Small Engines (Lawn Mowers, etc.): Troy Built Riding mower, idler pulley, pulleys

Question
I have a Troy Built 20 HP 46 in cut (3 blade) riding mower that has developed a vibration when the deck is engaged only. Have had a mechanic look at it and replaced some parts including the belt but didn't fix the problem. Watching the deck in operation (idled down) I can't see anything rotating that looks bent or warped. The only thing I see is the belt that provides power to the deck from the engine flops a bit as it comes off an idler pulley. The belt contacts the idler pulley (attached to the underside of the tractor) level and leaves the pulley at a angle to go to the first pulley on the deck. The pulley does have a tensioning spring attached to it, but I don't see the pulley "pulsing" as someone mentioned in another Q %26 A. With the deck all the way up it lessens it a little as the pulleys and belt is more inline, but it is there as long as the deck is engaged. Any ideas?

Answer
Bent or unbalanced blades?   Where the blades removed and not "seated" properly when reinstalled on the deck?  another option if nothing is bent is there is a bad bearing in one of the deck pulleys.

I suggest you pull the deck off the mower and inspect all linkages, blades, arbors, etc...

Pulling the deck off this mower is not real fun, but it can be done.

Happy Wrenching!