Head bolts Oil Or Not

[thomp1983]

Hi all,

Finally got the little AUC head back from the machine shop, I've fitted the head and hand tightened the head bolts to keep it all in place, I've used new head bolts, the information sheet that came with my new head gasket says to oil the threads and under the head of the bolt before tightening whereas autodata makes no mention of oiling the bolts.

Does anyone know which way is correct, does elsa state whether they should be oiled or not?

thanks

chris

Edited September 5, 2019 by thomp1983

[Rich]

It's not a practice that I partake in.

[mk2]

You are 100% correct. In fact each bolt should be screwed in and out of its corresponding hole a few times to make sure that threads run freely (lots of oil)- so when torquing everything down, they all have the correct torque. Oil under each seat also helps for the same reason. 

But there is a counter argument that says that it's irrelevant because when you use stretch bolts, the final pull on each bolt is exactly the same, as they stretch at the same limit (or should). So an extra half turn or less wont make any difference.... all to do with Young's modulus and that (from school...).

[oprn]

True Torque = wrench reading - friction.  Anything you can do to decrease the friction will get you closer to the true torque value. Dry, sticky or rusty threads will never be at the proper torque.

There should never be a dry thread in your life, lube or Loctite! Ask your local aircraft maintenance engineer. 

[Sausage]

Very light oil if you use it, just make sure threads in the hole and on the studs are clean. Dont chuck lots of oil down the hole or you can get a false bottom and crack the hole with hydraulics.

[oprn]

I like the anti-seize options like coppercote. Won't hydraulic.