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.
1-5
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