[urq] Engine mounts captive bolts : how to remove ?

[Louis-Alain Richard]

I am replacing both engine mounts on Eric's car. This time, after doing
the one on my car, I was prepared: move the oil cooler, unbolt the 17mm
nuts, use some oil on the rusty threads. The destroyed passenger side
mount felt to the ground in 30 minutes. 

Then, the fun part: with the judicious use of an angle grinder, cut the
remainder of the center stud so it can be removed from the engine
bracket (from under the car) without trying to unbolt the top nut. This
is important, unless you want to remove the airbox, the CIS tubing and
the exhaust manifold...

Overall, 60 minutes and the new hydraulic mount was installed. The old
one was the 1985 solid rubber mount, and it was in a sad state...

And while being there, why not install a new driver side mount ? It is
not destroyed, but it is 20 years old... So, this time, I figured it
will be an easy job because I have access from above for the top bolt,
and the top stud will not spin in the mount since the rubber is still
solidly attached to it. Easy job, I thought.

Then...