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How do I tension (adjust) mower drive belt for a Craftsman II riding mower model 917.257290?

While this mower is in great shape, it's clear we need to adjust the tension on the mower drive belt. But the manual isn't coming up and we really need some help with this task. Thanks.

Craftsman , Lawn Mowers , Lawn & Garden
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1 Answer from this member:
Manage My Life
This particular model manual is currently not available electronically through Manage My Home. But it can still be ordered through

Sears PartsDirect

or your Sears Store using the part number 137642.

The mower blades on this model disengages by loosening off the belt until it can slip, so it normally will be loose unless the blades are in use. But if your blades are slipping during cutting then the belt might still need some attention.

Some models use a cable to engage the belt but this particular model uses metal linkages to move the tensioner pulley assembly into the belt and take out the freeplay. And that linkage hooks directly to the engagement lever that you use when turning on the mower blades. So there is no actual adjustment points as there might be on some other models.

Unless a link or rod is bent or very badly worn or damaged in some other way, there is not likely to be much added play introduced into the belt from the engagement linkages themselves. But, as belts wear they do lose material and stretch somewhat and eventually that will make them run looser than when new. So, if the belt is slipping, it is more likely the belt itself is too worn to grip the pulleys properly and the belt will need replacing.

Looking at the parts

image below

from the PartsDirect site, the mower drive belt is shown as

item 20

, the tensioner pulley is

item 35

and the engagement lever you use to turn on the blades is

item 53

. The linkage rods and arms that connect the lever to the tensioner assembly are shown as

items 49 and 54


Even if it is the belt at fault, you should still check the movement of the lever and linkage and tensioner assembly just to be sure nothing is out of place or seems excessively worn or difficult to move.

And look over all the pulleys carefully for any signs of excess wear or dings or bends that might make it hard for the belt to grip or run straight. Often a dragging pulley due to worn bearings can also contribute to belt slip, so once you have the belt off check that all the pulleys on the mower deck spin freely and smoothly.

If you have any other questions or concerns, or this does not address the issue you had, feel free to submit another question here at Manage My Home and we will do our best to help further. Or, you can call


(800-469-4663) to see what options there are in your area for having the unit inspected and repaired by a professional.
by Manage My Life
July 10th, 2008
0 votes
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