78 Xs400-2e Acorn Nut torque setting

[Jester401]

My 78 Xs400-2e needed a new motor. So I pulled apart the spare one and the original one to make a nice new motor for the old girl. I tried looking in some old threads and the manual. Ive had no luck finding the torque specs on the acorn nuts holding the cylinder head to the block. The manual doesn't show the correct size of the nuts, the biggest nut spec they show is 10mm, however the 8 acorn nuts holding my head down are 14mm. Does anyone know the specs, or could give me an idea of a safe torque to apply? Thanks guys.

 

[kshansen]

When you say they are 14mm nuts are you talking about the size of the wrench or the diameter of the studs?

To be honest I've never removed the head from an XS400, but have worked on engines from small chainsaws to large Cat Diesel 16 cylinder generators that barely fit in an 18 wheel trailer. 14mm sounds big to me for a 400cc motorcycle head stud. The old Corvairs I used to play with only used 3/8 studs as I recall and that is a little under 10 mm.

 

[xschris]

It's on page 50 of the Haynes manual, which you can down load for free in the forum.

 

[Jester401]

Sorry, yes the size of the socket required to remove the acorn nut. I assume from the manual, they are talking stud size not the size of the fastener?

 

[kshansen]

So yes the size of the stud is what the manual refers to when they give a spec. for torque. This is the standard way for 99.9 % of the fasteners in the world. I say 99.9 because I'm sure some strange engineer some where has or will do it different.

And to add to the confusion I know there are application where you tighten some fasteners to a specific torque then advance a specific number of degrees and other places where you measure how long a bolt is then tighten till it is a set amount longer. But I don't think you will find these methods used on an old XS400!