On 2012-01-01, Steve B wrote:

Holy crap! All these years, I thought it was a baseline. X# of torque,
plus 1/8 turn (just because that's the way Grumpa did it), then a little
more just in case the unexpected happened.

You and gramps were WRONG!

Torque specs are based on several variables, but the purpose of torque
specs are the same. It's to take the fastener to the elongation
(stretch) point where the fastener will hold without coming loose. A
properly torqued fastener does not need a lock washer to prevent it
from loosening. It has been tightened to that fine point where the
threads will not deform or fail, yet are held in enough tension that
they will not loosen by themself.

Of course, this is under ideal and/or stable conditions and does not
take into account severe vibration or heat/cold contraction/expansion.
It also applies to bolts that are of certain materials, like grade 8
hardened bolts. Softer material fasteners are why lock washers or
other supplimentary devices (Loctite, lock nuts, etc) are sometimes
called for.

Regardless of the variables, when torque specs are provided, you do
NOT go "plus 1/8 turn".

As for sparkplugs, all sparkplugs have a compressible washer and it
should be replaced with a new one every single time a sparkplug is
removed, wether or not you are putting back the old spark plug or not.
If not, jes tighten till tight. Don't add an extra 1/8-1/4 turn.
Anohter old trick is always add oil! ....even if jes a couple drops
from the dirty crankcase dipstick. Also, Helicoils are OK if you
can't do better or have limited material dia to drill out, but key
inserts, like Keenserts, are a better product. Helicoil has had
quality issues and I've had to remove a bunch of 'em when it was
discovered a batch was defective.

nb

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Merry Christmas and a Happy New Year