Caterpillar 931 Sprocket Swap Guide

[MikePhua]

Why Owners Consider A Sprocket Swap
Undercarriage wear is the single largest lifetime cost on a crawler loader, often consuming 50–70% of total maintenance spend. Swapping sprockets at the right time protects chains and bushings, keeps track pitch in tolerance, and prevents shock loads that can damage final drives. On a Cat 931-series machine, correct sprocket selection and installation can add hundreds of hours before the next undercarriage intervention.
Know Your 931 Lineage First
The 931 family spans multiple generations with important undercarriage differences. The original 931 entered production in the mid-1970s and ran through the mid-1980s. Later 931B and 931C variants brought changes in final drives, chain types, and sometimes sprocket construction. That’s why a “will it fit” answer always starts with the exact model and serial prefix. As a baseline, published data places the first-generation 931 in the 1974–1986 window, and 931C machines later gained Series II and optional LGP setups that influence undercarriage geometry.
Key Terms Explained

• Pitch the center-to-center distance between adjacent chain pins; matching sprocket pitch to chain pitch is non-negotiable.
  
• SALT sealed and lubricated track; reduces internal wear and affects how chains wear in with new sprockets.
  
• Segmented vs one-piece sprocket some models use bolt-on segments around a carrier; others use a one-piece ring on a hub.
  
• Offset the lateral and axial positioning of the tooth ring relative to the hub; wrong offset misaligns chain and accelerates wear.
  
• Backlash small free movement of chain over teeth; too much indicates wear or pitch mismatch.
  

Compatibility Checklist Before You Buy
Create a simple worksheet and compare your machine to the candidate sprocket:

• Model and serial prefix of the loader
  
• Chain pitch (commonly 6.125 in on comparable loaders, but measure yours)
  
• Tooth count of the existing sprocket
  
• Bolt circle diameter, bolt size, and number of bolts on the hub or carrier
  
• Pilot (center bore) diameter and any locating steps
  
• Sprocket ring thickness and dish/offset relative to the mounting face
  
• Track gauge and whether your machine is standard or LGP
  

If any one of pitch, tooth count, bolt circle, pilot diameter, or offset do not match, treat the part as incompatible unless a reputable source documents an interchange. When in doubt, measure your current hardware with calipers and a tape and record values to the nearest 0.5 mm or 1⁄32 in.
When Segments Interchange And When They Don’t
Owners sometimes try to install a later 931C-style segment on an earlier 931 carrier. The usual blockers are different bolt patterns, ring offset, and tooth count. Even if the bolt circle matches, an offset difference as small as 3–5 mm can push the chain out of line, wearing bushings and tooth flanks quickly. Treat “looks close” as a red flag unless you can verify dimensions against the segment drawing or a trusted spec sheet.
Selecting Tooth Count And Pitch

• Tooth count must match the intended chain pitch and undercarriage geometry. Swapping to a different tooth count changes wrap angle and contact point; do this only if the OEM specifies it for your serial prefix.
  
• Pitch worn SALT chains can “stretch” (pin and bushing wear increases effective pitch). New sprockets on a badly stretched chain will hammer on the first dozen hours. If measured pitch growth exceeds your service limit, plan a chain turn or replacement with the sprocket.
  

Measure Wear Before You Swap

• Inspect tooth profile. A healthy profile has a balanced driving face and crest; a hooked profile signals replacement time.
  
• Check bushing wear and ovality. If bushing OD is under the service minimum, either turn the pins and bushings (if applicable) when you install the new sprocket or plan for a new chain.
  
• Verify track tension with the machine lifted; over-tight tracks accelerate sprocket wear.
  

Removal And Installation Overview

• Support and lockout park on level ground, block the machine, and lock out hydraulic controls and battery.
  
• Segment or ring removal break torque with a cross pattern. Mark one bolt position to track reassembly orientation.
  
• Surface prep wire-brush and solvent-clean the hub face and pilot. Chase threads with the correct tap/die.
  
• Install dry-fit first to ensure the pilot and bolt circle seat fully. Use new bolts and hardened washers. Tighten in 3 passes to final torque with a calibrated wrench. For typical Cat final drive flange bolts in this size class, expect high torques and use threadlocker as specified by your service manual; an example from a similar-class Cat final drive shows hub fasteners in the ~810 ± 70 N·m range, underscoring the need for proper tooling. Always follow your exact model’s spec.
  

Run-In Procedure

• After installation, run the loader slowly for 15–30 minutes, forward and reverse, to seat the chain on the teeth.
  
• Re-check bolt torque hot.
  
• Inspect after the first full shift for paint fretting at the joint line, shiny witness marks, or bolt movement.
  

Common Mistakes And Their Fixes

• Pitch mismatch rapid tooth and bushing wear, rhythmic clatter under load. Fix by matching sprocket pitch to measured chain pitch or by renewing the chain.
  
• Offset error chain rides hard on inner or outer tooth flank. Shim or replace with correct offset.
  
• Mixed segments installing one odd segment among five correct ones creates a “high spot” each revolution; replace as a set.
  
• Ignoring idlers and rollers a new sprocket with cupped idlers still pounds the chain; inspect the whole undercarriage.
  

Data Points Owners Can Track

• Hours to next torque check target 10 hours after install, then every 250 hours.
  
• Chain pitch growth retire or turn pins when growth exceeds ~0.5–1.0% of nominal pitch, per your service standard.
  
• Sprocket tooth height loss replace when height is down to the OEM discard limit or the driving face hooks visibly.
  
• Maintenance cost split undercarriage commonly 50–70% of lifetime maintenance on crawlers, so interventions that extend chain life have outsized payback.
  

Parts Strategy And Sourcing

• OEM vs aftermarket quality aftermarket rings and segments exist, but verify hardness spec, bolt torque guidance, and machining tolerances.
  
• Matched sets replacing sprockets without addressing a severely worn chain is false economy; budget for chain work if pitch is out of spec.
  
• LGP considerations wide shoes and longer gauge change loading on the tooth flanks; ensure the part is rated for your configuration.
  

A Shop-Floor Story
A municipal yard received a 931 with a “mystery” sprocket set that looked right but had a 2 mm offset difference. The loader tracked fine on concrete but started shedding metal in soft clay within a week. A straightedge laid across the chain showed the misalignment immediately; shimming to the OEM offset and resetting track tension stopped the wear. The lesson was simple measure, don’t eyeball.
Brief Historical Context
The 931 carved out the compact end of Cat’s crawler loader range in the 1970s, offering versatility on tight jobs where a dozer-loader hybrid excelled loading, backfilling, and light clearing. Later 931C Series II and LGP versions broadened the platform’s appeal with improved hydraulics and low-ground-pressure options for wet soils, while keeping owner-serviceable undercarriage components that make swaps like sprocket changes practical in the field. Published specifications show steady gains in operating weight and performance across the family as features evolved.
Practical Tools And Setup

• 3⁄4-in or 1-in drive torque wrench rated to your final torque
  
• Impact gun for removal only; finish with a torque wrench
  
• Threadlocker and anti-seize per service spec
  
• Calipers, micrometer, and a metric/imperial tape for measurements
  
• Straightedge and feeler gauges to check seating and alignment
  
• Lifting aid or crane segment rings are heavy and awkward
  

Preventive Maintenance Tips

• Keep track tension within spec; over-tension is a sprocket killer.
  
• Power-wash mud and fines from the sprocket and chain after wet jobs.
  
• Record pitch, bushing OD, and tooth height every 500 hours.
  
• Replace in matched pairs across the machine to avoid uneven loading.
  

Bottom Line
A successful 931 sprocket swap is 80% verification and 20% wrenching. Confirm pitch, tooth count, bolt circle, pilot diameter, and offset against your serial-prefix parts book, install with correct torque, and re-check early. Done right, you protect the most expensive wear group on the machine and keep your 931 pushing, loading, and earning with minimal downtime.