How Do You Remove Glow Plug Leads on a Kubota-Powered Bobcat 743

[MikePhua]

Understanding the Glow Plug System in Compact Diesel Equipment
Glow plugs are essential for cold-starting diesel engines, especially in compact machines like the Bobcat 743 equipped with Kubota diesel power. These plugs preheat the combustion chamber, allowing fuel to ignite even when ambient temperatures are low. Each glow plug is connected via an electrical lead, typically secured with a small nut or connector. Over time, corrosion, heat cycling, and tight engine compartments make removal difficult.
The Bobcat 743, introduced in the 1980s, is a skid steer loader powered by a Kubota V1702 diesel engine. It remains popular in small construction and agricultural operations due to its simplicity and reliability. However, servicing glow plugs on this model can be frustrating, especially when the leads are secured with knurled nuts lacking standard hex heads.
Terminology Notes

• Glow Plug: A heating element used to warm the combustion chamber in diesel engines before starting.
  
• Knurled Nut: A round nut with textured edges for grip, often lacking standard wrench flats.
  
• Ring Connector: A circular terminal crimped onto a wire, used to attach to threaded posts.
  
• Self-Locking Nut: A nut designed to resist loosening from vibration, sometimes confused with knurled types.
  

Challenges in Lead Removal
Operators often encounter glow plug leads that appear to be held by knurled thumb nuts with offset slots. These are not traditional hex nuts and may not respond to standard wrenches. In tight engine bays, such as the Bobcat 743, access is further restricted by injector lines and other components.
One user reported that only the front glow plug was heating properly, while the others remained cold. Attempts to remove the leads with pliers caused the entire electrical connector to rotate, risking wire damage. The concern was not just removing the plugs, but preserving the conductors—especially in remote areas where parts are hard to source.
Field-Tested Solutions and Techniques

• Use penetrating oil on the knurled nuts and allow time for it to soak. This reduces friction and loosens corrosion.
  
• Apply vice grips with knurled jaws to grip the nut securely without crushing it.
  
• Insert a stubby screwdriver into the slot to assist in turning, especially if the nut has a locking feature.
  
• Support the electrical connector with a pick or small pry tool to prevent twisting the wire.
  
• Use ignition wrenches—thin, flat tools designed for tight spaces—to access flats beneath the connector if present.
  

One technician noted that the “self-locking” description was likely a joke—the nuts are simply awkwardly shaped. Another mechanic recalled using stubby screwdrivers and patience to remove all but one plug without disturbing the injector lines.
Testing and Diagnosis
After removal, glow plugs can be tested by connecting them directly to a 12V battery. If they glow red hot within seconds, they are functional. In one case, all plugs worked fine after cleaning, suggesting that corrosion on the connectors—not the plugs themselves—was the root cause.
A final issue involved a hot wire connector that mimicked a functioning glow plug. Replacing the ring terminal resolved the heating imbalance, confirming that poor conductivity can cause misleading symptoms.
Recommendations for Maintenance and Repair

• Clean all connectors with contact cleaner before reinstallation
  
• Replace corroded ring terminals to ensure full current flow
  
• Use dielectric grease to prevent future oxidation
  
• Test plugs individually before assuming failure
  
• Plan for injector line removal if rear plugs are inaccessible
  

Conclusion
Removing glow plug leads on a Kubota-powered Bobcat 743 requires patience, the right tools, and an understanding of non-standard fasteners. While the plugs themselves may still function, corroded connectors and tight engine layouts complicate service. With careful technique and basic diagnostics, operators can restore cold-start reliability without replacing all components.