Check to see if it vibrates badly with the clutch / brake pedal fully depressed
Yes = engine problem
No = Drive problem
If yes, remover the drive belt & try again
Still vibrates all the time = major engine problem
Only vibrates at start up & shut down = loose mounting bolts.
Drive problems
Lump broken out of belt
Something stuck in a pulley
Broken or cracked pulley
idler pulley bearing broken
Tensioning arm pivot worn excessively .
