Engine vibration

[pasbogdan]

It is something vibrating starting with 3500 rpm until 4000 rpm.It is engine related not running gear because it does that in any gear,including stationary.It is aan stock opened and rebuild.Not needed bearings(0.05mm gaps),only a honing to get bores round again,new rings,head rebuild etc.Only converted to sm flywheel.Changed flywheel with another sm one from another engine that had no vibrations but problem still there.I imagined crank and fly wheel were not balanced,but it is not the only aan with sm flywheel without balancing.Could be front pulley?It is engines stock one.But it has no cracks,no visible play,runs perfect round.Vibration comes even when revs are getting down and pass that rpm area.It is not ignition or fuel related.
How should i explain vibration?it can be felt only in gas pedal and a little strange sound.Could be something auxiliary rotating part doing that?Pas pump,generator?

[ManiacuV6]

Even if is hard you ca ntake the belt for PAS pump + alternator out and see if it does the same. Did you used the right front pulley?

L.E.: Try to take the accesory belt out and try without.

[pasbogdan]

It was engines pulley,the one engine worked with.

[pasbogdan]

Solved.Put another front pulley with cracked rubber,and not running very round and there is no vibration
The old perfectly round running pulley was bad and this one,mounted just for test clearly visible not good solved my problem.

[JP]

Very lucky as I5 engines are balanced externally from factory (they remove weight from pulley and flywheel to balance engine) so changing pulley and flywheel from different engine means you make you're engine out of balance. If you are lucky the parts from other engine are close if unlucky the whole engine vibrates apart. Sounds like you were lucky

[pasbogdan]

This sounds strange.In case of dm flywheel if need to replace what should be done?Balance all system?Or front pulley damaged,same all system balanced?I think they are balanced separately.There is a large number of engines that need dm fly replacement even 3 times in their life time.
Maybe you know something particular of 20vt vag engines?But i have not seen in any repairing manuals requiring balance after fly or pulley change.
Best regards!

[A80Avant]

as far as i know, when i went to audi many years ago to ask about a DM flywheel, the chief mechanic there never mentioned anything about having the system rebalanced. Its good to have it done, but shame its not as easy as a 4cyl engine.

[Thuppu]

Balancing isn't so critical on these engines if you don't mind the vibrations. Some have changed rods and taken out more than 800hp/8500rpm's without rebalancing and the engine have hold up in one piece.