MCOH3304 Engine Rebuild Kit for Caterpillar 3304 Diesel Engine – Complete Overhaul Solution
Robust Structural Features and Performance Advantages
The MCOH3304 engine rebuild kit is a complete, premium-quality overhaul solution specifically engineered for the Caterpillar 3304 diesel engine. This 4-cylinder, naturally aspirated or turbocharged (3304T) engine is part of Caterpillar’s legendary 3300 series, known for exceptional durability and ease of maintenance. The MCOH3304 kit contains all critical internal components required to perform a full in-frame or out-of-frame rebuild, restoring the engine to like-new condition at a fraction of the cost of a new engine.
Structurally, the kit includes four high-quality cylinder liners manufactured from centrifugally cast high-chromium gray iron. Each liner features an induction-hardened internal bore with a precision plateau-honed cross-hatch finish that promotes rapid ring seating and maintains optimal oil retention throughout the engine’s service life. The liners are of the “wet” type, meaning they are in direct contact with engine coolant, requiring high-quality O-ring seals (included) to prevent coolant from leaking into the crankcase or combustion chamber.
The MCOH3304 kit supplies four pistons made from forged aluminum alloy with reinforced ring lands and an optimized combustion bowl that matches the 3304’s direct injection fuel spray pattern. For turbocharged 3304T variants, the pistons feature an internal cooling gallery that receives oil from piston cooling jets, dramatically reducing piston crown temperatures and preventing thermal cracking. The piston ring set includes a plasma-sprayed molybdenum top ring for exceptional scuff resistance, a cast-iron tapered second ring for oil control, and a three-piece steel oil control ring assembly with an expander spring. All rings are pre-gapped to Caterpillar’s original specifications.
The bearing complement includes a full set of tri-metal connecting rod bearings and main bearings (steel backing, copper-lead intermediate layer, and tin-babbitt overlay). These bearings are precision-crush ground to OEM clearances and feature an eccentric bore to form a proper oil wedge. Also included are thrust washers for crankshaft end-play control and, depending on the kit version, camshaft bearings. The full gasket set is comprehensive: a premium multi-layer steel (MLS) cylinder head gasket, elastomeric valve cover and oil pan gaskets, intake and exhaust manifold gaskets, timing cover seals, water pump gasket, turbocharger mounting gaskets (for turbo versions), and all necessary O-rings, dowel seals, and copper washers for injector and coolant passages. Many MCOH3304 kits also include piston cooling jets, connecting rod bolts (torque-to-yield or reusable), and valve stem seals.
All components in the MCOH3304 kit are sourced from ISO-9001 certified manufacturers and are dimensionally verified against Caterpillar’s published engineering standards. Rsolid Engine Parts offers both standard and oversize (0.010″, 0.020″, 0.030″) bearing sets and piston options to match crankshafts that have been reground. Each kit is carefully inspected, packaged with anti-corrosion protection, and labeled for easy identification during installation.
Core Working Principle of the MCOH3304 Engine Rebuild Kit
The Caterpillar 3304 is a 4-cylinder, 4-stroke, direct injection diesel engine with a bore of 114.3 mm (4.50 inches) and a stroke of 139.7 mm (5.50 inches), displacing approximately 5.7 liters (348 cubic inches). It is available in naturally aspirated (3304) and turbocharged (3304T) configurations, with power outputs ranging from 80 to 150 horsepower depending on application. The engine uses a mechanical inline injection pump (Robert Bosch or Caterpillar) and is renowned for its high torque rise and fuel efficiency.
Over thousands of operating hours – typically 8,000 to 12,000 hours in construction equipment or 10,000+ hours in generator sets – the engine’s internal components wear. The MCOH3304 kit functions by systematically replacing these critical wear-limited parts. As the engine runs, the pistons reciprocate within the cylinder liners at speeds up to 2,500 RPM. Combustion pressures reach approximately 1,600 psi (110 bar) in naturally aspirated versions and over 2,000 psi (138 bar) in turbocharged versions.
Over time, the cylinder liners lose their cross-hatch finish, become polished, or develop wear steps near the top of the ring travel. Piston rings lose radial tension and may become stuck in carbon-filled grooves, leading to blow-by (combustion gases past the rings) and oil consumption. Bearings develop fatigue cracks, copper-lead exposure, and increased clearance, which lowers oil pressure and can cause knocking. The cylinder head gasket may fail due to thermal cycling and high cylinder pressures, resulting in external coolant leaks or internal cross-contamination between oil and coolant passages.
When an overhaul is performed using the MCOH3304 kit, the technician removes the worn components and installs the new parts. New cylinder liners are pressed into the block, and their protrusion above the block deck is measured (typically 0.002–0.006″ or 0.05–0.15 mm) to ensure proper head gasket sealing. New pistons are assembled with fresh rings (ring gaps staggered 90° apart), then installed into the liners using a ring compressor. New rod bearings are fitted, and connecting rods are torqued to specification. New main bearings are installed (either by lowering the crankshaft or removing it), and crankshaft end play is checked with new thrust washers. The new MLS cylinder head gasket is placed, the cylinder head is reinstalled, and head bolts are torqued in three stages, often with a final angle torque. All new gaskets and seals are replaced. The result is an engine with restored compression, normalized oil consumption, eliminated blow-by, and recovered power output – effectively giving the engine a second life.
Primary Application Equipment
The Caterpillar 3304 diesel engine is widely used in construction, industrial, agricultural, and marine applications. The MCOH3304 rebuild kit is essential for maintaining these machines. Major applications include:
Construction Equipment
Caterpillar backhoe loaders – models such as 416, 426, 428, 436, 446 (many use the 3304 or 3304T)
Caterpillar wheel loaders – 920, 930, 936, 938 (early models)
Caterpillar motor graders – 120G, 130G, 140G (some variants)
Caterpillar excavators – 215, 225, 227, 229 (early models)
Caterpillar bulldozers – D4D, D4E, D5B, D5E
Caterpillar pipelayers and compactors
Industrial Equipment
Generator sets (60–120 kW prime power, 80–150 kW standby)
Industrial pumps (water, sewage, slurry, irrigation)
Air compressors (stationary and portable)
Drilling rigs (water well, blast hole)
Welding machines (diesel-driven welders)
Agricultural Equipment
Large tractors (e.g., Caterpillar Challenger 35, 45, and certain older agricultural crawlers)
Combine harvesters (auxiliary or main power)
Forage harvesters
Irrigation power units
Marine
Material Handling
When ordering the MCOH3304 kit, it is critical to provide the engine serial number and configuration (naturally aspirated vs. turbocharged, with or without piston cooling jets). Common 3304 serial number prefixes include 88M, 92M, 96M, 5LJ, 9N3, and others. Rsolid Engine Parts can assist with cross-referencing to ensure correct component fitment.
Common Failure Symptoms and Overhaul Replacement Guidelines
The following symptoms indicate that a Caterpillar 3304 engine requires a full overhaul using the MCOH3304 rebuild kit:
Excessive Crankcase Blow-by – Remove the oil fill cap or dipstick while the engine idles. If strong puffs of vapor or smoke emerge, combustion gases are leaking past worn piston rings. Severe blow-by can pressurize the crankcase, pushing oil out of the breather, past the rear main seal, and causing oil leaks. Measured crankcase pressure above 5–7 inches of water at rated speed is unacceptable.
High Oil Consumption (over 1 quart per 100 operating hours) – Blue exhaust smoke, frequent topping off, and oily residue in the air cleaner or exhaust indicate worn rings and liners. New rings and liners from the MCOH3304 kit will restore oil control.
Loss of Power and Poor Fuel Economy – The engine struggles to maintain RPM under load, such as when climbing a grade with a wheel loader or during heavy digging with a backhoe. Low compression due to worn rings, liners, or valves reduces torque output. A compression test should show 350–450 psi across all cylinders with no more than 10% variation.
Hard Starting, Especially Cold – Extended cranking times, white smoke during cranking (unburned fuel), or dependence on ether or glow plugs indicates low cranking compression. This is often accompanied by a noticeable increase in starting current draw.
Knocking Noises and Low Oil Pressure – A deep, rhythmic knock that worsens with load points to rod or main bearing wear. Low hot oil pressure (below 15 psi at idle or 30 psi at working RPM) confirms excessive bearing clearance. The new bearing set in the kit will restore proper oil pressure.
Coolant in Oil (Milky Oil) or Oil in Coolant – Emulsified oil (looks like chocolate milk) on the dipstick or an oily film in the coolant expansion tank signals a failed cylinder head gasket, cracked liner, or failed liner O-rings. The MLS head gasket and new liner seals in the kit address this.
Overhaul Replacement Guidelines Using MCOH3304 Kit – Performing a rebuild with this kit requires competent mechanical skills and proper tools. The standard procedure for an in-frame or out-of-frame overhaul: Drain all fluids and remove the engine or prepare for in-frame (remove radiator, oil pan, cylinder head). Remove the cylinder head and inspect for cracks. Remove the oil pan, oil pump, and pick-up tube. Push pistons and rods out through the top of the block. Remove cylinder liners using a liner puller tool. Clean the block deck and cylinder bores thoroughly. Install new liners with proper press fit and liner protrusion (use liner sealant on the lower O-ring groove). Measure crankshaft journals for ovality and taper; polish or regrind as needed. Select bearing sizes (standard or undersize). Install new main bearings (if keeping crankshaft in place, lower it slightly after removing main caps). Install new camshaft bearings if required. Assemble new pistons to connecting rods with new pins and rings (lubricate and stagger ring gaps). Install piston/rod assemblies with new rod bearings, torquing rod bolts to factory specification. Install new main bearings and thrust washers; torque main caps. Install new MLS cylinder head gasket and reinstall cylinder head. Torque head bolts in three stages (e.g., 50→100→150 ft-lbs plus 90° angle – refer to manual). Replace all gaskets, seals, O-rings, and cooling jets. Reinstall oil pump, oil pan with new gasket. Fill with break-in oil (15W-40 CI-4 or CK-4 with high zinc) and fresh coolant. Start the engine and run at 1000–1200 RPM for 5 minutes, checking for oil pressure, coolant leaks, and unusual noises. Allow the engine to warm up, then vary load for the first 50 hours, avoiding prolonged idle or full throttle. Change oil and filter after 50 hours. Rsolid Engine Parts provides a detailed torque specification sheet and installation guide with every MCOH3304 kit.
