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Ford Model SNNN-6006 Engine

The Ford Model SNNN-6006 is a 4-cylinder engine. It powers generator sets from Cummins/Onan, including the Model Not Specified.

Also known as: Ford Model SNNN-6006

Cylinders

On this pageSpecs Generator sets Maintenance FAQ Torque & specs Procedures Wiring

Engine specifications

Cylinders	4

Generator sets powered by this engine

Cummins/Onan Model Not Specified

Common problems

Voltage drops under heavy load
Cause: Engine lacks power. Poor compression. Faulty carburetion. Restricted air cleaner. Excessive choking. Carbon in cylinders. Restricted exhaust line.
Fix: See remedies for engine missing under heavy load. Tighten cylinder head and spark plugs. If still not corrected, grind the valves. Replace piston rings, if necessary. Check the fuel system. Clean, adjust or replace parts necessary. Clean and refill. See that choke opens properly. Remove carbon. Clean or increase the size.
Excessive oil consumption, light blue smoky exhaust
Cause: Poor compression, usually due to leaking valves.
Fix: Tighten cylinder head and plugs. If still not corrected, grind or replace valves. Oil leaks from engine or connections. This does not cause smoky exhaust. Tighten screws and connections. Oil too light or diluted. Drain, refill with correct oil. Too large bearing clearance. Replace. Oil pressure too high. Refer to symptoms of high oil pressure for remedies. Engine misfires. Refer to symptoms of engine misfires. Faulty ignition. Clean, adjust, or replace breaker points, plugs, condenser, coil, etc., or retime ignition. Unit operated at light or no load for long periods. No remedy needed. Too much oil. Drain excess oil.
Engine runs but current does not build up
Cause: Poor brush contact. Open circuit, Short circuit, or ground in generator.
Fix: See that brushes seat well, are free in holders, are not worn too short, and have good spring tension. See GENERATOR, replace part necessary.
Engine overheating
Cause: Overloaded.
Fix: Reduce load.
Engine misfires at light load
Cause: Carburetor idle adjustment set wrong or clogged. Spark plug gaps too narrow. Intake air leak. Faulty ignition. Uneven compression.
Fix: Adjust to correct gap. Tighten or replace gaskets. Clean, adjust, or replace breaker points, plugs, condenser, coils, etc., or retime ignition. Tighten cylinder head and spark plugs. If still not corrected, grind valves. Replace piston rings, if necessary. Worn intake valve stems. Replace valves.
Engine misfires at heavy load
Cause: Spark plugs defective. Faulty ignition.
Fix: Replace. Clean, adjust, or replace breaker points, plugs, condenser, coil, etc., or retime ignition.
Engine backfires at carburetor
Cause: Lean fuel mixture. Clogged fuel screen. Intake air leak.
Fix: Clean carburetor. Clean screen. Replace flange gaskets, tighten carburet. Poor fuel. Refill with good, fresh fuel. Spark too late. Retime ignition. Spark plug wires crossed. Install wires correctly. Intake valves leaking. Grind or replace.
Current steady but engine not misfiring
Cause: Speed too low. Poor commutation or brush contact. Loose connections. Fluctuating load.
Fix: Adjust governor to correct speed. Tighten connections. Correct any abnormal load condition causing trouble.
Black, smoky exhaust, excessive fuel consumption, fouling of spark plugs with black soot. Possible lack of power under heavy load
Cause: Fuel mixture too rich.
Fix: Adjust choke. Install needed carburetor parts, adjust float level. Choke not open. See that choke opens properly. Dirty air cleaner. Clean, refill to proper level.
Voltage low at far end of line but normal near power unit
Cause: Too small line wire for load
Fix: Install larger or extra wires or reduce and distance
Tappingsound
Cause: Taplet clearance too great
Fix: Adjust or replace tappets
Sharp metallic thud, especially when cold engine first started
Cause: Low oil supply
Fix: Add oil
Pinging sound when engine is rapidly accelerated or heavily loaded
Cause: Carbon in cylinders
Fix: Remove carbon
Noisy brushes
Cause: High mica between bars of commutator
Fix: Undercut mica.
Motors run too slowly and overheat at far end of line but not near power unit
Cause: Too small line wire for load
Fix: Install larger or extra wires, or reduce and distance

Compiled from service & troubleshooting documentation across every generator set that uses the Ford Model SNNN-6006.

Maintenance schedule

Item	Capacity	Part #	Interval
Air filter		—	50 hr
Fuel filter		—
Oil filter		—	50 hr
Battery		—
Belt		—	2500 hr
Coolant	14.0 quarts (U.S. Measure)	—
Coolant filter		—
Oil	4.0 quarts (u.s. Measure)	—
Spark plug		—	2500 hr

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

Service specifications

Type	Item	Value	Unit	Condition
Clearance	Overspeed switch magnet-to-fly arm air gap (minimum)	0.005	inches (0.13 mm)
Other	Battery specific gravity, fully charged	approximately 1.260	at 80°F (27°C)
Other	ECM fuse F1 (starter solenoid circuit)	20	amps
Other	ECM fuse F2 (fuel solenoid circuit)	20	amps
Other	ECM fuse F3 (continuous B+ to remote circuits)	15	amps
Other	ECM fuse F4 (ECM circuits)	5	amps
Other	ECM fuse F5 (engine gauge circuits)	5	amps
Other	Governor droop adjustment range	within 5	percent of nominal frequency (3 Hz for 60Hz sets, 2.5 Hz for 50Hz sets)
Pressure	Low Oil Pressure shutdown threshold	14	psi (97 kPa)
Pressure	Pre-Low Oil Pressure warning threshold (Detector control)	20	psi (138 kPa)
Resistance	PMG winding resistance (each of P2-P3, P3-P4, P4-P2)	approximately 4.4	ohms
Resistance	Stator/rotor insulation resistance minimum (exciter stator, exciter rotor, main rotor, main stator)	1	megohm (1,000,000 ohms)
Resistance	Voltage adjusting rheostat resistance range (MX321, PMG-excited)	0 to approximately 5,000	ohms
Resistance	Voltage adjusting rheostat resistance range (SX460, shunt-excited)	0 to approximately 1,500	ohms
Speed	Electronic Overspeed Module Cutout, 50 Hz sets (PMG-excited)	1800 to 1900	RPM
Speed	Electronic Overspeed Module Cutout, 60 Hz sets (PMG-excited)	2100 to 2200	RPM
Speed	Mechanical/Electronic Overspeed Switch Cutout, 50 Hz sets	1800 to 2100	RPM
Speed	Mechanical/Electronic Overspeed Switch Cutout, 60 Hz sets	2000 to 2200	RPM
Speed	Throttle lever idle/speed adjustment, 50 Hz sets	1650	RPM (55 Hertz)
Speed	Throttle lever idle/speed adjustment, 60 Hz sets	1980	RPM (66 Hertz)
Temperature	High Engine Temperature shutdown threshold	230	°F (110°C)
Temperature	Low Engine Temperature warning threshold	70	°F (21°C)
Temperature	Pre-High Engine Temperature warning threshold	220	°F (104°C)
Torque	Adaptor-to-engine bolts	35	ft-lbs (48 Nm)
Torque	Drive disc-to-flywheel bolts	50	ft-lbs (67 Nm)
Torque	Drive disc-to-rotor bolts	190	ft-lbs (257 Nm)
Torque	Exciter stator mounting screws	7	ft-lbs (10 Nm)
Torque	Generator end plate mounting bolts	25	ft-lbs (34 Nm)
Torque	Generator mounting bracket bolts (M10)	35	ft-lbs (47 Nm)
Torque	Generator mounting bracket bolts (M12)	65	ft-lbs (88 Nm)
Torque	Generator-to-adaptor bolts	40	ft-lbs (55 Nm)
Torque	Main rotor lead terminal torque	24	in-lbs (2.7 Nm)
Torque	Overspeed switch center rotor bolt	40	ft-lbs (54 Nm)
Torque	PMG rotor center bolt	40	ft-lbs (54 Nm)
Torque	Rectifier diode torque	36 to 42	in-lbs (4 to 4.8 Nm)
Torque	Rectifier pigtail terminal torque	24	in-lbs (2.7 Nm)
Torque	Surge suppresser terminal torque	24	in-lbs (2.7 Nm)
Voltage	Battery charging alternator normal output	12 to 14	VDC
Voltage	Magnetic speed pickup unit (MPU) minimum output at cranking speed	2.5	VDC	measured at governor controller terminals 10(-) and 11(+)
Voltage	Normal excitation voltage range	10 (no-load) to 40 (full-load)	VDC
Voltage	PMG output voltage minimum, 50 Hz sets	150	VAC
Voltage	PMG output voltage minimum, 60 Hz sets	180	VAC
Voltage	Voltage regulator trimmer adjustment range	±5	percent of nominal voltage

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

Procedures

Governor Adjustments (Type A Electric Governor) adjustment

Set selector switch S1 to OFF, S2 to appropriate model position.
Set pots initially: Gain 20%, I 20%, D 30%, Droop 0%.
Start set, adjust Speed pot for required frequency (60Hz=1800RPM or 50Hz=1500RPM) at operating temperature.
Disconnect load, turn Gain pot to 100% or until unstable, then back off until stable.
Adjust D and I pots similarly; readjust Speed if necessary.
Push throttle to minimum speed, release and observe overshoot (2-5 Hz acceptable); adjust I pot to reduce overshoot or hunting.

Servicing the PMG diagnostic

⚠ Touching uninsulated high voltage parts can result in severe personal injury or death.

Tools: Wheatstone bridge, digital ohmmeter

Disconnect leads P2, P3, P4 from voltage regulator.
Start engine and let speed stabilize.
Measure voltage across lead pairs P2-P3, P3-P4, P4-P2; should be at least 150 VAC (50Hz) or 180 VAC (60Hz).
Stop set and measure resistance across same lead pairs; each winding approximately 4.4 ohms.
Torque PMG rotor center bolt to 40 ft-lbs (54 Nm) when reassembling; stator leads must be at 12 o'clock.

Testing Exciter Stator Winding diagnostic

Tools: Wheatstone bridge, digital ohmmeter

Measure winding resistance with Wheatstone bridge or digital ohmmeter between the two stator leads X and XX.
Replace stator if resistance not as specified in Table 7-1.
Disconnect leads from terminals X and XX; measure insulation resistance between either lead and stator laminations with ohmmeter.
Replace stator if insulation resistance less than 1 megohm.

Testing the Exciter Rotor diagnostic

Tools: Wheatstone bridge, ohmmeter

Disconnect six rotor winding leads from rectifier terminal posts.
Measure resistance across each pair of rotor windings (U-V, V-W, W-U) with Wheatstone bridge.
Replace whole rotor shaft assembly if resistance not per Table 7-1.
Measure insulation resistance between any rotor winding lead/terminal and rotor laminations; replace if less than 1 megohm.

Testing the Float Switch Assembly diagnostic

Tools: ohmmeter, feeler gauge

Remove fuel pump control cover, disconnect wiring jack, unscrew assembly from top of day tank.
Test electrical continuity between each pair of colored leads while holding assembly vertical (should read zero/closed).
Lift each float to 1/8 inch (3mm) below C-clip stop and test continuity (should read infinity/open).
Use pipe thread sealant when replacing assembly.

Testing the Main Rotor (Generator Field) diagnostic

Tools: Wheatstone bridge, digital ohmmeter

Disconnect the two main rotor leads from the rotating rectifier assembly.
Measure resistance between the two leads with Wheatstone bridge or digital ohmmeter.
Replace rotor if resistance not per Table 7-1.
Reconnect rotor leads and torque terminals to 24 in-lbs (2.7 Nm).

Testing the Main Stator diagnostic

Tools: Wheatstone bridge

Measure resistance across each pair of stator leads (U1-U2, U5-U6, V1-V2, V5-V6, W1-W2, W5-W6) with Wheatstone bridge or 0.001-ohm precision ohmmeter.
Replace stator if resistance not per Table 7-1.
Disconnect all stator leads/taps; measure insulation resistance between any stator lead and laminations.
Replace stator if insulation resistance less than 1 megohm.

Testing the Rotating Rectifier Assembly diagnostic

⚠ Layers of dust can cause diodes to overheat and fail.

Tools: ohmmeter

Disconnect diode pigtails from terminal posts.
Measure resistance between each diode pigtail and its mounting plate; reverse probes and repeat.
Resistance should be high in one direction, low in the other; replace diode if high or low in both directions.
When replacing, apply heat-sink compound under diode head (avoid threads), torque diode to 36-42 in-lbs (4-4.8 Nm) and pigtail terminals to 24 in-lbs (2.7 Nm).

Flashing the Field (Self-Excited Generators) repair

Tools: diode, 3 amp fuse, 12 VDC battery

Shut down set, disconnect AVR.
Apply 110 to 220 VAC for 1 to 2 seconds to X and XX leads through a diode and 3 amp fuse.
Alternatively, with set running and disconnected from loads, apply 12 VDC battery for 1 to 2 seconds with correct polarity (+ to X, - to XX).

Reassembling the Generator repair

⚠ Never withdraw the generator leaving the rotor to hang by the drive discs.

Apply force to inner race of rotor bearing when pressing onto shaft; secure retaining clip.
Torque drive disc-to-rotor bolts to 190 ft-lbs (257 Nm).
Torque drive disc-to-flywheel bolts to 50 ft-lbs (67 Nm).
Torque exciter stator mounting screws to 7 ft-lbs (10 Nm).
Torque generator end plate mounting bolts to 25 ft-lbs (34 Nm).
Torque generator mounting bracket bolts to 65 ft-lbs (M12) or 35 ft-lbs (M10).
Torque generator-to-adaptor bolts to 40 ft-lbs (55 Nm).
Torque adaptor-to-engine bolts to 35 ft-lbs (48 Nm).

Removing and Disassembling the Generator repair

⚠ Accidentally dropping the generator can damage it and cause severe personal injury and death.

Tools: hoist, lifting straps

Disconnect starting battery cables (negative first).
Disconnect line cables, remote control wiring, engine wiring harness, and control leads (mark all for reconnection).
Attach hoist to generator output box, loosen mounting bolts, remove box.
Bar engine until one rotor pole points straight down.
Attach lifting eyes and hoist, remove two through bolts securing generator to isolation mounts.
Raise generator end approximately 1 inch (12 mm), block engine under flywheel housing.
Remove bolts securing generator drive discs to flywheel.
Loosen adapter casting bolts, carry full weight on hoist, remove bolts, pull generator away.

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

Voltage reconnection

Voltage	Phase	Connection	Leads	Notes
		Fault relay K8/K9 (Dry Contact Module)	K8=Over Crank, Low Oil Pressure, High Engine Temperature, Low Coolant Level, Low Fuel Level; K9=Low Fuel Level, Rupture Basin	Contact ratings: 40A max carry/break N.O. 12V coil, 30A N.C. 12V coil, 20A N.O./10A N.C. 24V coil
		TB3 (ECM alternative RUN/STOP/REMOTE connection)	TB3-1=REMOTE, TB3-2=RUN, TB3-3=STOP	Provides alternative direct connection to ECM for troubleshooting or customer connection

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 Ford Model SNNN-6006 engine?

The Ford Model SNNN-6006 powers 1 generator set(s), including Cummins/Onan Model Not Specified.

What is a common problem with the Ford Model SNNN-6006 engine?

A commonly reported issue on generators using the Ford Model SNNN-6006 is: Voltage drops under heavy load. Cause: Engine lacks power. Poor compression. Faulty carburetion. Restricted air cleaner. Excessive choking. Carbon in cylinders. Restricted exhaust line.. Fix: See remedies for engine missing under heavy load. Tighten cylinder head and spark plugs. If still not corrected, grind the valves. Replace piston rings, if necessary. Check the fuel system. Clean, adjust or replace parts necessary. Clean and refill. See that choke opens properly. Remove carbon. Clean or increase the size..