Re: Bolt torquing
Posted: Wed Apr 08, 2020 2:28 pm
Whenever you're changing a cylinder, after getting everything really clean
you need to get a pot of W100 oil and a 1/2 inch wide paint brush, and use
the brush to wipe down the threads and surfaces, and soak the nuts in the
oil. Oil should be running down. Wipe it off after. You want lots of oil both
on the threads, as well as the mating surfaces, to reduce the friction so that
your torque is used to tension the through bolt.
Mostly you need to overcome the static friction and get/keep them rotating with the lesser sliding friction.
Lycoming says in the DD Manual to hold the final torque (50 ft-lbs) for 5 seconds.
You would be amazed how often the through bolt nuts will jump at the end
of the 5 seconds!
It's very common for engine shops to observe "fretting" between the mating
surfaces of the crankcase halves, and they work against each other, because
the through bolts don't have enough tension.
I would expect Canadian engines to see this more often, because TC requires
AME to pull cylinders much more often than in the USA.