Maintenance Instructions REPLACING/REPAIRING61Blade Overload Shear BoltsThe cutting blade is keyed to the blade hub by two(2) shear bolts (10-24 x 5/8 in. stainless steel ma-chine screws). These bolts are designed to shearand protect the blade drive gearbox from damage ifthe blade encounters a shock load.Cutting Blade Shear BoltsNOTE: Tightening the 5/8-18 blade mounting nutto 60 ft-lb (81.3 N·m) is also important for propershock load protection. It is important to not over-tighten the mounting nut since this defeats (over-rides) the function of the shear bolts.If these bolts shear, remove the blade and installnew bolts. Refer to CHECKING/SERVICING in thissection for Sharpen Mower Blades which describesthe blade removal and installation procedure.After reinstalling the blade, check blade timing bymoving blades through one (1) complete revolu-tion. Make sure blade tips pass clear of each other.If timing is incorrect, refer to Mower Deck GearboxReplacement in this section.PTO Shear PinThe PTO drive shaft connection to the deck gearboxhas a shear pin to provide shock load protection to themower deck drive. This system provides primaryshock protection in case of blade impact and willnormally shear before the individual shear bolts onthe blade hub.When the PTO pin has sheared, use the followingprocedure to replace it:1. Loosen the two bolts securing the PTO shaftguard on the deck; lift the guard off. (Holes inguard are slotted for easy removal.)2. Rotate U-joint on shaft to align the shear pin holewith the hole (and shear pin fragment) in theshaft. Use a punch to drive the remaining portionof the old shear pin out.3. Install new shear pin and secure with cotter pin.PTO Shear PinIMPORTANT: Use only Walker P/N 8067-13shear pins for replacement to provide propershock protection -- these pins are hardened toshear under a specific amount of load.4. Reinstall the PTO shaft guard.Before operating the deck, inspect the blade over-load shear bolts and also check blade timing (on geardriven decks) by moving blades through one (1)complete revolution. Make sure blade tips passclear of each other. If timing is incorrect, refer toMower Deck Gearbox Replacement in this section.Mower BladesMower blades are removed and remounted as de-scribed in the Sharpen Mower Blades instructions.During the course of sharpening and inspectingmower blades, if there are any of the following con-ditions of wear or damage, blades should be re-placed for reasons of safety and performance of themachine:• An excessive amount of the flat section of theblade has been ground away (removed) when theblade is sharpened. Replace the blade when lessthan a 3/4 in. (19 mm) flat section remains at theblade tip.Cutting BladeShear BoltsCotter PinU-JointTube AssemblyShear PinSplit Spring PinU-JointShaft AssemblySet Screw