Engine mount bolt keeps breaking?

[LSOfreak]

on my mates vts, the bolt going through the middle of the drivers side engine mount had snapped causing mad vibations through the dash and rest of the car. I replaced it, but now 2 months later its done the same thing! why does this bolt keep snapping?
first time round, i checked to see if the other engine mounts were tight and they were

[KrisB]

What condition is the 'buffer' in? The bit with two bits of flappy rubber attached.

You need to use some decent bolts and dont overtighten them.

[Toms112]

As above how tight did you do them?

[LSOfreak]

not that tight only nipped it up. should they not be tight at all?

the round engine mount is fine, has two bits of flappy rubber on either side of it but they arent attached to anything, there literally just sitting there in between the mount and chassis. should they be attached to anything?