S4 Engine Rattle
 

Hi All Ia'm new to the forum. I have a B6 platform S4 with 68000 miles on the clock. It has the dreaded rattle on start.

Parculiar thing is I can leave it standing for 2 weeks when I start it hardly any noise stone cold engine.

If i drive it 2 miles leave it say 20mins then start it I get a load rattle for maybe 2 to 5 seconds.(Dont figure). I have had the engine flushed and a good quality oil put in which did seem to aleviate it for a short time about 600 miles but the rattle is back.

Any one got any Ideas on this one Odd as it is.
Andy

Do you have a recording of this "rattle"? I have a 2005 I have owned since new. almost 50k on it now. Maybe I can help you decipher the issue.

Hi s4Bloom

Thanks go the reply I will try and get a recording ASAP only trouble is it is unpredictable when it happens.

Thanks for now Andy

Timing chain rattle, from rear of engine. Usually as a result of a worn chain.

Replacement means an engine pull, breakages through ignored symptoms are not uncommon on the 4,2 V8 40V BBK motor.

does it sound like this?

Audi claims its totally normal and dont try to repair it. Many have had chain and guide failures. From the sound of some of them i hardly think its normal.

I'm dealing with the 'normal' chain rattle on my 2005 A6 4.2, which is essentially the same engine.

I'm of the notion that the rattle is NOT normal, despite what Audi says. (they also say that transmission fluids are 'lifetime').

My car rattled from when I purchased it with 127k miles. Since it was claimed to be 'normal', I didn't think much of it.

175k miles, and one of the chain guides let loose, went into the exhaust cam sprocket on the passenger side, causing the chain to skip one tooth, and the resulting misfire.

I'm in the process of repairs, which unfortunately involve replacing the heads, since the exhaust valves hit the pistons lightly.

I don't think that the failures of the guides are mileage related, but rather age related. The plastic guides get brittle with age and heat, and as the 'rattle' is the chains hitting them, they eventually break.

I've also seen a number of reported failures of the mechanical cam timing adjusters, where there is a pin which engages a machined hole internally, and the hole wears to the point where the pin will no longer engage. This also causes a misfire.

My opinion is that if you have a medium to high mileage 4.2 with the chain drive, pre FSI, then it would probably be a good idea to pre-emtively plan to replace the guides and tensioners at a minimum, and inspect the mechanical cam adjusters. It's not a trivial job, though, as the engine has to be pulled, and there are a few special tools. Parts prices aren't cheap either, and all parts are 'Audi' (even if sourced from other than Audi dealers). I've noticed that there are pretty big differences in pricing around the 'net, though, so it does pay to shop around.