Big end bearing cap bolts

[Tractor Dave]

Can the big end bearing cap bolts be re used and what is the torque setting?
they look like stretch bolts to us.
Thanks
Dave

[Mikes2]

65Nm - they only need renewed if the engine is completely dismantled

[Tractor Dave]

Thanks very much

[steve briance]

My book says big end torque figures are 30nm +90degrees which does indicate they are stretch bolts. The 64nm figure is for main bearing caps...

As for re using them, engineering types will say no you can't, others will tell you that you probably can once before the bolts thins too much through 'necking'. Stretch bolts work by deforming themselves at a certain load you want to apply to the part, my understanding is that you reduce the risk of over tightening as the bolt continues to stretch rather than clamping harder...

Be warned about the cost of replacing the big end bolts though, they are around £10 each from Audi. DO NOT be tempted to buy Febi items at around £4ish. I did that that and deformed the con rod by pressing the ever so slightly oversize bolt onto its hole.

[Tractor Dave]

Thanks. That's what we thought as they are only M8 bolts. 65 would have been way over!
The bolts all look good so we are going to 're use.

[Mikes2]

sorry about that. Misread your initial message. The AAN manual is available here : http://s2-audi.co.uk/work_shop.htm

[twenty valve]

30nm + 90 degrees is manufacturer standard for big end cap bolts. Refer to page 33 of the workshop manual.

http://s2-audi.co.uk/workshop/aan/aan.pdf (this manual is for the AAN engine but is the same for ABY and ADU)

They are stretch bolts so I would definately reccomend replacing them. I would never reuse them myself. It's no different to reusing head bolts.

The best way of fitting stretch bolts is to use a guage which allows you to measure the bolt length in situ. You can then follow the specs for the amount of stretch the bolt is designed for and tighten to suit. This is really gold standard, especially when using uprated/performance rods and bolts. Otherwise just use a decent toque wrench and follow the recommended specs.

[Tractor Dave]

Thanks very much. Very helpful.