Generac Power Systems GTV99O Service Manual page 15

SECTION 1: GENERAL INFORMATION
I
lfthe RPw loss isgrcaterthan 75 RPIV this indicates that the
grcunded cylinder with the least RPM loss is the weakest ot
the two cylinders. Look to th.t qlinderfora problem.
Example:
Engine RPM - Both cylinders = 3400 RPM
Engine RPM - #1 Cylindet Grcunded = 3300 RPM
Engine RPIV - *2 Cylinder Grounded = 3100 RPM
Conclusion:#1 cyllnder is weakest of the two cylinders.
EXA[4PLE:
cyl. #1
cyl. #2 Diff.
Eng. +l
165 PSI 160 Psl 5 Psl
Eng.42
175 PSI 155 PSI 20 Psl
lf compression is poor, look for:
. lnsufficient valve clearance
. Loose cyllnder head bolts
. Blown head gasket
. Bumed va ve5, valve seats and/or loose valve seats
. warped cylinder head
. warped valve stems
. Worn bofe and/or rings
. BDken conneding rods
CYLINDER
LEAKDOWN TESI
A cylinder leakdown tener may be used to test the sealing
capability of the compression
components of each cllinderand
quickly identit the prcblem cornponent.
THINGS WHIC]] AFFEEI-EO]ILIILNDIB!
l. Carburetion
2. Crankcase vacuum
3. lgnition timing
a. A partially sheared fl)4rvheelkey
willeffect ignition iimlng
and engine Peaformance.
TH]NGS
WHIC H AFFECT ONE CYL NDE R:
1. Spark plug
a. a fouled 5park plug may indicate that carburetor is out
of adjustment.
2. Leak in spark plug wire
3. Head gasket
4. lntake manifod
a. A leak ateiiherend ofthe intake maoifold wlllonly affecl
one cylinder, not both.
5. Valves
6. RLngs
8. Cylinder
NOTE: A twin cylindet engine wi runwe ononecylin-
der as long as the power rcquircd for the appli.ation does
not exceed the powet produced by the one cylinder
Figwe | -8. Cylindet Salan.e Test
The cy inder balance |en willa so detect a qlinderthat is not
functloning. When grcunding out one cylinder thete wil be
no RPIV loss. When the other qlinder ls grounded out the
enqine willsiop-
The fuel prcssurc can be checked using a pressure tester kit
(Generac P/N OC7977). This kt comes with an lntormatve
'How To' video.
CHECK COIVPRES5 ON:
lt has be€n determlnedthrolghtestinq
that a simple.nd accu
rate indication of comprcssion can be made as fo lows:
Remove both spark plugs and nsert a compresslon
gaugeinto
either cylinder (one cylinder at a tirne). Turn efglne over wilh
engine starter until there is no further ncrease in pressure.
Record this reading. Rep€ai pfocedure on olher cylirder and
rccord that reading. The d Ifefence beiween both cy inde6
shouldnoiexceed25%.
Morcthan25% indicates ossof com-
press on in the.ylinder wth lower presslre. see examp e.
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