I need the blade belt routing for dys 4500 42" cut

check belt possible stretched or worn

Your deck belt need tighten

Sounds as if the deck belt is stretched. Replace the belt and make sure it is routed correctly. When the belt is off of the unit, make sure each blade assembly rotates without resistance. One of the mandrel assemblies could be seized.

This is a Parts diagram website. Find your model then work through it until you find what you need
http://www.cubcadet.com/webapp/wcs/stores/servlet/ARIPartFinderView?storeId=10051&catalogId=14101&langId=-1#/s/CUT/782/

Hi, first check the spring that pulls on the idler pulley for lost tension then run the blades for a 10 to 15 minutes at half to full throttle. This is necessary to bed the new belt into the old pulleys. Regards Phil.

sounds like he bent a blade that's when the belt went

Please see Figure 23 under the subtitle Service/Adjustments. This is your blade belt routing information.
http://weborder.husqvarna.com/order_static/doc/HOUS/HOUS2005/HOUS2005_O0502018.pdf

Make sure the routing of the belt is correct....then check to see that you have obtained the correct belt

If you are missing the manual, for the said model,
I have found that the simplest way, of figuring out the correct route for the belt, is to remove the deck, and hold the replacement belt above the mechanism, with the tension from the engine end.
Then 'mock up' the replacing proceedure, bearing in mind the correct direction the tensioner/s, move in.
Then it's not too difficult to figure it out the correct route.
Hope that's clear enough, good luck.