10-22-2025, 08:08 PM
Komatsu D31P-16 and the 4D105-3 Engine
The Komatsu D31P-16 is a compact crawler dozer introduced in the mid-1990s, designed for grading, site prep, and forestry work. Powered by the Komatsu 4D105-3 diesel engine, it delivers around 80 horsepower and features a direct injection system, mechanical governor, and wet-sleeve cylinder design. Komatsu, founded in 1921, has produced millions of machines globally, and the D31 series remains a staple in compact dozer fleets across Asia and North America.
The 4D105-3 engine shares design lineage with earlier Komatsu engines and some Cummins clones, particularly in gasket layout and bolt torque procedures. This overlap has led to confusion about whether the head bolts are torque-to-yield (TTY) or reusable.
Terminology Notes
The Komatsu shop manual for the 4D105-3 engine does not explicitly state whether the head bolts are TTY. However, field experience and cross-referencing with similar engines suggest the following:
In Ontario, a field technician rebuilding a 4D105-3 engine found no mention of TTY bolts in the manual. He contacted a Cummins dealer and confirmed that the clone engine used reusable bolts if they passed the stretch test. He reused the original bolts after verifying with a gauge and completed the rebuild without issue.
In North Carolina, a farmer rebuilding his D31P-16 dozer replaced all head bolts as a precaution. He noted that the cost of new bolts was minor compared to the risk of head gasket failure, especially in a machine used for slope grading and forestry.
Recommendations for Rebuilders
While the Komatsu 4D105-3 engine does not explicitly require single-use head bolts, careful inspection is essential. If bolts show no signs of stretch and match specification, they can be reused. However, for peace of mind and long-term reliability, many rebuilders opt to replace them. In engine work, precision and caution always pay off.
The Komatsu D31P-16 is a compact crawler dozer introduced in the mid-1990s, designed for grading, site prep, and forestry work. Powered by the Komatsu 4D105-3 diesel engine, it delivers around 80 horsepower and features a direct injection system, mechanical governor, and wet-sleeve cylinder design. Komatsu, founded in 1921, has produced millions of machines globally, and the D31 series remains a staple in compact dozer fleets across Asia and North America.
The 4D105-3 engine shares design lineage with earlier Komatsu engines and some Cummins clones, particularly in gasket layout and bolt torque procedures. This overlap has led to confusion about whether the head bolts are torque-to-yield (TTY) or reusable.
Terminology Notes
- Torque-to-Yield (TTY): A bolt tightening method where bolts are stretched beyond their elastic limit, making them single-use only.
- Torque-and-Angle: A tightening method involving a specific torque followed by a measured angle turn, often used in TTY applications.
- Go/No-Go Gauge: A tool used to measure bolt stretch and determine reusability.
- Wet-Sleeve Engine: An engine design where cylinder sleeves are in direct contact with coolant, allowing easier rebuilds.
The Komatsu shop manual for the 4D105-3 engine does not explicitly state whether the head bolts are TTY. However, field experience and cross-referencing with similar engines suggest the following:
- Most Komatsu Engines of This Era Use Torque-and-Angle
This method does not automatically mean the bolts are TTY. Many bolts can be reused if they pass inspection.
- Bolt Stretch Must Be Checked
Lay the old bolts side by side and inspect for elongation. If threads appear uneven or the shank is visibly stretched, replacement is recommended.
- Cummins Clone Consideration
The 4D105-3 shares design traits with Cummins B-series engines. Cummins gasket kits often include a go/no-go gauge to test bolt stretch. If the Komatsu bolts match Cummins specs, the same gauge and criteria can be applied.
- Gasket Kits May Include Inspection Tools
Some Komatsu head gasket kits include a bolt stretch gauge. If available, use it to confirm reusability.
In Ontario, a field technician rebuilding a 4D105-3 engine found no mention of TTY bolts in the manual. He contacted a Cummins dealer and confirmed that the clone engine used reusable bolts if they passed the stretch test. He reused the original bolts after verifying with a gauge and completed the rebuild without issue.
In North Carolina, a farmer rebuilding his D31P-16 dozer replaced all head bolts as a precaution. He noted that the cost of new bolts was minor compared to the risk of head gasket failure, especially in a machine used for slope grading and forestry.
Recommendations for Rebuilders
- Inspect Each Bolt for Stretch and Thread Damage: Use a gauge or visual comparison.
- Replace Bolts If Uncertain: The cost is low, and failure is expensive.
- Use Proper Torque-and-Angle Procedure: Follow the sequence and specifications exactly.
- Check for Updated Service Bulletins: Manufacturers may revise torque specs or bolt classifications.
- Consider OEM Gasket Kits: These often include inspection tools and updated instructions.
While the Komatsu 4D105-3 engine does not explicitly require single-use head bolts, careful inspection is essential. If bolts show no signs of stretch and match specification, they can be reused. However, for peace of mind and long-term reliability, many rebuilders opt to replace them. In engine work, precision and caution always pay off.
