Most bolts used during repairs to farm equipment are safely tightened using an Armstrong torque wrench to reach torque values in the range of: “Two hands on the wrench and one foot pushing off the machine.”
But when nuts and bolts must be torqued accurately during repairs to engines, transmissions or components that are fussy about torque values, a torque wrench helps ensure fasteners are tightened to specifications.
The goal of torquing: Once a bolt is stretched to a specified length, it then acts as a spring, clamping components together.
Use these tips to ensure final torque values are accurate:
Lubrication. Unless specified otherwise, always lubricate fasteners before torquing. When a bolt is installed without lubrication, any binding between dry threads distorts the fastener’s final torque reading as indicated on a torque wrench.
Any lubricant is better than no lubricant, but in critical-torque situations like engine assembly, the wrong lubricant can lead to problems. Different lubricants have different coefficients of friction and can produce inaccurate final torque values. Cylinder head bolts, connecting rod bolts and other parts that require precise assembly usually specify in their instructions, or on their company’s website, what type of oil to use.
Accurate Measurement. Accurate torque is measured while a bolt is rotated.
“It takes more force to start a bolt turning than it does to keep it turning,” says Alan Davis, with Eagle Specialty Products. “If you stop to reset the wrench for another pull, the breakaway torque to start the bolt turning again is a distorted reading. Don’t mistake breakaway torque for actual torque.”
Avoid Fasteners. Lock washers and lock nuts complicate final torque readings.
“A traditional split-type lock washer creates extra friction as its ends dig into the metal,” says Chris Brown with ARP Fasteners. “Lock washers are mini-springs that can distort final torque readings. If you’re building an engine or something where final torque values are critical, don’t use locking fasteners.”
- Under/Over Torquing. Electro-solenoid control valves that control hydraulic flow on farm equipment are torque-sensitive. After the solenoid’s electric coil is removed, the cartridge of the actual valve can be sensitive to under- or over-torquing. Under-torquing encourages leaks. Over-torquing can force the valve’s orifices and poppets thousandths of an inch too far into the valve’s body, interfering with precise oil modulation. Torque values for standard 7/8” solenoid cartridge valves are often in the range of only 30 ft./lb. to 35 ft./lb.
- If You Don’t Know the Value. What if recommended torque value numbers are unknown? Manufacturers of valve covers, oil pans, hydraulic valves and other torque-sensitive components often list torque values on their websites.
