History and Development
The Caterpillar 235 is part of Cat’s 200-Series line, introduced in the early 1970s as Caterpillar expanded into full-size hydraulic excavators. The 235 was launched around 1973 to compete in the roughly 35-ton class sector. It was one of the foundational models that helped Cat establish its reputation in heavy excavators, complementing the 225 and later the 245 models. Over its production life, the 235 went through several series or “variants” (such as A, B, C, D) with incremental improvements in engine, hydraulic performance, undercarriage durability, and operator comfort. It was eventually phased out in favor of newer models with more modern emissions, more efficient hydraulics, and ergonomic improvements.
Key Specifications and Performance
Here are typical specifications for a Caterpillar 235 (varies depending on variant such as “B”, “C”, “D” etc.):

• Net Power: ~ 195 hp (≈ 145 kW) from a 6-cylinder CAT 3306 engine.
  
• Operating Weight: ~ 84,400 lbs (≈ 38,300 kg) for basic configurations. Some variants may be heavier with added attachments or wide track sets.
  
• Fuel Capacity: ~ 105 US gallons (≈ 397 liters).
  
• Hydraulic Flow: ~ 190 gallons/minute (≈ 720 liters/minute).
  
• Relief Valve Pressure: Approx. 1,000 psi (note: verify model variant, some heavy-duty attachments may require higher settings).
  

• Max digging depth: ~ 22.5 to ~ 26.5 ft depending on boom/ stick length.
  
• Max reach along ground: 35 to nearly 39 ft in longer boom/stick options.
  
• Max cutting or loading height: in the low 30-ft range (30-33 ft) depending on configuration.
  

• Width over tracks: approx. 11-12 ft depending on track width or gauge.
  
• Height to cab top: ~ 11 ft or slightly more in certain variants.
  
• Ground clearance, track gauge, shoe size, tail swing radius are variant dependent. Example: shoes ~ 30 in wide, tail swing ~ 11 ft in some cases.
  

• Stronger undercarriage components for longer track life.
  
• More efficient hydraulic systems to improve speed and digging force.
  
• Options for longer sticks and booms to increase reach.
  
• Wide gauge or “wide track” versions for better stability and lower ground pressure, especially useful when working in soft or wet terrain.
  

• Undercarriage wear: track shoes, rollers, idlers need periodic replacement.
  
• Hydraulic leaks: seals in boom, stick and bucket linkage, particularly in older machines.
  
• Engine maintenance: fuel, oil, cooling systems require care, especially in machines with many hours.
  

• Large-scale excavation and earthmoving projects.
  
• Mining overburden removal.
  
• Quarrying tasks.
  
• Heavy foundation work, trenching with deep sticks.
  
• Forestry, especially when outfitted with forestry guarding or thumbs.
  

• Always inspect the undercarriage: shoes, pins, bushings; replacing these can be expensive.
  
• Check hydraulic system for leaks, especially boom and stick cylinders. Old machines often have hard starts in cold or humid climates—inspect seals, pumps, fuel system.
  
• Evaluate boom/stick length and configuration — longer adds reach but also stress, possibly more maintenance.
  
• Verify operating hours and maintenance history. Units over ~ 15,000-20,000 hours still usable but expect higher maintenance costs.
  
• For transport: width, height, and weight make hauling expensive. Wide track or extended counterweights can increase dimensions.
  

Test Setup and Context

• Two machines of nearly the same weight were compared: the Waldon 5100 articulated loader at about 7,100 lb versus the CAT 236 skid steer at around 7,000 lb.
  
• Objective: Digging into a stockpile of excavated dirt (not a virgin pit), filling the bucket. Each machine took turns under identical conditions.
  

• The Waldon 5100 struggled to bite into the pile; it couldn’t get full bucket penetration. The front tires often spun, digging holes rather than pushing forward. Its bucket would only contact the surface, not deep enough for a full scoop.
  
• By contrast, the CAT 236 skewed forward into the pile, using the bucket and boom in sync to load it fully, with less wheel spin and more traction. It overcame the resistance of the material more effectively.
  

• Drivetrain & Differential Setup: The Waldon 5100 employs Dana 60 axles front and rear, both powered by hydraulic motors, but without locking or limited-slip differentials originally. This setup allows tires to slip more easily under load.
  
• The CAT 236’s skid steer design inherently keeps all wheels locked together in steering and drive functions, providing more consistent torque to all wheels during digging. This makes a major difference in traction under load. Participants in the test pointed to the lack of a locking differential on the Waldon as a key weakness.
  
• Weight Distribution & Center of Gravity: Skid steers tend to shift more weight rearward into the drive tires during loading and bucket lift. This improves traction. The Waldon, being articulated and with its front bucket geometry, cannot shift weight as effectively; its front end tends to get light or lose grip when the bucket enters the pile.
  
• Bucket Penetration & Boom/Kinematic Geometry: The CAT 236 could engage its bucket and boom more deeply; the Waldon’s geometry meant its bucket only skimmed the pile’s face rather than digging in. The deeper penetration gives more load per pass.
  

• The owner later installed a locking differential in the rear axle of the Waldon 5100, which yielded major improvement: it could push into dense material nearly like the skid steer. Then added one in the front axle too, which further reduced tire spin and improved bucket fill.
  
• Tire/tread selection was also noted: tires with better traction and possibly more aggressive treads helped. Proper tire pressure (neither overinflated nor underinflated) plays a role.
  

• For digging into stockpiles or other piled materials, machine types matter: skid steers or loaders with good front-traction and proper differentials will outperform articulated loaders without such features.
  
• If using an articulated loader in digging/stockpiling tasks, consider these enhancements:
  • Locking or limited-slip differentials on both front and rear axles
    
  • Appropriate tire tread designed for grip rather than just smooth surfaces
    
  • Operator technique: keeping bucket rolled back, lifting slightly as entering the pile to help weight transfer
    
• Check geometry: bucket shape, boom angle, load height—all affect penetration and load per bucket
  

Kobelco’s Compact Excavator Lineage
Kobelco Construction Machinery, a division of Kobe Steel founded in 1930, has long been recognized for its innovation in hydraulic excavators. The SK115SRDZ is part of Kobelco’s SR series, designed for reduced tail swing and urban maneuverability. With an operating weight around 11.5 metric tons and a 70–80 horsepower engine, the SK115SRDZ balances compact dimensions with full-size digging power. It features a two-speed travel system, pilot-controlled hydraulics, and a robust undercarriage suited for tight job sites and utility work.
Kobelco’s SRDZ designation typically refers to models equipped with zero tail swing and enhanced hydraulic dampening. These machines are popular in North America and Asia, with thousands sold since the early 2000s. Their reputation for smooth operation and fuel efficiency makes them a staple in rental fleets and owner-operator businesses.
Symptoms of Slow Tracking on Both Sides
When an SK115SRDZ begins tracking slowly on both sides, especially struggling to climb even slight grades, the issue is likely systemic rather than isolated to one travel motor. Operators may notice that switching from low to high travel speed yields only a marginal improvement, and other hydraulic functions—such as boom, arm, and bucket—continue to operate normally.
Terminology annotation:
- Tracking: The movement of the excavator via its crawler tracks, controlled by hydraulic motors. - Travel Speed Selector: A switch or lever that toggles between low and high-speed travel modes. - Gradeability: The machine’s ability to climb slopes, influenced by torque, traction, and hydraulic output.
This pattern suggests a reduction in hydraulic flow or pressure affecting both travel circuits simultaneously. Unlike a single motor failure, which would cause asymmetric tracking, bilateral slowness points to upstream issues in the hydraulic system.
Hydraulic Flow and Travel Motor Dependencies
The SK115SRDZ uses a variable displacement hydraulic pump to supply fluid to all functions, including travel. Travel motors are typically fed through a dedicated circuit with flow priority during movement. If the pump is underperforming or the travel circuit is restricted, both motors will suffer.
Potential causes include:

• Weak or worn hydraulic pump unable to maintain flow under load
  
• Clogged main hydraulic filter reducing system pressure
  
• Faulty travel speed solenoid or selector valve
  
• Contaminated pilot lines affecting control signal strength
  
• Internal leakage in the control valve block reducing effective pressure
  

• Check hydraulic fluid level and condition for contamination or aeration
  
• Inspect and replace the main hydraulic filter if clogged
  
• Measure system pressure at the travel circuit using a test port
  
• Verify travel speed solenoid voltage and resistance
  
• Inspect pilot pressure at the travel control valve
  

• Replace hydraulic filters every 500 operating hours
  
• Inspect solenoid connectors for corrosion and secure grounding
  
• Use OEM hydraulic fluid to maintain viscosity and additive compatibility
  
• Flush pilot lines during major service intervals
  
• Monitor travel motor case drain flow to detect internal leakage
  

Introduction and Purpose
Bucket teeth are replaceable, wear-resistant tips mounted on the leading edge of buckets for excavators, loaders, dozers and similar earthmoving equipment. They penetrate soil, rock, or other material. Over time they wear down, reducing digging efficiency, increasing fuel consumption, and risking damage to the bucket lip or adaptor. Knowing when to replace teeth can save time, money, and prolong machine life.

Key Terms and Components

• Bucket tooth: The replaceable tip fitted to the bucket’s cutting edge, used to break ground.
  
• Adaptor (Shank / Lip Shank): The fixed part of the bucket onto which the tooth attaches; the tooth slides onto or around the adaptor.
  
• Wear profile: The shape and dimensions of the tooth relative to its original design. As wear progresses, the profile flattens or shortens.
  
• Pin & lock/retaining system: Mechanism (pin, clip, retainer, or hammerless locking system) holding the tooth to the adaptor.
  
• Ground engaging tools (GET): A broader term covering bucket teeth, adaptors, tips, edges, etc.
  

1. Wear Percentage Benchmarks
   • Check manufacturer specifications: many OEMs provide metrics for when teeth have reached 25 %, 50 %, 75 % and 100 % wear. This helps in scheduling replacements.
     
   • A common informal guideline: change when teeth are worn down to about 30-40 % of the adaptor height or before the tooth’s effective height reduces too much, risking wear of the adaptor or lip.
     
2. Loss of Digging Performance
   • If penetration into material (soil, rock, frozen ground) becomes more difficult, more machine force or higher engine revs are required, fuel efficiency drops. This indicates teeth are dull.
     
   • The bucket may take longer per scoop or load fewer materials.
     
3. Visible Wear Indicators
   • Teeth reduced to “nubs” (very short tips) or flattened tips that no longer cut efficiently.
     
   • Uneven wear: some teeth much more worn than others, creating imbalance in load, stress points, or increased wear on certain adaptors.
     
   • Cracks, missing sections, or deformations.
     
4. Avoid Adaptor & Bucket Damage
   • Continuing to use worn teeth until they are too short can expose the adaptor, leading to its damage. Adaptor replacement is more expensive than tooth replacement.
     
   • Wear into the lip shank or bucket edge can lead to structural weakness.
     
5. Operating Conditions
   • Material type: abrasive soil, rock, frozen ground wears teeth faster. In harsh conditions, tooth life may be cut in half compared to softer soils.
     
   • Frequency of use: hours per day, load cycles, whether teeth are used for back-dragging or pushing fill, which wear the bottom surface more.
     
   • Environmental factors: presence of sand, grit; moisture; impulse loads (hitting rock) accelerate wear.
     
6. Cost vs Productivity Trade-off
   • There is an economic point where replacing teeth earlier, when minor wear is visible but before productivity suffers, can save money (fuel, labor, time).
     
   • If machine is loading trucks waiting around, delaying replacement causes delays costing more than the cost of new teeth.
     

• Inspect teeth weekly (or daily in harsh conditions).
  
• Measure tooth height or compare with unused spare or OEM spec. Document original vs current height.
  
• When teeth reach about 30-40 % wear (height lost), plan replacement.
  
• Monitor digging efficiency: fuel consumption, time per load. If these degrade, it’s a trigger.
  
• Replace missing teeth immediately — never run with gaps, as this damages surrounding teeth and adaptor.
  
• Replace locking pins / retainers when replacing teeth; worn or loose hardware reduces tooth life and safety.
  

• OEMs may specify that when wear reaches 50 % (half the tooth height), the tooth should be changed to avoid damage.
  
• In softer soil, a set of GET may last 100-200 hours; in rock or frozen conditions, maybe 30-70 hours.
  
• Replacement cost: depending on machine size and tooth design, individual teeth can cost from tens to hundreds of dollars; adaptors much more.
  

Origins and Purpose
The P&H 4100XPC is a massive electric rope shovel built for large-scale mining operations. Developed by Joy Global (now part of Komatsu Mining), this class of shovel embodies over a century of engineering expertise in designing machines able to move huge volumes of material with efficiency and reliability. Intended for loading trucks, digging benches, and removing overburden in open pit mines, the 4100XPC answers needs for scale, durability, and low cost per ton moved.
Technical Specifications

• Nominal Payload: ~ 99.8-108.9 metric tons (≈ 110-120 short tons) per dipper fill.
  
• Dipper Capacity (SAE struck): ~ 52.8-61.2 m³ (69-82 yd³). With 2:1 geometry (for certain digging conditions): ~ 58.3-67.6 m³ (≈ 74.4-88.4 yd³).
  
• Production Rates: Between ~ 7,834 to 10,444 metric tons per hour, depending on configuration and material; in short tons roughly 8,635-11,513 TPH.
  
• Working Ranges: Cutting height ~ 16.8 m (≈ 55 ft 2 in), radius of cut ~ 23.9 m (≈ 78 ft 8 in), dumping height with door open ~ 9.5 m (≈ 31 ft).
  
• Weight & Undercarriage Options: Working weight ~ 1,532,235 kg (≈ 3,378,000 lb) with standard shoes 76 in (≈ 1930 mm), and slightly more with wider shoes (87 in / 2210 mm). Ground pressure is roughly 63 psi ( 434 kPa) with standard shoes, dropping to ~ 55 psi (~ 380 kPa) with optional wider shoes.
  

• AC Drive System: Uses an AC (alternating current) electric drive with IGBT inverters, enabling more precise motor control, improved efficiency, and high availability.
  
• Centurion Supervisory Controller: A control system that integrates machine subsystems (crowd, hoist, swing, propel) and provides diagnostics, operator feedback, and production monitoring.
  
• Dipper / Bucket System: “Optima” dippers with mine-matched wear packages and geometry; twin-leg dipper handle and rack & pinion mechanisms help stability, penetration, and reduced wear.
  
• Swing, Propel, Hoist: Planetary gears used in swing and propel for high torque; dual hoist motors; splash lubrication for various enclosed gear cases to extend service intervals and reduce maintenance.
  

• Hoist Rope Wear & Replacement: Rope life varies widely depending on material, moisture, and impact from the dipper or debris. Frequent visual inspections are essential. Plan rope change-out crews and safety protocols for working aloft on booms.
  
• Wear on Teeth and GET (Ground Engaging Tools): Bucket lips, adapters, teeth experience high abrasion. Use mine-matched GET styles; track performance metrics to know when to change them before production suffers or structural damage occurs.
  
• Undercarriage Support & Protection: Given the dipper handle geometry and swing arcs, there is risk of dipper-to-track interference. The machine includes a Track Shield system and delta style undercarriage to help mitigate damage.
  
• Lubrication & Cooling: Gear cases and motors need proper lubrication. Enclosed gear cases with splash lube filtration help, but ensuring oil quality and cooling capacity remains in spec is necessary, especially in hot environments.
  
• Operator Comfort & Safety: Cab features include features like air suspension seats, climate control, visibility improvements. Well-maintained cab features reduce fatigue, improve safety, and indirectly increase productivity.
  

The Rise of Women in Heavy Equipment
For decades, the world of cranes, bulldozers, and excavators was seen as a male-dominated domain. But the tide has been shifting. In recent years, more women have entered the heavy equipment industry, not just as operators but as trainers, mechanics, and site supervisors. According to the U.S. Bureau of Labor Statistics, the number of female construction equipment operators grew by over 30% between 2010 and 2020, a trend driven by changing cultural norms and targeted recruitment efforts.
One standout example is a grandmother from Phoenix who became a certified crane operator in her 50s, defying expectations and proving that age and gender are no barriers to mastering complex machinery. Her story is emblematic of a broader movement toward inclusivity in skilled trades.
Crane Operation and Certification Pathways
Operating a crane requires precision, spatial awareness, and a deep understanding of load dynamics. Certification typically involves classroom instruction, hands-on training, and passing a written and practical exam. In the United States, the National Commission for the Certification of Crane Operators (NCCCO) sets the standard for licensing.
Terminology annotation:
- Boom Length: The extendable arm of the crane, which determines reach and lifting height. - Load Chart: A reference table showing the maximum safe lifting capacity at various boom angles and extensions. - Swing Radius: The circular area around the crane within which the boom can rotate, critical for site planning and safety.
The grandmother in question trained on a hydraulic mobile crane with a telescoping boom, mastering the controls and safety protocols with the same rigor as any younger trainee. Her instructors noted her attention to detail and calm demeanor under pressure—traits essential for safe lifting operations.
Overcoming Bias and Building Confidence
Entering a male-dominated field often comes with skepticism and subtle resistance. Many women report being underestimated or excluded from certain tasks. But persistence and competence tend to win respect over time. In this case, the operator’s background as a caregiver and homemaker gave her a unique perspective on risk management and multitasking—skills that translated well to crane operation.
Anecdotal stories from job sites reveal that once female operators demonstrate proficiency, they are often entrusted with more complex lifts and given leadership roles. One foreman recalled assigning a female operator to lift HVAC units onto a high-rise roof, noting that her precision and communication outperformed more seasoned male colleagues.
Equipment Evolution and Accessibility
Modern cranes have become more user-friendly, with digital load indicators, joystick controls, and ergonomic cabs. These advancements reduce physical strain and make the machines more accessible to operators of all body types. Manufacturers like Liebherr, Manitowoc, and Tadano have invested in cab design that accommodates a wider range of users, including adjustable seats, low-effort controls, and climate systems.
Terminology annotation:
- Hydraulic Crane: A crane powered by hydraulic cylinders, offering smooth and powerful lifting. - Telescoping Boom: A boom that extends in sections, allowing variable reach without changing the base position. - Load Moment Indicator (LMI): A system that warns the operator when the crane approaches its lifting limits.
These features not only improve safety but also open the door for older operators or those with limited physical strength to perform demanding tasks.
Training Programs and Outreach Initiatives
Organizations across the country have launched initiatives to recruit and train women in heavy equipment. Programs like Women in Construction Week, NAWIC mentorships, and union-sponsored apprenticeships offer pathways into the trades. Some vocational schools now offer women-only cohorts to foster confidence and peer support.
In Arizona, where the grandmother crane operator trained, local unions partnered with community colleges to offer subsidized certification programs. These efforts have led to a noticeable uptick in female enrollment and job placement.
Lessons from the Field and Practical Advice
For aspiring operators of any age or gender, the key to success lies in preparation and mindset. Recommendations include:

• Study load charts thoroughly and understand the physics of lifting
  
• Practice hand signals and radio communication for teamwork
  
• Maintain situational awareness, especially during blind lifts
  
• Respect the machine’s limits and never override safety systems
  

The Landscape of Heavy Equipment Sales
The market for heavy machinery—bulldozers, excavators, loaders, cranes, and haulers—has always relied on a network of sellers ranging from global dealerships to small independent traders. Sellers play a crucial role in connecting manufacturers with contractors, farmers, loggers, and municipalities. While major corporations dominate new equipment distribution, a significant percentage of transactions, especially in North America, involve second-hand units. According to industry data, roughly 60% of heavy equipment transactions in the United States each year are used machines, which underlines the importance of trustworthy sellers in this sector.
Types of Sellers

• Large dealerships: Authorized distributors tied to major brands like Caterpillar, Komatsu, or John Deere. They provide warranty coverage, financing, and certified technicians.
  
• Independent brokers: Small businesses or individuals who source machines from auctions, trade-ins, or private sellers and resell them for profit.
  
• Auction houses: Regional and international players such as Ritchie Bros., where thousands of machines change hands annually.
  
• Online platforms: Digital marketplaces that allow equipment owners to connect directly with buyers. These have grown significantly in the last decade due to convenience and global reach.
  

1. Transparency of Condition – Sellers may present equipment in top visual condition while overlooking hidden issues like worn hydraulic pumps or transmission problems. For example, an excavator freshly painted may mask undercarriage wear worth tens of thousands in repairs.
   
2. Pricing Practices – Some sellers overprice used units, hoping to attract inexperienced buyers. Others may underprice to move inventory quickly, which can create suspicion about hidden defects.
   
3. Paperwork and Provenance – Titles, maintenance records, and hour meters are not always accurate. Odometer or hour-meter tampering has been reported in certain markets, leading to disputes.
   
4. After-Sale Support – Large dealerships often provide ongoing support, while small sellers may disappear once the deal is completed.
   

• Always request a detailed inspection report or commission a third-party mechanic to evaluate the machine.
  
• Ask for oil sample analysis, which can reveal engine or hydraulic system wear not visible during inspection.
  
• Check seller reputation through references or industry associations. A seller who has been in business for decades is less likely to risk damaging credibility.
  
• Negotiate for short-term warranties, even in used sales, to ensure machinery performs as described.
  
• Use escrow services or formal contracts when purchasing from new sellers or online platforms.
  

Development History
The Caterpillar D4 series has been in production since the mid-20th century, evolving from small, reliable track-type tractors into modern dozers equipped with advanced hydraulics and electronics. The D4H Series II, often abbreviated as D4H-II, was introduced in the late 1980s and produced into the 1990s. It represented a significant leap in efficiency compared to earlier models, with improvements in operator comfort, hydrostatic steering, and power delivery. Caterpillar designed it as a balance between compact size and sufficient horsepower to tackle heavy grading, land clearing, and utility construction projects.
By the early 1990s, Caterpillar had sold thousands of D4H machines globally. It became popular not only in North America but also in Europe and Asia, where medium-sized dozers were in demand for infrastructure projects. Its reputation for reliability and serviceability kept it in use for decades, with many still operating today in logging, road construction, and quarry environments.

Key Specifications
The Caterpillar D4H-II typically featured the following parameters:

• Engine: Caterpillar 3304 turbocharged diesel
  
• Horsepower: around 135 hp at the flywheel
  
• Operating weight: approximately 32,000 lb depending on configuration
  
• Transmission: powershift with torque divider
  
• Blade capacity: between 3.5 to 4.5 cubic yards depending on the blade type
  
• Track gauge: 71 in (variable depending on undercarriage)
  

• Undercarriage wear – Tracks, rollers, and idlers wear out quickly in abrasive environments. Regular measurement of track pitch and bushing turn schedules extend life.
  
• Steering clutch or differential steering problems – Operators sometimes report sluggish steering or difficulty maintaining turns under load. Checking hydraulic pressures and adjusting control linkages are early troubleshooting steps.
  
• Hydraulic leaks – Seals on blade lift and tilt cylinders are known wear points. Regular inspection prevents contamination of the hydraulic system.
  
• Cooling system challenges – Clogged radiators or water pump wear can lead to overheating. Flushing the system and ensuring correct coolant type are essential.
  

The Legacy of the 955K
Caterpillar’s 955K crawler loader was introduced in the late 1960s as part of the company’s evolution in mid-size track loaders. Designed for versatility in earthmoving, land clearing, and material handling, the 955K featured a D330C diesel engine producing around 115 horsepower, paired with a powershift transmission and a rugged undercarriage. The machine weighed approximately 32,000 lbs and offered a bucket capacity of 1.5 to 2 cubic yards depending on configuration.
Caterpillar, founded in 1925, had by then become a global leader in heavy equipment. The 955K was a popular choice for contractors and landowners alike, with thousands sold across North America. Its successor, the 955L, introduced the 3304 engine and refined hydraulics, but the K model remained a workhorse in the field for decades.
Auction Find and Initial Assessment
One operator acquired a well-worn 955K at a local auction with plans to use it for brush clearing on a hunting ranch. The machine had undergone several modifications, including the installation of a dozer blade from a D5 or D6 in place of the original bucket, which was still in good condition. The loader arms had been patched with heavy steel, preventing the original safety bar from engaging, prompting the fabrication of a custom support bar to safely work beneath the raised arms.
Terminology annotation:
- Loader Arms: The hydraulic arms that raise and lower the bucket or blade. - Safety Bar: A mechanical lockout device used to secure the loader arms during maintenance. - Guillotine Risk: A colloquial term for the danger posed by unsupported loader arms falling unexpectedly.
The undercarriage appeared solid, but the left track sagged despite repeated greasing, suggesting a failed recoil spring or damaged tensioner piston. This issue required immediate attention to prevent derailment or uneven wear.
Cooling System Overhaul and Radiator Discovery
During initial operation, the machine overheated, forcing multiple shutdowns. Inspection revealed coolant spraying from pinholes in the radiator core, which was heavily clogged and partially blocked. Upon disassembly, the operator discovered that the radiator had been replaced with one from a later 955L model, including a full-length hydraulic cooler that was not connected and occupied valuable space.
The decision was made to rebuild the radiator using the original top and bottom tanks and a new core of correct dimensions. Several bolts broke during disassembly, requiring thread repair and careful reassembly. The hydraulic cooler was removed to restore airflow and cooling efficiency.
Terminology annotation:
- Radiator Core: The central section of the radiator where coolant flows and heat is dissipated. - Hydraulic Cooler: A heat exchanger used to cool hydraulic fluid, often integrated with the radiator in heavy equipment. - Stop Leak: A chemical additive used to seal minor leaks in cooling systems, which can cause long-term clogging and corrosion.
Field mechanics often warn against excessive use of stop leak products, as they can block narrow passages in the radiator and oil cooler, reducing thermal efficiency and increasing the risk of overheating.
Engine Identification and Filter Conversion
The machine’s engine was initially believed to be a D330C, but debate arose over whether it might be a 3304, given the serial number and modifications. The 85J prefix on the machine indicated a late-model 955K, just before the transition to the L series. According to Caterpillar production data, the switch to the 3304 engine occurred at serial number 85J4672, confirming that this unit likely retained the original D330C.
The operator sought to convert the oil filter system from a cartridge-style element to a spin-on filter for easier maintenance. The existing filter base was leaking and outdated. While some conversions are straightforward—such as using a D7G filter base on a D7F engine—the compatibility between early and late 3304 oil coolers required verification before sourcing parts.
Terminology annotation:
- Spin-On Filter: A self-contained oil filter that screws onto a threaded base, simplifying replacement. - Cartridge Filter: A replaceable filter element housed within a permanent base, requiring more labor to service. - Oil Cooler: A component that regulates engine oil temperature by transferring heat to the coolant or ambient air.
Operators converting filter systems should confirm mounting flange dimensions, oil flow direction, and pressure ratings to avoid mismatched components that could restrict flow or cause leaks.
Loader Blade and Undercarriage Modifications
The dozer blade mounted to the 955K was adapted from a larger machine, requiring custom brackets and altered geometry. Observers noted cut-down dozer shoes and unusual blade supports, suggesting extensive field modification. While functional, such changes can affect balance, hydraulic response, and visibility.
The undercarriage appeared to be from a D5, which shares similar dimensions but may differ in sprocket pitch and recoil spring strength. Matching track components across models requires careful measurement of:

• Track pitch (distance between pin centers)
  
• Shoe width and grouser height
  
• Idler and sprocket alignment
  
• Recoil spring preload and tensioner stroke
  

• Document all serial numbers and component origins
  
• Avoid mixing cooling system parts across models without verifying airflow and fit
  
• Use thread chasers and anti-seize on radiator bolts to prevent future breakage
  
• Install a loader arm support bar if the original safety system is compromised
  
• Pressure test the radiator and oil cooler before reassembly
  

History of the HD6 Dozer
The HD6 was produced by Allis-Chalmers from about 1955 through 1974. During that period they built over 25,000 units of various HD6 variants.  It was made as a crawler-tractor / small dozer for agricultural and light industrial work.  Its engine is a 5.6-liter 4-cylinder diesel, delivering roughly 57 horsepower (net) and capable of around 45 drawbar horsepower in tests.  The weight is in the range of 12,400 to 13,400 pounds (≈ 5,600 to 6,100 kg) depending on version.
Because of its robust design, many HD6s are now collectors’ items. Owners often restore old units, sometimes with the goal of having them show-quality. Repainting is a significant part of such restorations.

Repainting the HD6 Dozer
When repainting an HD6, several technical and aesthetic aspects need attention to get a result that both honors the original and holds up over time.
Paint Color and Authentic Appearance

• The classic color for Allis-Chalmers HD6 is the signature “AC orange.” Over decades, paints fade, change in hue, or are reformulated. In some areas, the exact old formula was discontinued for regulatory reasons.
  
• One restorer noted that the newer AC orange from standard supply cans ended up being lighter than the original, especially in sunny climates where UV exposure accelerates fading.
  

• Sand-blasting or media blasting the old paint off to bare metal ensures no residual layers that might peel later.
  
• Rust treatment: any rusted metal must be cleaned and treated (e.g. with rust converter or primer) to avoid under-surface corrosion after repaint.
  
• Weld and body repairs: any dents or damaged metal should be straightened, filled, and ground smooth.
  

• Use of proper primers is important—for adhesion, corrosion protection, and long life. Zinc-rich primers or epoxy primers are often used.
  
• Top coats: either enamel, urethane, or polyurethane finishes. Each type offers different UV and weather resistance. Urethane/polyurethanes are often more expensive but hold up better outdoors.
  
• Protective clear coats may be applied to avoid oxidation or chalking.
  

• Attention to detail: bolts, fasteners, decals, nameplates, the grill, vent screens, the operator’s station—these must frequently be masked or removed to paint properly.
  
• Undercarriage parts: tracks, rollers, idlers often are painted or at least cleaned and rust-proofed.
  

• A repaint to show quality (strip down, restoration, high-quality finish) can take hundreds of man-hours.
  
• Material costs include paint, primer, masking, body filler, equipment rental or purchase, and possibly sand-blasting.
  
• For example, material cost for a full dozer repaint might run several thousand dollars depending on region and paint type; labor even more.
  

• Test small paint samples in sun and shade to see if color shifts under UV before full paint job.
  
• Keep the HD6 stored under cover when not in use or display outdoors avoided midday brightness to preserve color.
  
• Use quality masking to protect non-painted parts. Remove decals and nameplates and replace if worn.
  
• If original AC orange formula is unavailable, select a modern equivalent and note that a slight difference may exist but that weathering tends to bring them closer over time.
  
• Repaint schedule: every 10-15 years for show machines; for working machines, maintain touch-ups and rust repair as needed to avoid large repaint jobs.