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newSchoolWorks.com › VoTechWorks › Building & Construction › Heavy Equipment Operation › Heavy Equipment Maintenance › Lesson 4
BLD-HEAV08-08 · Lesson 4 · 10 clock hours · practice

Undercarriage, Track, and Tire Inspection

Objective. Students measure track sag, sprocket wear, and idler condition on a tracked machine and tire pressure and tread depth on a wheeled machine, then compare all measurements to OEM service limits and correctly classify each component as serviceable, monitor, or replace.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a licensed professional engineer or master tradesperson or by a certification or approval body. It is a study draft and may contain errors. Do not use it as instructions for work on a job site or on live equipment. Always follow your instructor, your supervising professional, and current official references and regulations.

VoTechWorks program approval and accreditation are still in progress. Credentials are issued only by the certifying bodies named in each program, after their own exams.

Why Undercarriage and Tire Inspection Matters

The undercarriage of a tracked machine — crawler dozer, excavator, or track loader — is one of the most expensive systems on the machine. Industry estimates consistently place undercarriage replacement costs among the highest maintenance expenses in a machine's life cycle. On wheeled machines, tire condition directly affects load capacity, stability, and fuel efficiency. Catching wear early and classifying each component correctly as serviceable, monitor, or replace protects the machine, meets OEM warranty requirements, and keeps you and your crew safe.

Track Sag Measurement

Track tension is controlled by the track adjuster (a grease-filled cylinder that pushes the front idler forward or backward). Too tight a track accelerates wear on rollers, idlers, sprockets, and links. Too loose a track risks de-tracking — the track jumping off the sprocket under load — which can injure anyone nearby and disable the machine immediately.

Procedure:

1. Park the machine on firm, level ground and engage the parking brake.

2. Clean mud and debris from the track before measuring — packed material creates a false reading.

3. Place a straightedge across the top of the track, spanning from the front idler to the rear carrier roller (or per the OEM-specified span in the service manual).

4. Use a tape measure to find the greatest distance between the bottom of the straightedge and the top surface of the track shoe at mid-span. This distance is the sag.

5. Compare your measurement to the OEM specification. A typical specification range might be expressed as a band (e.g., a minimum and maximum sag in inches or millimeters); always use the actual service manual for the machine in front of you.

Undercarriage Component Inspection

Track shoes protect the links and provide traction. Inspect each shoe for broken grousers (the raised ridges) and worn pads. A broken grouser reduces traction and can crack adjacent links.

Track links stretch as they wear. Use an undercarriage wear gauge or dial caliper to measure link pitch (the center-to-center distance between pins). Compare to the OEM new and maximum worn dimensions. Elongation beyond the OEM limit means the chain must be replaced or it will slip on the sprocket.

Rollers and idlers carry the machine's weight. Look for flat spots, which create pounding, and check seals for oil weeping. A wet, oily roller end is a leaking seal — schedule replacement before the bearing runs dry.

Sprocket teeth drive the track. Look for hook wear: the leading face of the tooth becomes concave (hooked) rather than convex. Hooked sprockets accelerate link wear dramatically. If the links are serviceable but the sprocket is hooked, replace the sprocket first.

Idler Condition

The front idler guides the track and absorbs impact. Check the flange for cracks or heavy gouging. A damaged flange allows the track to drift sideways and de-track. Also check the idler mounting bracket for cracks and the recoil spring assembly for signs of collapse.

Tire Inspection on Wheeled Machines

Tire pressure is checked with a calibrated gauge against the cold-inflation specification on the machine's door placard or OEM service manual. "Cold" means the machine has not operated for at least a few hours; heat from operation raises pressure and gives a false reading. Under-inflated tires flex excessively, generate heat, and can fail catastrophically. Over-inflated tires reduce the tire's contact patch and increase impact damage risk.

Tread depth is checked at the shallowest point across the tread. Most construction tires include wear indicators (raised bars in the tread grooves); when the tread surface is flush with the indicator, the tire has reached minimum serviceable depth. Use a tread depth gauge or a dial caliper in the groove.

Sidewall inspection looks for cuts, chunking (pieces torn away), bulges, and bead damage. A sidewall bulge indicates internal ply separation — the tire must be removed from service immediately regardless of tread depth or pressure.

Classification: Serviceable, Monitor, or Replace

| Classification | Meaning |

|---|---|

| Serviceable | Measurement within OEM limits; no action needed |

| Monitor | Approaching OEM limit; re-check at next scheduled interval |

| Replace | At or beyond OEM limit; remove from service before next operation |

Every entry on your inspection worksheet must have a measurement, an OEM limit for reference, and one of these three classifications with a written reason.

Safety Points

Key terms9

Track sagThe measured distance between a straightedge laid across the top of a track and the highest point of the track at mid-span; used to determine correct track tension.
Track adjusterA grease-filled or hydraulic cylinder that moves the front idler forward or backward to set and maintain correct track tension.
Link pitchThe center-to-center distance between two consecutive track pins; an increase in this measurement indicates link elongation (stretch wear).
Hook wearA concave, hooked profile that develops on the leading face of sprocket teeth as they wear; accelerates track-link wear and requires sprocket replacement.
Cold-inflation pressureThe correct tire pressure specified by the OEM when the tire has not been operated recently and heat has not raised internal air pressure; the reference value for all tire-pressure checks.
Wear indicatorA raised bar molded into the base of a tire's tread grooves; when the tread surface is flush with this bar, the tire has reached minimum serviceable tread depth.
De-trackingThe condition in which a track jumps off the sprocket and idler, typically caused by excessively loose track tension or a worn front-idler flange.
Undercarriage wear gaugeA specialized tool used to measure track-link pitch, grouser height, and other undercarriage dimensions and compare them to OEM wear limits.
Serviceable/Monitor/Replace classificationA three-tier decision system used on inspection worksheets: serviceable means within limits, monitor means approaching limits, replace means at or beyond limits.

Worked examples4

1. The OEM service manual specifies a track sag of 1.5 in to 2.0 in (38 mm to 51 mm). You place a straightedge across the top of the dozer track and measure 2.6 in (66 mm) of sag at mid-span. Classify this component and state the required action.
  1. Step 1 — Identify the OEM specification: minimum sag = 1.5 in, maximum sag = 2.0 in.
  2. Step 2 — Record the measured value: 2.6 in.
  3. Step 3 — Compare: 2.6 in is greater than the 2.0 in maximum limit.
  4. Step 4 — Classify: The measured sag exceeds the OEM maximum, so the track is too loose.
  5. Step 5 — Required action: Add grease to the track adjuster to tension the track until the sag falls within 1.5–2.0 in, then re-measure to confirm.
Answer: Classify as REPLACE/ADJUST — track tension is out of specification (too loose). Tighten the track adjuster and re-verify sag before returning the machine to service.
2. You measure track-link pitch on a dozer using an undercarriage wear gauge. The OEM new pitch is 7.48 in (190 mm) and the maximum worn pitch is 7.87 in (200 mm). Your gauge reads 7.72 in (196 mm). Classify the links.
  1. Step 1 — Identify OEM limits: new pitch = 7.48 in; maximum worn pitch = 7.87 in.
  2. Step 2 — Record measured pitch: 7.72 in.
  3. Step 3 — Calculate wear: 7.72 − 7.48 = 0.24 in of elongation.
  4. Step 4 — Calculate remaining allowable wear: 7.87 − 7.72 = 0.15 in remaining before reaching the limit.
  5. Step 5 — Classify: The links are still within the maximum limit but have used 0.24 in of the total 0.39 in allowable wear (about 62% worn). They are approaching the limit.
Answer: Classify as MONITOR — within OEM limit but significantly worn. Re-inspect at the next scheduled interval and track the rate of wear.
3. A wheel loader's door placard lists a cold-inflation pressure of 65 psi for all four tires. After a morning shift, you measure the right-front tire at 72 psi. Should you deflate the tire to 65 psi?
  1. Step 1 — Note that the machine has been operating; the tire is hot from use.
  2. Step 2 — Recall that OEM cold-inflation spec applies to a cold tire; heat from operation raises pressure above the cold value — this is normal and expected.
  3. Step 3 — Deflating a hot tire to the cold spec would leave it under-inflated once it cools, creating a hazard.
  4. Step 4 — Correct action: Allow the tire to cool for several hours, then re-check pressure against the 65 psi cold spec.
Answer: Do NOT deflate. The elevated reading is normal heat-related pressure rise. Re-check when the tire is cold and compare to the 65 psi specification at that time.
4. You are checking the ±5% tolerance for worksheet accuracy. The instructor's reference measurement for track sag is 1.80 in. What is the acceptable range for a student's recorded measurement to be within ±5%?
  1. Step 1 — Calculate 5% of the reference value: 1.80 in × 0.05 = 0.09 in.
  2. Step 2 — Subtract to find the lower bound: 1.80 − 0.09 = 1.71 in.
  3. Step 3 — Add to find the upper bound: 1.80 + 0.09 = 1.89 in.
  4. Step 4 — Any student measurement between 1.71 in and 1.89 in is within the ±5% tolerance.
Answer: Acceptable student measurement range: 1.71 in to 1.89 in.

The math in this lesson2

Learners compute a ±5% acceptable range around a 1.80-inch reference track sag.
7.RP.3N-Q.3
Brush up in the math halls at newSchoolWorks.com:
In class: Instructor demonstrates track-sag measurement on a dozer by jacking the track at mid-point and using a straightedge and tape to find the sag distance; explains how over-tight tracks cause accelerated component wear and loose tracks risk de-tracking; students record the OEM sag specification from the service manual and compare to the measured value. · Working in pairs, students inspect all undercarriage components on the dozer — track shoes for broken grousers and worn pads, track links for elongation using a wear gauge, rollers and idlers for flat spots and leaks, sprocket teeth for hook wear — entering each finding and measurement on an undercarriage inspection worksheet with pass/fail/monitor columns. · Students move to a wheel loader, check all four tire pressures with a calibrated gauge and compare to the OEM cold-inflation spec on the door placard, inspect sidewalls and tread for cuts, chunking, and wear-indicator depth, then complete a tire-service record and recommend an action (inflate, monitor, or replace) for each tire with a written justification.
Materials: Tracked dozer and wheel loader (in yard or lab bay); OEM service manuals for both machines; straightedge and tape measure; undercarriage wear gauge set; dial caliper; tire-pressure gauge (calibrated); floor jack and jack stands; undercarriage inspection worksheet; tire service record form; chalk for marking; PPE; NCCER HEO Level 2 undercarriage module
Check: All measurements on both worksheets are within ±5% of the instructor-measured reference values, and every serviceable/monitor/replace classification matches the OEM limit table; a completed, legible worksheet with all measurement fields filled in is required; students scoring below 80% on classification decisions retest after reviewing the OEM limit table with the instructor.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

NCCER Heavy Equipment — Undercarriage Maintenance
1. When measuring track sag, why must you clean all mud and packed debris from the track before taking the measurement?
NCCER Heavy Equipment — Undercarriage Maintenance
2. A track that is adjusted too tight will most directly cause which of the following?
NCCER Heavy Equipment — Undercarriage Maintenance
3. Hook wear on a sprocket tooth is best described as:
OSHA 10 — Hazard Recognition and Control
4. Before reaching under or alongside a tracked machine to measure track sag, the FIRST safety action is to:
NCCER Heavy Equipment — Wheeled Machine Maintenance
5. The OEM cold-inflation pressure for a wheel loader tire is 65 psi. You check a tire that has been sitting overnight and read 58 psi. What is the correct classification and action?
NCCER Heavy Equipment — Wheeled Machine Maintenance
6. During a tire inspection you find that the tread surface is flush with the wear-indicator bars in multiple tread grooves. You should classify this tire as:
NCCER Heavy Equipment — Undercarriage Maintenance
7. You measure track-link pitch at 7.91 in. The OEM new pitch is 7.48 in and the maximum worn limit is 7.87 in. Which classification is correct?
NCCER Heavy Equipment — Undercarriage Maintenance
8. A roller on a crawler dozer shows oil weeping from the end seal during your inspection. The correct immediate action is to:
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