Older Craftsman 42" New belt is too loose

[audiomagnate]

I went to use my vintage but well cared for Craftsman 42" 917.255580 mower and noticed that the blades wouldn't engage. I looked underneath and saw the belt was in very poor shape so I ordered a replacement belt indicated in the owner's manual, part no. 130969. I checked the length with the worn belt before installation and it was the same as the old one. The new belt slips just like the old one. I have checked all the pulleys and bearings the operation of the moving idler pulley and all is good. It seems a shorter belt would fix the problem but I know that's not a proper fix. I adjusted the retainer on the idler clutch rod to close to its end point, but the belt is still too lose to engage the blade.

 

[bertsmobile1]

Like water running over a rock, a soft belt will wear the pulleys so the belt sits deeper which shortens the belt run.
Add to that wear in the deck hangers can also change the effective belt length.

It is a regular event to fit a smaller belt on high hour mowers.

The caveat on this is when a V pulley shows polishing on the root of the V then the pulley is worn out and needs to be replaced.
Similar story with flat idlers, they get wear grooves in them making them smaller.

Finally the tension arm on the deck floggs the hole out oval and that makes a massive difference to the effective belt length.

 

[shiftsuper175607]

I went to use my vintage but well cared for Craftsman 42" 917.255580 mower and noticed that the blades wouldn't engage. I looked underneath and saw the belt was in very poor shape so I ordered a replacement belt indicated in the owner's manual, part no. 130969. I checked the length with the worn belt before installation and it was the same as the old one. The new belt slips just like the old one. I have checked all the pulleys and bearings the operation of the moving idler pulley and all is good. It seems a shorter belt would fix the problem but I know that's not a proper fix. I adjusted the retainer on the idler clutch rod to close to its end point, but the belt is still too lose to engage the blade.

.
If the correct length belt is loose now...You have the belt routed wrong.
Easy to do.

The belt is outside a retainer pin as it goes around a pulley or something else like on the wrong side of an idler.

Some belts are loose until you engage the drive lever.