Jacobsen J-125AS User manual

I
ENGINE SERVICE MANUAL
I
HORIZONTAL
•
• VERTICAL
c:;OB-& • J-125VBS
)~~
J-125AS •
•
17 lfl • J-125VES
'4. 0
J-1251
•
~ A.o
• J-175VES
~LAW~
J-125G •
• J-175VDSJ
•
J-175A-B-C-CA
•
J-225VASJ
•
JACOBSEN MANUFACTURING COMPANY
Racine, Wisconsin
PRICE $1.50

, - ~ L - ----- -
' ' • ·
··'-'1.
FOREWORD
The Jacobsen single cylinder, two cycle, air cooled engine has been pioneered
and developed to produce smooth and ample power at remarkable low crank-
shaft speeds.
To maintain the · dependability of these engines, Jacobsen has compiled this new
Service Manual for your use. Instructions have been kept to a minimum , but
essential details and suggestions are included to help provide customer satis-
faction and fast service.
HOW TO USE THE SERVICE MANUAL
In addition to furnishing all trouble-shooting, specifications and data for the 1959-60 en-
gines , this manual is basically divided into minor and major overhaul. To avoid dupli-
cation , these ..- sections describe overhaul of the Jacobsen engines from a general viewpoint.
Specific instructions for model variations are covered in separate paragraphs.
The disassembly and reassembly procedure is simplified by references to the exploded
views which indicate the disassembly of parts by numerical sequence. Wherever neces-
sary, these procedures are described in detail.
HOW TO ORDER REPAIR PARTS
Refer to 1959 or 1960 master parts list and order replacement parts as follows:
1. Specify the correct part number for each item. Do not order by item number.
2. The serial number of the mower being repaired must be used to find the correct
part number. Engine parts in the list are arranged according to mower model and
serial number.
3. Find item number of part required. Use the serial number key to locate quantity
and correct part number.
WHAT THE MANUAL WILL DO FOR YOU
You can provide better service to your customers, save yourself delays, and eliminate un-
necessary calls to the factory by studying this service manual carefully and using it for
handy reference.
1

Mower
JACOBSEN SERVICE POLICY
Products Warranty
Jacobsen Products are guaranteed to the original retail purchaser for one
(1) year from date of purchase. The Jacobsen Manufacturing Company will
replace free of charge f. o. b. Authorized Service Station or Authorized
Service Distributor any part found to be defective when returned , TRANS-
PORTATION CHARGES PREPAID.
The warranty will not apply to any products repaired or altered outside
of our factory or any Authorized Service Station which, in the Company's
judgment affects its condition or operation. Neither will the warranty ap-
ply to any failures resulting from misuse, negligence, or accident.
The Company also reserves the right to incorporate any changes in design
without obligation to make these changes on units previously sold.
TYPES OF 1959-1960 JACOBSEN ENGINES AND STARTING SERIAL NUMBERS
Engine
1959 1960
Model Type
Bore & Stroke Model No. &
Starting Serial No. Model No . &
Starting Serial No.
9" Edge-R-Trim J-100-H
2" x 1-1 /2" 32A9 6663
9" Edge-R-Trim
J-125-H
2" x 1-1 / 2"
10" Trimo
J-100-V
2" x 1-1 / 2"
3110 5228
10" Trimo J-125-V
2" x 1-1 / 2"
18" Pacer
J-100-H
2" x 1-1 / 2"
42C18 17073
18-" Pacer
J-125-H
2" x 1- 1/ 2"
18" Turbo-Cut J-100-V
2" x 1-1 / 2"
34Bl8 129987
18" Turbo-Cut
J-125-V
2" x 1-1 / 2"
18" Turbo -Vac J-125-V
2" x 1-1 /2" 7518 9101
20" Scepter J-125-V
2" x 1-1 / 2"
8020 1601
21" Lawn Queen
J-100-H
2" x 1-1 / 2"
2C21 75403
21" Manor J-125-H
2" x 1-1 / 2"
28F21 36749
21" Turbo-Cut J-175-V
2-1 / 8" x 1-3 / 4"
21" Turbo-Cut SP J-175-V
2-1 / 8" x 1-3 / 4"
35C21 42629
22" Putting Green J-175-H
2-1 / 8" x 1-3 / 4"
9A22 18791
22" Scepter J-175-V
2-1 / 8" x 1-3 / 4"
8022 1601
24" Rotary SP
J-225-V
2-1 / 4" x2"
40A24 6351
24" Estate
J-175-H
2-1 / 8" x 1-3 / 4"
8A24 18146
24" Estate
J-175-H
2-1 / 8" x 1-3 / 4"
8B24 1601
26" Estate
J-175-H
2-1 / 8" x 1-3 / 4"
26" Estate
J-175-H
2-1 / 8" x 1-3 / 4"
26" Lawn King J-175-H
2-1 / 8" x 1-3 / 4"
12A26 12057
Note: Letters Hand V following numbers in Engine Type designate
Horizontal and Vertical Engines.
2
32B9 7863
8610 1601
42C18 21560
34C18 133087
75A18 14101
80A20 9601
2D21 78203
28F21 39749
39C21 42856
35D21 43130
9A22 20156
80A22 8601
8A26 1601
8B26 1601 .
12A26 12557

CONTENTS
Page
Foreword • • . . • . • • • • 1
How To Use The Service Manual 1
How To Order Repair Parts . • 1
What The Manual Will Do For You 1
Jacobsen Service Policy . . • • • . 2
Types of 1959 -1960 Jacobsen Engines and Starting Serial Numbers 2
1959 -1960 Jacobsen Engine Models Illustrated . • • • • • • • 4
Paragraph
SECTION I - SERVICE AND OPERATION
1. 1 Setting Up a Service Shop .
1. 2 Engine Model Identification
1. 3 Principles of Operation
1. 4 Care of Jacobsen Engine
General
Spark Plug . . . • •
Air Cleaner . • • •
Exhaust Ports and Muffler
1. 5 Fuels and Lubricants
SECTION II -ENGINE TROUBLE SHOOTING
2. 1 General Information •
Engine Trouble Chart
SECTION III -SERVICE DATA
Page
5
5
5
7
7
7
7
7
7
8
9
3. 1 General Information • . . • . . 11
3. 2 Specifications . • . . . . • . . 11
3. 3 Service Tolerance and Clearances 12
3. 4 Torque Da ta . • . . • • • . . 12
SECTION IV -MINOR OVERHAUL INSTRUCTIONS
4.1 General Information
13
4.2 Magneto Overhaul
13
" 4. 3
Carburetor Overhaul
16
4. 4
Fuel Line and Tank
18
4.5
Adjustments
18
4.6 starter Overhaul
19
Paragraph
SECTION V - MAJOR OVERHAUL
5.1 General Information .•
5. 2 Engine Disassembly • •
5. 3 Cleaning and Inspection
5. 4 Repair and Replacement
5. 5 Engine Reassembly . •
SECTION VI -ENGINE EXPLODED VIEWS
Page
20
20
21
22
22
6. 1 General Information • . . • • . • • 23
J-100 &J-125 Engine Disassembly Sequence
Horizontal Engine Exploded View . 24
Vertical Engine Exploded View • . 25
Engine Short Block Exploded View 26
Carburetor Exploded View • . . . 27.
Magneto Exploded View • • . . . 28
Automatic Rewind starter Exploded View 28
J-175 Engine Disassembly Sequence
Horizontal Engine Exploded View • 29
Vertical Engine Exploded View • . 30
Engine Short Block Exploded View 31
Carburetor Exploded View • . . • 32
Magneto Exploded View • • • • . 33
Automatic Rewind starter Exploded View 33
J-225 Engine Disassembly Sequence
Vertical Engine Exploded View • • • 34
Engine Short Block Exploded View 35
Carburetor Exploded View . . . . 36
Ma gneto Exploded View • • . . . 37
Automatic Rewind starter Exploded View · 37
3

SECTION I - SERVICE AND OPERATION--------------
J-125 Vertical Engine
J-100 Horizontal Engine J-175 Vertical
Gyro ..
Start-Spring Starter ..
J-175 Vertical Engine
J-175 Horizontal Engine
J-225 Vertical Engine
4

------------ENGINE SERVICE MANUAL
1. 1 SETTING UP A SERVICE SHOP
When setting up a service shop consider these three
things:
a. Available space
b. Repair business volume
c. Tool and equipment investment
Plan available floor space for most efficient use
in handling minor and major overhaul. Include a
suitable area for repair parts storage.
When planning the shop, use the repair business
volume expected to determine the total space need-
ed. Be sure to allow for expansion. Tools and
equipment are important for a profitable operation .
Arrange the shop for easy access and use of floor
mounted equipment.
Keep regular shop tools and Jacobsen special tools
in their proper places to eliminate lost time in
hunting for the right tool. Use test equipment for
diagnosing troubles and checking repaired units to
maintain a complete service and to save time in
performing repair services.
The following list of suggested tools and equipment
can be used as a guide for setting up a new serv-
ice shop.
Drill Press 1/ 2" Chuck
Set of Fraction Drills 1/16" to 1/ 2"
Wire Gauge Drills 1 to 60
1/ 211 Portable Electric Drill
Set of Easy-out Extractors
Tap and Die Set NF and NC
Air Compressor Welding and Cutting Gas
Arc Welder Bench Grinder 8" Wheel
Arbor Press 12-1 / 2" 3 ton
Vises 5
11
to 8
11
open
Taper Pin Reamer Set 0 to 5
Hand Reamer 1/ 411 to 1"
Expansion Hand Reamer 7/ 16
11
to 1"
Dial Test Indicator Combination Square Set
Telescoping Gauges Set 1/ 211 to 2-1 / 8"
Inside Micrometer 2
11
to 3
11
Micrometer Calipers 0" to 1"
Micrometer Calipers l 11 to 2"
Micrometer Calipers 211 to 3"
Hoist 500 lb. Electric
Bearing Puller Attachment
Grip Gear and Wheel Puller
Bed Knife Grinder (Ideal)*
Reel Grinder (Ideal or Modern)*
Impakdriver Set No. 67*
Torque Wrench -In. Lbs. & Ft. Lbs.
Steam Cleaner Cylinder Hone
Benches Parts Bins
Magneto Tester Lapping Machine
* Special equipment
1.2 ENGINE MODEL IDENTIFICATION
Jacobsen 2 cycle engines are built with horizon-
tal or vertical crankshafts in horsepowers ranging
from 1. .8 to 4. 25 H.P. They are also identified
by the Mower type and size indicated on the ser-
ial number plate. To further the identity of an
engine, measure the stroke and bore and refer to
specifications pages 11 and 12, for applicable infor-
mation.
The following engines, with variations, are the 1959
and 1960 models.
2" BORE X 1-1/2" STROKE - 1. 8, 2. 0 & 2. 25
H.P.
Jl 00 & J125 SERIES - Horizontal Crankshaft
2" BORE X 1-1/2" STROKE - 1. 8 & 2. 25 H.P.
JlOO & Jl25 SERIES - Vertical Crankshaft
2-1/8" BORE X 1-3/4" STROKE -3. 0 H.P.
Jl 75 SERIES - Horizontal Crankshaft
2-1/8" BORE X 1-3/4" STROKE -3. 0 H.P.
Jl 75 SERIES - Vertical Crankshaft
2-1 / 4" BORE X 211 STROKE - 4. 25 H.P.
J225 SERIES - Vertical Crankshaft
1. 3 PRINCIPLES OF OPERATION
The Jacobsen two cycle engine is a single cylinder
engine that fires every time the piston is moved
to the top of the stroke. Complicated valves and
lifters are not required because the piston takes
over some of the valve function in obtaining a pow-
er stroke each revolution of the crankshaft. The
use of ports, covered and uncovered by the move-
ment of the piston acts as a valve in controlling
the filling and emptying of the cylinder. Lubrica-
tion of all moving parts , is assured by a fuel mix-
ture of lubricating oil and gasoline.
The mixture of fuel and air is drawn from the
carburetor and into the crankcase when the piston
moves away from the crankshaft, creating a slight
vacuum in the crankcase. At the end of the stroke
the piston direction reverses and while moving into
the crankcase a slight pressure is built up. When
the piston moves far enough the intake ports are
uncovered to allow the mixture to enter the cylin-
der from the crankcase. The compressed charge
expands and drives out the exhaust gas through the
exhaust ports on the other side of the cylinder.
The charge is compressed as the piston again
moves away from the crankshaft sealing the in-
take and exhaust ports.
5

SECTION I - SERVICE AND OPERATION--------------
CHOKE L EVER
Figure 1. Jacobsen Engine Cross Section
Both ports are covered by the piston except for a
short time at the extreme end of the stroke near the
crankshaft.
When the piston has completed the compression of
the fuel mixture at the end of the stroke, away from
the crankshaft, the spark plug ignites the charge.
As it expands, the burning gases drive the piston
away to produce the power stroke on the crankshaft.
This two-stroke cycle is repeated each time the
piston reaches the end of the stroke to uncover the
ports.
The carburetor provides a combustible mixture of
fuel and air to the cylinder for ignition. Fuel is
metered to a stream of air flowing through a venturi
into the cylinder. The proportion of fuel to air is
controlled by a needle valve. The air flow atomizes
the fuel as it is drawn into the engine. Proportion
of fuel to air is important for efficient burning of
fuel. An excess of fuel (rich) produces partial com-
bustion due to insufficient air and results in sluggish
operation of the engine. An excess of air (lean) pro-
duces slow burning of fuel with a resultant loss of
power.
A float chamber maintains a steady supply of fuel
for the fuel-air mixture. Filling of the chamber
raises the float to shut off the flow of fuel. As fuel
is used , the float settles and opens the supply line
for additional fuel.
A flywheel type magneto (figure 2) , a high tension
wire and a spark plug complete the ignition system.
The magneto, a stationary self-contained generating
unit , includes the armature plate assembly (lamina-
tions and ignition coil), condenser and breaker point
6
assembly. The permanent magnet built into the fly-
wheel revolves around the stationary pole pieces in
the armature plate assembly. As the ends of the
magnet pass by the pole pieces, an alternating mag-
netic flux is established through the ignition coil. A
current is generated in the primary circuit during
the period that the breaker points are closed. A cam
located on the crankshaft opens the points when the
primary current is at a maximum. Interruption of
the current breaks the magnetic field around the coil.
The collapse of the magnetic field induces a high
voltage through the secondary winding of the coil ,
which is then carried through the high tension wire
to the spark plug. The current then jumps the spark
plug gap to ignite the fuel charge in the cylinder.
Each revolution of the crankshaft repeats the cycle
of ignition. The condenser, connected across the
contacts , absorbs the current which tends to contin-
ue after breaking contact. This hastens the collapse
of the magnetic field and reduces pitting of breaker
points by absorbing the sparking across the points.
The governor assembly is a simple unit consisting
of a governor vane located adjacent to the flywheel
and is connected by linkage to the carburetor throttle
lever. The air current produced by the flywheel acts
upon the governor vane. A governor spring has an
opposing effect on the vane. An equilibrium between
air force on the vane and the governor spring force
is created in this way, maintaining the selected
speed. If the speed of the engine drops due to a
sudden load,the air current produced by the flywheel
is reduced. Since the force exerted by the governor
spring is greater, it reacts on the throttle lever to
open the throttle and provide more fuel and air to the
engine. The engine speed increases until the equi-
librium of the air force and the governor spring is
at the proper balance for the new load condition.

CONDENSER
Figure 2. Magneto Assembly
1. 4 CARE OF JACOBSEN ENGINE
GENERAL - An engine received for service will
reveal characteristics or faults of operation that
will aid in proper servicing. For instance, oper-
ating an engine with too rich a fuel mixture or use
of a poor grade of lubricating oil will hasten carbon
formation on spark plu g, cylinder exhaust and in-
take port holes, piston, cylinder head and muffler.
Carbon formation at any of these points will reduce
engine power considerably. Build-up of carbon de-
posits can prevent an engine from running. When-
ever reinstalling cylinder head or muffler, use new
gaskets and tighten securely. If cylinder he ad is
not tightened securely, compression leaks will re-
sult.
Recognition of operation characteristics is a time
saver when performing minor or major overhaul.
SPARK PLUG - Normally a spark will jump the
gap between electrodes approximately 3000 times
a minute. It is important that a plug be kept clean
and the electrodes gapped to O. 035 ". Clean and
reset gap during every overhaul. Deposits on the
electrodes are sometimes caused by lead in gaso-
line or additives in oil. Proper adjustment of ca r-
buretor, correct types of gasoline and oil and the
recommended fuel mixture will prevent excessive
deposits and keep fouling of the plu g at a minimum.
Always be sure seat on cylinder head is clean and
that the copper gasket is used with the spark plug.
NOTE: Always use a "J " type spark plug to min-
imize bridging of the electrodes by foreign depos-
its.
ENGINE SERVICE MANUAL
AIR CLEANER - Three types of air cleaners are
used on Jacobsen engines: an aluminum foil type
cleaner, a paper filter or an oil bath type cleaner.
All are subject to clogging and restricting the flow
of air to the carburetor. An inadequate supply of
air will prevent engine from producing maximum
power and also cause the excessive fuel in the
mixture to burn improperly. Carbon will build up
at a fast rate in the cylinder and add to inefficient
operation of the engine. To properly clean the air
cleaner remove from engine and disassemble.
FOIL TYPE CLEANER. Wash and rinse thoroughly
in gasoline or other solvent. Shake off gasoline or
solvent and immerse in clean SAE 30 oil. Allow
excess oil to drain off before installing.
PAPER FILTER. Brush or wipe outside of cleaner.
Tap gently to loosen dirt from inside of filter.
Do not oil or wash filter. Filter can also be clean-
ed by gently blowing compressed air from the in-
side. If, after extended use, filter is too dirty
to clean properly, replace with a new filter.
OIL BATH TYPE CLEANER. Remove cover from
oil reservoir and dump out old oil. Wash cleaner
in gasoline or other solvent. Dry cleaner thor-
oughly. Refill to level indicated by arrow with
same grade of oil used for engine lubrication . .
EXHAUST PORTS AND MUFFLER
To clean carbon remove muffler and scrape and
clean all carbon from inside muffler. Use a
screwdriver or similar tool to clean out carbon
from exhaust ports. Make sure piston is at bottom
dead center when scraping ports.
When further disassembly is required to clean out
carbon from engine , remove cylinder head. Scrape
carbon from cylinder head , clean off top of piston
and also clean carbon deposits from intake ports.
To reach ports rotate crankshaft until piston reaches
bottom dead center.
1. 5 FUELS AND LUBRICANTS
Proper mixture of good REGULAR GASOLINE,
GRADE -70 to 85 octane , and non-detergent oil
is necessary to obtain top performance and trouble-
free operation of two-cycle engines. Do not use
low octane gasoline or cleaning fluid. This will
cause engine over-heating , pre-ignition, sticking
rings, excessive carbon in exhaust ports , and foul.:.
ing of the spark plug.
The oil mixed with gasoline lubricates all moving
parts of the engine as the fuel-air mixture is drawn
into the crankcase and cylinder. Always mix a half
pint of Jacobsen oil or a high quality outboard
motor oil to each gallon of regular grade gasoline
in a separate clean container. Never use dirty
gasoline or oil.
Use SAE 30 oil , if it is necessary to use other
than Jacobsen or outboard motor oil.
7

SECTION II -ENGINE TROUBLE SHOOTING ------------
2. 1 GENERAL INFORMATION
The most common areas of engine troubles are
the fuel and ignition systems. Before analyzing
an improperly running engine, make sure tank is
filled with fresh clean fuel of the proper mixture,
ignition has a good spark and all operating adjust-
ments are correct. Make a systematic check of
the engine's performance as follows and then use
the TROUBLE CHART to find the trouble.
Use this systematic method for checking out en-
gine hard starting or lack of power:
A. Check spark plug
Clean if necessary or replace. Set gap
at . 035"
9" Edge-R-Trim (32A9 & 32B9)
10" Trimo (3110 & 8610)
18" Pacer (42C18)
18" Turbo-Cut (34B18 & 34C18)
18" Turbo-Vac (7518 & 75A18)
20" Scepter (8020 & 80A20)
21" Lawn Queen (2C21 & 2D21)
21" Manor (28F21)
21" Turbo-Cut (39B21 & 39C21)
21" Turbo-Cut SP (35C21 & 35D21)
22" Putting Green (9A22)
22" Scepter (8022 & 80A22)
24" Estate (8A24 & 8B24)
24" Rotary SP (40A24)
26" Estate (8A26 & 8B26)
26" Lawn King (12A26)
B. Check carburetor
Initial settings now recommended:
Idle -1 turn open
Power - 1-1/4 turns open
See that the air cleaner, the screen in the shut-
off valve, and the screen in the float bowl cover
are clean.
C. Check engine speed
Proper speed adjustment is essential for best per-
formance and engine protection. Follow this guide
for correct settings: (See figure 3)
RPM Idle
RPM Top Speed
1500 to 2000 3000
to 3300
1500 to 2000 3400
to 3600
1300to 1600 Up to 3500
1500 to 1800 3000
to 3200
1500 to 2000 3400
to 3500
1500 to 1800 3000
to 3200
1300 to 1600 Up
to 3500
1300 to 1600
Up to 3500
1500 to 1800 3000
to 3200
1500 to 1800
Up
to 3500
1500 to 1800 Up
to 3400
1500 to 1800 3000 to 3200
1300to 1600 Up
to 3800
1900 to 2100
Up to 3750
1300to 1600 Up
to 3800
1300to 1600
Up
to 3200
NOTE:
Use Vibra-Tak to check RPM's (figure 3).
D. Check magneto output
Magneto can now be checked quickly without re-
moving it from the engine by using the special
No. S14281 Wico Test Plug shown in figure 4.
The test plug is for use in testing magneto out-
put at starting speeds. Note that the engine spark
plug is left in place when this test is being made.
If no spark is present during the test then follow
these steps to check the entire magneto:
1. Remove flywheel. Inspect the breaker points
for pitting or corrosion and, if necessary, dress
the points with a point file. Set the breaker
points to • 020", then clean points by drawing
a piece of hard paper such as card stock be-
tween them.
2. Drill a 1/ 8" vent hole in breaker box on Wico
or Phelan magneto as shown in figure 2. This
8
will ventilate the breaker box and prevent the
formation of moisture from condensation and
oxidation of breaker points.
3. Check the stop switch wire overall for breaks
in the insulation, for shorting at the terminal
on the tank panel or carburetor throttle control
and check all other wires for shorts and loose-
ness.
4. Reinstall the flywheel and again check for . spark.
5. If the spark is still weak or does not exist use
a tester such as a Graham or Merc-0-Tronic
to check the coil and condenser.
If the magneto tests satisfactorily and the engine
still will not start or is hard to start when cold
or hot, follow the steps listed in the adjoining
check chart.
I