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DHLG420E Engine

The DHLG420E is an engine. It powers generator sets from Cummins/Onan, including the P9500df.

Also known as: DHLG420E

On this pageSpecsGenerator setsMaintenanceFAQService intervalsTorque & specsFluidsProcedures

Engine specifications

Generator sets powered by this engine

1
Cummins/Onan P9500df

Common problems

5
  • Push button start is not working and the cranking speed drops after each attempt.
    Cause: 1. Battery is not adequately charged.
    Fix: 1. Turn the engine switch to “STOP” and hook up the battery charger for 1 hour. 2. Try manually starting the generator to let the battery charge while it is operating.
  • Generator suddenly stops running.
    Cause: 1. Generator is out of fuel. 2. The low oil shut down switch has stopped the engine. 3. Too much load.
    Fix: 1. Check fuel level and add fuel if necessary. 2. Check oil level and add oil if necessary. 3. Restart the generator and reduce the load.
  • Frost on the propane tank or regulator.
    Cause: 1. This can be a normal occurrence caused when liquid propane changes phase to a gas. 2. The propane tank is not equipped with an OPD (rollover protection device) and has been stored in a horizontal position allowing liquid propane to enter the downstream fuel handling equipment.
    Fix: 1. As this can be normal, providing all the propane fuel handling equipment is functioning normally, no remedy is needed. 2. If you suspect your propane fuel tank is
  • Engine will not start or remain running while trying to start.
    Cause: 1. Fuel shutoff valve is in the OFF position. 2. Generator is out of gasoline. 3. Fuel flow is obstructed. 4. Starting battery may have insufficient charge (only for electric start models). 5. Dirty air filter. 6. Low oil level shut down switch is preventing the unit from starting.
    Fix: 1. Move the fuel shutoff valve to the ON position. 2. Add gasoline to the generator. 3. Inspect and clean fuel delivery passages. 4. On electric start models only, check battery output and charge battery as necessary. 5. Check and clean the air filter. 6. Check oil level and add oil if necessary. 7. Firmly push down on the spark plug boot to ensure the boot is fully engaged 8. Remove and check the spark plug. Replace if faulty. 9. Check and clean the spark arrestor. 10. Drain fuel and replace with fresh fuel.
  • Engine runs erratic; does not hold a steady RPM.
    Cause: 1. Dirty air filter. 2. Applied loads maybe cycling on and off.
    Fix: 1. Clean the air filter. 2. As applied loads cycle, changes in engine speed may occur; this is a normal condition.

Compiled from service & troubleshooting documentation across every generator set that uses the DHLG420E.

Maintenance schedule

ItemSpecCapacityPart #Interval
Air filterA058U975300 hr eBay
Fuel filterA064N124100 hr Amazon eBay
Battery12V/6.5 Ah100557 eBay
Oil1.1 L—50 hr
Spark plug0.024 – 0.032 in. (0.60 – 0.80 mm)A064D660300 hr Amazon eBay

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

Service intervals

9
ItemActionHoursMonthsNotes
Engine OilChange50 hr6 moFirst service — After first 20 hours or first month of use
Air FilterClean50 hr6 moservice more frequently if dry/dusty
Fuel FilterClean100 hr6 moauthorized Cummins service dealer; check/clean
Spark ArrestorCheck100 hr6 mocheck/clean
Spark PlugCheck100 hr6 mocheck/clean
Air FilterReplace300 hr12 mo
Idle SpeedAdjust300 hr12 moauthorized Cummins service dealer; check/adjust
Spark PlugReplace300 hr12 mo
Valve ClearanceAdjust300 hr12 moauthorized Cummins service dealer

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

6
TypeItemValueUnitCondition
GapSpark plug gap0.027-0.032in. (0.70-0.80mm)
PressureLP fuel pressure at large tank outlet14-10inches of water column
TorqueValve lash jam nut (exhaust)8-12N.mcold
TorqueValve lash jam nut (intake)8-12N.mcold
Valve clearanceExhaust Valve Lash0.0043 ± 0.0051in. (0.11 ± 0.13 mm)
Valve clearanceIntake Valve Lash0.0035 ± 0.0043in. (0.09 ± 0.11 mm)

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

FluidGradeStandardAmbientCapacityNotes
Engine oil10W301.1 L4-stroke/cycle engine oil only, never 2-stroke; synthetic oil acceptable substitute
FuelUnleaded gasoline, max 10% ethanol, 87 octane or higher6.6 Gallonstank size

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

Procedures

9
Checking and Adjusting Valve Lash adjustment

⚠ Must be done when engine is cold

Tools: feeler gauge

  1. Remove rocker arm cover and carefully remove gasket, replace if torn or damaged
  2. Remove spark plug so engine can be rotated more easily
  3. Rotate engine to top dead center (TDC) of compression stroke
  4. Confirm both rocker arms are loose at TDC on compression stroke; if not, rotate engine 360 degrees
  5. Insert feeler gauge between rocker arm and push rod to check clearance
  6. If adjustment required, hold adjusting nut and loosen jam nut
  7. Turn adjusting nut to obtain correct valve lash
  8. Hold adjusting nut and tighten jam nut to 106 in-lb (12 N.m)
  9. Recheck valve lash after tightening jam nut
  10. Perform for both intake and exhaust valves
  11. Install rocker arm cover, gasket and spark plug
Changing Engine Oil maintenance

⚠ Never dispose of used oil into sewer, ground, or waterways

Tools: oil pan

  1. Operate or maintain generator on flat surface
  2. Stop engine
  3. Let engine cool for several minutes
  4. Place oil pan under oil drain plug
  5. Clean around oil drain plug with damp rag
  6. Remove oil drain plug
  7. Allow oil to completely drain
  8. Replace oil drain plug
  9. Fill crankcase with oil per Adding Engine Oil procedure
Checking Engine Oil maintenance

⚠ Internal pressure can build in crankcase while running; allow oil to cool before removing dipstick

  1. Operate or maintain generator on flat surface
  2. Stop engine if running
  3. Let engine cool for several minutes
  4. Clean around oil fill plug/dipstick with damp rag
  5. Remove oil fill plug/dipstick
  6. Thread dipstick all the way back in, remove and check oil level between H and L lines
Cleaning the Air Filter maintenance

⚠ Never use gasoline or flammable solvents to clean air filter

  1. Turn off generator and let cool for several minutes
  2. Move generator to flat, level surface
  3. Unclip clips on top and bottom of air filter cover
  4. Remove black coarse air filters
  5. Wash foam air filter elements in household detergent soap and warm water, slowly squeeze to clean
  6. Rinse in clean water with slow squeezing action
  7. Dispose of used soap solution properly
  8. Dry air filter elements with slow firm squeezing action
  9. Coat dry air filters with clean engine oil
  10. Squeeze filters to remove excess oil
  11. Install filters back into unit: gray (fine) filter first, then black (coarse) filter outside
  12. Install air filter cover and secure assembly
Cleaning the Spark Arrestor maintenance

⚠ Check and clean after every 100 hours of use or 6 months

Tools: wire brush

  1. Generator must be cold to perform this maintenance
  2. Move to flat, level surface
  3. Remove 6 screws holding muffler cover in place
  4. Locate screw on tip of muffler, remove, pull spark arrestor out
  5. Replace spark arrestor screen if torn/ripped (only use Cummins spark arrestors)
  6. If not torn, clean using wire brush, commercial solvent, or compressed air
  7. Install spark arrestor back into muffler, fully pushed in tight on tip
  8. Replace muffler cover and tighten all 6 screws
Draining Carburetor Float Bowl maintenance

Tools: fuel pan

  1. Make sure generator is off and away from open flames
  2. Place pan under carburetor assembly
  3. Loosen screw at bottom of bowl and allow gas to drain out
  4. After all gas has drained, tighten screw
Spark Plug Maintenance maintenance

⚠ Never apply side load when removing spark plug

Tools: 13/16" spark plug socket wrench

  1. Stop generator and let cool for several minutes
  2. Move generator to flat, level surface
  3. Remove spark plug boot by pulling directly away from engine
  4. Clean area around spark plug
  5. Remove spark plug using 13/16" spark plug socket wrench
  6. Place clean rag over opening to prevent dirt entering combustion chamber
  7. Inspect spark plug for cracked/chipped insulator, excessive wear, gap (0.027-0.032 in.)
  8. Hand-thread spark plug back in until it bottoms out, then turn with wrench to fully seat
  9. Replace spark plug boot, ensuring full engagement
Storing Generator maintenance

⚠ Gasoline stored for as little as 60 days can go bad

  1. Switch Engine Switch to STOP so generator does not draw power from battery
  2. Clean the generator
  3. Drain all gasoline from fuel tank as best as possible
  4. With fuel shut off valve open, start engine and run until remaining gasoline in lines/carburetor is consumed and engine shuts off
  5. Close fuel shut off valve
  6. Drain remaining gas in carburetor float bowl
  7. Change the oil
  8. Remove spark plug, place about 1 tablespoon of oil in spark plug opening, pull recoil handle several times to distribute oil
  9. Replace spark plug
  10. Move generator to a clean, dry place for storage
Battery Replacement repair
  1. Remove spark plug wire from spark plug
  2. Loosen and remove bolt on battery hold-down plate, swing plate out
  3. Tip battery forward slightly to access battery cables
  4. Disconnect black negative cable first
  5. Disconnect red positive cable second and remove battery
  6. Install new battery into generator frame
  7. Connect red positive cable to battery first
  8. Connect black negative cable to battery second
  9. Install battery hold-down plate using nuts removed earlier
  10. Install spark plug wire onto spark plug

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 DHLG420E engine?

The DHLG420E powers 1 generator set(s), including Cummins/Onan P9500df.

How often should you change the oil in the DHLG420E?

The DHLG420E oil change interval is every 50 hours.

What is a common problem with the DHLG420E engine?

A commonly reported issue on generators using the DHLG420E is: Push button start is not working and the cranking speed drops after each attempt.. Cause: 1. Battery is not adequately charged.. Fix: 1. Turn the engine switch to “STOP” and hook up the battery charger for 1 hour. 2. Try manually starting the generator to let the battery charge while it is operating..