Join Date: Oct 2013
Location: Chilliwack, BC, Canada
Fastener installation & tightening tips
Likely everyone here knows the following but just in case:
An area which causes newbies to wrenching a lot of grief is
improper tightening procedure. When installing a set of bolts or
screws into an assembly, never but never start and tighten them one at
a time! Never!
This is asking to break something.
Always, always, always look and/or probe each of the holes with a dowel
or other gauge to ensure that the holes are not partially filled with
debris or liquid. How many times have I seen an oil filled hole cause
the casting to crack, blow out the back or under-tighten? Huge number!
Always look to make sure that the two parts are fitting together in
proper alignment and then start all of the bolts/screws a few (turns
by hand if at all possible).
Now, since all have been started the same number of turns, the amount
of each which protrudes should be very similar. If one or some are
markedly shorter or longer there is a clue that something requires
investigation. Perhaps some of the bolts are longer than others for a
Too often bolts of the wrong length are installed into holes which
causes them to have insufficient numbers of threads engaged and the
threads pull out of the casting; or the bolts are too long and bottom
out in the holes. After bottoming the bolt's tightening can pull
threads out of the casting, push the bottom of the hole out the other
side, crack the casting, flare the end of the bolt so it cannot be
withdrawn, lots of fun! Sometimes what happens is that the tightening
of the bolt is applied against the bottom of the hole and so there is
no clamping force applied by the bolt. This results is blown gasket,
warped/broken parts, etc.
Once all are started, turn them down until all gently touch the
surface of the part and then begin tightening by use of a torque
wrench as per manufacturer's recommendations. If the maker does not
specify, going to 10% of recommended torque on each and then working
up to 50%, 70-80%, 90%, 100%, then back again at 100% works well.
Another caution: don't work around in a series fashion when
tightening! Start at one bolt then go across to the one most opposite,
back to the one next the first, then back to the one on the other side.