Morris Minor Owners Club

dirt between flywheel/crankshaft faces will cause vibration same as brake disc/hub face . been caught out by both. re john newton.

Engine back in and vibration has gone!
To recap: nothing wrong found but after reassembling and refitting I tested compressions. All now at 160 psi. No idea what caused cylinders 3 & 4 to read at 180 previously.
Just as a final twist after refitting I could not get the car to idle properly, it would drive okay, but not tick over. After much head-scratching and rechecking tappets, mixture and timing several times I remembered that I had fitted new plugs. They were the same as had been fitted but the old ones went back in and that was it. Now ticks over and goes quite well. Put it in for an mot today... fingers crossed.

checked the tension on it and said it's fine

If either the engine steady bar from the cylinder head to the bulkhead or the gearbox restraint wire are too tight, either/both can very easily cause a vibration, especially on idle.

160psi on all cylinders sounds very much better than before.

Now to enjoy your newly 'smooth running' car!