Kohler LH630-775 Service Manual page 25

Section 3
Troubleshooting
Compression Test
A compression test is best performed on a warm
engine. Clean any dirt or debris away from the base of
the spark plugs before removing them. Be sure the
choke is off, and the throttle is wide open during the
test. Compression should be at least 160 psi and
should not vary more than 15% between cylinders.
Cylinder Leakdown Test
A cylinder leakdown test can be a valuable alternative
to a compression test. By pressurizing the combustion
chamber from an external air source you can
determine if the valves or rings are leaking, and how
badly.
Cylinder Leakdown Tester (see Section 2) is a
relatively simple, inexpensive leakdown tester for
small engines. The tester includes a quick disconnect
for attaching the adapter hose and a holding tool.
Leakdown Test Instructions
1. Run engine 3-5 minutes to warm it up.
2. Remove spark plugs, dipstick, and air filter from
engine.
3. Rotate crankshaft until piston (of cylinder being
tested) is at top dead center (TDC) of
compression stroke. You will need to hold the
engine in this position while testing. The holding
tool supplied with the tester can be used if the
PTO end of the crankshaft is accessible. Slide the
Air escaping at oil fill tube .................................................................. Defective rings, worn cylinder walls, or blown
Air escaping from exhaust outlet ....................................................... Defective exhaust valve/improper seating.
Air escaping from carburetor inlet ..................................................... 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
Gauge reading in ''high'' (red) zone .................................................. Rings and/or cylinder have considerable wear.
Cooling Leakage Test
A pressure test can be performed as a simple means of
determining whether the cooling system may have a
problem. The test procedure, possible results, and
recommended corrective action are covered in Section 7.
3.4
holding tool onto the crankshaft and adjust the
set screw to fit in the key slot. Install a 3/8"
breaker bar into the square hole of the holding
tool, so it is perpendicular to both the holding
tool and crankshaft PTO. If the flywheel end is
more accessible, you can use a breaker bar and
socket on the flywheel nut/screw to hold it in
position. You may need an assistant to hold the
breaker bar during testing.
If the engine is mounted in a piece of equipment,
you may be able to hold it by clamping or
wedging a driven component. Just be certain that
the engine cannot rotate off of TDC in either
direction.
4. Install the adapter hose into the spark plug hole,
but do not attach it to the tester at this time.
5. Connect an adequate air source to the tester.
6. Turn the regulator knob in the increase
(clockwise) direction until the gauge needle is in
the yellow "set" area at the low end of the scale.
7. Connect tester quick-disconnect to the adapter.
Note the gauge reading and listen for escaping air
at the carburetor intake, exhaust outlet, and oil
fill/dipstick tube.
8. Check your test results against the table below:
Leakdown Test Results
head gasket.
present. Customer should start planning for
overhaul or replacement.
Engine should be reconditioned or replaced.