Craftsman 48" mower deck idler pulley tension spring part number. Model # of tractor is 917.273241

Hi,
This machine seems to have two springs, One is #179479 and the other is #174371. I will attach a deck graphic. A note is that often these units seize at the pivot.
Peace,
Clarke

I agree with Clarke, seize frequently. The spring may not be the issue but a rusted pivot. Here is the link so you can zoom in for a better peak but get your WD40 ready http://www.searspartsdirect.com/part...dMod=917273241