Kohler Command PRO CH740NG [19/88] Troubleshooting

1924 690 30 Rev. D KohlerEngines.com

Troubleshooting

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 difﬁ cult 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 ﬁ lter 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 ﬂ ywheel end is more accessible, use a breaker bar and socket on ﬂ ywheel 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 ﬁ rmly 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.