Cummins NTA-855-L4 Big Cam Diesel Engine Workshop & Rebuild Manual
Instant Answer & Quick Specs Box
Engineering Overview & Technical Coverage
The Cummins NTA-855-L4 is an iconic, turbocharged and aftercooled 14.0-liter inline-six heavy-duty industrial and commercial diesel engine. Renowned across heavy civil machinery, mining shovels, generator drive sets, and commercial fleets, the NTA-855 platform features heavy-duty cast block construction with replaceable wet liners, mechanical Unit Fuel Injection (PT System), and robust overhead valvetrain architecture. This official shop and rebuild manual provides comprehensive disassembly, component inspection, tolerance wear limits, and overhaul procedures.
Critical Engineering Specifications & Tightening Sequence
| Component / Fastener | Imperial Specification | Metric Specification | Tightening Procedure / Notes |
|---|---|---|---|
| Cylinder Head Step 1 | 20 – 25 ft-lbs | 27 – 34 N·m | Snug sequence starting from inner center bolts outward |
| Cylinder Head Step 2 | 80 – 100 ft-lbs | 108 – 136 N·m | Intermediate torque pass across all head capscrews |
| Cylinder Head Final Step | 265 – 305 ft-lbs | 359 – 414 N·m | Final cross-pattern pass. Lube threads with clean engine oil |
| Intake Valve Lash (Cold) | 0.011 in (Alum) / 0.013 in (Cast) | 0.28 mm / 0.33 mm | Adjust with feeler gauge at closed valve positioning |
| Exhaust Valve Lash (Cold) | 0.023 in (Alum) / 0.025 in (Cast) | 0.58 mm / 0.64 mm | Adjust locknut to 40–45 ft-lbs (54–61 Nm) torque |
| Rocker Housing Capscrews | 55 – 65 ft-lbs | 75 – 89 N·m | Even tightening sequence across rocker box base |
| Main Bearing Journal Clearance | 0.0015 – 0.0050 in (Max 0.007″) | 0.038 – 0.130 mm (Max 0.18 mm) | Precision plastigauge / micrometric clearance inspection |
| Connecting Rod Journal Clearance | 0.0015 – 0.0045 in (Max 0.007″) | 0.038 – 0.114 mm (Max 0.18 mm) | Maximum allowable wear limit before rod reconditioning |
Complete Service Chapter Directory
- Group 0 – Engine Disassembly: Safe shop rigging, lifting bracket anchors, fluid draining, intake/exhaust manifold detachment, and sub-assembly breakdown.
- Group 1 – Cylinder Block & Liners: Block counterbore depth measurement, packing ring seating, lower bore out-of-round checks, and camshaft bushing bore inspection.
- Group 2 – Cylinder Head: Valve seat angle grinding, spring load testing, crosshead guides, injector sleeve reaming, and vacuum leak testing.
- Group 3 – Rocker Lever Assembly: Cam follower roller lash, shaft oil gallery cleaning, rocker arm bushing clearances, and push tube straightness checks.
- Group 4 – Cam Followers & Push Tubes: Tappet inspect procedures, injector actuation lever alignment, and follower guide alignment.
- Group 7 – Lubricating System: High-volume oil pump clearances, pressure regulator spring tension, oil cooler core testing, and sump capacity specs.
- Group 14 – Engine Assembly & Rebuild: Step-by-step main bearing seating, piston ring stagger, cylinder head torque sequence, PT injector timing, and dyno run-in schedules.
- Group 18 – Wear Limits & Master Torque Tables: Complete fast-reference wear limits, clearance blueprints, fastener torque tables, and oil grade selection guidelines.
Heavy Equipment Mechanics: Free Interactive Calculation Suite
Calculate fastener stretch, torque unit conversions (Nm to ft-lbs), engine displacement, and compression ratio online in seconds:
Open Diesel Mechanic Calculators →Frequently Asked Questions
What is the final cylinder head bolt torque on a Cummins NTA-855 engine?
The cylinder head capscrews on Cummins NTA-855 engines must be torqued in 3 steps: Step 1 to 20–25 ft-lbs (27–34 Nm), Step 2 to 80–100 ft-lbs (108–136 Nm), and the final step to 265–305 ft-lbs (359–414 Nm) following the factory spiraling cross-pattern starting from the center outward.
What are the valve clearance settings for cold adjustment?
For engines with aluminum rocker housings, intake valve cold clearance is 0.011 in (0.28 mm) and exhaust is 0.023 in (0.58 mm). For engines with cast iron housings, set intake clearance to 0.013 in (0.33 mm) and exhaust to 0.025 in (0.64 mm).
