Why does the deck belt on my Craftsman rider SN 917.276863 come off. I purchesed an undersized belt and it comes off. Purchased a OE belt and it comes off.

Dan, Mower deck belt diagram /replacement links below. "I hope this helped you out, if so let me know by pressing the helpful button. Check out some of my other posts if you need more tips and info."

Riding Mower Deck Belt Diagram DIY
Riding Mower and Garden Tractor Belt Routing Diagrams
deck belt diagram craftsman riding mower Google Search

Look under the the left foot rest,there is a belt installation diagram. It will show how to install the belt correctly. It is real simple to replace belt,but the belt must be installed on the pulleys,correctly or it will fail,every time. Sincerely,Brad Locke

make sure you didnt put on upside down if you removed deck check how your belt is run on each pulley look for belt off pulley

Do the blades need sharpening? Check the belts for tightness and the spring that holds the tension. what stops? The blades stop, but the belt is still turning? Check to also make sure the blades turn freely with the belt disengaged. you may have a spindle problem too.

Here is a link to the manual:

http://www.managemylife.com/mmh/owner_manuals/18750/CRAFTSMAN-Lawn,-Riding-Mower-Rear-Engine-L0908170?brand_name_search=536270321+CRAFTSMAN'

Belt could be slipping or worn.
See "How To Check
And Adjust The Clutch" and also "How To Adjust The Speed control lever

I own a Craftsman rider, DTY 4000, 25 HP Kohler, 48" cut, 137 Hrs. It eats a belt about every mowing or two. Did all the stuff you did. Good luck from Sears. Had cousin who is owns a lawn & garden repair business look at it today. Says the prob. is this - The drive belt pulley (elec clutch) has too a narrow "V" and the angle of wear between it and the deck when the deck is in the lowered (mowing) position is too severe. If you notice with the deck in the fully raised position the pulleys line up perfectly. Then drop your deck and see how tightly bent the belt is downward and it makes sense as to why(my) belt would first roll over then break in a few minutes. The elec clutch pulley is sold as one unit PT No. 179334 $250.00, but I'm sure it would come with the same narrow V pulley. Waiting for word from my cousin. My last Sears Mower. Cannot even sell it in good faith.

Look for oil dripping from engine onto exhaust and/or onto drive belt.
Hot oil smokes..

Depend on the rider. Seems each one is a little different to keep you on your toes Get me the make model and Serial number and I can be of more help www.nnyparts.com

http://shop.ebay.com/?_from=R40&_trksid=p3907.m38.l1313&_nkw=craftsman+rider+belts&_sacat=See-All-Categories

They do have some for your rider here on ebay.

You can also Go to http://www3.sears.com/ Enter your correct model number (the one under the seat; starts with 917) then continue to the diagrams list

I usually jack up the front of the tractor and drop the deck as far down as it will go and have at it. You only have to remove a few belt guards and a rod or two and route the belt around the pulleys.Remember the v part of the belt goes in the v pulleys and the flat part of your new belt goes on the flat pulleys. And be sure to look at the diagram on the deck or in your manual.Hope this will help you. donnyb60