, but also assume there would be a fair bit of strip down?

Yeah they are a bit, especially the left one. I did my seals (tensioners were fine) when the engine was out. You have the water pipe to work around on the left side which is the main hurdle.

Best do you cam cover gaskets as well and you will need to replace the metal gaskets that the tensioners sit on as well. And all the bolts holding down the cams, as they are TTY.

Hopefully someone else on here has done them with engine in the car, as the process will be different. I had my cam lock bar on when doing it and was following the Elsawin guide as well (need to time the intake one correctly to the exhaust by counting chain links)

Didn't nobby do a write-up of changing his recently?

If so, that would be awesome to see. Anyone have a link??

Here you go:

viewtopic.php?f=2&t=120552&p=798508

Thank you!

Having a skim, Nobby mentioned afterwards that it did not solve the rattle, maybe made it a bit better - but his issue I think was not as bad as mine as his was doing it at certain revs etc I believe.

Wouldn't want to spend the 20+ hours on it and it not solve it

But making perfect sense, and can't think what else would be causing the constant rattle at the top rear of the engine?

Maybe a cam follower but they're not known for failing. Doesn't mean it can't, though. Rattle sounds like chain issue. Tapping would suggest cam or follower issue.

If it's a rattle, I'd say it's the tensioners. A follower, I'd expect to be more of a tapping noise.

Permanent rattle could be badly worn cam tensioner pads - worth maybe taking the valve covers off to see if you can see wear. They wear in different places though as one bank has a fixed pad above the tensioner and on the other side the fixed pad is on the bottom.

I could hear (and feel if you touch the tensioner housing) was rattling with the car at idle.

Remember there is also a tensioner down at the bottom of the engine for the oil pump. Not heard many problems with those though.