Test 25 - Check Engine / Cylinder Leak Down; Test / Compression Test - DeWalt DXGN4500 Manual

See Figure 1-10. Loosen rocker arm jam nut. Turn
1.
pivot ball stud while checking clearance between
rocker arm and valve stem with a feeler gauge.
Figure 1-10. Adjusting Valve Clearance
See Figure 1-11. When clearance is correct, hold
2.
pivot ball stud with Allen wrench and tighten rocker
arm jam nut to specified torque with a crow foot
wrench. After tightening jam nut, recheck valve
clearance to make sure it did not change.
Rocker Arm Jam Nut ft-lbs
4209 to 12
Figure 1-11. Tightening Jam Nut
Install Rocker Arm Cover
Use a new rocker arm cover gasket. Install rocker
1.
arm cover and retain with four screws.
Results
Adjust valves to specification and test. If problem
continues, refer to flow chart.
Test 25 – Check Engine / Cylinder
Leak Down Test / Compression Test
General Theory
Most engine problems may be classified as one, or a
combination of the following:
• Will not start
Diagnostic Repair Manual
• Starts hard
• Lack power
• Runs rough
• Vibration
• Overheating
• High oil consumption
General Theory
The Cylinder Leak Down Tester (Figure 44) checks
sealing (compression) ability of engine by measuring air
leakage from combustion chamber. Compression loss
can present many different symptoms. This test detects
the section of the engine where the fault lies before
000258
disassembling the engine.
Procedure
Remove spark plug.
1.
Gain access to flywheel. Remove valve cover.
2.
Rotate engine crankshaft until the piston reaches
3.
top dead center (TDC). Both valves should be
closed.
Lock flywheel at top dead center.
4.
Attach cylinder leak down tester adapter to spark
5.
plug hole.
Connect an air source of at least 90 psi to the leak
6.
down tester.
Adjust regulated pressure on gauge to 80 psi.
7.
Read right hand gauge on tester for cylinder
8.
pressure.
acceptable. Use good judgment, and listen for air
escaping at carburetor, exhaust, and crankcase
breather. This determines where the fault lies.
Figure 1-12. Spark Tester
Results
• Air escapes at carburetor – check intake valve.
• Air escapes through exhaust – check exhaust
valve.
• Air escapes through breather – check piston rings.
•
Air escapes from cylinder head – replace head
gasket.
Section 3 Engine Diagnostic Tests
20 percent leakage is normally
33