Compression Test; Cylinder Leakdown Test; Leakdown Test Instructions; Leakdown Test Results - Kohler CH940-CH1000 Service Manual

Compression Test

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 command twins)

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 disconnect for attaching adapter hose and a holding tool.

Leakdown Test Instructions

Run engine for 3-5 minutes to warm it up.
1.
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 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 increase (clockwise) 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.

Leakdown Test Results

Air escaping from crankcase breather.
Air escaping from exhaust system.
Air escaping from intake.
Gauge reading in "low" (green) zone.
Gauge reading in "moderate" (yellow) zone.
Gauge reading in "high" (red) zone.
62 690 01 Rev. C
Ring or cylinder worn.
Defective exhaust valve/improper seating.
Defective intake valve/improper seating.
Piston rings and cylinder in good condition.
Engine is still usable, but there is some wear present.
Customer should start planning for overhaul or
replacement.
Rings and/or cylinder have considerable wear. Engine
should be reconditioned or replaced.
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