OK - good words Grizld1 - but a couple of additional points:
- the smaller fasteners are, indeed, for the "rocker-box" which carries all of the rocker arms, etc. and so strictly speaking, they do not relate directly to cylinder head sealing as do the 8 big "acorn" nuts - BUT - there are parts of those "rocker-boxes" which can leak too, so I like to re-torque everything.
- on the matter of lubrication of fasteners: YES - they do need to be lubricated.
- An dirty/un-lubricated fastener (particularly if the underside of the head of the fastener is not cleaned and lubed) will not utilize the applied torque to create what you REALLY want which is a vertical force that acts to squeeze the head and barrel assembly down onto the engine block.
To understand the reason for thread lubrication - you must accept that we do
not really want to rotate the fastener at all. What we are
actually trying to achieve is a vertical squeezing force to secure the cylinder head to the barrel and then press that assembly down onto the engine block. Unfortunately, the only way we can produce that squeezing force is to use the spiral threads of the cylinder head nuts, bolts and studs to translate a rotary "torque" into an axial (i.e. vertical) force. In effect, the applied wrench torque is a surrogate measurement of the squeezing force that we need to seal the engine against the combustion gases.
If you are having trouble with those concepts (and many engineering students do...), try this mental exercise:
- imagine that the fastener is sticky in its threads and underside of the fastener head - due to rust, dirt, crap - on the fastener and the parts into which it is threaded - and you are using your torque wrench to tighten it;
- now imagine that the degree of stickiness increases as you continue to tighten it;
- now imagine that the fastener REALLY sticks firmly as you try to turn it with your torque wrench;
- now imagine that some nasty previous owner actually WELDED the threads and head of the fastener to the cylinder head of the engine - and you come along with your torque wrench to torque that engine head back on;
How much of your applied torque - would be helping to tighten down the fastener to produce that vertical squeezing force you need to compress the head gasket and seal the combustion chambers of that engine....?
ANSWER:
none of it.
The fastener is not turning
at all because it is
welded to the cylinder head - and since it is not turning, NO squeezing force is produced by your torque wrench - no matter how hard you turn it.
The wrench will "click" -
confirming that you applied the correct amount of torque - but the engine will
still leak because the head and barrel assembly is not being squeezed together and the gasket has not been compressed.
Grizld1 is correct in his note about how to clean and lubricate the threads (one at a time etc.) but I would suggest that once this has been done, it is not necessary to repeat that task if you are re-torquing the engine just a short time after it has been apart and the fasteners have been cleaned. I also agree with XS650D that backing the fastener off half a turn and then re-torquing it is a good practice to overcome any "stiction" that might have formed since the last time that fastener was torqued.
In any event, failing to clean and lubricate a fastener is NOT a good practice when assembling
or servicing an engine.
Pete
