what the heck is a balance chain switch please?

[Sooz]

Drove 300+ miles on Sunday - beautiful drive and absolutely no indications that there was anything wrong with the car.

Got in the next morning and tried to start her - turned over for a couple of secs then nothing.... following 8 hours+on the back of the RAC and their dodgy contractor lorry, my car is now being stripped down by the local audi maindealer and having pulled the engine apart, they tell me the balance chain(?) has snapped....

Thing is I have no idea what this is, what it means or how on god's earth it could happen - can anyone offer any info to help me get my brain around this???

[Audi A4 Lover]

What car/engine is it?

[Sooz]

It's an Audi A4 TDI. Registered Jan 2005 (04 plate) with 90,000 miles.... 130bhp and 2litre....

[a8 tech]

Crank shaft balance chain,its common and you may require a full engine as it normally pops out through the oil pump casing.
Its normally the spocket teeth strip causing the chain to jump off.
I posted a picture of this ages ago.

[cricky]

Hi Folks, this problem is a complete nightmare and Audi don't appear to give a toss, but luckily for me I found an Audi expert in Coventry who converted my 2.0 Tdi BLB engine to a gear driven oil pump, basically converting it to a BRE engine, if you live anywhere near Coventry or can get your can there, I highly recomend this guy, his name is Mike and his mobile number is 07970 478931, he fixed mine for under £1,000 inc parts, with a warranty and that was including a cam belt kit with water pump.
He also has an Ebay shop where he sells Audi A4 Tdi engines and also offers a fitting service if your engine is screwed, take a look at this link 2.0 TDI engine AUDI, BLB on eBay (end time 10-Dec-10 19:44:41 GMT) or contact him via his Ebay user name volksbreakers. Any work is undertaken and he speacialises in Vw/ Audi, in paricular the 2.0 Tdis, but will quote you for anything, give him a go.
By the way, I am not related in anyway, nor do I have any financial interest in this guy, I am just passing on someone who I found to be great, when Audi quoted me over 2K !!