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Generac Power Systems Recreational Vehicle Generator 5413 User Manual

Page 62

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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.

PROCEDURE:
1. Remove a spark plug.
2. Gain access to the flywheel. Remove the valve

cover.

3. Rotate the engine crankshaft until the piston

reaches top dead center (TDC). Both valves

should be closed.

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 at least 90 psi to the leak

down tester.

7. Adjust the regulated pressure on the gauge to 80

psi.

8. Read the right hand gauge on the tester for cyl-

inder pressure. 20 percent leakage is normally

acceptable. Use good judgement, and listen for air

escaping at the carburetor, the exhaust, and the

crankcase breather. This will determine where the

fault lies.

9. Repeat Steps 1 through 8 on remaining cylinder.

RESULTS:

Air escapes at the carburetor – 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 gas-

ket should be replaced.

CHECk COMPRESSION:
Lost or reduced engine compression can result in (a)

failure of the engine to start, or (b) 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

high oil consumption).

NOTE: It is extremely difficult to obtain an accu-

rate compression reading without special equip-

ment. For that reason, compression values are

not published for the V-Twin engine. Testing has

proven that an accurate compression indication

can be obtained using the following method.

PROCEDURE:
1. Remove both spark plugs.
2. Insert a compression gauge into either cylinder.
3. Crank the engine until there is no further increase

in pressure.

4. Record the highest reading obtained.
5. Repeat the procedure for the remaining cylinder

and record the highest reading.

RESULTS:
The difference in pressure between the two cylinders

should not exceed 25 percent. If the difference is

greater than 25 percent, loss of compression in the

lowest reading cylinder is indicated.
Example 1: If the pressure reading of cylinder #1 is

165 psi and of cylinder #2, 160 psi, the difference is

5 psi. Divide “5” by the highest reading (165) to obtain

the percentage of 3.0 percent.
Example 2: No. 1 cylinder reads 160 psi; No. 2 cylinder

reads 100 psi. The difference is 60 psi. Divide “60” by

“160” to obtain “37.5” percent. Loss of compression in

No. 2 cylinder is indicated.
If compression is poor, look for one or more of the fol-

lowing causes:

Loose cylinder head bolts.

Failed cylinder head gasket.

Burned valves or valve seats.

Insufficient valve clearance.

Warped cylinder head.

Warped valve stem.

Worn or broken piston ring(s).

Worn or damaged cylinder bore.

Broken connecting rod.

Worn valve seats or valves.

Worn valve guides.

NOTE: Refer to Engine Service manual P/N xxxxxx

for further engine service information.

TEST 36 – CHECk OIL PRESSURE SWITCH

DISCUSSION:
Also see “Operational Analysis” on Pages 18-23. The

Low Oil Pressure Switch is normally-closed, but is

held open by engine oil pressure during cranking and

startup. Should oil pressure drop below a safe level,

the switch contacts will close to ground the Wire 85

circuit. Printed Circuit Board action will then initiate an

automatic shutdown.
If the switch fails CLOSED, the engine will crank and

start, but will then shut down after a few seconds.
If the switch fails OPEN, low oil pressure will not result

in automatic shutdown.

Page 60

Section 7
DIAGNOSTIC TESTS