Identifying and Replacing Cutting Edges on a John Deere 850B Semi-U Blade

[MikePhua]

The 850B and Its Blade Configuration
The John Deere 850B crawler dozer was introduced in the late 1980s as part of Deere’s mid-size earthmoving lineup. Designed for grading, pushing, and site preparation, the 850B featured a turbocharged diesel engine, hydrostatic transmission, and a range of blade options. One of the more specialized configurations includes a 152-inch semi-U blade manufactured by Rockland, a company known for custom blade assemblies and heavy-duty attachments.
Unlike standard straight blades, the semi-U blade combines the capacity of a U-blade with the versatility of a straight edge, making it ideal for bulk material movement while retaining some grading precision. The cutting edge system on this blade typically includes four center sections and two wing end bits, each bolted to the moldboard with countersunk hardware.
Terminology Annotation
- Cutting Edge: A replaceable steel wear strip bolted to the bottom of a dozer blade, designed to absorb abrasion and protect the moldboard.
- End Bit: The outermost cutting edge segment, often curved or angled to assist with material retention and blade penetration.
- Bolt Hole Pattern: The spacing and arrangement of bolt holes used to secure cutting edges; critical for part compatibility.
- Semi-U Blade: A hybrid blade design with curved wings and a flat center, offering increased capacity and better side spill control.
Challenges in Identifying Replacement Parts
When the original blade tag is missing, identifying the correct cutting edge set becomes a matter of measurement and deduction. In one case, the operator noted that the blade had four center sections and two outer wings, but neither Rockland nor Deere could immediately confirm the part numbers. This is common with older machines or custom blade assemblies, where documentation may be lost and modifications made over time.
The key measurements taken included:

• Overall blade width: 152 inches
  
• End bit length: approximately 13.5 inches (worn from original 13.75)
  
• End bit height: around 6.5 inches
  
• Bolt spacing: roughly 3.75 inches horizontally, 2.5 inches vertically
  
• Outer cup dimensions: listed at 16.1 inches in catalogs, but actual replacements measured closer to 13.5 inches
  

These discrepancies suggest either a custom Rockland configuration or a legacy part no longer listed under standard Deere catalogs.
A Story from the Field
In Wisconsin, a dozer operator working on a road base project needed to replace the cutting edges on his 850B. After weeks of back-and-forth with suppliers, he contacted Equipment Blades, a company specializing in aftermarket wear parts. Their team cross-referenced dimensions and bolt patterns, eventually identifying the correct end bits and center sections. The new parts fit perfectly, despite catalog inconsistencies. The operator later noted that the biggest challenge was not the installation—but simply finding someone who understood the blade’s configuration.
Recommended Part Numbers and Specifications
Based on field measurements and supplier feedback, the following parts were identified:

• Center Cutting Edge Sections: Standard 6-hole or 5-hole edges compatible with Deere bolt patterns
  
• End Bits: Likely Rockland-specific, but similar to Deere T58191 and T58192 in shape and bolt layout
  
• Bolt Specs: 3/4-inch diameter, countersunk, Grade 8 hardware recommended
  
• Edge Thickness: 0.75 inches
  
• Edge Width: 8 inches
  
• Edge Lengths: Center sections vary; end bits approximately 13.44 inches
  

Always confirm hole spacing and edge dimensions before ordering, especially when dealing with worn components or aftermarket blades.
Installation Tips and Best Practices
To ensure proper fit and longevity:

• Clean the moldboard surface thoroughly before installation
  
• Use anti-seize compound on bolts to ease future removal
  
• Torque bolts to manufacturer spec, typically 250–300 ft-lbs for 3/4-inch hardware
  
• Replace all sections simultaneously to maintain even wear
  
• Inspect blade curvature and wing alignment before tightening end bits
  

If modifying edge length, use a plasma cutter or high-speed abrasive saw, and bevel the cut edge to prevent stress fractures.
Industry Trends and Support Options
As of 2025, aftermarket blade suppliers have expanded their databases to include legacy configurations and custom assemblies. Companies like Equipment Blades and Black Cat Wear Parts offer dimensional matching services and CAD-based verification. Meanwhile, Rockland continues to produce custom blades, though older models may require manual measurement and bolt pattern tracing.
Some operators have begun 3D scanning blade faces to generate digital templates for edge fabrication, especially when dealing with discontinued parts.
Conclusion
Replacing cutting edges on a John Deere 850B with a Rockland semi-U blade requires careful measurement, part matching, and supplier collaboration. With the right approach, even undocumented blade assemblies can be serviced effectively. For operators maintaining older dozers, understanding bolt patterns, wear profiles, and blade geometry is essential to keeping machines productive and protected.