Generac Power Systems MC ALTERNATOR User Manual
MC ALTERNATOR
DIAGNOSTIC REPAIR MANUAL
ISSUED JANUARY 1979
P.0, BOX 8, WAUKESHA. WISCONSIN 53186
PRINTED IN U.S.A.
51834
This Repair Manual is provided to aid the technician in the
analysis and repair of malfunctions that might occur in the
MC alternator or its engine. Keep the Manual in a safe place
and refer to it whenever necessary.
All information, illustrations and specifications contained
in this Manual are based on the latest product information
available at the time of publication. Generac reserves the
right to make changes in any product at any time without no
tice.
GENERAC
P.O.BOX 8
WAUKESHA. WISCONSIN 53186
PART I
GENERAL
Section 1.1
1.1.1
1.1.2
1.1.3
1.1.4
• 1.1.5
1.1.6
Section 1.2
Section 1.3
SPECIFICATIONS
Model Numbers
Fuels and Oils
Torque Specifications (General)
Torque Specifications (Special)
Sectional View
Engine Specifications
WIRING DIAGRAMS
SPECIAL TOOLS
SPECIFICATIONS
1.1.T-M0DEL NUMBERS
SECTION 1.1
Model No,
Wattage Capacitv
Voltage
MC-35
6894
3500 3500 3800
120* 120* 120*
Maximum Amperes 29,2 at 120 V, 31,7 at 120 V.
Phase 1-Phase 1 1-Phase 1-Phase 1-Phase
Frequency
Voltage
Regulation
Solid state voltage regulator maintains 120 Volts AC
(±27o) at 60 Hertz
MC-35
6895
MC-38
6938
MC-38
69 39
MC-40
6896
3800 4000
120* 120*
33.3 at 120 V.
1 -Phasel_1-Phase
60 Hertz at 3600 rpm
Batterv Charge 0-10 Amperes at 12 Volts DC
Gross Weight
(wet)
Engine Part No,
Bore
Stroke
Displacement
48078 48078
Approximately 127 pounds
48078 48078 48078
78 mm
62 mm
296 cc
Governed Speed 3720 rpm at no-load
Ignition System
Starting System
Cranking Current
Average Fuel
Consumption
Type of Fuel
Pump
Mech,
12 Volt DC electric (Ring Gear)
Approximately 0,70 Gallons per Hour
Elec, Mech,
Solid State
Approximately 90 Amperes
Elec, Mech, ■ Elec,
MC-40
6897 ..
4000
120*
48078
'Factory connected for 120 Volt AC output only. Unit is reconnectable
to provide dual voltage output.
1.1.2-FUELS AND OILS
RECOMMENDED FUEL
Use NON-LEADED gasoline. Leaded REGULAR grade gasoline is an acceptab
le substitute. Do not use any highly leaded, premium gasoline,
RECOMMENDED OIL
I
Use oil classified ”For Service SC,
SD or SE”, as shown in the CHART at
USE OIL CLASSIFIED "FOR SERVICE SC, SD, or SE"
---------------------------------------
USE SAE 10 W
Of 10W-30OIL
^-----------------------------
USE SAE 30 OIL
USE SAE 20 W
or 10W-30 OIL
right.
-10“F. 10“F. 32'F.
■22^C. •12.2'^C. O'C.
TEMFERATURE RANGE ANTICIPATED BEFORE NEXT OIL CHANGE
1,1-1
1.1.3- TORQUE SPECIFICATIONS (GENERAL)
STANDARD TORQUE VALUES
Grade 2
BOLT SIZE
1/4-20
1/4-28
5/16-18
5/16-24
3/8-16
3/8-24
7/16-14
7/16-20
1/2-13
1/2-20
9/16-12
9/16-18
5/8-11 92
5/8-18 105
3/4-10
3/4-16 180 140
7/8-9
7/8-14
1-8 300
1-14
DRY LUB
5
6
11
13 10
20
23 17
32
36 27
49
55
70
78
165 125
200
225
340 260
15
25
38
42 85
54 110
60
71
81
155
170
230
All Values in FOOT-POUNDS
DRY
4
5 10
8 17
19
31 24
35
49
55 42
75
120
150
170
270
295 230
395
435
590
680
Grade 5
LUB
8
13 21
15
27
38
58
65
84
93
115
130
205
305
335
455
5.10
DRY LUB
6 10
7
12
24
38 29
43
61 47
68
93 72
105
135
150
185
210
330
365
530'
585 450
795 610
Grade 7
16 24
18
33
52
80
105
115
145
160
250
280 420
405
DRY LUB
8
9 14
12
27
44 34
49
70 54
78
105
120 90
155 120
170
210
240
375 290
605 455
670
905 695
Grade 8
9
11
18
21
38
60
82
132
165
185
320
515
GRADE
BOLT HEAD
SYMBOL
o
1.1.4- TORQUE SPECIFICATIONS (SPECIAL)
Spark Plug
Cylinder Head Bolts
Connecting Rod Cap Bolts
Engine Gear Cover Bolts
Blower Fan (Special M14 Hex Nut)
Rotor Bolt
Mechanical Fuel Pump Bolts
INCH-POUNDS FOOT-POUNDS
216-264
264-348
216-264
90-110
600-660 50-55
180-200
25-30
18-22
22-29
18-22
7.5-9
15-17
1.1-2
г=
ID
о о
о о
^ BREAKER ^
—
о
—J
U)
I
1.1.6-ENGINE SPECIFICATIONS
INCHES METRIC
Spark Plug Gap
Valve Spring Length
Valve Spring Compression Length
Valve Seat Width
Valve Tappet Clearance
Crankshaft End Play
Piston Diameter (at skirt)
Piston Pin Diameter
Width of Compression Grooves
Width of Oil Ring Groove
Width of Compression Rings
0.035
0.009 mm
1.2995 33.000 mm
1.0236
0.039-
26.000 mm
1-2 mm
0.079
0.0039-
0.1-0.2 mm
0.0078
0.0039-
0.1-0.3 mm
0.0118
3.067-
3.068
0.7080-
0.7086
0.0797-
0.0805
0.1584-
0.1593
0.0775-
0.0784
77.91-
77.93 mm
17.989 mm-
18.000 mm
2.025 mm-
2.045 ram
4.025 mm-
4.045 mm
1.970 mm-
1.990 mm
Width of Oil Ring
Ring End Gap
Maximum Permissible Out-of-Roundness
of Crankpin
Connecting Rod to Crankpin Clearance
Valve Spring Force
0.1560-
0.1570
0.0078-
0.0157
3.970 mm-
3.990 mm
0.2 - 0.4
mm
0.002 0.05 mm
0.001-
0.002
14.81-
19.76 lbs
0.030-
0.050 mm
kilograms
6.72-8.96
1.1-4
K>
I
6896- 0
6897- 0
co
гп
о
g i
>r
Isa
CD
XI
>
CD
N5
ro
FUSE-
m
—14
--
@—
iTt>
L&ceND
C6 ChO«.B SOvKNOlO
c& c>*cutT BrmAiKClt
O OiOOB
FP FoCL Pur^-ei.CCTRlC(ir »OPPl^tfcO^
F& FuBc BOwBnO'D
C FKikHt C«OUNO
>4M hOU« MtT«H
IM iCNiTlOM N\OOOUt
vS STikTO«
l-T CICMT
LOW OlC BW>TCm
»cm p«iNTto Cimcj'T mo*^«o
s m-TK«!««
sc «Tk.«Te<« &OLBNo>o
Sw BTOP-ST^RT Switch
i^imi tmut
-----
1
REMOTE PANEL
STO
0 1
7
0 1
2
o—
—o
c
TART
p
tu
----
1
1 e
ffh
-2
------
6
MODELS 6894-1,-2
6895- 1,-2
6896- 1,-2
6897- 1,-2,-3
6938- 0
6939- 0
ю
I
со
о
о
оо
to
о
со
N>
i
4ï^
О
О
05
ОО
СО
I
RED CONNECTOR PLUG
0
RED RECEPTACLE
oKslCel
CjlLjlCa
11 '—
T1
120
V.
CUSTOMERS
CONNECTIONS
FACTORY WIRING CONNECTIONS
120 VOLTS ONLY
1
44
22
V
120VT 120V.
•—4*—>
-240V, -
CUSTOMER
CONNECTIONS
-CD □ d]
j
-----
-L
[4] rs: Cel
RED CONNECTOR
PLUG
RED
RECEPTACLE
N
RECONNECTED FOR
120/240 VOLT
OUTPUT
1.2-5
SECTION 1.3
SPECIAL TOOLS
ELEHTRICAL TEST PLUG
The Electrical Test Plug facilit
ates the testing of electrical
components in circuits that pass
through the red and white stator
can receptacles, or through the
Ignition Module receptacle. Use
the Test Plug in any diagnostic
test that calls for connection of
the VOM test probes to pins in
these receptacles. Order Part No.
27069.
INSULATION BREAKDOWN TESTER
Resistance testing of alternator compon
ents with an Ohmmeter is generally valid.
Such resistance tests will nearly always
indicate the presence of an open or shor
ted condition. However, some malfunctions
do not become evident until an electrical
load is applied across the defective'com
ponent. The insulation breakdown tester
permits a component to be tested under a
simulated load condition, by applying a
selected voltage to the component. Follow
the tester manufacturer’s instructions
strictly when using the tester.
SPARK T.ESTER
The Spark Tester is used to check for pro
per ignition spark with the engine cranking.
Order Part' No. 41503.
ROTOR REMOVAL KIT
The Rotor Removal Kit consists of a 3/8-24
TAP, 3/8-24 BOLT, and threaded studs o'f
varying lengths. The kit is used for remo
val of the rotor. Order Part No. 41079.
LOAD BANK
The Load Bank is used to apply an
electrical load to alternators..
The unit is equipped with a Volt
meter, Ammmeter and Frequency Me
ter, as well as the necessary
switches for selecting the desir
ed load. Specify Model No. 5515,
1.3-2
PART II
TROUBLE DIAGNOSIS
Section 2.1
2.1.1
Section 2.2
Section 2,3
- DIAGNOSTIC FLOW CHARTS
- Introduction
Engine won’t Crank
Engine Cranks, won’t Start
Engine starts hard - Runs Rough
Switch set to STOP - Engine Keeps Running
AC Voltage Low
AC Power Low
AC Voltage High
No AC Voltage
- Diagnostic Tests
- Battery Charge Circuit Tests
SECTION 2.1
DIAGNOSTIC FLOW CHARTS
2.1.1-INTROUUCTION
The DIAGNOSTIC FLOW CHARTS that follow are intended for use with the
DIAGNOSTIC TESTS in Section 2.2, Test numbers assigned in the FLOW
CHART are identical to the numbers assigned to specific tests in Sec
tion 2.2.
ENGINE WON’T CRANK
TEST 1
15 Amp
Page
2.2-1
Fuse
BAD
Replace Rise
TEST 4
Starter
Solenoid
I i
|Repl
TEST 7
Page 1
2.2-2|iGOODZ^
ace
Page]
Starter
Ring Gear
______
BAD
9 0/,
1
“GOODI^
'GOOD
1
TEST 2 Page
Battery
9.2-1*—GOOD--^ Start/Stop
2.2-1
BAD
<>
Recharge or
Replace
;GOOD
TEST 5
Starter
Motor
L___1
--------1
Replace
ENGINE
SEIZED
Page 1
2.2-3 |—■ GOODI^
GOOD
7F1
idJ
ll
BAD
TEST 3
Cr-r,- i-^U
Switch
~1 r
Page
2.2-2
BAD
Replace Switch
TEST 6 Page
Starter
Drive Gear
2.2-4
Replace
n
Replace
0
Repair
or
Replace
ENGINE CRANKS, WON’T START
TEST 8
Check
Spark
Page
2.2-^’
If
IF SPARK CHECKS GOOD
GO TO TEST 15
TEST 11
Spark
Plug
Page
2.2-5
BAD
TEST 9
________ _______
OIL LEVEL LOW |
iz
IFILL TANK
........-nnnn-
TEST 12
Ignition
Module
IbadI
Page
Page I
2.2-6 ^GOOD =CH
TEST 10
Low Oil
Switch
ba:
REPAIR/REPLACE
TEST 13
Ignition
Stator
IBAD
Page
2.2-5
D
Page
2.2-6
n
n
Replace
TEST 14 Page
Ignition *2 2-7
Coil I * I
I
I REPLACE
TEST 16
No Fuel
Flow
Page
2.2-8
|Replace|
IF SPARK CHECKS GOOD I
O
TEST 17
4 Amp
.BAD Fuse
;GOOD:
GO TO TEST 15
:G00D:
Page
2.2-8
r
:good:
5
¡Replace
TEST 15
Low Fuel
LOW
FILL TANK
TEST 18
Printed
Circuit
Page
2.2-8
Page
2.2-9
GO TO TEST
23
2.1-2
BAD
Except 6897-4
See Section 2.4
IREFIACEI
;G00D;
GO TO TEST 19
TEST 19
Fuel
Filter
Page
2.2-9
IGOOD;
TEST 20
Fuel
Lock-Off ;
Solenoid
Page
L2-10
____
TEST 21
Fuel
Pump |2.2-lC
1
Page
bad!
REPLACE
TEST 22 Page
Check
Installation_
IF FUEL FLOW IS GOOD
GO TO TEST 23
--------------------
2.2-11
2
ADJUST
JETS
test:! BAD
1 .
D
BA
T
REPLACE
:GOOD:
TEST 23 Pagel
Carburetor 2.2-11”^^^
u
REPLACE
CARBURETOR
CHANG E¡f>
TEST
BAD
2
REPLACE
TEST 24 Page
L
Compression!.2-13
GOOD
ICO TO TEST 29
Iz
CHECK
FLOAT Z^BAD^Z^^
SEAT
0
CHECK 1
FLOAT ::;>bad;i::>
LEVEL
REPLACE
SEAT
ADJUST
KLOAT i
LEVEL
GO TO TEST 27
TEST
;BAD
TEST 25 page! ^
Vi n A J _ I
Head
Gasket^
_____
| o
Iz
BAD
2
REPLACE
GASKET
5
Itest
TEST 26| Page
Valves 2.2-14
iz
REPAIR
I
[TEST
2.1-3
IF COMPRESSION IS GOOD, GO TO TEST 29r
TEST 27
Rings 2
.. 1 i ’
BAD
V
REPIACE
17
TEST
Page
-.2-14
■good:
TEST 28 Page
Cylinder 2.2-14
\ I I ‘ *
BAD
REPAIR
TEST 29
77
TEST
ENGINE STARTS HARD - RUNS ROUGH
Timing
Page
Z.2-14
2.1-4
A
REPAIR
REPLACE
SWITCH SET TO STOP - ENGINE KEEPS RUNNING
TEST 3 jPagej
Replace Switch
REPAIR
2.1-5
A-C VOLTAGE LOW
TEST 33
Check
Frequency
B/1Id
TEST 32
Governor
Bi
<
2.2-17
____
2.2-17
L
Page
:good
i
Page
A-C POWER LOW
2*1-6
A-C VOLTAGE HIGH
TEST 36
Check
Output ;
Voltage
TEST 36
Check
Output
Voltage
Page
>.2-19
____
Page
^2-19
ZZBAD
1
CHECK CUSTOMER WIRING|<r^IZZZ.GOOD
NO A-C VOLTAGE
TEST 38
Main
Circuit .
Breaker
Page
^2-20
____
1
:good:
TEST 37
Sensing
Transformer
BAD
Replace
Transformer
TEST
TEST 39
check Rotor2 2-20“
j Paee
12.2-19
J_____
Pag£
GOOD
<>
Check Customer
____
Wiring
TEST
TEST 40
Check Field
Boost
Check Wire ^^0-
No. 14
____
Page
2.2-21lC>
BAD
iZ
REPLACE
TEST
CHECK VOLTAGE* _
TO ROTOR I
\ t
BAD
0
Jcheck No. 4 Wire
1 for 12 Volts
^~li
GOOD
BAD
¡REPLACE
¡TEST
IGOOD
testIcT^
,
________Iz__________
.•Replace Printed
"[Circuit Board
■ 2.1-7
SECTION 2.2
DIAGNOSTIC TESTS
TEST 1-15 AMPFUSE
Remove and visually inspect the 15
Amp Fuse. Replace, if Fuse element
has melted. A more thorough check
may be made with a Volt-Ohm-Milli-
ammeter, as follows
1. )-Set VOM to ”+DC” and to "Rxl”
scale.
2. )-Connect meter test probes and
”Zero’^ the meter.
3. )-Connect meter test probes to
Fuse ends. Meter needle should
swing upscale to ’^0” ohms (continu
ity). If meter needle does not move
upscale, replace the Fuse.
RESULTS:-Fuse tests bad
Fuse tests good
TEST 2-BATTERY
Check Battery condition, as well as
the condition, cleanliness and sec
urity of battery cables and connec
tions .
RESULTS:-Battery, cables or connections,
check bad
Battery, cables or connections,
check good
............
.......
.
.Install new 15 Amp Fuse
.Continue tests
.Recharge or replace de
fective Battery. Repair,
clean or replace defect
ive cables or connection
.Continue tests
2.2-1
TEST3-ST0P/START SWITCH
Left Hand
10 (Ground)
Remove 15 Amp Fuse to disconnect
starting circuit. Remove panel
top cover. Disconnect wires from
switch terminals to prevent int
eraction. Set VOM to "+DC” and to
"Rxl” scale, then zero the meter.
Connect meter test probes to the
switch center and right hand ter
minals (as viewed from switch
rear). Meter needle should not
TT,^-<rQ H QT.ri rph at START - meter
Connect VOM test probes to Switch
center and left terminals (as vi
ewed from switch rear). Hold the
Switch at START - meter needle
should not move. Release the Switch
to NEUTRAL - meter needle should
not move. Hold the Switch at STOP needle should swing upscale to ”0",
.Install new Stop/Start Switch
.Connect Switch wires, install
top panel and 15 Amp Fuse,
Continue tests.
A.)- Set Stop/Start Switch to START
and back to NEUTRAL several times.
An audible ’’click" should be heard
as the solenoid actuates.
2.2-2
RESULTS:- Solenoid actuates, engine
does not crank
...............
Continue tests in Paragraph B
Solenoid does not actuate.•...Continue tests in Paragraph D
B. )- Set VOM to ”+DC” and to a scale greater than 12 Volts DC. Connect
the NEGATIVE (COMMON) test probe to ground. Connect the POSITIVE (+)
probe to the battery cable connection on the solenoid. Meter should in
dicate approximately 12 Volts DC.
RESULTS: - Meter reads 12 Volts DC
Meter reads less than 12
.....
....
Continue tests in Paragraph C
.Check for open or shorted wire
Volts DC (or loose connection) between
Battery and Starter Solenoid
C. )- Connect POSITIVE (+)'meter test probe to starter cable connection
on solenoid. Connect NEGATIVE (COMMON) probe to ground. Hold Stop/Start
Switch at START - meter should indicate approximately 12 Volts DC.
RESULTS:- Meter does not read
12 Volts DC.....
Meter reads 12 Volts and
..........
.....
...Install new Starter Solenoid
Continue tests in DIAGNOSTIC
Solenoid checks good FLOW CHARTS
D. )- Set VOM to ”+DC” and to a scale greater than 12 Volts. Connect the
meter POSITIVE (+) test probe to one of the small terminals on the sol
enoid. Connect the remaining probe to ground. Meter needle should read
approximately 12 Volts DC. With one probe'still connected to ground,
connect the remaining terminal to the other small terminal on the solen
oid - meter should indicate approximately 12 Volts DC.
RESULTS:- Meter indicates 12 Volts......Continue tests
Meter does NOT read 12 Volts..Repeat Tests 1, 2 and 3. When
sure that these tests are good
and 12 Volts is not indicated
in Test 4.D., replace solenoid
TEST 5-STARTER MOTOR
Set VOM to ”-hDC” and to a scale
greater than 12 Volts DC. Conn
ect VOM positive (4-) test probe
to the Starter terminal lug and
COMMON (-) test probe to frame
ground. Hold Stop/Start switch
at START. Meter should indicate
approximately 12 Volts DC and
starter motor should run.
Starter runs.................................Continue tests
Meter indicates 12 Volts DC,
Starter does not run
.......................
Meter does not indicate 12 Volts
........
Replace Starter
Check Starter cable
2.2-3
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