The idler arm on my craftsman riding lawn mower will not freely move to tighten the belt. It only moves about 1/4 inch model number 247-289010

Unhook every thing from it spray with PB Blaster WD 40 or some type lube , keep working it until it moves freely .
Luck

This is odd, I answered this question earlier today but my answer has disappeared. RW which idler; mower deck or transmission? I guess it doesn't matter all that much because DG's answer is what I usually do. I have several Sears tractors and from time to time they all have some issue with engaging the blade. Sears arms do not have grease fitting and the shaft can rust if you don't use the mower frequently.