im trying to isolate an engine vibration prominent at 1000 to 1100 rpm.at idle or under load not moving.i found a nvh formula to find the engine firing hertz.rpm , divided by 60, times half number of cylinders.1050/60=17.5x3=52.5 firing order hertz.how do I determine the source of vibration from the 52.5 hz reading?original engine was replaced,by another technician,cutomer stated vibration felt at tip in.new rebuilt engine ran 9 days,we received vehicle not running.low compression on cylinder 5,found broken intake valve spring and bent intake valve.piston had small half moon mark from valve contact.replaced cylinder head,vibration at 1000 rpm.we replaced engine under warranty believed had bent rod,installed new motor still has vibration,ran with belt off and torque convertor unbolted,vibration still present,replaced harmonic balancer then replaced flex plate.still have vibration.

John Reed
Owner/Technician
Reed's Auto Service
Wharton, Texas, USA