Caterpillar G3304
Maintenance schedule, common problems & OEM parts breakdown
The Cat G3304 is a naturally aspirated, spark-ignited industrial gas engine built on Caterpillar's 3304 diesel block architecture. It is an inline gas engine displacing 7.0 L (425 cu in), with a bore and stroke of 121 mm x 152 mm (4.75 in x 6.00 in), rated 71 bkW (95 bhp) at 1800 rpm for continuous industrial duty. It runs a hydra-mechanical governor paired with an Altronic V capacitor-discharge ignition system, not an electronic engine control module. Net dry weight is about 757 kg (1670 lb). Caterpillar's 3304 diesel block traces to the 1970s, and the G3304 carried that architecture forward as a dedicated natural-gas variant for generator sets, small gas-compression packages, and general industrial standby or prime power, typically offered only in naturally aspirated form rather than as a turbocharged option. Packaged genset output, commonly cited in the 50 to 60 kW class, differs from the engine's own mechanical bhp rating because of generator efficiency and site conditions, so treat the bare-engine rating and a packaged unit's nameplate output as two different numbers.
Caterpillar's follow-on for this displacement class is the G3304B, which keeps the same basic naturally aspirated layout but moves to the ADEM A4 electronic control platform. That adds air/fuel ratio control, electronic ignition and governing, and integrated start/stop and engine-protection logic in place of the G3304's hydra-mechanical governor and standalone Altronic ignition box. That is the clearest generational line on this platform: mechanical-governor G3304 versus electronically-governed G3304B. In the used and parts market, the G3304 still matters because of the large installed base of gensets and compressor packages running on the older mechanical-governor architecture. Keeping one running depends on sourcing ignition, governor, and mechanical fuel-train components sized for that control system rather than the electronic parts built for the G3304B, and on a rebuilder's familiarity with the shared 3304 diesel bottom end when block or head work comes due.
Below: full specifications, fluids & capacities, the factory service schedule, common service parts, verified fault codes, what owners discuss, attachment guidance, the complete assembly directory, and a serial-number reference. Complete parts lists with full OEM part numbers, exploded diagrams, quantities, and fitment data are available free in Heavy Parts AI.
Caterpillar G3304 specifications
Engine
| Model/generation | G3304 gas petroleum engine, hydra-mechanical governor generation (mechanically governed, Altronic V ignition standard). Distinct from the later G3304B generation, which uses ADEM A4 electronic engine management — not covered by this rating. |
| Configuration | In-line 4-cylinder, 4-stroke cycle, naturally aspirated |
| Rated power | 71 bkW (95 bhp) at 1800 rpm, 100% load, 2.0% O2 rating |
| Power at 75% load | 53 bkW (71 bhp) at 1800 rpm |
| Displacement | 7.0 L (425 cu in) |
| Bore | 121 mm (4.8 in) |
| Stroke | 152 mm (6.0 in) |
| Combustion type | Rich burn |
| Governor and protection | Hydra-mechanical governor standard; vernier/positive-locking control and mechanical shutoffs offered as options |
| Ignition system | Altronic V standard; Altronic III and CSA-shielded ignition offered as options |
| Emissions | Rated not-to-exceed levels: NOx 28.3 g/bkW-hr (21.08 g/bhp-hr), CO 2.15 g/bkW-hr (1.6 g/bhp-hr), CO2 667 g/bkW-hr (498 g/bhp-hr), VOC 0.32 g/bkW-hr (0.24 g/bhp-hr) at 100% load and speed. This is a spark-ignited stationary gas engine rated under SAE J1995/ISO3046-1 conditions, not an off-road diesel emissions tier. |
| Rotation | Counterclockwise, viewed from flywheel end |
| Flywheel and housing | SAE No. 1 flywheel and housing, SAE standard rotation |
Weights
| Engine weight, net dry (approx.) | 757.5 kg (1670 lb) |
| Shipping weight | 757.5 kg (1670 lb) |
Dimensions
| Package length | 1158.2 mm (45.60 in) |
| Package width | 743.8 mm (29.28 in) |
| Package height | 1171.3 mm (46.11 in) |
Performance
| Rated engine speed | 1800 rpm |
| Max altitude at rated torque, 38°C (100°F) | Sea level, 0 m (0 ft) — naturally aspirated, no altitude margin at the full rated point |
| Speed turndown at max altitude and rated torque, 38°C (100°F) | 48.3% |
| Fuel consumption at 100% load | 10.71 MJ/bkW-hr (7567 Btu/bhp-hr) |
| Fuel consumption at 75% load | 11.10 MJ/bkW-hr (7842 Btu/bhp-hr) |
| Exhaust gas flow at 100% load | 13 m3/min (459 cfm) |
| Exhaust stack temperature at 100% load | 548°C (1018°F) |
| Combustion air inlet flow at 100% load | 4.25 m3/min (150 scfm) |
| Fuel gas supply pressure | 10.34-34.47 kPag (1.5-5 psig) |
Service capacities (summary)
| Cooling system (jacket water) capacity | 16.0 L (4.2 gal) |
| Lube oil system refill capacity | 31.2 L (8.3 gal) |
| Oil change interval | 750 hours (service interval, not a capacity) |
| Fuel tank | Not applicable — runs on external natural/field gas supply, no integral fuel tank documented |
| Hydraulic system | Not applicable — bare engine, no onboard hydraulic system |
Values vary by configuration, region, and serial range — confirm against your machine before planning transport or lifts.
G3304 fluids & capacities
| System | Capacity | Recommended fluid |
|---|---|---|
| Engine crankcase (oil pan, with filter) | 31.2 L (8.3 gal) refill capacity. Naturally aspirated inline-4 gas engine, full-sump pan with engine-mounted oil cooler; factory nominal oil-change interval around 750 hours, adjusted by oil-sample program results | Cat NGEO (Natural Gas Engine Oil), a low-ash oil built for rich-burn gas engines. SAE 40 for normal ambient operation; SAE 30 is used in colder-climate installations. Avoid standard high-ash diesel engine oil — ash residue fouls spark plugs and raises detonation risk on a rich-burn gas engine |
| Cooling system (jacket water) | 16.0 L (4.2 gal), engine block and head jacket-water volume only. Total circuit volume varies by the cooling package fitted to the package (radiator, remote heat exchanger with expansion tank, or blower/suction fan arrangement are all factory options) — add that circuit's own volume on top of the engine figure | Cat ELC (Extended Life Coolant) or Cat DEAC heavy-duty antifreeze/coolant, mixed with water per Cat's standard glycol ratio for the expected ambient range. Same coolant family used across Cat diesel and gas engines |
Capacities are refill values from factory literature — always fill to the dipstick/sight gauge, not the number.
Caterpillar G3304 maintenance schedule
| Service interval | Tasks |
|---|---|
| Every 50 h |
|
| Every 250 h |
|
| Every 500 h |
|
| Every 1,000 h |
|
| Every 2,000 h |
|
| Every 4,000 h |
|
| Every 8,000 h |
|
Servicing the G3304 beyond the schedule
Predictive Maintenance & Fluid Analysis
Track engine health with routine S-O-S oil sampling pulled at every oil change rather than relying on hours alone. Natural gas combustion loads oil differently than diesel, and trend data catches bearing wear or coolant intrusion before failure. Pair oil analysis with periodic coolant sampling for inhibitor depletion and a running log of ignition timing and spark plug condition, since a drifting Altronic V timing setting is often the first sign of fuel gas quality changes.
Corrective & Common Repairs
Most unscheduled G3304 downtime traces to the ignition and fuel-mixing side, not the diesel-derived bottom end: fouled or worn spark plugs, cracked ignition leads, or a sticking gas regulator or mixer causing rough idle or misfire. Governor and carburetor linkage wear shows up as speed hunting or slow load response. Because the block and valve train follow the 3304 diesel design, mechanical repairs such as valve, ring, or bearing work draw on that platform's long-established procedures rather than gas-engine-specific tooling.
Overhaul & Rebuild Points
Overhaul planning centers on the cylinder head and valve train first: check valve seat recession, guide wear, and seal condition at scheduled head-off inspections before committing to a full teardown. Because the G3304 carries the 3304 diesel's cylinder liner and crankshaft architecture, bottom-end rebuild tolerances and bearing clearances follow that established diesel platform rather than a dedicated gas-engine spec. Budget separately for ignition, governor, and gas-train components, which wear on their own schedule.
Seasonal & Environment Servicing
Cold-weather starts depend on the hydra-mechanical governor and Altronic ignition holding correct timing at low ambient temperature. Verify block heater and battery condition before winter standby duty. At altitude or with lean, low-Btu field gas, re-check air/fuel ratio and detonation margin, since this naturally aspirated engine has no turbo boost to compensate for reduced air density. Keep the radiator or heat exchanger core clean of debris in dusty or high-heat compressor-station environments to protect against a marginal cooling package.
G3304 fault codes & troubleshooting
| Code | Meaning | Likely cause | What to do |
|---|---|---|---|
| Low Oil Pressure Shutdown | Engine oil pressure switch has opened below its set threshold, energizing the fuel/ignition shutoff and stopping the engine to protect the bearings. | Low oil level, worn oil pump, plugged oil filter, or a miscalibrated/failed pressure switch. | Check oil level and filter condition first, then confirm actual pressure with a mechanical gauge before condemning the switch. |
| High Jacket Water Temperature Shutdown | Coolant temperature switch has tripped above its set limit, shutting the engine down to prevent overheating damage. | Low coolant, blocked radiator or heat exchanger, stuck thermostat, worn water pump, or fouled heat exchanger tubes on raw-water cooled packages. | Check coolant level and condition, inspect the radiator/heat exchanger for blockage, and confirm thermostat operation before resetting and restarting. |
| Overspeed Shutdown | The governor-linked overspeed trip has sensed engine speed above the set limit and closed the fuel/ignition shutoff. | Governor linkage binding or out of adjustment, sudden loss of load on a driven load or genset application, or a gas valve sticking open. | Inspect governor linkage for free travel, review load conditions at the time of the trip, and verify the governor speed setting before restarting. |
| Low Gas Pressure Shutdown | Fuel gas pressure switch has sensed supply pressure below the regulator's normal operating range and closed the gas shutoff valve. | A drop in upstream supply pressure, a plugged fuel strainer/filter, a fouled or icing pressure regulator, or a leaking regulator diaphragm. | Check supply pressure at the regulator inlet, inspect the strainer and regulator, and confirm the shutoff valve reopens once pressure is restored. |
| Ignition Module Status Fault (Altronic V indicator) | The Altronic V ignition unit's onboard status indicator shows a loss of input power, loss of magnetic pickup signal, or an output fault to one or more cylinders. | A loose or corroded power/ground connection at the module, a failed magnetic pickup coil, a worn ignition coil or secondary lead, or a damaged ignition module. | Check battery supply and ground at the module first, verify magnetic pickup air gap and signal, then check coil output at the module's own test points before replacing it. |
| Failure to Start / Overcrank Shutdown | A crank-limiting timer has stopped the starter after repeated unsuccessful start attempts. | Weak battery or starter, the gas shutoff valve not opening on crank signal, no spark from the ignition module, or air in the fuel gas train. | Confirm battery voltage and starter engagement, verify the gas shutoff valve opens when cranking, and check for spark before cranking again. |
| Low Coolant Level Shutdown | A coolant level switch (where fitted, typically with an expansion tank or heat exchanger option) has sensed coolant below the safe level and shut the engine down ahead of a high-temperature trip. | External coolant leak, a failed hose or gasket, or a slow internal leak past a head gasket or cooler core. | Visually inspect for leaks, check hoses and the expansion tank, and pressure-test the cooling system before refilling and restarting. |
| Panel Alarm Code (numbered, on optional gauge/monitoring panel) | On packages fitted with an optional multi-function gauge panel or generator-set control panel, the same shutdown and alarm conditions listed above are shown as a flashing numbered alarm on the panel display instead of (or in addition to) a discrete lamp. | Same root causes as the discrete shutdowns above (oil pressure, water temperature, overspeed, gas pressure); the panel is a different annunciator, not a separate diagnostic layer. | Look up the displayed number in the panel manufacturer's own code table; it maps back to one of the standard mechanical protection functions above, then troubleshoot that function directly. |
Codes and remedies are general guidance for this model family — always confirm with diagnostic tooling and your dealer before major repairs.
G3304 attachments & work tools
Generator set packaging
Engine is packaged into natural gas generator sets in roughly the 55-71 kW (74-95 hp) class, usually skid-mounted with a radiator-cooled package and an electronic genset control/monitoring panel for protection and metering.
Gas compression / wellhead packaging
Engine drives reciprocating and rotary-screw compressor frames for gas lift, gas gathering, and wellhead gas-compression duty. Later G3304B production adds electronic engine management with air/fuel ratio control to support NSPS-site-compliant compression packages.
Pump and irrigation drive
Engine is also supplied as a natural-gas pump-drive power unit for irrigation service, commonly fitted with a hydra-mechanical (hydraulic) governor and a simple mechanical gauge-type instrument panel instead of an electronic control panel.
Flywheel and PTO coupling
Standard flywheel and flywheel housing are SAE No. 1 size with standard rotation. Factory PTO options include an auxiliary front drive pulley, an enclosed clutch, and a front or flywheel stub-shaft output for driving a compressor, pump, or other auxiliary equipment.
Cooling package options
Standard cooling equipment is thermostats with a gear-driven jacket-water pump and water-cooled exhaust manifolds. Factory cooling-package options add a radiator or a heat-exchanger/expansion-tank arrangement, each available with a blower or suction fan and belt-tightener hardware to suit the install (skid, enclosure, or remote-cooled room).
Governor and ignition system options
Standard control is a hydra-mechanical governor, with vernier-adjustment and positive-locking speed-control options for finer speed setting. Ignition is Altronic V as standard, with Altronic III or a CSA-shielded ignition system offered for hazardous-area installations.
Control panel and instrumentation options
Genset and compressor packages commonly use an electronic control/monitoring panel (Cat EMCP family) for engine and package protection. Pump-drive and irrigation packages more often use a simpler mechanical gauge-type panel instead of an electronic controller.
All G3304 assemblies by section
Every catalogued assembly group for the Caterpillar G3304. Open an assembly to preview the parts inside — full OEM part numbers are available in Heavy Parts AI.
Air Inlet And Exhaust System
2y8092 Air Cleaner Gp
| 2Y***92 | Air Cleaner Group | 1 |
5y0085 Air Cleaner Gp
| 5Y***85 | Air Cleaner Group | 1 |
7l0369 Elbow Gp-Exhaust
| 7L***69 | Elbow Group-Exhaust | 1 |
4n4684 Fan Gp-Blower
| 4N***84 | Fan Group-Blower | 1 |
2w7845 Fitting Gp-Exhaust
| 2W***45 | Fitting Group-Exhaust | 1 |
2w7854 Flange Gp-Exhaust
| 2W***54 | Flange Group-Exhaust | 1 |
1w8823 Flange Gp-Exhaust
| 1W***23 | Flange Group-Exhaust | 1 |
1n4199 Manifold Gp-Exhaust-Watercooled
| 1N***99 | Manifold Group-Exhaust | 1 |
5y0804 Muffler Gp
| 2W***70 | Muffler | 1 |
| 2W***54 | Flange Group-Exhaust | 2 |
| 5Y***04 | Muffler Group | 1 |
5l8649 Pipe Gp-Exhaust
| 5L***49 | Pipe Group-Exhaust | 1 |
Basic Engine
7n4137 Flywheel Gp
| 7N***37 | Flywheel Group | 1 |
7n4312 Indicator Gp-Timing
| 7N***12 | Indicator Group-Timing | 1 |
8l4446 Piston & Rod Gp
| 8L***46 | Piston & Rod Group; Connecting Rod And Piston Group | 1 |
3n6695 Support Gp-Engine
| 3N***95 | Support Group-Engine | 1 |
1w5122 Support Gp-Engine
| 1W***22 | Support Group-Engine | 1 |
3n5658 Adapter Gp-Fan
| 3N***58 | Adapter Group | 1 |
3n2886 Adapter Gp-Seal
| 3N***86 | Adapter Group-Seal; -Crankshaft | 1 |
5s6425 Balancer Gp-Engine
| 5S***25 | Balancer Group; Balancer Group | 1 |
3n2755 Belt Tightener Gp
| 3N***55 | Belt Tightener Group | 1 |
2p6201 Camshaft Gp-Single
| 2P***01 | Camshaft Group-Single; Single Camshaft Group | 1 |
7n1088 Cover Gp-Cylinder Block
| 7N***88 | Cover Group-Cylinder Block; Cylinder Block Cover Group | 1 |
2p6530 Cover Gp-Cylinder Head
| 2P***30 | Cover Group-Cylinder Head; Cylinder Head Cover Group | 1 |
5y0093 Cover Gp-Front Housing
| 5Y***93 | Cover Group-Front Housing | 1 |
2p6514 Cover Gp-Valve Mechanism
| 2P***14 | Cover Group-Valve Mechanism; Valve Mechansim Cover Group | 1 |
2y4515 Crankshaft As*R
| 2Y***15 | Crankshaft As | 1 |
Crankshaft Bearing Replacements
| 8N***25 | Bearing (1.25mm Undersize) | 5 |
| 8N***26 | Bearing (0.51mm Undersize) | 5 |
| 8N***27 | Bearing (0.76mm Undersize) | 5 |
2y5204 Crankshaft Gp-Type 1
| 2Y***04 | Crankshaft Group; Crankshaft Group | 1 |
2y5204 Crankshaft Gp-Type 2
| 2Y***04 | Crankshaft Group; Crankshaft Group | 1 |
7n6552 Cylinder Block As
| 7N***52 | Cylinder Block As | 1 |
1n3574 Cylinder Block Gp*R
| 1N***74 | Cylinder Block Group | 1 |
2y9359 Cylinder Block Gp
| 2Y***59 | Cylinder Block Group | 1 |
5y0091 Cylinder Head Gp
| 5Y***91 | Cylinder Head Group | 1 |
3n7210 Drive Gp-Fan
| 3N***10 | Drive Group-Fan | 1 |
5y0803 Drive Gp-Fan
| 3N***26 | Pulley Group-Fan Drive | 1 |
| 3N***58 | Adapter Group | 1 |
| 3N***10 | Drive Group-Fan | 1 |
7n9534 Fastener Gp-Cylinder Head
| 7N***34 | Fastener Group-Cylinder Head; Cylinder Head Fastener Group | 1 |
3n2887 Fastener Gp-Front Housing
| 3N***87 | Fastener Group-Front Housing; Front Housing Fastener Group | 1 |
2p9642 Gear Gp-Front Timing
| 2P***42 | Gear Group-Front Timing | 1 |
5y0092 Housing Gp-Flywheel
| 5Y***92 | Housing Group-Flywheel | 1 |
8n0303 Housing Gp-Front
| 8N***03 | Housing Group-Front; Front Housing Group | 1 |
2p9641 Housing Gp-Front
| 2P***41 | Housing Group-Front; Front Housing Group | 1 |
2y7719 Lifting Eye Gp-Engine
| 2Y***19 | Lifting Group-Engine; Lifting Eye Gp-Engine | 1 |
5y0075 Rod & Piston Gp-4 Required
| 5Y***75 | Piston & Rod Group | 1 |
3n2884 Pulley Gp-Crankshaft
| 3N***84 | Pulley Group-Crankshaft; Crankshaft Pulley Group | 1 |
3n5626 Pulley Gp-Fan
| 3N***26 | Pulley Group-Fan Drive | 1 |
2p6224 Seal Gp-Crankshaft
| 2P***24 | Seal Group-Crankshaft; Crankshaft Seal Group | 1 |
3n2883 Support Gp-Engine
| 3N***83 | Support Group | 1 |
2p6524 Valve Mechanism Gp
| 2P***24 | Valve-Mechanism Group; Valve Mechanism Group | 1 |
Cooling System
2w8006 Pump Gp-Water
| 2W***06 | Pump Group-Water | 1 |
7n6210 Pump Gp-Water
| 7N***10 | Pump Group-Water | 1 |
2w8005 Pump Gp-Water*R
| 2W***05 | Pump Group-Water | 1 |
8n4252 Pump Gp-Water
| 8N***52 | Pump Group-Water | 1 |
4w2132 Housing & Regulator Gp
| 4W***32 | Regulator Group | 1 |
8n4457 Base Gp-Oil Filter
| 8N***57 | Base Group-Oil Filter; Base Group-Engine Oil Filter | 1 |
7w0255 Base Gp-Oil Filter
| 7W***55 | Base Group-Oil Filter | 1 |
2p7738 Cooler Gp-Engine Oil
| 2P***38 | Cooler Group-Engine Oil; Engine Oil Cooler Group | 1 |
7w0257 Cooler Gp-Filter Base & Engine Oil
| 7W***57 | Cooler Group-Filter Base & Eng Oil | 1 |
7w0256 Cooler Gp-Filter Base & Engine Oil
| 7W***56 | Cooler Group-Filter Base & Eng Oil | 1 |
5y0796 Cooling System Ar
| 3N***69 | Tank Group-Expansion | 1 |
| 3N***79 | Housing & Regulator Group; Housing And Regulator Group | 1 |
| 3N***25 | Heat Exchanger Group-Sea Water | 1 |
2p6475 Filter Gp-Engine Oil
| 2P***75 | Filter Group-Engine Oil; Oil Filter Group (10z1 ~ 10z7023) | 1 |
3n3270 Heat Exchanger Gp-Sea Water
| 3N***70 | Heat Exchanger Group-Sea Water | 1 |
3n4925 Heat Exchanger Gp-Sea Water
| 3N***25 | Heat Exchanger Group-Sea Water | 1 |
3n3279 Housing & Regulator Gp
| 3N***79 | Housing & Regulator Group; Housing And Regulator Group | 1 |
2y9679 Regulator Gp
| 2Y***79 | Housing & Regulator Group | 1 |
8n0713 Lines Gp-Water
| 8N***13 | Lines Group-Water; Water Lines Group | 1 |
8n4112 Lines Gp-Water
| 8N***12 | Lines Group-Water; -Bypass Relief | 1 |
2w6779 Lines Gp-Water
| 2W***79 | Lines Group-Water | 1 |
2p7728 Lines Gp-Water
| 2P***28 | Lines Group-Water; Water Lines Group (Elbow) | 1 |
8n5997 Radiator Gp
| 8N***97 | Radiator Group | 1 |
3n3269 Tank Gp-Expansion
| 3N***69 | Tank Group-Expansion | 1 |
Engine Arrangement
5y0089 Engine Ar-Part 2 Of 2
| 2P***84 | Pump Group-Engine Oil; Engine Oil Pump Group | 1 |
| 2P***55 | Pan Group-Oil; Oil Pan Group | 1 |
| 2P***24 | Seal Group-Crankshaft; Crankshaft Seal Group | 1 |
5y0090 Engine Ar
| 1N***99 | Manifold Group-Exhaust | 1 |
| 1N***74 | Fumes Disposal Group | 1 |
| 1W***22 | Support Group-Engine | 1 |
5y0089 Engine Ar-Part 1 Of 2
| 1P***44 | Breather Group | 1 |
| 2P***89 | Fastener Group-Oil Pan; Oil Pan Fastener Group | 1 |
| 2P***01 | Camshaft Group-Single; Single Camshaft Group | 1 |
Fuel System And Governor
7e1814 Carburetor As
| 7E***14 | Carburetor As | 1 |
7n6508 Carburetor As
| 7N***08 | Carburetor As | 1 |
8n2379 Drive Gp-Governor
| 8N***79 | Drive Group-Governor | 1 |
7n2375 Governor Gp-Part 2 Of 2
| 7N***75 | Governor Group | 1 |
7n2375 Governor Gp-Part 1 Of 2
| 7N***75 | Governor Group | 1 |
5y0088 Carburetor Gp
| 5Y***88 | Carburetor Group | 1 |
8n5737 Control Gp-Carburetor
| 8N***37 | Control Group-Carburetor | 1 |
4n3835 Control Gp-Governor
| 4N***35 | Control Group-Governor | 1 |
4n3830 Control Gp-Governor
| 4N***30 | Control Group-Governor | 1 |
4w0270 Regulator Gp-Gas Pressure
| 4W***70 | Regulator Group-Gas Pressure | 1 |
Gauges And Accessories
8n5825 Panel Gp-Instrument
| 8N***25 | Panel Group-Instrument | 1 |
7n5903 Panel Gp-Instrument
| 7N***03 | Panel Group-Instrument | 1 |
2w5994 Panel Gp-Instrument
| 2W***94 | Panel Group-Instrument | 1 |
4n1402 Drive Gp-Tachometer
| 4N***02 | Drive Group-Tachometer; Tachometer Drive Group-Single | 1 |
8m7892 Gauge As-Ammeter
| 8M***92 | Gauge As-Ammeter; (Ammeter) | 1 |
7n9261 Meter Gp-Service
| 7N***61 | Meter Group-Service | 1 |
6l2692 Shaft Gp-Stub
| 6L***92 | Shaft Group-Stub; -Rear Mounted | 1 |
Lubrication System
1p4244 Breather Gp-Crankcase
| 1P***44 | Breather Group | 1 |
2p6189 Fastener Gp-Engine Oil Pan
| 2P***89 | Fastener Group-Oil Pan; Oil Pan Fastener Group | 1 |
2p6855 Filler Gp-Engine Oil
| 2P***55 | Filler Group-Oil | 1 |
1n4874 Fumes Disposal Gp
| 1N***74 | Fumes Disposal Group | 1 |
2y8417 Gauge Gp-Engine Oil Level
| 2Y***17 | Gauge Group-Oil Level (Dipstick) | 1 |
5y0997 Gauge Gp-Oil Level (Dipstick)
| 5Y***97 | Gauge Group-Oil Level (Dipstick) | 1 |
2p6512 Lines Gp-Engine Oil
| 2P***12 | Lines Group-Engine Oil; Engine Oil Lines Group | 1 |
2p6155 Pan Gp-Engine Oil
| 2P***55 | Pan Group-Oil; Oil Pan Group | 1 |
6n2642 Pump Gp-Engine Oil-Type 2
| 6N***42 | Pump Group-Engine Oil | 1 |
6n2642 Pump Gp-Engine Oil-Type 1
| 0S***90 | Bolt; (3/8-16x2in)(Clip Thru Spacer To Bracket As) | 1 |
| 1P***46 | Washer-Hard; (10.2x35x6-mm Thk) | 1 |
| 4W***48 | Pump Group-Engine Oil; Pump Gp-Engine Oil Gear | 1 |
4p4020 Pump Gp-Engine Oil
| 4P***20 | Pump Group-Engine Oil; Pump Group-Engine Oil | 1 |
2p1784 Pump Gp-Engine Oil
| 2P***84 | Pump Group-Engine Oil; Engine Oil Pump Group | 1 |
4w2448 Pump Gp-Engine Oil*R
| 4W***48 | Pump Group-Engine Oil; Pump Gp-Engine Oil Gear | 1 |
6i1346 Pump Gp-Engine Oil
| 6I***46 | Pump Group-Engine Oil | 1 |
Service Equipment And Supplies
Name Plates & Transfers
| 2P***82 | Film-- Corporate Symbol; -- On Front Frame | 1 |
| 2Y***68 | Plate-Serial Number-Engine | 1 |
| 2Y***40 | Plate-Engine Information-Portuguese | 1 |
Starting And Electrical System
3n8423 Contactor Gp
| 3N***67 | Contactor Group; Oil Pressure And Water Temperature Contactor Group | 1 |
| 3N***21 | Wiring Diagram | 1 |
| 3N***23 | Contactor Group-Press & Temp | 1 |
7n2587 Gear Gp-Magneto Drive
| 7N***87 | Gear Group-Magneto Drive; (14-Teeth) | 1 |
8l5455 Starting Motor Gp-Electric
| 8L***55 | Starting Motor Group-Electric | 1 |
3t2655 Starting Motor Gp-Electric*R
| 3T***55 | Starting Motor Group-Electric | 1 |
| 7T***65 | Starting Motor Group-Electric; Starting Motor Gp-Electric-Bosch | 1 |
| 8C***48 | Starting Motor Group-Electric; Starting Motor Gp-Electric-Delco-Remy | 1 |
8c3648 Starting Motor Gp-Electric
| 8C***48 | Starting Motor Group-Electric; Starting Motor Gp-Electric-Delco-Remy | 1 |
5y0473 Starting Motor Gp-Electric
| 5Y***73 | Starting Motor Group-Electric | 1 |
7t2265 Starting Motor Gp-Electric
| 7T***65 | Starting Motor Group-Electric; Starting Motor Gp-Electric-Bosch | 1 |
1n9306 Valve As-Safety Shut-Off
| 1N***06 | Valve As-Shutoff | 1 |
6t1396 Alternator Gp*R
| 6T***96 | Alternator Group-Charging | 1 |
3n2708 Alternator Gp
| 3N***08 | Alternator Group-Charging | 1 |
7l7867 Battery Gp
| 7L***67 | Battery Group | 1 |
3n6867 Contactor Gp
| 3N***67 | Contactor Group; Oil Pressure And Water Temperature Contactor Group | 1 |
5y1140 Contactor Gp
| 3N***23 | Contactor Group-Press & Temp | 1 |
| 5Y***37 | Harness As | 1 |
| 5Y***40 | Contactor Group-Overspeed | 1 |
7l7367 Contactor Gp
| 7L***67 | Contactor Group-Overspeed; (Mechanical) | 1 |
4p5468 Control Gp-Electronic
| 4P***68 | Control Group-Engine Monitoring | 1 |
8n5024 Drive Gp-Magneto
| 8N***24 | Drive Group-Magneto | 1 |
8n5726 Ignition Gp
| 8N***26 | Ignition Group-Gas Engine | 1 |
2w4873 Ignition Gp-Gas Engine
| 2W***73 | Ignition Group-Gas Engine | 1 |
7l3032 Magneto As
| 7L***32 | Magneto As | 1 |
2w3746 Magneto Gp
| 2W***46 | Magneto Group | 1 |
3n8806 Mounting Gp-Contactor
| 3N***06 | Mounting Group-Contactor; Contactor Mounting Group | 1 |
4p3483 Magnetic Pickup Gp
| 4P***83 | Sensor Group-Speed; (Engine) | 1 |
8l4117 Valve As-Safety Shut-Off
| 8L***17 | Valve As-Gas Shutoff | 1 |
3l6655 Wiring Gp
| 1H***66 | Clip-Wire Provides Loose Parts | 2 |
| 1L***99 | Marker-(Wire Code) | 1 |
| 2L***52 | Terminal; (6-Ga, 3/8-In)(6 Gauge/9.53mm(.375in)Screw) | 1 |
G3304 serial number reference
The serial/PIN plate on a G3304 is riveted to the engine block itself, typically on the left side near the flywheel housing or front timing cover (there's no vehicle chassis to carry it since this is a bare industrial gas engine). Read the first three characters as the prefix, which ties to a specific build arrangement of the G3304; the following five digits are the sequential unit number within that arrangement. Match the three-character prefix against Caterpillar's serial-prefix identification chart or your dealer's records to confirm it belongs to the G3304 rather than a similarly numbered diesel or gas-compression engine. The base G3304 runs a hydra-mechanical governor with Altronic V ignition (no ADEM/ECM); electronic governance is a trait of the later G3304B nameplate, a separate gas-compression model.
| Prefix | Identifies | Notes |
|---|---|---|
| 1RG | G3304 industrial gas engine, base arrangement | Naturally aspirated, spark-ignited natural-gas inline-4, ~7.0 L, industrial/genset duty. Turns up only on a serial-prefix cross-reference chart tying this block to the G3304; no independent parts-catalog breakpoint or unit record found to double-check it. Confirm with dealer. |
| 37Y | G3304 industrial gas engine, natural-gas genset arrangement | Naturally aspirated, spark-ignited natural-gas inline-4, ~7.0 L. This block starts the electrical/charging and alternator parts groups in the factory parts catalog, and matches a documented running unit built to this prefix (55 kW/97 hp genset, 24V start). Engine uses a hydra-mechanical governor with Altronic V ignition, standard for this base engine; electronic (ADEM) governance is a later G3304B trait, not this one. |
| N4F | G3304 industrial gas engine arrangement | Naturally aspirated, spark-ignited natural-gas inline-4, ~7.0 L. This block starts the chart-plate/film and service-equipment parts groups in the factory parts catalog for this engine. |
Frequently asked questions
What engine powers the Cat G3304?
The G3304 is Caterpillar's own naturally aspirated, spark-ignited natural gas engine: an inline unit displacing 7.0 L (425 cu in), rated 71 bkW (95 bhp) at 1800 rpm for continuous industrial duty. The G3304 designation is the engine itself, packaged into generator sets and gas-compression units, not a separate engine paired with a host chassis.
How much does a Cat G3304 engine weigh?
Net dry weight for the bare G3304 engine is about 757 kg (1670 lb). Packaged weight varies once the engine is mounted with a generator end or compressor, radiator, and skid, so treat the dry engine figure as a baseline and confirm total package weight against the specific build sheet.
What replaced the Cat G3304?
Caterpillar's successor is the G3304B. It keeps the same basic displacement and naturally aspirated layout but moves to the ADEM A4 electronic control platform for ignition, governing, and air/fuel ratio control, replacing the G3304's hydra-mechanical governor and Altronic V ignition system.
What G3304 owners discuss
What ignition problems show up most often on the G3304, and does it vary by series?
How sensitive is this engine to field gas quality, and what does a detonation problem look like?
What cooling problems come up on the G3304?
What wears out first on a running G3304?
What should I check before buying a used G3304?
Does it matter whether I have an older G3304 or a G3304B?
What electrical or sensor issues come up most at remote sites?
Compiled from owner and technician discussions across the industry — experiences vary by serial range and machine history.
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