08300505 Idler Pulley Tensioner Extension Spring Fits Ariens | Gravely 991073 991074 991075 991085 991086 Lawn Mower

What It Is

This idler pulley tensioner extension spring (part 08300505) provides tension to the mower deck belt on Ariens and Gravely zero-turn mowers, ensuring the blade pulley system operates smoothly without belt slippage.

Fitment & Compatibility

• Direct OEM replacements: Fits Ariens part 08300505 and Gravely part 991073, 991074, 991075, 991085, 991086.
• Common models: Ariens Zoom 42/50/52/54/60 decks; Gravely ZT HD, ZTX, ZTXL, Pro-Turn series. Verify your deck size and model year (2000s–2020s) against OEM parts lookup.
• Before buying: Measure the spring’s free length (approx. 3.5–4 inches) and coil diameter (0.5–0.6 inches) to confirm match. Check your existing spring for wear or breakage—if it’s stretched or rusty, replace.
• Aftermarket note: This is an aftermarket spring, not OEM. It matches OEM specs but may have slightly different finish. Confirm your mower’s belt routing diagram uses a spring of this length.

Key Things to Know

• Quality: Made from steel with zinc coating for corrosion resistance. 4.4/5 rating with 19 reviews suggests good durability for the price.
• Installation difficulty: Easy—requires only pliers or a spring puller. No special tools needed. Risk of spring snapping if overstretched; use a safety tool.
• Common gotcha: The spring can pop loose during installation if not anchored securely. Ensure the hook ends seat fully in the pulley arm and deck bracket.
• Belt tension: If the deck belt still slips after installing, check the idler pulley bearing (separate part) for wear—a bad pulley can cause premature spring fatigue.

Should You Buy It

If your Ariens or Gravely mower’s deck belt is loose or the original spring is broken or stretched, this is a cost-effective, direct-fit replacement. It’s ideal for DIY repairs on common zero-turn models from the 2000s onward. Avoid if you need an OEM part for warranty or if your pulley arm is damaged—then replace the whole tensioner assembly.