|
In large diesel engines (3000hp) on the connecting
rod bolts the bolt stretch method is often used. This involved
measuring the bolt free length and then applying the bolt and tightening to
reach a predetermined bolt stretch. It was then pinned and that was
that. Difficult to do inside the small openings available to us on our
engines. Also the bolt head and end had a machined surface to facilitate
measurement.
If you are worried about the resistance of the stop
nut or self locking nut you can always use a castellated nut and split pin or
the double lock nut method. You do have a valid point there and maybe one
of our AME correspondents can enlighten us as to what the correct practice is in
the aviation world.
The important things to look at when using bolts is
that the amount of preload on the bolt will prevent the bolt being subject to
reversing stress cycles, thereby avoiding fatigue and fracture. The other
important point is that the mating surfaces being clamped must be in full
contact with each other to avoid flexing which could cause the stress
reversal. This is for tensile loading. If the bolt is in shear then
a different calculation is involved to size the bolt and the tensile loading of
the bolt is secondary to the shear resistance. Torque is important to load
the bolt and keep the surfaces firmly in contact with each other to assist
the shear resistance of the bolt.
Ian B. Crowe
LNC 2 C-FKRO
|