The repair to the harmonic dampener – a new unit for $100CDN -changed the sound and duration of the vibration, but did not remove it. So it looks like a two part problem and something else is causing vibration also.
Time to eliminate all possibilities one at a time. First some references say that a faulty dist. cap with a hair line fracture or wires inducing a charge in an adjacent wire – especially between 5 and 7 which fire after each other – can cause vibration.
So off with the cap, but no apparent cracks. There is a smear of oil on the inside and maybe that is allowing spark to jump. Best solution – replace the cap and rotor. I made sure all the wires had 1/8″-1/4″ of spacing wherever possible.
That done I pulled all the plugs to see if any cylinder was not burning clean. #5 was not all that clean and it had a cracked boot. This was a new wire set.
I’m planning on buying a set of wire wound anti-static wires so I just used some special electrical tape that bonds to itself and wrapped up the plug. #6 plug was also damaged some so I wrapped it as well. A good argument for keeping the spark plug shields in place. The originals had rusted off and I didn’t replace them. I now have a set on order!
Next: After a short test drive there was still no improvement. I did check the flex plate, but I couldn’t see any cracks around the torque converter attaching bolts. Next I’m going to pull the inspection cover, detach the torque converter and push it back into the trans and have a good look at the bolts holding the flex plate to the end of the crank.