13.5 hp Craftsman lawn mower 5-speed

This video shows several belt patterns for various mowers. I am assuming you are wanting the deck belt and not the drive belt. 4 seconds into the video is the standard craftsman 42 inch belt path. The belt at the bottom is put on the engine pulley. Tip from my own experince make sure that the belt is under the belt guides or you will ruin a belt in short order. Your model number is under the seat and is also a scanable barcode. Another tip is to snap a photo of your model numbers. This is handy when you need parts. More accurate and readable than writing it down. Riding Mower Deck Belt Diagram DIY

http://www.managemylife.com/mmh/pd_download/lis_pdf/OWNM/L0806845.pdf
page 13

Are you asking what size belt to use or are you asking what other size belt, like you want to use one a little smaller or a little larger? If that is the case, what difficulty are you having that you would need to do that? Did you put a Craftsman deck on a Poulan or something odd like that?

I believe you may have the belt over one or more of the belt retainers next to the pulleys. They are 5 or 6 inches long and about a 1/4 inch in diameter. You have to loosen them when you put the belt on then adjust them to where they are just barely touching the back of the belt. They keep the belt from jumping off.

Assuming you mean the deck belt, since you don't specify, it is part number 144200 The same as Craftsman. AYP, Poulan, and several others. You can purchase it at most sears stores or order it on line

Check for a broken or dislodged belt

look under the running board most are on there

need a diagram of how to put a deck belt on a 15.5 hp/38" cut 5 speed poulan lawn mower model number 9601200-3801

Go to searspartsdirect.com and enter your model number in the space on the right of the page. When the list of illustrations comes up click on ground drive. This will show you the correct installation of the drive belt. Or do you mean " How the Heck do you put this on?"

Really hard to say without looking at it but it sounds like a pully has seperated or is trying to come apart they are made in two peaces.