Generac Power Systems 9 kW NG Benutzerhandbuch

Page 137

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  cylinder 

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

gasket 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)

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

DISCUSSION:
Circuit board action during shutdown will ground Wire 
18.  Wire  18  is  connected  to  the  Ignition  Magneto(s). 
The  grounded  magneto  will  not  be  able  to  produce 
spark.

PROCEDURE:

1.  On V-twin  generators,  remove Wire  18  from  the  stud 

located  above  the  oil  cooler.  On  single  cylinder  gen-

erators, disconnect Wire 18 at the bullet connector. See 

Figures 32 or 33.

DC CONTROL