A serious point to consider as to whether the factory recommended lift
points are safe depends on how they are loaded ie. in what direction
does the force diagram and tension in the connections between the hook
of the hoist and the two brackets fitted to the rocker studs. With the
loads from the chains or rope/webbing slings vertical there is plenty of
capacity with the studs in tension. When the ropes/slings are shortened
in length, the forces on the brackets and studs becomes a side load (
draw a diagram of the hook point: rope lengths: distance between the two
rocker studs. The shorter the rope/slings the greater the side and
therefore the BENDING LOAD on the bracket/studs.
Chains used as two fixed lengths between studs and hook are extremely
bad when the engine/transmission are tilted to clear the body. The
effect of this is to transfer the majority of the load/force onto the
back chain as the front chain lifts towards the hook. Fixed 'leg'
ropes/slings are the same unless they are free to slide through the
'bite' of the hook allowing the weight/load to be equalised between both
'legs' of the rope/sling/chains and therefore loading each stud with 50%
of the weight.
Longer 'legs' of rope/sling/chains are much better but the ability of
the engine crane to raise sufficiently becomes an issue. The garage
(shop) ceiling height and dont forget that the car will raise up on the
springs as the crane takes the weight of the bloody great boat anchor (
that I love).
Remember granddad's old under the tree lifting mechanism, much higher
than todays portable units
Look up any riggers handbook or talk to a mathematician about the
'force' diagram which can create serious side - bending - loads into
the studs.
A rocker stud or any grade 8 bolt of this diameter will lift tonnes in a
direct tension situation. Brackets must be tightened down onto rocker
pedestal
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