Diesel engine assembly is a work with high technical requirements and rigorous procedures. Any negligence in details may lead to degraded engine performance, premature wear, or even serious failures. The following are the key points that must be noted during diesel engine assembly, categorized by core processes:
I. Assembly Environment and Preparations
Assembly must be carried out in a dust-free, dry special workshop to prevent dust and impurities from entering oil passages, cylinders, or bearings, which would otherwise accelerate component wear.
All components (such as cylinder block, crankshaft, piston, oil passages, etc.) must be thoroughly cleaned with a special cleaning agent and blown dry with compressed air to ensure no oil contamination, carbon deposits, or metal debris.
Cylinder head gaskets, O-rings, self-locking nuts, spring washers, etc., shall all be replaced with new ones; reuse of old parts is prohibited. O-rings in the fuel system must be replaced, and silicone-containing sealants are forbidden to avoid chemical corrosion.
II. Assembly Specifications for Key Components
1. Piston and Connecting Rod Assembly
When installing piston rings, the openings of each ring should be staggered at 120° to avoid air leakage or oil blow-by caused by aligned openings.
Pistons and connecting rods have clear assembly direction marks, which must be aligned accordingly to prevent movement interference due to reversed installation.
Connecting rod bolts should be tightened in stages to the specified torque, and the angle method shall be adopted to ensure the pre-tightening force meets the standard.
2. Crankshaft and Main Bearing Installation
Inspect the crankshaft journals for scratches or scorching before installation; main bearing shells are not interchangeable.
Main bearing cap bolts should be tightened step by step in sequence, and finally fastened using the “torque + angle” method (e.g., first tighten to 100 Nm, then rotate 180°±6°).
After assembly, check the crankshaft axial clearance (should be between 0.08–0.278 mm) and rotating torque (should be < 10 Nm) to ensure no jamming.
3. Cylinder Head Installation
Cylinder head bolts must be tightened symmetrically from the middle to both sides in 2–3 steps to prevent seal failure caused by cylinder head deformation.
Aluminum alloy cylinder heads shall be fastened in a cold state, while cast iron cylinder heads can be retightened after a warm-up to improve sealing.
III. Bolt Tightening and Torque Control
All critical bolts must be tightened with a torque wrench. Tightening by experience or forcibly with ordinary wrenches is strictly prohibited.
IV. Lubrication and Sealing Management
1. Pre-lubrication Treatment
All relative motion surfaces (such as bearing shells, camshafts, piston pins, etc.) should be coated with clean engine oil before assembly to reduce initial dry friction during startup.
2. Sealing Assurance
Gaskets on all joint surfaces shall be intact and coated with grease to enhance sealing.
After assembly, inspect for “three leaks” (oil leakage, water leakage, air leakage).
The cooling system, fuel system, and lubrication system shall all undergo pressure testing to verify sealing performance.
V. Assembly Sequence and Tool Usage
Strictly follow the assembly sequence provided by the manufacturer; do not change steps arbitrarily.
Use special tools as much as possible (such as piston ring compressors, oil seal installers, guide tightening devices) to avoid knocking and damaging part surfaces.
Do not strike parts directly with a steel hammer; use a copper rod or rubber hammer if necessary.
VI. Post-assembly Inspection and Testing
1. Manual Cranking Inspection
After assembly, rotate the crankshaft by hand to check for jamming, abnormal noise, or uneven resistance.
2. Pre-start Inspection Items
Confirm that the levels of lubricating oil and coolant are normal.
Check that all wire harnesses are securely connected with no looseness.
Ensure all pipelines (fuel, air, cooling) are correctly connected and leak-free.
3. Cold Running-in and Hot Test Run
The recommended cold running-in time is 1–2 hours at a speed of 1000–1500 r/min to facilitate the running-in of friction pair surfaces.
During the hot test, load gradually and monitor parameters such as oil pressure (no less than 0.1 MPa at idle speed), water temperature, and exhaust color.