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Hercules D Series Engine

The Hercules D Series is an engine. It powers generator sets from Hercules, including the D-1500, D-1700, D-2000 and D-2300.

Also known as: Hercules Engines, Inc. D Series

On this pageSpecs Generator sets Maintenance FAQ Service intervals Torque & specs Fluids Procedures

Engine specifications

Generator sets powered by this engine

Hercules D-1500Hercules D-1700Hercules D-2000Hercules D-2300Hercules D-3400

Common problems

Fuel filters dirty or plugged
Fix: Para 5-13.
Fan belt loose or slipping
Fix: Para 5-9.
Electric fuel shutoff not functioning
Fix: X
Wrong type of lubricating oil
Fix: X
Wrong type of luboil
Fix: X
Worn pistons, rings, etc.
Fix: X
Water system piped incorrectly
Fix: X
Valves sticking
Fix: X
Valves leaking
Fix: Para 5-26.
Valves incorrectly adjusted
Fix: X
Throttle linkage adjustment incorrect or sticking
Fix: X
Thermostat missing
Fix: Para 5-10.
Sticking or fouled nozzle
Fix: Para 5-15.
Scored pistons
Fix: X
Rocker arm shaft upside down
Fix: Para 5-24.

Compiled from service & troubleshooting documentation across every generator set that uses the Hercules D Series.

Maintenance schedule

Item	Spec	Part #	Interval
Air filter	Under normal conditions, dry-type air cleaners require servicing every 50 hours of operation, However, under extremely dusty conditions, the air cleaner must be cleaned daily.	—	50 hr
Fuel filter	Clean the air cleaner on a normal 50-hour schedule as indicated in paragraph 3-2e.	—	50 hr
Oil filter	Replace the oil filter and gasket with this oil change. In normal operation, the oil filter Should be replaced at every other oil change.	—	100 hr
Battery	Add mineral-free or distilled water if necessary so that the water level is in accordance with battery manufacturer's recommendations.	—	100 hr
Belt	Inspect the fan belt(s) for wear and deterioration, Check alignment and belt tension, Adjust the tension so that the belt deflects 3/4 inch with thumb pressure at a point midway between pulleys. Too tight a belt will damage bearings; too loose a belt will slip causing - engine overheating and belt wear.	—	100 hr
Coolant		—
Coolant filter	Drain the pipe plug in the bottom of the fuel oil filter and drain accumulated water and sediment.	—	100 hr
Oil	Change at every other oil change.	—	100 hr
Spark plug		—

Pooled from every document that names this exact engine — confirm the interval and part number against your unit's serial number.

Service intervals

Item	Action	Hours	Notes
Drive belts	Adjust	8 hr	First service — Tighten new belts after 8 hours of operation.
Air cleaner	Clean	50 hr	Clean on normal 50-hour schedule.
Battery electrolyte level	Check	50 hr	Add mineral-free or distilled water if necessary.
Crankcase breather	Clean	50 hr	Clean every time oil is changed.
Crankcase oil	Change	50 hr	50 hours or 1500 miles; new/reconditioned engines start with 50-hour oil change periods; may increase to 100 hours under normal conditions.
Fan belt tension	Check	50 hr	Inspect for wear; adjust tension so belt deflects 3/4 inch with thumb pressure midway between pulleys.
Fuel filters	Drain	50 hr	Drain accumulated water and sediment from bottom of fuel oil filter.
Radiator air flow	Check	50 hr	Check exterior of radiator core air passages for dirt, grease, or chaff; clean with solvent and blow dry.
Alternator	Lubricate	100 hr	Add 3 to 5 drops of medium grade engine oil to oilers or oil wicks in end heads.
Fuel filters	Clean	100 hr	Remove filter and replace elements; if spin-on type, discard and replace.
Oil filter	Change	100 hr	Replace at every other oil change; add 1 extra quart of engine oil.
Starting motor	Lubricate	100 hr	Some have oil cup; others lubricated at overhaul.
Alternator	Inspect	500 hr	Inspect for broken wires; check connections clean and tight; brushes must slide freely; replace if worn to less than half length.
Battery	Check	500 hr	Clean top and cable ends with water and baking soda; check specific gravity; inspect for cracks, corrosion.
Cooling system hoses	Inspect	500 hr	Inspect for leakage, damage, or signs of deterioration; replace if necessary.
Fuel nozzles	Check	500 hr	Check operating pressure; nominal opening pressure 2750 psi; new assemblies set at 2900 psi.
Fuel tank	Drain	500 hr	Open drain at bottom of fuel tank and drain accumulated water or sediment.

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Service specifications

Type	Item	Value	Unit	Condition
Clearance	Camshaft bearing bore	2.1870 to 2.1889	inch
Clearance	Camshaft end play	0.005 to 0.008	inch	normal
Clearance	Camshaft end play - maximum	0.012	inch
Clearance	Camshaft gear backlash	0.0015 to 0.0025	inch
Clearance	Connecting rod bearing clearance	0.001 to 0.003	inch	new parts
Clearance	Connecting rod bearing clearance - maximum allowable with used parts	0.005	inch	used parts
Clearance	Connecting rod side clearance	0.005 to 0.012	inch
Clearance	Connecting rod side clearance - maximum	0.020	inch
Clearance	Crankshaft end thrust	0.005 to 0.010	inch	new bearings
Clearance	Crankshaft end thrust - maximum allowable	0.015	inch
Clearance	Cylinder bore out-of-round maximum	0.0030	inch
Clearance	Cylinder bore taper maximum	0.0020	inch
Clearance	Cylinder head out-of-flatness maximum	0.005	inch	on width or length
Clearance	Exhaust valve guide ream diameter	0.3750 to 0.3760	inch
Clearance	Fan belt deflection	3/4	inch	thumb pressure at midpoint between pulleys
Clearance	Idler gear shaft direct pull	32	pounds	must withstand
Clearance	Intake valve guide ream diameter	0.3740 to 0.3750	inch
Clearance	Main bearing bore	3.0665 to 3.0670	inch
Clearance	Oil pump drive shaft minimum diameter	0.6220	inch	at bearing points
Clearance	Oil pump idler shaft minimum diameter	0.6220	inch	at gear bearing area
Clearance	Piston pin bushing bore maximum	1.2523	inch
Clearance	Piston pin clearance in connecting rod maximum	0.0012	inch
Clearance	Piston pin clearance in piston maximum	0.0005	inch
Clearance	Piston pin minimum diameter	1.2478	inch
Clearance	Piston ring gap	0.010 to 0.020	inch
Clearance	Rocker arm bore diameter maximum	0.8665	inch
Clearance	Rocker arm shaft diameter minimum	0.8560	inch
Clearance	Valve guide installation depth	1.3800	inch	from lower edge of valve guide to gasket face of cylinder head
Clearance	Water pump impeller clearance	0.010	inch	between impeller and straightedge across rear face of pump body
Injection timing	Fuel injection pump timing - non-speed advance pumps	28° BTDC
Injection timing	Fuel injection pump timing - speed advance pumps	20° BTDC
Pressure	Engine oil pressure	40 to 60	psi	full engine speed
Pressure	Fuel nozzle opening pressure	2750	psi	nominal
Pressure	Fuel nozzle opening pressure - new assemblies	2900	psi	factory set
Pressure	Fuel transfer pump pressure	3 to 4-1/2	psi	engine at approximately 1800 rpm
Temperature	Thermostat fully open	200 ±5	°F
Temperature	Thermostat opening	180	°F	starts to open
Torque	Cam thrust plate bolt	9	foot-pounds
Torque	Camshaft gear nut	130	foot-pounds
Torque	Connecting rod bolts	70	foot-pounds
Torque	Crankshaft pulley	125	foot-pounds
Torque	Cylinder head 5/8 inch stud nut	160	foot-pounds
Torque	Cylinder head 5/8 inch stud nut	175	foot-pounds
Torque	Cylinder head 9/16 inch stud nut	147	foot-pounds
Torque	Drive gear nut (Roosa)	65	foot-pounds
Torque	Drive gear nut (Roosa)	85	foot-pounds
Torque	Exhaust manifold nut	20	foot-pounds
Torque	Flywheel housing nuts and cap screws	60	foot-pounds
Torque	Flywheel-to-crankshaft bolt	80	foot-pounds
Torque	Fuel line (Bosch pump)	25	foot-pounds
Torque	Fuel line (Roosa pump)	20	foot-pounds
Torque	Fuel pump attaching nut	15	foot-pounds
Torque	Gear cover attaching bolt	15	foot-pounds
Torque	Gear housing attaching bolt	40	foot-pounds
Torque	Idler gear capscrew (Use Loctite)	25	foot-pounds
Torque	Injector nozzle flange bolt	20	foot-pounds
Torque	Intake manifold nut	20	foot-pounds
Torque	Main bearing cap screw - center	100	foot-pounds
Torque	Main bearing cap screw - front	130	foot-pounds
Torque	Main bearing cap screw - intermediate	130	foot-pounds

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Recommended fluids

Fluid	Grade	Standard	Notes
Coolant	clean water or antifreeze solution		Use antifreeze if engine will be subjected to ambient air temperatures below freezing; check solution with hydrometer.
Engine oil		API Classification: Naturally Aspirated Diesel (MIL-L-2104B or C) CC (Single Viscosity) or CD; Turbocharged Diesel Engine (MIL-L-2104C) CD	Select viscosity grade according to ambient temperature from Table 3-4.
Engine oil	10W		Ambient air temperature -10° to 30° F. Use single viscosity, low ash oil with API classification CC (single viscosity) or CD.
Engine oil	15W-40	CD Classification only	Multigrade oils with CD Classification only are acceptable for Diesel engines; -10° F and up.
Engine oil	20 - 20W		Ambient air temperature 30° to 60° F.
Engine oil	30		Ambient air temperature 40° F and up.
Fuel	No. 2 distillate fuels, summer and winter grades	ASTM Designation D-975	Flash point 125°F minimum; carbon residue 0.39 percent; water and sediment 0.10 percent by volume maximum; ash 0.02 percent by weight maximum; distillation 90 percent 640 maximum, 540 minimum; viscosity at 100°F 2.0 centistokes minimum, 4.3 centistokes maximum; sulphur 1.0 percent maximum; cetane number 45 minimum.

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Procedures

Valve Clearance Adjustment adjustment

Tools: Feeler gauge

Rotate crankshaft until both intake and exhaust valves of No. 1 cylinder are fully closed.
For cold engine, use 0.016- or 0.017-inch feeler gauge between rocker arm and valve stem; adjust screw until it just touches pushrod.
Adjust remaining valves in firing order.
Start engine and warm to operating temperature.
With engine running at slow idle, check for 0.015 inch clearance; adjust as required.
Reinstall cylinder head cover and gasket.

Fuel Transfer Pump Testing diagnostic

Tools: Pressure gauge, 3/8-18 NPTF tee

Disconnect fuel line from fuel filter and install 3/8-18 NPTF tee in fuel filter base.
Connect fuel line and pressure gauge to pipe tee.
Start engine and run at approximately 1800 rpm.
Gauge should register 3 to 4-1/2 psi.
Replace fuel pump if pressure is less than 3 psi.
If no gauge, disconnect fuel line at fuel filter, crank engine, and check forceful fuel flow.

100 Hour or 3000 Mile Maintenance maintenance

Repeat daily and 50-hour maintenance.
Change oil filter; add 1 extra quart of engine oil.
Clean fuel filters; replace elements or spin-on filter.
Lubricate starting motor if oil cup provided.
Lubricate alternator with 3 to 5 drops of medium grade engine oil.

50 Hour or 1500 Mile Maintenance maintenance

Repeat daily maintenance.
Change crankcase oil; drain hot oil and refill to FULL mark.
Check radiator air flow; clean exterior core passages.
Drain fuel filters of water and sediment.
Clean air cleaner.
Clean crankcase breather.
Check fan belt tension; adjust to 3/4 inch deflection.
Check battery electrolyte level.

500 Hour or 12,000 Mile Maintenance maintenance

⚠ Fuel nozzle and holder assemblies should only be disassembled, cleaned, and adjusted by a competent fuel system technician.

Tools: Hydrometer, Fuel nozzle testing fixture

Repeat daily, 50-hour, and 100-hour maintenance.
Check cooling system hoses; replace if necessary.
Check fuel nozzles; check opening pressure.
Drain fuel tank of water and sediment.
Check battery; clean and check specific gravity.
Inspect alternator; replace worn brushes.
Perform engine tuneup as required by engine performance.

Air Cleaner Service maintenance

Tools: Compressed air

Remove filter element from air cleaner.
Clean by blowing compressed air through element from inside out.
Do not apply air closer than 2 inches and do not use more than 50 psi pressure.
Move air jet up and down filter, slowly rotating element, until no more dust is removed.
Replace element after it can no longer be effectively cleaned.

Daily Maintenance maintenance

Check overall condition for leaks; tighten, repair, or replace as necessary.
Check oil level before operation; add to FULL mark.
Check radiator coolant level.
Check fuel tank; fill at end of day's operation.
Check air cleaner; service dry-type at 50 hours or daily in dusty conditions.

Oil Filter and Lines Removal maintenance

Drain oil from crankcase.
Disconnect and remove oil line assemblies from oil filter and cylinder block or oil cooler.
Remove oil filter element from base assembly.
Remove base assembly from mounting bracket.

Cold Weather Starting operation

Use cold starting aids if available.
If spray-type starting aid is used, do not spray into manifold unless engine is being cranked.
In extremely cold temperatures of 0°F and below, heat water, oil, and air if necessary.
Conserve battery output.

Priming the Fuel System operation

Place manual stop control in STOP position.
Open bleed valve at fuel injection pump inlet.
Use hand priming lever or pump to purge air until air-free fuel flows.
On electric fuel pump, energize pump with start switch until purged.
Close bleed valve.
Place manual stop control in RUN position.

Routine Starting operation

⚠ Do not crank engine for more than 15 seconds at a time.

Check adequate fuel supply.
Check lubricating oil level at FULL mark.
Check coolant level in radiator.
Inspect installation for secure parts and no loose tools.
Place throttle control lever at half open position.
Be sure stop control is not in STOP position.
Operate start switch to crank engine.

Stopping operation

⚠ Do not leave electric fuel shutoff solenoid energized for extended periods unless engine is running.

Close throttle and allow engine to cool down at idle.
On electric fuel shutoff, place start switch in OFF position.
On manual shutoff only, operate stop control to STOP position.
If below freezing and no antifreeze, drain complete coolant system.

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Common questions

Which generators use the Hercules D Series engine?

The Hercules D Series powers 5 generator set(s), including Hercules D-1500, Hercules D-1700, Hercules D-2000, Hercules D-2300, Hercules D-3400.

How often should you change the oil in the Hercules D Series?

The Hercules D Series oil change interval is every 100 hours.

What is a common problem with the Hercules D Series engine?

A commonly reported issue on generators using the Hercules D Series is: Fuel filters dirty or plugged. Fix: Para 5-13..