Generac Power Systems 55, 75, 65 manual Down Test / Compression Test, Check Compression

Page 66

Section 7

DIAGNOSTIC TESTS

TEST 38 - CHECK ENGINE / CYLINDER LEAK

DOWN TEST / COMPRESSION TEST

GENERAL:

Most engine problems may be classified as one or a combination of the following:

❏Will not start.

❏Starts hard.

❏Lack of power.

❏Runs rough.

❏Vibration.

❏Overheating.

❏High oil consumption.

DISCUSSION:

The Cylinder Leak Down Tester checks the sealing (compression) ability of the engine by measuring air leakage from the combustion chamber. Compression loss can present many different symptoms. This test is designed to detect the section of the engine where the fault lies before disassembling the engine.

PROCEDURE:

One or more of the following will usually cause loss of compression:

❏Blown or leaking cylinder head gasket.

❏Improperly seated or sticking-valves.

❏Worn Piston rings or cylinder. (This will also result in high oil consumption).

NOTE: It is extremely difficult to obtain an accu- rate compression reading without special equip- ment. For that reason, compression values are not published for the V-Twin engine. Testing has proven that an accurate compression indication can be obtained using the following method.

PROCEDURE:

1.Remove both spark plugs.

2.Insert a compression gauge into either cylinder.

3.Crank the engine until there is no further increase in pressure.

4.Record the highest reading obtained.

5.Repeat the procedure for the remaining cylinder and record the highest reading.

RESULTS:

1.Remove a spark plug.

2.Gain access to the flywheel. Remove the valve cover.

3.Rotate the engine crankshaft until the piston reaches top dead center (TDC). Both valves should be closed.

4.Lock the flywheel at top dead center.

5.Attach cylinder leak down tester adapter to spark plug hole.

6.Connect an air source of at least 90 psi to the leak down tester.

7.Adjust the regulated pressure on the gauge to 80 psi.

8.Read the right hand gauge on the tester for cylinder pressure. 20 percent leakage is normally acceptable. Use good judgement, and listen for air escaping at the carburetor, the exhaust, and the crankcase breather. This will determine where the fault lies.

9.Repeat Steps 1 through 8 on remaining cylinder.

RESULTS:

❏Air escapes at the carburetor – check intake valve.

❏Air escapes through the exhaust – check exhaust valve.

❏Air escapes through the breather – check piston rings.

❏Air escapes from the cylinder head – the head gas- ket should be replaced.

CHECK COMPRESSION:

Lost or reduced engine compression can result in (a) failure of the engine to start, or (b) rough operation.

The difference in pressure between the two cylinders should not exceed 25 percent. If the difference is greater than 25 percent, loss of compression in the lowest reading cylinder is indicated.

Example 1: If the pressure reading of cylinder #1 is 165 psi and of cylinder #2, 160 psi, the difference is 5 psi. Divide "5" by the highest reading (165) to obtain the percentage of 3.0 percent.

Example 2: No. 1 cylinder reads 160 psi; No. 2 cylin- der reads 100 psi. The difference is 60 psi. Divide "60" by "160" to obtain "37.5" percent. Loss of compression in No. 2 cylinder is indicated.

If compression is poor, look for one or more of the fol- lowing causes:

❏Loose cylinder head bolts.

❏Failed cylinder head gasket.

❏Burned valves or valve seats.

❏Insufficient valve clearance.

❏Warped cylinder head.

❏Warped valve stem.

❏Worn or broken piston ring(s).

❏Worn or damaged cylinder bore.

❏Broken connecting rod.

❏Worn valve seats or valves.

❏Worn valve guides.

NOTE: Refer to Engine Service manual No. 0E2081 for further engine service information.

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Contents Diagnostic Repair Manual Safety Replacement PartsTable of Contents Section Specifications & Charts Section Exploded Views / Part NumbersMagnetism Electromagnetic FieldsElectromagnetic Induction Simple AC Generator More Sophisticated AC GeneratorGenerator Operating Diagram Field Boost Generator AC Connection SystemLine Breakers 120 Volts only Connection for 120 Volts Only Reconnection for Dual Voltage OutputRotor Assembly Stator AssemblyExcitation Circuit Components Battery Charge ComponentsBrush Holder GeneralVoltage Regulator Adjustment ProcedureCrankcase Breather DescriptionControl Panel Component Identification Install BreatherInstall oil vapor collector and retainer Check BreatherInsulation Resistance Testers Cleaning the GeneratorEffects of Dirt and Moisture Drying the GeneratorCloth or Compressed AIR Brushing and Vacuum CleaningStator Insulation Resistance Stator SHORT-TO-GROUND TestsTesting Rotor Insulation Testing Rotor InsulationTesting Stator Insulation MegohmmeterMeasuring AC Voltage MetersVOM Measuring DC VoltageMeasuring AC Frequency Measuring CurrentMeasuring Resistance Ampere Electrical UnitsOhms LAW VoltIntroduction Operational AnalysisCircuit CONDITION- Rest Circuit CONDITION- Priming Circuit CONDITION- Cranking Circuit CONDITION-RUNNING Choke Heater CHCircuit CONDITION- Shutdown Circuit CONDITION- Fault Shutdown Sure Switch LOPBattery Cables BatteryRecommended Battery Engine Controller Circuit BoardFuel Primer Switch START-STOP SwitchAMP Fuse Starter Contactor Relay Starter Motor Troubleshooting Flowcharts Troubleshooting Flowcharts Troubleshooting Flowcharts Troubleshooting Flowcharts Troubleshooting Flowcharts Troubleshooting Flowcharts Troubleshooting Flowcharts Troubleshooting Flowcharts Troubleshooting Flowcharts Troubleshooting Flowcharts Troubleshooting Flowcharts Test 2- Check Engine Governor ProcedureTest 1- Check NO-LOAD Voltage Frequency DiscussionTest 4- Fixed Excitation TEST/ROTOR AMP Draw Governor AdjustmentTest 3- Test Excitation Circuit Breaker If continuity was indicated, go to TestSet the VOM to measure AC voltage Test 5- Wire ContinuityRe-connect Wire 11 and Wire 22 to the Voltage Regulator Set a VOM to its Rx1 scaleTest 6- Check Field Boost Test 7 Test Stator DPE WindingIf field boost checks good, replace the Voltage Regulator 11S 22S Test 8- Check Sensing Leads / Power WindingsAcross Wires Ohms Model OhmsTest 9- Check Brush Leads Test 10 Check Brushes & Slip RingsTest 12 Check Main Circuit Breaker Test 11- Check Rotor AssemblyTance Tests Procedure Replace the Rotor if it fails the testBattery Charge Rectifier BCR is a full wave rectifier Test 15 Check Battery Charge OutputTest 16 Check Battery Charge Rectifier Test 13- Check Load Voltage Frequency10. Battery Charge Rectifier Short to GroundAlso see Fuel Primer Switch, Test 19- Test Primer SwitchSet a VOM to read battery voltage 12 VDC Test 18 TRY Cranking the EngineTest 20- Check Fuel Pump 13. The LPG Fuel Solenoid FSTest 22- Check Battery & Cables Test 23- Check Power Supply to Circuit BoardTest 21- Check 7.5 AMP Fuse Test 24 Check START-STOP Switch 17. Start-Stop SwitchTest 26- Check Starter Contactor Relay Set a VOM to measure DC voltage 12 VDCTest 26A Check Starter Contactor Test 27 Check Starter MotorConditions Affecting Starter Motor Performance Measuring Current Checking the PinionTools for Starter Performance Test TachometerTest Bracket Testing Starter MotorTest 28- Check Fuel Supply Remove Starter Motor28 LP Gas Carburetion Diagram Discussion LPG ModelsBattery voltage is not measured, proceed to Step Test 29 Check Wire 14 Power SupplyTest 30 Check Wire Crank the engine. The meter should indicate battery voltageTest 31 Check Fuel Solenoid Gasoline Models Test 32 Check Ignition SparkCylinder Balance Test Conclusion No cylinder is weakest of the two cylindersTest 34 Check and Adjust Ignition Magnetos Test 33 Check Spark Plugs37. Setting Ignition Magneto Armature Air Gap Checking Flywheel Magnet Test 35 Check Valve AdjustmentAdjusting Valve Clearance Flywheel KEYInstall Rocker ARM Cover Test 36 Check CarburetionTest 37 Check Choke Solenoid 43. Connector Repeat Steps 1 through 8 on remaining cylinder Adjust the regulated pressure on the gauge to 80 psiDown Test / Compression Test Check CompressionTest 39 Check OIL Pressure Switch Test 40 Test OIL Temperature SwitchIf all steps check GOOD, go to Test Test 41 Test Choke Heater Test 42 Check LPG Fuel SolenoidShort to Ground 49. Fuel Solenoid Stator Removal Major DisassemblyENCLOSURE/PANEL Removal Rotor RemovalBelt Tensioning Engine RemovalStarter Removal FLYWHEEL/MAGNETO Removal Page Section Exploded Views / Part Numbers Part NO. QTY Description Enclosure Drawing No E1011-B QTY Description Sheet Metal Drawing No E1012-E QTY Description Flywheel Assy GT-990Control Panel Drawing No E1013-A Switch 6A Spdt Not Shown Wire ASM GRD STD ConnSwitch Spdt ON-MOM-ON PANEL, TOP ControlTwin Engine Drawing No E1014-B ASSEMBLY, Head #1 ASSEMBLY, Crankcase RVASSEMBLY, Breather ASSEMBLY, OIL Fill CAPLP Regulator Drawing No E1530 SOLENOID, Twin Regulator CASTING, Twin Regulator HousingWasher Flat M4 SPRING-SOLENOID PlungerSpecifications & Charts Generator Specifications Nominal Resistances of Generator Windings AT 68FEngine Speeds and Voltage Specifications Page Electrical Data Electrical Data PO BOX 297 WHITEWATER, WI

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