Kohler command pro PCH740 User manual

PCH680, PCH740
Service Manual
Propane Electronic Fuel Injection (EFI)
KohlerEngines.com24 690 32 Rev. A 1
2 Safety
3 Maintenance
5 Specifications
14 Tools and Aids
17 Troubleshooting
21 Air Cleaner/Intake
22 Propane Electronic Fuel Injection (EFI) System
47 Lubrication System
49 Electrical System
54 Starter System
58 Disassembly/Inspection and Service
74 Reassembly
IMPORTANT: Read all safety precautions and instructions carefully before operating equipment. Refer to operating
instruction of equipment that this engine powers.
Ensure engine is stopped and level before performing any maintenance or service.

Safety
2 24 690 32 Rev. AKohlerEngines.com
SAFETY PRECAUTIONS
WARNING: A hazard that could result in death, serious injury, or substantial property damage.
CAUTION: A hazard that could result in minor personal injury or property damage.
NOTE: is used to notify people of important installation, operation, or maintenance information.
WARNING
Explosive Fuel can
cause fires and severe
burns.
If a gaseous odor is
detected, ventilate
area and contact an
authorized service
technician.
Propane is extremely flammable
and is heavier than air and tends
to settle in low areas where a
spark or flame could ignite gas.
Do not start or operate this engine
in a poorly ventilated area where
leaking gas could accumulate and
endanger safety of persons in
area.
To ensure personal safety,
installation and repair of propane
fuel supply systems must be
performed only by qualified
propane system technicians.
Improperly installed and
maintained propane equipment
could cause fuel supply system or
other components to malfunction,
causing gas leaks.
Observe federal, state and local
laws governing propane fuel,
storage, and systems.
WARNING
Rotating Parts can cause
severe injury.
Stay away while engine
is in operation.
Keep hands, feet, hair, and
clothing away from all moving
parts to prevent injury. Never
operate engine with covers,
shrouds, or guards removed.
CAUTION
Failure to utilize or
reassemble debris
screen as designed could
result in debris screen
failure and serious
personal injury.
WARNING
Carbon Monoxide can
cause severe nausea,
fainting or death.
Avoid inhaling exhaust
fumes.
Engine exhaust gases contain
poisonous carbon monoxide.
Carbon monoxide is odorless,
colorless, and can cause death if
inhaled.
WARNING
Accidental Starts can
cause severe injury or
death.
Disconnect and ground
spark plug lead(s) before
servicing.
Before working on engine or
equipment, disable engine as
follows: 1) Disconnect spark plug
lead(s). 2) Disconnect negative (–)
battery cable from battery.
WARNING
Hot Parts can cause
severe burns.
Do not touch engine
while operating or just
after stopping.
Never operate engine with heat
shields or guards removed.
WARNING
Cleaning Solvents can
cause severe injury or
death.
Use only in well
ventilated areas away
from ignition sources.
Carburetor cleaners and solvents
are extremely flammable. Follow
cleaner manufacturer’s warnings
and instructions on its proper and
safe use. Never use gasoline as a
cleaning agent.
CAUTION
Electrical Shock can
cause injury.
Do not touch wires while
engine is running.
CAUTION
Damaging Crankshaft
and Flywheel can cause
personal injury.
Using improper procedures can
lead to broken fragments. Broken
fragments could be thrown from
engine. Always observe and use
precautions and procedures when
installing flywheel.
WARNING
High Pressure Fluids can
puncture skin and cause
severe injury or death.
Do not work on fuel
system without proper
training or safety
equipment.
Fluid puncture injuries are highly
toxic and hazardous. If an injury
occurs, seek immediate medical
attention.

Maintenance
324 690 32 Rev. A KohlerEngines.com
MAINTENANCE INSTRUCTIONS
WARNING
Before working on engine or equipment, disable engine as
follows: 1) Disconnect spark plug lead(s). 2) Disconnect
negative (–) battery cable from battery.
Accidental Starts can cause severe injury or
death.
Disconnect and ground spark plug lead(s)
before servicing.
Normal maintenance, replacement or repair of emission control devices and systems may be performed by any repair
establishment or individual; however, warranty repairs must be performed by a Kohler authorized dealer.
MAINTENANCE SCHEDULE
Every 25 Hours1
●Service/replace low-profile precleaner (if equipped). Air Cleaner/Intake
Every 100 Hours1
●Check oil cooler fins, clean as necessary (if equipped). Air Cleaner/Intake
●Change oil. Lubrication System
●Replace low-profile air cleaner element (if equipped). Air Cleaner/Intake
●Remove cooling shrouds and clean cooling areas. Air Cleaner/Intake
Every 150 Hours1
●Check heavy-duty filter minder. Air Cleaner/Intake
●Inspect heavy-duty air filter paper element and inlet screen area. Air Cleaner/Intake
Every 200 Hours1
●Change oil filter. Lubrication System
●Replace unique EFI fuel filters.
Every 300 Hours1
●Replace heavy-duty air cleaner element and check inner element. Air Cleaner/Intake
Every 500 Hours or Annually1
●Check all lines (high pressure/vacuum) including fittings for leaks. Fuel System
●Drain vaporizer/regulator of accumulated fuel deposits. Fuel System
●Replace spark plugs and set gap. Electrical System
Every 500 Hours or Annually1,2
●Inspect lock-off assembly for damage/leakage. Fuel System
●Have combustion deposits removed if using non-synthetic oil.
Every 600 Hours or Annually1
●Replace heavy-duty air cleaner inner element. Air Cleaner/Intake
Every 1500 Hours1,2
●Have vaporizer/regulator tested. Fuel System
1Perform these procedures more frequently under severe, dusty, dirty conditions.
2Must be performed by a Kohler authorized dealer or qualified propane personnel only.
REPAIRS/SERVICE PARTS
Kohler genuine service parts can be purchased from Kohler authorized dealers. To find a local Kohler authorized
dealer visit KohlerEngines.com or call 1-800-544-2444 (U.S. and Canada).

Maintenance
4 24 690 32 Rev. AKohlerEngines.com
OIL RECOMMENDATIONS
Synthetic oil is recommended for use in propane fueled
engines. Non-synthetic oil must be low ash* rated oil.
Oils (including synthetic) must meet API (American
Petroleum Institute) service class SG, SH, SJ, or SL.
Select viscosity based on air temperature at time of
operation as shown in table below.
*Low ash is defined as less than 1% sulfated ash.
FUEL RECOMMENDATIONS
WARNING
Explosive Fuel can cause fires and severe
burns.
If a gaseous odor is detected, ventilate area
and contact an authorized service technician.
Propane is extremely flammable and is heavier than
air and tends to settle in low areas where a spark or
flame could ignite gas. Do not start or operate this
engine in a poorly ventilated area where leaking gas
could accumulate and endanger safety of persons in
area.
To ensure personal safety, installation and repair of
propane fuel supply systems must be performed only
by qualified propane system technicians. Improperly
installed and maintained propane equipment could
cause fuel supply system or other components to
malfunction, causing gas leaks.
Observe federal, state and local laws governing
propane fuel, storage, and systems.
This engine is certified to operate on commercial
propane (per GPA STD 2140). If you have any
questions, contact your propane supplier.
Propane from an appropriate propane fuel tank (supplied
separately) is required to operate this engine.
STORAGE
If engine will be out of service for 2 months or more
follow procedure below.
1. Change oil while engine is still warm from operation.
Remove spark plug(s) and pour about 1 oz. of
engine oil into cylinder(s). Replace spark plug(s) and
crank engine slowly to distribute oil.
2. Disconnect negative (-) battery cable.
3. Separate propane tank from unit and store
separately in an area designated for safe propane
tank storage.
4. Store engine in a clean, dry place.

Specifications
524 690 32 Rev. A KohlerEngines.com
Dimensions in millimeters.
Inch equivalents shown in [ ].
FLYWHEEL SIDE
138.19
[5.440]
AIR FILTER COVER
ASSEMBLY REMOVAL
VALVE COVER
29.24 [1.151]
SPARK PLUG BOOT
94.01
[3.701]
413.75
[16.289]
OIL FILL
132.54
[5.218]
AIR FILTER COVER
ASSEMBLY REMOVAL
231.81 [9.126]
SAFETY AIR FILTER
ELEMENT REMOVAL
344.13 [13.548]
PRIMARY AIR FILTER
ELEMENT REMOVAL
41.35 [1.628]
SPARK PLUG
BOOT REMOVAL
71.27 [2.806]
SPARK PLUG REMOVAL
71.04 [2.797]
SPARK PLUG
REMOVAL
320.71
[12.626]
SPARK
PLUG
BOOT
REMOVAL
319.21
[12.567]
SPARK
PLUG
REMOVAL
29.81 [1.174]
SPARK PLUG BOOT
OIL FILTER
20˚ 20˚
319.10
[12.563]
SPARK
PLUG
REMOVAL
320.65
[12.624]
SPARK
PLUG
BOOT
REMOVAL
70.11 [2.760]
SPARK PLUG
BOOT REMOVAL
15.50
[0.610]
OIL FILTER
REMOVAL
92.10
[3.626] ENGINE MOUNTING SURFACE
MOUNTING HOLE“A” ENGINE
184.20
[7.252]
134.79
[5.307]
139.99
[5.512]
CRANKSHAFT
4X Ø 10.3 [0.406] MOUNTING HOLES (THRU)
ENGINE MOUNTING SURFACE
MOUNTING HOLE“A”
LIFT STRAP
444.77
[17.511]
STARTER SIDE
51.00
[2.008]
OIL DRAIN PLUG 3/8”NPT
12.28
[0.483]
89.00
[3.504]
67.50
[2.657]
MUFFLER MOUNTING
BOSSES
12.00
[0.472]
EXHAUST
PORT #1
50.00
[1.969]
SPARK PLUG
OIL FILL
DIPSTICK
30.00
[1.181]
SPARK PLUG
OIL FILTER SIDE
ENGINE MOUNTING SURFACE
OIL DRAIN PLUG 3/8”NPT
353.02
[13.898]
209.95
[8.266]
51.95
[2.045]
MOUNTING
HOLE“A”
67.50
[2.657]
MUFFLER MOUNTING
BOSSES
32.00
[1.260]
EXHAUST
PORT #2
622.28
[24.499]
REGULATOR RECTIFIER
101.45
[3.994]
85.50
[3.366]
155.52
[6.123]
152.08
[5.987]
OIL FILTER
64.02
[2.520]
99.93
[3.934]
52.75
[2.077]
OIL FILTER
4.07
[0.160]
PILOT 89.00
[3.504]
12.28
[0.483]
15.07
[0.593]
Ø 28.45 [1.120]
Ø 47.0-50.0
7/16-20 UNF-2B INCH 38.1
CTSK Ø 12.5-14.5 X 60˚
4 X Ø 25.0
7/16-14 UNF-2B INCH 21.0
CTSK Ø 13.5 X 90˚
LIFT STRAP
334.79
[13.181]
75.28
[2.964]
122.11
[4.808]
308.12
[12.131]
SOLENOID
SHIFT
STARTER
65.00
[2.559]
MUFFLER
MOUNTING
30˚
30˚
M8 X 1.25
4 STUDS
50.00
[1.969]
EXHAUST
PORT #1
MOUNTING
HOLES
50.00
[1.969]
EXHAUST
PORT #2
MOUNTING
HOLES
283.58
[11.164]
MUFFLER
MOUNTING
PTO SIDE
REGULATOR ASSEMBLY
ENGINE MOUNTING SURFACE
MOUNTING HOLE“A”
4 X Ø 25.0
3/8-16 UNC-2B INCH 21.0
CTSK Ø 12.0 X 90˚
4 X Ø 21.0
5/16-24 UNF-2B INCH 17.0
CTSK Ø 7.0 X 90˚
PILOT Ø 146.05 [5.750]
Engine Dimensions with Heavy-Duty Air Cleaner

Specifications
6 24 690 32 Rev. AKohlerEngines.com
Engine Dimensions with Low-Profile Air Cleaner
Dimensions in millimeters.
Inch equivalents shown in [ ].
FLYWHEEL SIDE
299.14
[11.777]
413.75
[16.289]
59.90 [2.358]
AIR CLEANER
COVER REMOVAL
OIL FILL
VALVE COVER
VALVE COVER
AIR CLEANER COVER
72.41
[2.851]
SPARK PLUG
REMOVAL
72.87
[2.869]
SPARK PLUG
REMOVAL
319.23
[12.568]
SPARK PLUG
REMOVAL
320.88
[12.633]
SPARK
PLUG
BOOT
REMOVAL 18.53
[0.729]
OIL FILTER
REMOVAL
20˚ 20˚
29.24
[1.151]
SPARK PLUG
BOOT
473.01
[18.622]
319.12
[12.564]
SPARK PLUG
REMOVAL
320.68
[12.625]
SPARK
PLUG
BOOT
REMOVAL
CRANKSHAFT
ENGINE MOUNTING SURFACE
ENGINE
MOUNTING HOLE “A”
134.80
[5.307]
139.99
[5.512]
184.20
[7.252]
92.10
[3.626]
4X Ø 10.8 [0.425] MOUNTING HOLES (THRU)
70.21
[2.764]
SPARK
PLUG
BOOT
REMOVAL
71.29
[2.807]
SPARK PLUG
BOOT
REMOVAL
29.47
[1.160]
SPARK PLUG
BOOT
444.
6
[17.5
0
LIFT STRAP
STARTER SIDE
ENGINE MOUNTING SURFACE
MOUNTING HOLE“A”
89.00
[3.504]
51.00
[2.008]
12.26
[0.483]
OIL DRAIN PLUG 3/8 NPT [INCH]
50.00 [1.969]
SPARK PLUG
REGULATOR RECTIFIER
ENGINE MOUNTING SURFACE
OIL FILTER SIDE
DIPSTICK OIL FILL
64.02
[2.520]
155.58
[6.125]
4.04
[0.159]
PILOT
152.08
[5.987]
OIL FILTER
52.75 [2.077]
OIL FILTER
99.96
[3.939]
89.00
[3.504]
MOUNTING HOLE “A” 51.00
[2.008]
15.07
[0.593]
12.26
[0.483]
OIL DRAIN PLUG 3/8”NPT
Ø 36.25 [1.427]
95.50
[3.760]
113.15
[4.455]
X Ø 47.5-50.0
5/8-18 UNF-2B INCH 38.1
CTSK Ø 19.0-21.0 X 60˚
115.90
[4.563]
353.02
[13.898]
69.02
[2.717]
30.00 [1.181]
SPARK PLUG
PTO SIDE
REGULATOR ASSEMBLY
ENGINE MOUNTING SURFACE
308.12
[12.131]
334.79
[13.181]
75.29
[2.964]
SOLENOID SHIFT STARTER
MOUNTING HOLE“A”
LIFT STRAP
PILOT Ø 146.05
[5.750]
4 X Ø 21.0
5/16-24 UNF-2B INCH 17.0
CTSK Ø 7.0 X 90˚
4 X Ø 25.0
3/8-16 UNC-2B INCH 21.0
CTSK Ø 12.0 X 90˚
4 X Ø 25.0
7/16-14 UNF-2B INCH 21.0
CTSK Ø 13.5 X 90˚

Specifications
724 690 32 Rev. A KohlerEngines.com
ENGINE IDENTIFICATION NUMBERS
Kohler engine identification numbers (model, specification and serial) should be referenced for efficient repair,
ordering correct parts, and engine replacement.
Model. . . . . . . . . . . . . . . . . . . . . PCH680
Propane EFI Command Engine
Horizontal Shaft
Numerical Designation
Specification . . . . . . . . . . . . . . . PCH680-3001
Serial . . . . . . . . . . . . . . . . . . . . . 4323500328
Year Manufactured Code Factory Code
Code Year
43 2013
44 2014
45 2015
GENERAL SPECIFICATIONS3,6 PCH680, PCH740
Bore 83 mm (3.27 in.)
Stroke 69 mm (2.72 in.)
Displacement 747 cc (45.6 cu. in.)
Oil Capacity (refill) 1.6-1.9 L (1.7-2.0 U.S. qt.)
Maximum Angle of Operation
(@ full oil level)425°
TORQUE SPECIFICATIONS3,5 PCH680, PCH740
Blower Housing
Into cored aluminum hole or weld nut
M5
M6
Into extruded hole in sheet metal
M5
M6
6.2 N·m (55 in. lb.) into new holes
4.0 N·m (35 in. lb.) into used holes
10.7 N·m (95 in. lb.) into new holes
7.3 N·m (65 in. lb.) into used holes
2.8 N·m (25 in. lb.) into new holes
2.3 N·m (20 in. lb.) into used holes
2.8 N·m (25 in. lb.) into new holes
2.3 N·m (20 in. lb.) into used holes
Closure Plate
Fastener 25.6 N·m (227 in. lb.)
Connecting Rod
Cap Fastener (torque in increments) 13.6 N·m (120 in. lb.)
3 Values are in Metric units. Values in parentheses are English equivalents.
4Exceeding maximum angle of operation may cause engine damage from insufficient lubrication.
5Lubricate threads with engine oil prior to assembly.
6Any and all horsepower (hp) references by Kohler are Certified Power Ratings and per SAE J1940 & J1995 hp
standards. Details on Certified Power Ratings can be found at KohlerEngines.com.

Specifications
8 24 690 32 Rev. AKohlerEngines.com
TORQUE SPECIFICATIONS3,5 PCH680, PCH740
Crankcase
Breather Cover Fastener 11.3 N·m (100 in. lb.) into new holes
7.3 N·m (65 in. lb.) into used holes
Oil Temperature Sensor (into breather cover) 7.3 N·m (65 in. lb.)
Oil Drain Plug 13.6 N·m (10 ft. lb.)
Cylinder Head
Hex Flange Nut (torque in 2 increments) first to 16.9 N·m (150 in. lb.)
finally to 33.9 N·m (300 in. lb.)
Rocker Arm Screw 11.9 N·m (105 in. lb.)
Fan/Flywheel
Flywheel Retaining Screw 71.6 N·m (52.8 ft. lb.)
Metal Debris Screen Fastener (to flywheel) 9.9 N·m (88 in. lb.)
Fuel Vaporizer/Regulator/Lock-Off
Regulator to Bracket Nut 19.8 N·m (175 in. lb.)
Regulator Bracket Mounting Screw 11.9 N·m (105 in. lb.)
Lock-Off Valve Body Nut 6.5 N·m (57 in. lb.)
Lock-Off Valve Body 20 N·m (177 in. lb.)
Fuel Outlet Fitting Mounting Screws 2.9 N·m (26 in. lb.)
Fuel Inlet Fitting 20 N·m (177 in. lb.)
Governor
Lever Nut 7.1 N·m (63 in. lb.)
Ignition
Spark Plug 27 N·m (20 ft. lb.)
Coil Fastener 10.2 N·m (90 in. lb.)
Crankshaft Position Sensor Screw 6.2 N·m (55 in. lb.)
Crankshaft Position Sensor Bracket Screw 7.3 N·m (65 in. lb.)
Electronic Control Unit Screw 6.2 N·m (55 in. lb.)
Rectifier-Regulator Ground Strap Fastener 2.8 N·m (25 in. lb.) into new holes
2.3 N·m (20 in. lb.) into used holes
Rectifier-Regulator Fastener 1.4 N·m (12.6 in. lb.)
Intake Manifold
Fastener (torque in 2 increments) first to 7.8 N·m (69 in. lb.)
finally to 10.5 N·m (93 in. lb.)
Manifold Absolute Pressure (MAP) Sensor Fastener 7.3 N·m (65 in. lb.)
Air Cleaner to Throttle Body Fastener Nut 8.2 N·m (73 in. lb.)
Air Cleaner Mounting Bracket Fastener 5.8 N·m (51 in. lb.)
Fuel Injector Cap Fastener 7.3 N·m (65 in. lb.)
Muffler
Retaining Nut 27.8 N·m (246 in. lb.)
Oxygen Sensor 50.1 N·m (37 ft . lb.)
3 Values are in Metric units. Values in parentheses are English equivalents.
5Lubricate threads with engine oil prior to assembly.

Specifications
924 690 32 Rev. A KohlerEngines.com
TORQUE SPECIFICATIONS3,5 PCH680, PCH740
Oil Cooler
Oil Cooler/Adapter Nipple 28.5 N·m (21 ft . lb.)
Fastener
Into Blower Housing
Between Oil Cooler Hoses
2.8 N·m (25 in. lb.)
2.3 N·m (20 in. lb.)
Speed Control Bracket
Fastener assembled to cylinder heads 10.7 N·m (95 in. lb.) into new holes
7.3 N·m (65 in. lb.) into used holes
Fastener assembled to blower housing 2.8 N·m (25 in. lb.) into new holes
2.3 N·m (20 in. lb.) into used holes
Starter Assembly
Thru Bolt 5.6-9.0 N·m (49-79 in. lb.)
Mounting Screw 16.0 N·m (142 in. lb.)
Brush Holder Mounting Screw 2.5-3.3 N·m (22-29 in. lb.)
Starter Solenoid
Mounting Hardware 4.0-6.0 N·m (35-53 in. lb.)
Nut, Positive (+) Brush Lead 8.0-11.0 N·m (71-97 in. lb.)
Stator
Mounting Screw 6.2 N·m (55 in. lb.) into new holes
4.0 N·m (35 in. lb.) into used holes
Valve Cover
Fastener 6.2 N·m (55 in. lb.)
CLEARANCE
SPECIFICATIONS3PCH680, PCH740
Camshaft
End Play (with shim) 0.101/0.406 mm (0.0040/0.0160 in.)
Running Clearance 0.025/0.105 mm (0.001/0.004 in.)
Bore I.D.
New
Max. Wear Limit
20.000/20.025 mm (0.7874/0.7884 in.)
20.038 mm (0.7889 in.)
Bearing Surface O.D.
New
Max. Wear Limit
19.920/19.975 mm (0.7843/0.7864 in.)
19.914 mm (0.7840 in.)
3 Values are in Metric units. Values in parentheses are English equivalents.
5Lubricate threads with engine oil prior to assembly.

Specifications
10 24 690 32 Rev. AKohlerEngines.com
CLEARANCE
SPECIFICATIONS3PCH680, PCH740
Connecting Rod
Connecting Rod-to-Crankpin
Running Clearance @ 21°C
(70°F)
New
Max. Wear Limit
0.043/0.073 mm (0.0017/0.0029 in.)
0.088 mm (0.0035 in.)
Connecting Rod-to-Crankpin
Side Clearance 0.26/0.63 mm (0.0102/0.0248 in.)
Connecting Rod-to-Piston Pin
Running Clearance @ 21°C
(70°F)
0.015/0.028 mm (0.0006/0.0011 in.)
Piston Pin End I.D. @ 21°C
(70°F)
New
Max. Wear Limit
17.015/17.023 mm (0.6699/0.6702 in.)
17.036 mm (0.6707 in.)
Crankcase
Governor Cross Shaft Bore I.D.
New
Max. Wear Limit
8.025/8.075 mm (0.3159/0.3179 in.)
8.088 mm (0.3184 in.)
Crankshaft
End Play (free) 0.025/0.635 mm (0.001/0.025 in.)
Bore (in crankcase)
New
Max. Wear Limit
40.972/40.997 mm (1.6131/1.6141 in.)
41.011 mm (1.6146 in.)
Bore (in closure plate)
New 40.974/41.000 mm (1.6131/1.6141 in.)
Crankshaft to Sleeve Bearing
(closure plate) Running
Clearance
New
0.03/0.12 mm (0.001/0.005 in.)
Crankshaft Bore (closure
plate)-to-Crankshaft Running
Clearance
New
0.039/0.087 mm (0.0015/0.0034 in.)
Flywheel End Main Bearing
Journal
O.D. - New
O.D. - Max. Wear Limit
Max. Taper Limit
Max. Out-of-Round Limit
40.913/40.935 mm (1.6107/1.6116 in.)
40.843 mm (1.608 in.)
0.022 mm (0.0009 in.)
0.025 mm (0.0010 in.)
Closure Plate End Main Bearing
Journal
O.D. - New
O.D. - Max. Wear Limit
Max. Taper Limit
Max. Out-of-Round Limit
40.913/40.935 mm (1.6107/1.6116 in.)
40.843 mm (1.608 in.)
0.022 mm (0.0009 in.)
0.025 mm (0.0010 in.)
Connecting Rod Journal
O.D. - New
O.D. - Max. Wear Limit
Max. Taper Limit
Max. Out-of-Round Limit
35.950/35.973 mm (1.4153/1.4163 in.)
35.941 mm (1.415 in.)
0.018 mm (0.0007 in.)
0.025 mm (0.0010 in.)
Crankshaft T.I.R.
PTO End, Crank in Engine
Entire Crank, in V-Blocks
0.279 mm (0.0110 in.)
0.10 mm (0.0039 in.)
3 Values are in Metric units. Values in parentheses are English equivalents.
5Lubricate threads with engine oil prior to assembly. 5Lubricate threads with engine oil prior to assembly.

Specifications
1124 690 32 Rev. A KohlerEngines.com
CLEARANCE
SPECIFICATIONS3PCH680, PCH740
Cylinder Bore
Bore I.D.
New 83.006/83.031 mm (3.2680/3.2689 in.)
O.D. - Max. Wear Limit 83.081 mm (3.2709 in.)
Max. Out-of-Round Limit 0.120 mm (0.0047 in.)
Max. Taper 0.05 mm (0.0020 in.)
Cylinder Head
Max. Out-of-Flatness 0.01 mm (0.004 in.)
Governor
Governor Cross Shaft -to-
Crankcase Running Clearance
0.025/0.126 mm (0.0009/0.0049 in.)
Cross Shaft O.D.
New
Max. Wear Limit
7.949/8.000 mm (0.3129/0.3149 in.)
7.936 mm (0.3124 in.)
Governor Gear Shaft -to-
Governor Gear Running
Clearance
0.090/0.160 mm (0.0035/0.0063 in.)
Gear Shaft O.D.
New
Max. Wear Limit
5.990/6.000 mm (0.2358/0.2362 in.)
5.977 mm (0.2353 in.)
Ignition
Spark Plug Gap 0.76 mm (0.030 in.)
Crankshaft Position Sensor Air
Gap 0.2-0.7 mm (0.008-0.027 in.)
Piston, Piston Rings, and Piston
Pin
Piston-to-Piston Pin Running
Clearance
0.006/0.017 mm (0.0002/0.0007 in.)
Pin Bore I.D.
New
Max. Wear Limit
17.006/17.012 mm (0.6695/0.6698 in.)
17.025 mm (0.6703 in.)
Pin O.D.
New
Max. Wear Limit
16.995/17.000 mm (0.6691/0.6693 in.)
16.994 mm (0.6691 in.)
Top Compression Ring-to-
Groove Side Clearance
0.030/0.070 mm (0.001/0.0026 in.)
Middle Compression Ring-to-
Groove Side Clearance
0.030/0.070 mm (0.001/0.0026 in.)
Oil Control Ring-to-Groove Side
Clearance
0.060/0.190 mm (0.0022/0.0073 in.)
Top Compression Ring End Gap
New Bore 0.189/0.277 mm (0.0074/0.0109 in.)
Used Bore (Max.) 0.531 mm (0.0209 in.)
Center Compression Ring End
Gap
New Bore 1.519/1.797 mm (0.0598/0.0708 in.)
Used Bore (Max.) 2.051 mm (0.0808 in.)
3 Values are in Metric units. Values in parentheses are English equivalents.

Specifications
12 24 690 32 Rev. AKohlerEngines.com
CLEARANCE
SPECIFICATIONS3PCH680, PCH740
Piston, Piston Rings, and Piston Pin (continued)
Thrust Face O.D. 782.978 mm (3.2668 in.)
Max. Wear Limit 82.833 mm (3.2611 in.)
Piston Thrust Face-to Cylinder
Bore7Running Clearance
New 0.019/0.062 mm (0.0007/0.0024 in.)
Valves and Valve Lifters
Hydraulic Lifter to Crankcase
Running Clearance
0.011/0.048 mm (0.0004/0.0019 in.)
Intake Valve Stem-to-Valve
Guide Running Clearance
0.040/0.078 mm (0.0016/0.0031 in.)
Exhaust Valve Stem-to-Valve
Guide Running Clearance
0.052/0.090 mm (0.0020/0.0035 in.)
Intake Valve Guide I.D.
New
Max. Wear Limit
7.040/7.060 mm (0.2772/0.2780 in.)
7.134 mm (0.2809 in.)
Exhaust Valve Guide I.D.
New
Max. Wear Limit
7.040/7.060 mm (0.2772/0.2780 in.)
7.159 mm (0.2819 in.)
Valve Guide Reamer Size
Standard
0.25 mm O.S.
7.050 mm (0.2776 in.)
7.300 mm (0.2874 in.)
Intake Valve Minimum Lift 8.07 mm (0.3177 in.)
Exhaust Valve Minimum Lift 8.07 mm (0.3177 in.)
Nominal Valve Seat Angle 45°
3 Values are in Metric units. Values in parentheses are English equivalents.
7Measure 6 mm (0.236 in.) above bottom of piston skirt at right angles to piston pin.

Specifications
1324 690 32 Rev. A KohlerEngines.com
GENERAL TORQUE VALUES
Metric Fastener Torque Recommendations for Standard Applications
Property Class Noncritical
Fasteners
Into Aluminum
Size 4.8 5.8 8.8 10.9 12.9
Tightening Torque: N·m (in. lb.) ± 10%
M4 1.2 (11) 1.7 (15) 2.9 (26) 4.1 (36) 5.0 (44) 2.0 (18)
M5 2.5 (22) 3.2 (28) 5.8 (51) 8.1 (72) 9.7 (86) 4.0 (35)
M6 4.3 (38) 5.7 (50) 9.9 (88) 14.0 (124) 16.5 (146) 6.8 (60)
M8 10.5 (93) 13.6 (120) 24.4 (216) 33.9 (300) 40.7 (360) 17.0 (150)
Tightening Torque: N·m (ft. lb.) ± 10%
M10 21.7 (16) 27.1 (20) 47.5 (35) 66.4 (49) 81.4 (60) 33.9 (25)
M12 36.6 (27) 47.5 (35) 82.7 (61) 116.6 (86) 139.7 (103) 61.0 (45)
M14 58.3 (43) 76.4 (56) 131.5 (97) 184.4 (136) 219.7 (162) 94.9 (70)
Torque Conversions
N·m = in. lb. x 0.113 in. lb. = N·m x 8.85
N·m = ft. lb. x 1.356 ft. lb. = N·m x 0.737
English Fastener Torque Recommendations for Standard Applications
Bolts, Screws, Nuts and Fasteners Assembled Into Cast Iron or Steel Grade 2 or 5 Fasteners
Into Aluminum
Size Grade 2 Grade 5 Grade 8
Tightening Torque: N·m (in. lb.) ± 20%
8-32 2.3 (20) 2.8 (25) — 2.3 (20)
10-24 3.6 (32) 4.5 (40) — 3.6 (32)
10-32 3.6 (32) 4.5 (40) — —
1/4-20 7.9 (70) 13.0 (115) 18.7 (165) 7.9 (70)
1/4-28 9.6 (85) 15.8 (140) 22.6 (200) —
5/16-18 17.0 (150) 28.3 (250) 39.6 (350) 17.0 (150)
5/16-24 18.7 (165) 30.5 (270) — —
3/8-16 29.4 (260) — — —
3/8-24 33.9 (300) — — —
Tightening Torque: N·m (ft. lb.) ± 20%
5/16-24 — — 40.7 (30) —
3/8-16 — 47.5 (35) 67.8 (50) —
3/8-24 — 54.2 (40) 81.4 (60) —
7/16-14 47.5 (35) 74.6 (55) 108.5 (80) —
7/16-20 61.0 (45) 101.7 (75) 142.5 (105) —
1/2-13 67.8 (50) 108.5 (80) 155.9 (115) —
1/2-20 94.9 (70) 142.4 (105) 223.7 (165) —
9/16-12 101.7 (75) 169.5 (125) 237.3 (175) —
9/16-18 135.6 (100) 223.7 (165) 311.9 (230) —
5/8-11 149.5 (110) 244.1 (180) 352.6 (260) —
5/8-18 189.8 (140) 311.9 (230) 447.5 (330) —
3/4-10 199.3 (147) 332.2 (245) 474.6 (350) —
3/4-16 271.2 (200) 440.7 (325) 637.3 (470) —

Tools and Aids
14 24 690 32 Rev. AKohlerEngines.com
Certain quality tools are designed to help you perform specific disassembly, repair, and reassembly procedures. By
using these tools, you can properly service engines easier, faster, and safer! In addition, you’ll increase your service
capabilities and customer satisfaction by decreasing engine downtime.
Here is a list of tools and their source.
SEPARATE TOOL SUPPLIERS
Kohler Tools
Contact your local Kohler source of
supply.
SE Tools
415 Howard St.
Lapeer, MI 48446
Phone [phone]
Toll Free 800-664-2981
Fax [phone]
Design Technology Inc.
768 Burr Oak Drive
Westmont, IL 60559
Phone [phone]
Fax [phone]
TOOLS
Description Source/Part No.
Alcohol Content Tester
For testing alcohol content (%) in reformulated/oxygenated fuels.
Kohler 25 455 11-S
Camshaft Endplay Plate
For checking camshaft endplay.
SE Tools KLR-82405
Camshaft Seal Protector (Aegis)
For protecting seal during camshaft installation.
SE Tools KLR-82417
Cylinder Leakdown Tester
For checking combustion retention and if cylinder, piston, rings, or valves are worn.
Individual component available:
Adapter 12 mm x 14 mm (Required for leakdown test on XT-6 engines)
Kohler 25 761 05-S
Design Technology Inc.
DTI-731-03
Dealer Tool Kit (Domestic)
Complete kit of Kohler required tools.
Components of 25 761 39-S
Ignition System Tester
Cylinder Leakdown Tester
Oil Pressure Test Kit
Rectifier-Regulator Tester (120 V AC/60Hz)
Kohler 25 761 39-S
Kohler 25 455 01-S
Kohler 25 761 05-S
Kohler 25 761 06-S
Kohler 25 761 20-S
Dealer Tool Kit (International)
Complete kit of Kohler required tools.
Components of 25 761 42-S
Ignition System Tester
Cylinder Leakdown Tester
Oil Pressure Test Kit
Rectifier-Regulator Tester (240 V AC/50Hz)
Kohler 25 761 42-S
Kohler 25 455 01-S
Kohler 25 761 05-S
Kohler 25 761 06-S
Kohler 25 761 41-S
Digital Vacuum/Pressure Tester
For checking crankcase vacuum.
Individual component available:
Rubber Adapter Plug
Design Technology Inc.
DTI-721-01
Design Technology Inc.
DTI-721-10
Electronic Fuel Injection (EFI) Diagnostic Software
For Laptop or Desktop PC.
Kohler 25 761 23-S
EFI Service Kit
For troubleshooting and setting up an EFI engine.
Components of 24 761 01-S
Fuel Pressure Tester
Noid Light
90° Adapter
In-line "T" Fitting
Code Plug, Red Wire
Code Plug, Blue Wire
Shrader Valve Adapter Hose
Kohler 24 761 01-S
Design Technology Inc.
DTI-019
DTI-021
DTI-023
DTI-035
DTI-027
DTI-029
DTI-037
Flywheel Puller
For properly removing flywheel from engine.
SE Tools KLR-82408

Tools and Aids
1524 690 32 Rev. A KohlerEngines.com
TOOLS
Description Source/Part No.
Hydraulic Valve Lifter Tool
For removing and installing hydraulic lifters.
Kohler 25 761 38-S
Ignition System Tester
For testing output on all systems, including CD.
Kohler 25 455 01-S
Inductive Tachometer (Digital)
For checking operating speed (RPM) of an engine.
Design Technology Inc.
DTI-110
Offset Wrench (K and M Series)
For removing and reinstalling cylinder barrel retaining nuts.
Kohler 52 455 04-S
Oil Pressure Test Kit
For testing/verifying oil pressure on pressure lubricated engines.
Kohler 25 761 06-S
Rectifier-Regulator Tester (120 volt current)
Rectifier-Regulator Tester (240 volt current)
For testing rectifier-regulators.
Components of 25 761 20-S and 25 761 41-S
CS-PRO Regulator Test Harness
Special Regulator Test Harness with Diode
Kohler 25 761 20-S
Kohler 25 761 41-S
Design Technology Inc.
DTI-031
DTI-033
Spark Advance Module (SAM) Tester
For testing SAM (ASAM and DSAM) on engines with SMART-SPARK™.
Kohler 25 761 40-S
Starter Servicing Kit (All Starters)
For removing and reinstalling drive retaining rings and brushes.
Individual component available:
Starter Brush Holding Tool (Solenoid Shift)
SE Tools KLR-82411
SE Tools KLR-82416
Triad/OHC Timing Tool Set
For holding cam gears and crankshaft in timed position while installing timing belt.
Kohler 28 761 01-S
Valve Guide Reamer (K and M Series)
For properly sizing valve guides after installation.
Design Technology Inc.
DTI-K828
Valve Guide Reamer O.S. (Command Series)
For reaming worn valve guides to accept replacement oversize valves. Can be used
in low-speed drill press or with handle below for hand reaming.
Kohler 25 455 12-S
Reamer Handle
For hand reaming using Kohler 25 455 12-S reamer.
Design Technology Inc.
DTI-K830
AIDS
Description Source/Part No.
Camshaft Lubricant (Valspar ZZ613) Kohler 25 357 14-S
Dielectric Grease (GE/Novaguard G661) Kohler 25 357 11-S
Dielectric Grease Loctite®51360
Kohler Electric Starter Drive Lubricant (Inertia Drive) Kohler 52 357 01-S
Kohler Electric Starter Drive Lubricant (Solenoid Shift) Kohler 52 357 02-S
RTV Silicone Sealant
Loctite®5900®Heavy Body in 4 oz. aerosol dispenser.
Only oxime-based, oil resistant RTV sealants, such as those listed, are approved
for use. Loctite®Nos. 5900®or 5910®are recommended for best sealing
characteristics.
Kohler 25 597 07-S
Loctite®5910®
Loctite®Ultra Black 598™
Loctite®Ultra Blue 587™
Loctite®Ultra Copper 5920™
Spline Drive Lubricant Kohler 25 357 12-S

Tools and Aids
16 24 690 32 Rev. AKohlerEngines.com
FLYWHEEL HOLDING TOOL ROCKER ARM/CRANKSHAFT TOOL
A flywheel holding tool can be made out of an old junk
flywheel ring gear and used in place of a strap wrench.
1. Using an abrasive cut-off wheel, cut out a six tooth
segment of ring gear as shown.
2. Grind off any burrs or sharp edges.
3. Invert segment and place it between ignition bosses
on crankcase so tool teeth engage flywheel ring
gear teeth. Bosses will lock tool and flywheel in
position for loosening, tightening, or removing with a
puller.
A spanner wrench to lift rocker arms or turn crankshaft
may be made out of an old junk connecting rod.
1. Find a used connecting rod from a 10 HP or larger
engine. Remove and discard rod cap.
2. Remove studs of a Posi-Lock rod or grind off
aligning steps of a Command rod, so joint surface is
flat.
3. Find a 1 in. long capscrew with correct thread size to
match threads in connecting rod.
4. Use a flat washer with correct I.D. to slip on
capscrew and approximately 1 in. O.D. Assemble
capscrew and washer to joint surface of rod.

1724 690 32 Rev. A KohlerEngines.com
Troubleshooting
Engine Cranks But Will Not Start
●Battery connected backwards.
●Blown fuse.
●Carburetor solenoid malfunction.
●Choke not closing.
●Clogged fuel line or fuel filter.
●Diode in wiring harness failed in open circuit mode.
●DSAI or DSAM malfunction.
●Empty fuel tank.
●Faulty electronic control unit.
●Faulty ignition coil(s).
●Faulty spark plug(s).
●Fuel pump malfunction-vacuum hose clogged or
leaking.
●Fuel shut-off valve closed.
●Ignition module(s) faulty or improperly gapped.
●Insufficient voltage to electronic control unit.
●Interlock switch is engaged or faulty.
●Key switch or kill switch in OFF position.
●Low oil level.
●Quality of fuel (dirt, water, stale, mixture).
●SMART-SPARKTM malfunction.
●Spark plug lead(s) disconnected.
Engine Starts But Does Not Keep Running
●Faulty carburetor.
●Faulty cylinder head gasket.
●Faulty or misadjusted choke or throttle controls.
●Fuel pump malfunction-vacuum hose clogged or
leaking.
●Intake system leak.
●Loose wires or connections that intermittently ground
ignition kill circuit.
●Quality of fuel (dirt, water, stale, mixture).
●Restricted fuel tank cap vent.
Engine Starts Hard
●Clogged fuel line or fuel filter.
●Engine overheated.
●Faulty ACR mechanism.
●Faulty or misadjusted choke or throttle controls.
●Faulty spark plug(s).
●Flywheel key sheared.
●Fuel pump malfunction-vacuum hose clogged or
leaking.
●Interlock switch is engaged or faulty.
●Loose wires or connections that intermittently ground
ignition kill circuit.
●Low compression.
●Quality of fuel (dirt, water, stale, mixture).
●Weak spark.
TROUBLESHOOTING GUIDE
When troubles occur, be sure to check simple causes which, at first, may seem too obvious to be considered. For
example, a starting problem could be caused by an empty fuel tank.
Some general common causes of engine troubles are listed below and vary by engine specification. Use these to
locate causing factors.
Engine Will Not Crank
●Battery is discharged.
●Faulty electric starter or solenoid.
●Faulty key switch or ignition switch.
●Interlock switch is engaged or faulty.
●Loose wires or connections that intermittently ground
ignition kill circuit.
●Pawls not engaging in drive cup.
●Seized internal engine components.
Engine Runs But Misses
●Carburetor adjusted incorrectly.
●Engine overheated.
●Faulty spark plug(s).
●Ignition module(s) faulty or improperly gapped.
●Incorrect crankshaft position sensor air gap.
●Interlock switch is engaged or faulty.
●Loose wires or connections that intermittently ground
ignition kill circuit.
●Quality of fuel (dirt, water, stale, mixture).
●Spark plug lead(s) disconnected.
●Spark plug lead boot loose on plug.
●Spark plug lead loose.
Engine Will Not Idle
●Engine overheated.
●Faulty spark plug(s).
●Idle fuel adjusting needle(s) improperly set.
●Idle speed adjusting screw improperly set.
●Inadequate fuel supply.
●Low compression.
●Quality of fuel (dirt, water, stale, mixture).
●Restricted fuel tank cap vent.
Engine Overheats
●Cooling fan broken.
●Excessive engine load.
●Fan belt failed/off.
●Faulty carburetor.
●High crankcase oil level.
●Lean fuel mixture.
●Low cooling system fluid level.
●Low crankcase oil level.
●Radiator, and/or cooling system components clogged,
restricted, or leaking.
●Water pump belt failed/broken.
●Water pump malfunction.
Engine Knocks
●Excessive engine load.
●Hydraulic lifter malfunction.
●Incorrect oil viscosity/type.
●Internal wear or damage.
●Low crankcase oil level.
●Quality of fuel (dirt, water, stale, mixture).

Troubleshooting
18 24 690 32 Rev. AKohlerEngines.com
Engine Loses Power
●Dirty air cleaner element.
●Engine overheated.
●Excessive engine load.
●Restricted exhaust.
●Faulty spark plug(s).
●High crankcase oil level.
●Incorrect governor setting.
●Low battery.
●Low compression.
●Low crankcase oil level.
●Quality of fuel (dirt, water, stale, mixture).
Engine Uses Excessive Amount of Oil
●Loose or improperly torqued fasteners.
●Blown head gasket/overheated.
●Breather reed broken.
●Clogged, broken, or inoperative crankcase breather.
●Crankcase overfilled.
●Incorrect oil viscosity/type.
●Worn cylinder bore.
●Worn or broken piston rings.
●Worn valve stems/valve guides.
Oil Leaks from Oil Seals, Gaskets
●Breather reed broken.
●Clogged, broken, or inoperative crankcase breather.
●Loose or improperly torqued fasteners.
●Piston blow by, or leaky valves.
●Restricted exhaust.
EXTERNAL ENGINE INSPECTION
NOTE: It is good practice to drain oil at a location away
from workbench. Be sure to allow ample time for
complete drainage.
Before cleaning or disassembling engine, make a
thorough inspection of its external appearance and
condition. This inspection can give clues to what
might be found inside engines (and cause) when it is
disassembled.
●Check for buildup of dirt and debris on crankcase,
cooling fins, grass screen, and other external surfaces.
Dirt or debris on these areas can cause overheating.
●Check for obvious fuel and oil leaks, and damaged
components. Excessive oil leakage can indicate a
clogged or inoperative breather, worn or damaged
seals or gaskets, or loose fasteners.
●Check air cleaner cover and base for damage or
indications of improper fit and seal.
●Check air cleaner element. Look for holes, tears,
cracked or damaged sealing surfaces, or other
damage that could allow unfiltered air into engine. A
dirty or clogged element could indicate insufficient or
improper maintenance.
●Check carburetor throat for dirt. Dirt in throat is further
indication that air cleaner was not functioning properly.
●Check if oil level is within operating range on dipstick.
If it is above, sniff for gasoline odor.
●Check condition of oil. Drain oil into a container; it
should flow freely. Check for metal chips and other
foreign particles.
Sludge is a natural by-product of combustion; a small
accumulation is normal. Excessive sludge formation
could indicate over rich fuel settings, weak ignition,
overextended oil change interval or wrong weight or
type of oil was used.
CLEANING ENGINE
WARNING
Cleaning Solvents can cause severe injury or
death.
Use only in well ventilated areas away from
ignition sources.
Carburetor cleaners and solvents are extremely
flammable. Follow cleaner manufacturer’s warnings
and instructions on its proper and safe use. Never use
gasoline as a cleaning agent.
After inspecting external condition of engine, clean
engine thoroughly before disassembly. Clean individual
components as engine is disassembled. Only clean
parts can be accurately inspected and gauged for wear
or damage. There are many commercially available
cleaners that will quickly remove grease, oil, and grime
from engine parts. When such a cleaner is used, follow
manufacturer’s instructions and safety precautions
carefully.
Make sure all traces of cleaner are removed before
engine is reassembled and placed into operation. Even
small amounts of these cleaners can quickly break down
lubricating properties of engine oil.

1924 690 32 Rev. A KohlerEngines.com
Troubleshooting
Condition Conclusion
Crankcase breather clogged or inoperative. NOTE: If breather is integral part of valve cover and
cannot be serviced separately, replace valve
cover and recheck pressure.
Disassemble breather, clean parts thoroughly, check
sealing surfaces for flatness, reassemble, and recheck
pressure.
Seals and/or gaskets leaking. Loose or improperly torque
fasteners.
Replace all worn or damaged seals and gaskets. Make
sure all fasteners are tightened securely. Use appropriate
torque valves and sequences when necessary.
Piston blow by or leaky valves (confirm by inspecting
components).
Recondition piston, rings, cylinder bore, valves and
valves guides.
Restricted exhaust. Check exhaust screen/spark arrestor (if equipped). Clean
or replace as needed. Repair or replace any other
damaged/restricted muffler or exhaust system parts.
CRANKCASE VACUUM TEST
WARNING
Carbon Monoxide can cause severe nausea,
fainting or death.
Avoid inhaling exhaust fumes.
Engine exhaust gases contain poisonous carbon
monoxide. Carbon monoxide is odorless, colorless,
and can cause death if inhaled.
To test crankcase vacuum with manometer:
1. Insert rubber stopper into oil fill hole. Be sure pinch
clamp is installed on hose and use tapered adapters
to connect hose between stopper and one
manometer tube. Leave other tube open to
atmosphere. Check that water level in manometer is
at 0 line. Make sure pinch clamp is closed.
2. Start engine and run no-load high speed.
3. Open clamp and note water level in tube.
Level in engine side should be a minimum of 10.2
cm (4 in.) above level in open side.
If level in engine side is less than specified (low/no
vacuum), or level in engine side is lower than level in
open side (pressure), check for conditions in table
below.
4. Close pinch clamp before stopping engine.
To test crankcase vacuum with vacuum/pressure gauge:
1. Remove dipstick or oil fill plug/cap.
2. Install adapter into oil fill//dipstick tube opening,
upside down over end of a small diameter dipstick
tube, or directly into engine if a tube is not used.
Insert barbed gauge fitting into hole in stopper.
3. Run engine and observe gauge reading.
Analog tester–needle movement to left of 0 is a
vacuum, and movement to right indicates a pressure.
Digital tester–depress test button on top of tester.
Crankcase vacuum should be a minimum of 10.2 cm
(4 in.) of water. If reading is below specification, or if
pressure is present, check table below for possible
causes and conclusions.
WARNING
Rotating Parts can cause severe injury.
Stay away while engine is in operation.
Keep hands, feet, hair, and clothing away from all
moving parts to prevent injury. Never operate engine
with covers, shrouds, or guards removed.
A partial vacuum should be present in crankcase when engine is operating. Pressure in crankcase (normally caused
by a clogged or improperly assembled breather) can cause oil to be forced out at oil seals, gaskets, or other available
spots.
Crankcase vacuum is best measured with either a water manometer or a vacuum gauge. Complete instructions are
provided in kits.

Troubleshooting
20 24 690 32 Rev. AKohlerEngines.com
COMPRESSION TEST
For Command Twins:
A compression test is best performed on a warm engine. Clean any dirt or debris away from base of spark plug(s)
before removing them. Be sure choke is off, and throttle is wide open during test. Compression should be at least 160
psi and should not vary more than 15% between cylinders.
All other models:
These engines are equipped with an automatic compression release (ACR) mechanism. It is difficult to obtain an
accurate compression reading because of ACR mechanism. As an alternative, use cylinder leakdown test described
below.
CYLINDER LEAKDOWN TEST
A cylinder leakdown test can be a valuable alternative to a compression test. By pressurizing combustion chamber
from an external air source you can determine if valves or rings are leaking, and how badly.
Cylinder leakdown tester is a relatively simple, inexpensive leakdown tester for small engines. This tester includes a
quick-connect for attaching adapter hose and a holding tool.
1. Run engine for 3-5 minutes to warm it up.
2. Remove spark plug(s) and air filter from engine.
3. Rotate crankshaft until piston (of cylinder being tested) is at top dead center (TDC) of compression stroke. Hold
engine in this position while testing. Holding tool supplied with tester can be used if PTO end of crankshaft is
accessible. Lock holding tool onto crankshaft. Install a 3/8 in. breaker bar into hole/slot of holding tool, so it is
perpendicular to both holding tool and crankshaft PTO.
If flywheel end is more accessible, use a breaker bar and socket on flywheel nut/screw to hold it in position. An
assistant may be needed to hold breaker bar during testing. If engine is mounted in a piece of equipment, it may
be possible to hold it by clamping or wedging a driven component. Just be certain that engine cannot rotate off of
TDC in either direction.
4. Install adapter into spark plug hole, but do not attach it to tester at this time.
5. Turn regulator knob completely counterclockwise.
6. Connect an air source of at least 50 psi to tester.
7. Turn regulator knob clockwise (increase direction) until gauge needle is in yellow set area at low end of scale.
8. Connect tester quick-connect to adapter hose. While firmly holding engine at TDC, gradually open tester valve.
Note gauge reading and listen for escaping air at combustion air intake, exhaust outlet, and crankcase breather.
Condition Conclusion
Air escaping from crankcase breather. Ring or cylinder worn.
Air escaping from exhaust system. Defective exhaust valve/improper seating.
Air escaping from intake. Defective intake valve/improper seating.
Gauge reading in low (green) zone. Piston rings and cylinder in good condition.
Gauge reading in moderate (yellow) zone. Engine is still usable, but there is some wear present.
Customer should start planning for overhaul or
replacement.
Gauge reading in high (red) zone. Rings and/or cylinder have considerable wear. Engine
should be reconditioned or replaced.