Consider where these bolts are threaded

Question:

I have a problem with a previous “Mechanic On Duty” answer when you recommended that an engine hoist be attached so the bolt is in shear (January). You state that a bolt is weaker in shear than in tension—OK.

However, with proper thread engagement, the pullout value in tension should be more than the tension allowable. If you are willing to think of it in another way—how much tension is on the head bolts when the head is torqued down? (Assuming that the head bolts/studs would be used for attachment.)

Answer:

As I explained in the previous answer, my reason for preferring to attach engine lift chains in such a way that the force of the mass of the engine is acting in shear on the bolts rather than in tension has less to do with the strength of the bolts— in shear or tension—and more to do with the strength of what these bolts are threaded into.

If you use a new bolt made in America or somewhere else where manufacturing standards are honestly adhered to, you can have great confidence in that bolt’s ability to bear the weight.

But what about the threads in your head or block? These threads are likely many decades old. Have they been significantly weakened from corrosion, wear, damage from cross-threading, damage from installation of an incorrectly sized bolt, etc? Probably not, but why take the chance if there’s no reason to?