Stainless bolts - torque settings

My feelings are,Don't use them. They have an annoying tendency to come loose. 

Hello Chas - What category of stainless are they made from ?  I'm not sure that there is a direct read-across to the high tensile steel as used for the Norton twins head bolts.  I suppose that you could use the manufacturer's data sheets that should be available or have a reasonable guess..... For instance a mild steel bolt  in 3.8 inch  should be about 20 ft lbs but a high tensile bolt could be anywhere between 32 and 56 ft lbs dependant on the spec. A 5/16 inch bolt in mild steel might be 11 ft lbs but again high tensile may be between 19 and 32 ft lbs.  Best to start low and feel the the bolt with a good ring spanner after each torque step and  if it feels like it is stretching the bolt back off and chuck that one away.  Some stainless steels are not suitable for head bolts because instead of stretching they just snap.  Good luck, Howard 

I've been told not to use stainless bolts for the engine, but previous owner fitted the four main head bolts in stainless and I haven't changed them because they've not given me any problems.

They are greased when they go in, which is what I assumed Norton expected (i.e. would they really have been dry?), so the surfaces of cast iron and stainless are lubricated.  So since the thread surfaces look like any other, I just use the book torque figure.

Buyer beware!  All I can say it that it works for me.

I've never considered a torque wrench on others.  I just do it by hand and feel, relative to the first four.  Which "three into the alloy head" do you mean?  The front three nuts are on steel studs into the cast iron barrel and are so hidden away I can't imagine why changing them to stainless is worth doing.  Where are the three into alloy?

The studs into the head - two immediately below the exhaust port and the central one at the rear are 3/8 inch with the nut being 3/8 inch BSC and into the head 3/8 inch BSF.  They are difficult to torque up.  They are prone to stripping in the head and there are various threads on this topic elsewhere on the Forums.   Cheers, Howard

I'm with you now. I should be... I had the middle one helicoiled some years ago. But it's invisible so neither my nut nor stud are stainless.

As already mentioned torque versus bolt tension is different with lubrication and bolt material. But the important thing is to get the same tension in all same size bolts. Needed for getting equal pressure around the whole head gasket to keep cylinder gases and oil where they should be. If the engineer who designed the engine did his job right, recommended torque values should keep it leakfree and with a wide marigin to bolts breaking. Even with different thread friction. Some high-tech companies nowadays uses angular tightening values instead of torque wrenches where bolt tension is critical.

Update. Took off the head on a 650 engine today that has been lying around a couple of years since I bought it. The four side side bolts must have been fastened by a bodybuilding gorilla. The centre bolt and the rear nut was completely loose. Remaining nuts normal torque. No signs of leaks and the head surface was flat. Am I surpriced, yes.