Glow Plug Sourcing and Track Tensioning on the Mitsubishi MM35B Mini Excavator

[MikePhua]

The Mitsubishi MM35B and Its Compact Utility Legacy
The Mitsubishi MM35B is a compact hydraulic excavator designed for light construction, landscaping, and utility trenching. Produced during the late 1990s and early 2000s, it featured a zero-tail swing design and a Mitsubishi S4L diesel engine—a four-cylinder, water-cooled unit known for its fuel efficiency and cold-start reliability. Mitsubishi Heavy Industries, with a long history in industrial machinery, built the MM-series to compete with other Japanese compact excavators like Kubota’s KX series and Yanmar’s B-series.
Though no longer in production, the MM35B remains in use across North America and Asia, particularly among small contractors and landowners who value its mechanical simplicity and low operating cost. However, sourcing parts—especially engine components and undercarriage fittings—can be challenging due to limited aftermarket support and regional distribution gaps.
Where to Find Glow Plugs for the S4L Engine
Glow plugs are essential for cold-weather starting in diesel engines, especially in compact machines with small displacement. The S4L engine used in the MM35B shares design similarities with the Mitsubishi L3E, which was widely used in turf equipment, generators, and compact tractors. This cross-application opens up sourcing options beyond traditional construction parts suppliers.
Recommended sourcing strategies:

• Identify the exact glow plug model by removing one and measuring thread size, length, and voltage rating
  
• Cross-reference with turf equipment suppliers, especially those servicing TORO mowers and compact tractors
  
• Search by engine model (S4L or L3E) rather than machine model to expand compatibility
  
• Use part numbers from Pel-Job or other OEMs that used Mitsubishi engines in their compact excavators
  
• Contact diesel engine rebuild shops that stock glow plugs for industrial applications
  

One technician found a compatible head gasket for a Pel-Job EB12.4 by sourcing through a TORO dealer, suggesting that glow plugs may also be interchangeable across brands using the same engine block.
Track Tensioning and the Idler Roller Grease Bolt
Track tension on mini excavators is typically maintained by a grease-filled hydraulic cylinder behind the front idler. Adding grease pushes the idler forward, tightening the track. To release tension—such as when reinstalling a thrown track—pressure must be relieved from this cylinder.
On the MM35B, the grease fitting appears as a small zerk (grease nipple), which may confuse operators expecting a larger bleed bolt. In reality, the zerk is part of a larger assembly that includes a check valve and piston housing. Removing the zerk fitting allows grease to escape and pressure to drop, retracting the idler.
Steps to release track tension:

• Safely elevate the track using the boom and blade
  
• Clean the area around the grease fitting to prevent contamination
  
• Unscrew the zerk slowly to allow grease to escape
  
• Monitor idler movement and stop once sufficient slack is achieved
  
• Reinstall the track and reapply grease to restore tension
  

Some machines use a dedicated bleed bolt with a hex head, but the MM35B integrates this function into the zerk assembly. Operators unfamiliar with this design may overlook the release method, leading to unnecessary disassembly.
Preventing Track Loss and Improving Undercarriage Longevity
Thrown tracks are common in mini excavators operating on uneven terrain or with worn undercarriage components. To reduce the risk:

• Maintain proper track tension and inspect weekly
  
• Replace worn sprockets, rollers, and idlers as needed
  
• Avoid sharp turns on soft or sloped ground
  
• Clean mud and debris from the undercarriage after each use
  
• Use high-quality grease with water-resistant additives for the tensioning cylinder
  

A contractor in Oregon reported that his MM35B threw a track after hitting a root cluster. After learning how to relieve pressure through the zerk fitting, he was able to reinstall the track without tools or disassembly—saving hours of downtime.
Conclusion
Maintaining the Mitsubishi MM35B requires a blend of mechanical intuition and cross-industry resourcefulness. Glow plugs for the S4L engine can be sourced through turf equipment channels, while track tensioning relies on understanding the integrated grease fitting design. With proper care and a bit of ingenuity, this compact excavator continues to serve reliably in the field. For owners willing to dig into the details, the MM35B proves that small machines can still deliver big results.