Kingpin
A kingpin is a metal pin that protrudes from a trailer’s bolster plate (upper coupler). It is the connection/pivot point between a semi-trailer and a semi-tractor.
Key Points
Connection Point: Serves as the primary connection/pivot point for the trailer, allowing it to turn and maneuver with the tractor.
Durability: Made from high-strength steel to withstand the significant forces and stresses during towing.
Safety: Ensures a secure connection between the tractor and trailer, preventing accidental decoupling.
Inspecting
Frequent inspections of the kingpin and upper coupler is crucial for ensuring the safe and reliable operation of a semi-trailer.
- Visual Inspection:
- Check for Damage: Look for any visible signs of wear, cracks, or deformation on the kingpin.
- Inspect the Mounting: Ensure the kingpin is securely mounted to the trailer’s upper coupler plate. Any looseness can cause excessive movement and wear.
- Flatness Check:
- Use a Straight Edge: Place a 48-inch straight edge or a large metal right-angle square across the upper coupler plate. Check for any bumps, valleys, or warping that could affect the kingpin’s alignment.
- Bent Kingpin Check:
- Use a Square or Gage: Using a square or a specialized kingpin gage, check if the kingpin is bent. A bent kingpin can interfere with proper fifth wheel locking and accelerate wear.
- Length Check:
- Measure the Kingpin: Ensure the kingpin is the correct length for proper coupling with the fifth wheel. Use a kingpin gage to measure the length and compare it with the manufacturer’s specifications.
- Wear Measurement:
- Check for Wear: Measure the diameter of the kingpin at various points. If the wear exceeds 1/8 inch on either the 2-inch or 2-7/8-inch diameter, the kingpin should be replaced.
- Movement Check:
- Use a Dial Indicator: Install a dial indicator on the I-beam and measure any movement by rocking the wheel up and down. Excessive movement indicates worn bushings or a loose kingpin.
- Secure Connection:
- Inspect the Mounting: Ensure the kingpin is securely mounted to the upper coupler. Any looseness can cause rapid wear and unsafe conditions.