ENGINE/DC CONTROL
PART 4
Page 129
Section 4.5
Diagnostic Tests
Results
1. Clean, re-gap or replace plugs as necessary, re-test.
2. If spark plugs are good, refer back to flow chart.
Table 23.
Engine
Size
kW
Rating
Plug
Gap
Recommended
Plug
Manufacture
410 cc 8 0.030
inch
RC14YC Champion
530 cc 10 0.030
inch
BPR6HS NGK
990 cc 12-17 0.040
inch
RC14YC Champion
999 cc 20 0.030
inch
RC12YC Champion
TEST 58 – CHECK ENGINE / CYLINDER LEAK
DOWN TEST / COMPRESSION TEST
Introduction
Performing the following test procedures will accurately
diagnose some of the most common problems:
•Will not start
•Lack of power
•Runs Rough
•Vibration
•Overheating
•High Oil Consumption
CYLINDER LEAK DOWN TEST
Discussion
The Cylinder Leak Down Tester checks the sealing
(compression) ability of the engine by measuring air leakage
from the combustion chamber. Compression loss can present
many different symptoms. This test is designed to detect the
section of the engine where the fault lies before disassembling
the engine. Figure 139 represents a standard Tester available
on the market.
Note: Refer to Manufactures instructions for variations of
this procedure.
Procedure
1. Remove the spark plug from the front cylinder.
2. Gain access to the flywheel. Remove the valve cover.
3. Rotate the engine crankshaft until the piston reaches top
dead center (TDC). In this position, both the intake and
exhaust valves will be closed. If the engine is not properly
position at TDC the results of the test may be inaccurate
at diagnosing a problem.
INLET GUAGE
PRESSURE SET
POINT
RED RANGE INDICATES
UNACCEPTABLE LEAKAGE
GREEN RANGE INDICATES
ACCEPTABLE LEAKAGE
NEEDLE INDICATES
MINIMAL AIR LEAKAGE
AIR PRESSURE
REGULATOR
REGULATOR
ADJUSTMENT
KNOB
COMPRESSED
AIR IN
OUTLET GUAGE
PRESSURE
TO SPARK
PLUG HOLE
OUTLET
GUAGE
0
0
0
Figure 139. Cylinder Leakdown Tester
4. Lock the flywheel at top dead center.
5. Attach cylinder leak down tester adapter to spark plug
hole.
6. Connect an air source of 90 PSI to the cylinder leak down
tester.
7. Adjust the regulated pressure on the gauge to 80 PSI.
8. Read the right hand gauge on the tester for cylinder
pressure. A leakage of 20 percent is normally acceptable.
Use good judgment, and listen for air escaping at the
carburetor (air intake), the exhaust, and the crankcase
breather. This will determine where the fault lies.
9. Repeat Step 1 through 8 on remaining cylinder.
Results
•Air escapes at the carburetor (air intake)– check intake valve
•Air escapes through the exhaust – check exhaust valve
•Air escapes through the breather – check piston rings
•Air escapes from the cylinder head – the head gasket should
be replaced.
CHECK COMPRESSION
Discussion
Lost or reduced engine compression can result in a failure of
the engine to start, or a rough operation. One or more of the
following will usually cause loss of compression:
•Blown or leaking cylinder head gasket
•Improperly seated or sticking-valves
•Worn piston rings or cylinder. ( This will also result in a high
oil consumption)
For single cylinder engines, the minimum allowable compression
pressure for a cold engine is 60 PSI. Compression values are
difficult to obtain accurately without special equipment. For
this reason, compression values are not published for the
larger engines. However, testing has proven that an accurate
indication of compression in the cylinder can be obtained by
using the following procedure.
To Next Page
Loading...
Need help?
General
