Motor Mount - problem and questions.

Situation: We have a 1958 Chris Craft with an inboard 6-cylinder engine.
Manual says the engine weights about 800 lbs. To do some of the hull & rib
work we took the engine out. The engine was mounted to the boat using 4
motor mounts, one on each corner. These mounts (probably like most mounts)
were two plates of steel with rubber separating them.

Looking at the old mounts, we decided that the back two were bad enough to
replace but that the front two could be reused. So I bought two new ones
and a few weeks ago we replaced the engine. The two rear mounts (where more
of the weight is because the engine sets on a tilt angle) were the new
mounts. The front mounts were re-used.

After setting for a week (no in-water use, the engine has not even been run)
the left front mount "sagged" and the rubber split from the steel. OK,
that's just a bad call on our part for not replacing the front mounts.

The back left mount, which was new, also came apart. On one hand I figure:
Well, it was probably holding almost twice the weight it should have been,
so that figures. On the other hand I think: Normally one of these mounts
is supposed to handle engine vibration, the torque of the engine trying to
turn the prop, the thrust of prop, heat from the engine, and years of use.

So two questions:
#1: How are these made? Do they glue / epoxy the rubber to the steel or is
it just injection molded or what?

#2: Does it seem strange that a new mount would come apart under these
conditions or not?


Thanks,
Gary