37420-11201 OEM Crankshaft – For Mitsubishi S12R Diesel Engine
For operators of Mitsubishi S12R engines – whether in marine propulsion, prime power generation, offshore support vessels, or heavy-duty industrial applications – the crankshaft is the backbone of the entire engine. It converts the reciprocating motion of the pistons into rotational torque, transmitting power to the propeller, generator, or driven equipment. The 37420-11201 OEM crankshaft is a factory-specification replacement engineered specifically for the S12R platform, delivering exceptional strength, precise balance, and long-term reliability under the most demanding continuous-load conditions.
As a critical rotating assembly component, this crankshaft is manufactured to Mitsubishi Heavy Industries' exacting standards, ensuring a direct drop-in fit with no modifications required. In this comprehensive guide, we examine its advanced engineering, compatible engine models, common failure signs, professional installation best practices, and why Rsolid Engine Parts is the trusted global supplier for Mitsubishi engine components.
1. Structural Features & Advantages of the 37420-11201 Crankshaft
The 37420-11201 is a precision-engineered crankshaft designed specifically for the high-torque, high-reliability demands of the S12R engine family. Its design incorporates several heavy-duty features:
High-strength forged steel construction – Manufactured from premium micro-alloyed forged steel, this crankshaft offers exceptional tensile strength, fatigue resistance, and toughness. The forging process aligns the grain structure, providing superior resistance to bending and torsional stresses compared to cast alternatives. This is critical for the high cylinder pressures and torque outputs of the 12-cylinder S12R.
Induction-hardened journal surfaces – All main bearing journals and crankpins undergo an induction-hardening process to achieve a surface hardness of HRC 55-62, providing a durable wear layer that resists scoring, galling, and fatigue. The hardened surface extends bearing life and maintains precise clearances over thousands of operating hours.
Precision-ground and micro-polished journals – All bearing surfaces are ground to sub-micron tolerances and micro-polished to a mirror finish (Ra ≤ 0.2 µm). This reduces friction, minimises bearing wear, and ensures consistent oil film formation for optimal lubrication.
Optimised counterweight design – The crankshaft features precisely calculated counterweights to balance the reciprocating and rotating masses of the 12-cylinder V-configuration engine. This minimises torsional vibration, reduces main bearing loads, and ensures smooth operation across the entire RPM range.
Integral gear drive – The crankshaft includes precision-machined gear teeth for driving the timing gear train, ensuring accurate camshaft and injection pump timing. The gear is integrated into the forging for maximum strength and reliability.
Large-diameter main journals – Designed with oversized main bearing journals to accommodate the high radial loads of the 12-cylinder S12R, providing a large bearing surface area that reduces specific loading and extends bearing life.
Drilled oil galleries – Precision-drilled internal oil passages supply pressurised oil to the connecting rod bearings and crankpins, ensuring adequate lubrication even under extreme loads and high temperatures.
Direct fitment – The 37420-11201 is dimensionally identical to the original Mitsubishi crankshaft, requiring no machining or modifications for installation. It includes all necessary mounting features, including the flywheel flange and damper mounting surfaces.
Operational benefits for vessel owners and plant engineers:
Restored engine balance – A new OEM crankshaft ensures proper dynamic balance, reducing vibration and extending main bearing life.
Improved reliability – Forged steel construction and hardened journals deliver exceptional durability, even under continuous full-load operation.
Reduced maintenance costs – Precision-ground journals and optimised lubrication reduce bearing wear, extending overhaul intervals.
Smoother operation – Optimised counterweights and dynamic balancing reduce engine vibration, improving crew comfort and reducing stress on ancillary components.
100% direct fit – Identical to the original Mitsubishi crankshaft – no modifications required.
2. Compatible Engine Models & Typical Applications
The 37420-11201 crankshaft is specifically engineered for the Mitsubishi S12R series – a 12-cylinder, V-configuration, 4-stroke, water-cooled diesel engine widely used in marine and industrial applications.
| Engine Model | Typical Applications |
|---|
| Mitsubishi S12R-PTA | Marine propulsion (tugboats, fishing vessels, coastal freighters), prime power generation |
| Mitsubishi S12R-MPTA | Marine propulsion for larger vessels, offshore support vessels |
| Mitsubishi S12R (Genset variants) | Prime and standby power generation for industrial plants, data centres, offshore platforms |
| Mitsubishi S12R (Industrial) | Compressor drives, pumping stations, drilling rigs |
Engine Specifications (S12R series):
Cylinder configuration: V12
Displacement: Approximately 51 litres (verify with engine manual)
Bore x stroke: OEM standard – verify with engine manual
Method of operation: 4-cycle, water-cooled, direct injection, turbocharged (varies by variant)
Critical cross-reference: The 37420-11201 is the genuine Mitsubishi service part number for the S12R crankshaft. Always verify your engine serial number (e.g., S12R-****) and the existing crankshaft part number before ordering. This crankshaft is supplied as a complete assembly; new main bearings, thrust washers, and seals should be installed simultaneously.
3. Common Failure Modes & Installation/Replacement Recommendations
Typical Warning Signs That Your Crankshaft Needs Attention
Excessive engine vibration – Unusual vibration at certain RPM ranges may indicate a bent or out-of-balance crankshaft, often caused by a connecting rod failure or over-speed event.
Knocking or metallic noise – A deep, rhythmic knocking noise, especially under load, can indicate worn main or connecting rod bearings, often resulting from a damaged journal.
Low oil pressure – Worn journal surfaces increase bearing clearances, reducing oil pressure – especially noticeable at idle.
Metal particles in the oil – Finding bearing material or steel particles in the oil filter or sump indicates active crankshaft or bearing wear.
Visible scoring or discolouration – Inspecting the crankshaft during overhaul may reveal scoring, galling, or heat discolouration on journals.
Cracks or fractures – Visible cracks, especially in the fillet radius or around keyways, indicate fatigue failure – immediate replacement is required.
Professional Installation Best Practices
Installing a new 37420-11201 crankshaft is a complex procedure requiring precision and meticulous attention to detail. Follow these essential steps:
Clean and inspect the cylinder block – Thoroughly clean the crankcase and main bearing bores. Inspect the block for cracks, especially around the main bearing webs. Measure the main bearing bore alignment and roundness using a dial bore gauge.
Check main bearing clearances – Install new main bearing shells (upper and lower). Measure the bearing clearance using plastigauge or a dial bore gauge. The clearance should be within the engine manual's specified range (typically 0.05 – 0.10 mm – confirm with manual). Select the correct bearing grade if adjustments are needed.
Lubricate bearing surfaces – Coat the main bearing shells and crankshaft journals with clean engine oil or specialised assembly lubricant.
Install the crankshaft – Carefully lower the crankshaft into the main bearing bores, ensuring it seats squarely. Do not force it – if it does not seat easily, check for debris or misalignment.
Install main bearing caps – Install the main bearing caps with new bolts, tightening them in the specified sequence and torque. For the S12R, typical torque is 250–350 N·m plus a 90° angle-tighten (consult your engine manual for exact values). Use a calibrated torque wrench and angle gauge.
Check crankshaft end float – After torquing, measure the crankshaft end float (thrust bearing clearance) using a dial gauge. It should be within the specified range (typically 0.10 – 0.30 mm). Adjust by selecting the correct thrust washer thickness if required.
Check crankshaft rotation – After installation, the crankshaft should rotate smoothly by hand with minimal resistance. Tight spots indicate misalignment or incorrect clearances.
Install connecting rods and pistons – Attach the connecting rods to the crankshaft, ensuring the correct orientation and bearing clearances. Torque the connecting rod bolts to the manufacturer's specification.
Install the timing gear train – Install the timing gears, ensuring all timing marks are correctly aligned. Verify camshaft timing and injection pump timing as per the engine manual.
Install the flywheel and damper – Install the flywheel and torsional vibration damper, tightening the retaining bolts to the specified torque.
Prime the lubrication system – Before starting, prime the engine oil system using an external pump to ensure oil reaches all bearing surfaces.
Break-in procedure – After complete reassembly, start the engine and run at low idle (no load) for 15-20 minutes. Gradually apply load over the next 8-10 hours. Change the engine oil and filter after the initial break-in period.
4. Why Rsolid Engine Parts Is Your Preferred Global Supplier
Rsolid Engine Parts has been a premier supplier of Mitsubishi, Yanmar, and Caterpillar diesel components for over 15 years, serving marine fleets, power plants, and workshops across six continents. Here is why the 37420-11201 crankshaft from Rsolid is the intelligent choice:
OEM-equivalent quality – Manufactured to ISO 9001:2015 and IATF 16949 standards, using identical forged steel, heat-treatment, and grinding processes as genuine Mitsubishi crankshafts.
100% dimensional inspection – Every crankshaft is inspected for journal diameter, roundness, straightness, and surface finish using advanced CMM equipment.
Complete installation kits – We offer the crankshaft together with new main bearings, thrust washers, and seals in a convenient kit – simplifying your overhaul.
Global inventory and rapid dispatch – Strategically warehoused in Asia, Europe, and North America, ensuring 3-7 working day delivery to most international ports and airports.
Competitive wholesale pricing – Attractive volume discounts for workshops, fleet operators, and parts distributors.
Free expert technical support – Our in-house diesel engineers provide installation guides, torque specifications, and troubleshooting via WhatsApp or email.
Solid warranty – 12 months / 2,000 operating hours against manufacturing defects and premature wear.
Contact Rsolid Engine Parts Today
📧 Email: amy@rinjector.com
📱 WhatsApp: +86 15975376778
Whether you need a single 37420-11201 crankshaft for a major overhaul or a complete rotating assembly for your Mitsubishi S12R, Amy and her team will provide a detailed quotation, stock confirmation, and shipping schedule within 2 hours. We also supply complementary parts – main bearings, connecting rods, pistons, cylinder liners, and gasket sets – for comprehensive engine rebuilds.
Choose the 37420-11201 OEM crankshaft from Rsolid – engineered for uncompromised durability, smooth operation, and reliable power for your Mitsubishi S12R engine.
