Mower deck Craftsman DGS 6500 - model 917-288461 - mower deck belt popping off?

Help please! I'm original owner of this Craftsman DGS 6500 - have LOVED every use - 300+ hours - about 7 years now. (3 acre parcel)
I've routinely removed the deck, replaced drive and mower deck belts often, do most all maintenance myself, (including pulleys) however recently the mower deck belt pops off the minute I drop the deck to cut.
I'm mad at myself for being so stupid, and I hate the idea of bringing to Weingartz to have them charge upwards of 500 bucks to tell me an obvious reson why this is happening.
I hope this is the correct forum, ANY help would be appreciated!
thanks!

If you are not actually mowing at the time there is only 4 reasons why the belt jumps strait off when engaged
1) pulley jambes so the belt loops and drops off
2) pulleys badly out of alignment
3) fluctuating tension causing pulley to bounce off
4) wear in the system so the correct size belt is now too long.

Set the deck height to the spot where the belt run is closest to level before you engage the blades
Check the blade brake fully disengages before the belt engages watch you fingers.
Turn the blades on without the engine running and check the tension in the belt.
With older mowers I oft find I have to fit a smaller belt.
Standard Kevlar mower belts are in 1" increments but unaffiliated mower repairs like myself can use aftermarket parts and in many cases I can go down in fractions of an inch.
Downside is these model specific belts are substantially more expensive.

<a href="http://www.searspartsdirect.com/model-part/917288461/0247/1509200/p0805029/00008.html" target="_blank">http://www.searspartsdirect.com/model-part/917288461/0247/1509200/p0805029/00008.html</a><br>
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Remove idler arm, item 43, from top of deck & inspect for wear as well as hardware associated with idler arm, probably has quite a bit of sloppy play when moving arm up & down. I had the same problem a few years ago & replaced 3/8" bolt grade 5 with a grade 8 bolt 7/16" with new washers & a self locking nut, had to drill deck to 7/16".

Thanks for the replies guys, Mark, I am familiar with the idler arm you've mentioned - actually, the play in all of the components were closely looked over - I removed the entire deck from the tractor numerous times, and have replaced all of the pulleys and associated hardware with sears parts (from the sears ordering system) ?
the idler arm has "maybe" 1/16th' play, hardly a wiggle, you think its worth removing this again...? i'm hopeful possibly the belt size might be the issue...

mechanic mark said:

<a href="http://www.searspartsdirect.com/model-part/917288461/0247/1509200/p0805029/00008.html" target="_blank">http://www.searspartsdirect.com/model-part/917288461/0247/1509200/p0805029/00008.html</a><br>
<br>
Remove idler arm, item 43, from top of deck & inspect for wear as well as hardware associated with idler arm, probably has quite a bit of sloppy play when moving arm up & down. I had the same problem a few years ago & replaced 3/8" bolt grade 5 with a grade 8 bolt 7/16" with new washers & a self locking nut, had to drill deck to 7/16".

Click to expand...

As the pulleys wear the grooves get deeper so the belt gets slacker.
Two easy options re to fit a slightly shorter belt or a slightly bigger idler.

DEcks wear, springs loose tension etc etc etc all adds up while it is out check all of the pulleys for damage & up / down play

rich macomb said:

Thanks for the replies guys, Mark, I am familiar with the idler arm you've mentioned - actually, the play in all of the components were closely looked over - I removed the entire deck from the tractor numerous times, and have replaced all of the pulleys and associated hardware with sears parts (from the sears ordering system) ?
the idler arm has "maybe" 1/16th' play, hardly a wiggle, you think its worth removing this again...? i'm hopeful possibly the belt size might be the issue...

Click to expand...

No to removing deck again, belt may be culprit as you say.

mechanic mark said:

No to removing deck again, belt may be culprit as you say.

Click to expand...

Ok Guys, thanks again for all the suggestions but I found it SO much easier to call the local Lawn and Garden Pro's and let them fix it - sometimes the easiest answer to a problem is the most obvious (ie: let the professionals do it) Having 3 month warranty on the work they did to repair is also nice (not to mention a full tuneup and blade sharpening and delivery of the tractor both ways and tightening of the steering column) all for 200 bucks....

I'm thinking that even if I need to have the tractor in the shop annually its still a fraction of what a new tractor this size, OR having a service do my lawn i'm far ahead.

cheers!

Good thought Rich. I work on the tractors I've had over the years. Fixed the easy stuff too. Belts, blades, mandrels. oil and filter changes. I think I'm over it too. Truth be told I think I "fixed" my last Craftsman until it fell completely apart, lol. Just gonna pay the nice man with the shop.