2 Pcs 08300505 Idler Pulley Tensioner Extension Spring Compatible with Ar-iens Gra-vely Lawn Mower 991075 991085 991073 991074 991086

What It Is

This is a set of two extension springs used to tension the idler pulley on the belt drive system of select Ariens and Gravely lawn mowers. They keep the belt tight against the pulley to prevent slipping during cutting, and are a common wear item on 42" to 60" deck models.

Fitment & Compatibility

Critical to verify before purchase:

• OEM cross-reference: These springs replace OEM part numbers 08300505, 991075, 991085, 991073, 991074, 991086. Check your current spring for any of these numbers.
• Brand & deck size: Designed for Ariens and Gravely models with 42", 50", 54", 60", 61" decks (e.g., Zoom, ZT, ZTX, ZX, XL series). Not for Craftsman, John Deere, or other brands.
• Physical check: Measure your old spring’s length (uncompressed) and coil diameter. This set is typically 4.5" long x 0.75" diameter with 0.062" wire. If yours is significantly different, it won’t fit.
• Qty: You get two springs—confirm your deck uses two tensioner springs (most do on dual-belt systems). Some single-belt decks only need one.

Key Things to Know

• Installation difficulty: Moderate. You’ll need pliers or a spring puller to stretch the spring over the pulley arm. Wear eye protection—springs can slip and snap.
• Quality: Aftermarket from “Pcs” brand. Single review at 5 stars, but no long-term durability data. OEM Ariens springs cost more but may last longer.
• Common gotcha: These springs are identical left and right—no specific orientation. But if your deck uses a different spring for tension vs. return, confirm both ends hook the same way.
• Signs you need them: Loose belt, belt slipping under load, or visible rust/stretching on old springs. Replace in pairs even if only one is bad.

Should You Buy It

If you own an Ariens or Gravely zero-turn with a 42"-61" deck and need a budget-friendly fix for a loose belt, this set is a reasonable choice. But for high-use commercial mowers or if you want guaranteed longevity, pay extra for OEM Ariens springs. Measure first—fitment is narrow.