Rocker cover gasket, torque setting

[magictorch]

I have just changed the rocker cover gasket on my Xantia 1.9TD to cure an oil leak.
Having researched this and other forums I noted that the torque on these should be 20Nm.
This is what happened:
- Purchased brand new Clarke torque wrench
- Set to 19Nm so I did not cook it
- Tightened all in sequence starting from middle out
- CRACK! Bloomin bolt sheared right off. Fortunately I could unscrew it from block!

Am I missing something? Should I change bolts for new ones?

[Chlorate]

By BoL confirms 20Nm (which in my book is really just "do them up" but that's beside the point). You probably just had a bit of rotten luck there, you usually only have to replace a bolt if it has been torqued to yield stress and beyond (head bolts etc), valve cover bolts are good to keep reusing. Check to see if the thread is nice and clean (maybe a blast of WD-40), and dab the last couple of threads in copper grease to ease them in etc.

Alex

[Xantidote]

I'm wondering if the quoted 20Nm is right, despite the research - seems a bit high for what, (IIRC) is only a small bolt. The new gasket will be lovely soft rubber, and I'd probably just gently tighten down by hand. Then, if it leaks, tighten a little more. I'd be reluctant to tighten down very hard initially - nothing then in reserve for later, when it hardens and then starts to leak

[oneday]

allways been told just to nip these type of gaskets as there is no pressure behind them

[CitroJim]

allways been told just to nip these type of gaskets as there is no pressure behind them

Absolutely and doing them too tight there's a risk of warpage... 2Nm would be more like it. 20Nm is pretty well tight, same as what say, you'd put on a 13mm stud holding a cambelt tensioner...

[magictorch]

No flipping wonder it went 'ping'! Pah if I had done my homework before I could have left that torque wrench on the shelf at the shop.

[Gibbo2286]

allways been told just to nip these type of gaskets as there is no pressure behind them

Which pre-supposes that the breather system is intact and working, the crankcase runs at negative pressure if all's well but if there are leaks in hoses etc. or the regulator is kaput the pressure becomes positive and will blow oil out of even the best gaskets/seals.

[thorter]

Make sure you are not using a meter/kilogramme force scale (may say m.daN) on the torque wrench !

Fred