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

ENGINE SERVICE MANUAL
figure 3. Checking RPM with VISRA-TAK figure 4. Checking Spark with
Test Plug
ENGINE TROUBLE CHART
Trouble
I
Remedy
IGNITION
Weak spark or intermittent spark
A. Magneto points dirty or improperly set.
B. Weak condenser or coil.
C. Fungus or oxide coating on breaker.
D. Loose or broken wires.
Black carbon or sooty deposit
A. Excessive oil in fuel mixture.
B. Points dirty or out of adjustment.
C. Wrong spark plug heat range.
D. Carburetor setting too rich.
Carbon and lead bridging of plug gap.
A. Caused by gas and oil with high additives being
used.
B. Excessive carbon in ~ylinder head, on piston
head, or in exhaust ports.
C. Engine overheating.
D. Engine runs too fast.
A. Dress , adjust to .020", and clean.
B. Check and replace if necessary.
C. Clean with a household detergent. Drill a 1/ 8"
vent hole in the breaker box.
D. Tighten or replace.
A. Check for correct fuel mixture.
B. Clean and adjust spark plug gap to . 035 ".
C. Install plug in correct heat range set at . 035".
D. Set power adjustment 1-1 / 4 turns initially and
readjust to optimum.
A. Use different brand of non-detergent or low-
deter g ent oil. Also try different brand of reg-
ular grade gasoline. DO NOT USE WHITE GAS
UNLESS IT IS MARINE GASOLINE.
B. Clean carbon from cylinder head, piston, and
exhaust ports.
C. Clean grass , dirt, etc. from cooling fins of
cylinder and from starter screen.
D. Clean dirt and grass from governor vane and
governor linkage. Readjust linkage for correct
speed.
9

SECTION II -ENGINE TROUBLE SHOOTING ------------
ENGINE TROUBLE CHART (Cont)
Trouble
I
Remedy
CARBURETOR
Engine floods
A. Choke improperly adjusted.
B. Float improperly set.
C. Dirt in needle and seat.
D. High speed needle improperly set.
E. Air filter dirty.
Engine starves
A. Float valve corroded or gummed so that needle
valve doesn't open.
B. Water or foreign matter in the fuel.
C. Float level set too low.
D. Air filter dirty.
E. High speed needle improperly set.
F. Plugged vent in the gas cap.
G. Idle adjustment improperly set.
H. Heat range of spark plug too high.
I. Screen in carburetor and shut-off valve plugged.
J. Kinked fuel line.
A. Adjust choke linkage and shutter.
B. Adjust float level.
C. Clean or replace needle and seat.
D. Set high speed needle 1-1 / 4 turns open and re-
adjust to optimum.
E. Clean air filter or replace.
A. Clean or replace valve.
B. Clean carburetor and fuel tank.
C. Reset float level.
D. Clean air filter or replace.
E. Set high speed needle 1-1 / 4 turns open and re-
adjust to optimum.
F. Clean or replace cap.
G. Set idle adjustment 1 turn open.
H. Use lower heat range plug.
I. Clean or replace.
J. Replace line. Correct position of fitting in fuel
tank.
COMPRESSION
A. Loose spark plug.
B. Loose head or blown head gasket.
C. Piston rings carboned, worn, or broken.
D. Galled or burned piston.
E. Worn cylinder.
F. Poor lubrication.
G. Worn or damaged piston ring grooves.
H. Defective crankshaft oil seals.
10
A. Tighten spark plug.
B. Tighten head or replace head gasket.
C. Remove, clean, or replace.
D. Clean cylinder wall and replace piston.
E. Rebore and fit new oversize piston or replace.
F. Use proper fuel mixture.
G. Replace piston and rings.
H. Place small amount of oil around crankshaft
at oil seal. If oil is drawn into engine, seal
is leaking. Replace seal.

SECTION Ill - SERVICE DATA
\
·----- -~ - - -.-- --- -
l
3.1 GENERAL INFORMATIO.N K',' ~ '
\ . , ~<;· \1; ·r·!. i ·1 .
To provide the best service for .1 tt c i?~ . s e # i' ~~ ? · ..: · c, y~1e
engines follow the factory recommended specifica-
tions, tolerances and clearances, torque data and
special tools. The following data is applicable to
all 1959-1960 engine models.
Jacobsen engines can be disassembled and reas-
sembled with standard shop tools. However several
tools are recommended for particular functions of
repair:
A. Flywheel Knockout Nut - threads onto crank-
shaft to facilitate flywheel removal.
B. Timing Gage and Flywheel Holder - used to
RING
COMPRESSOR
J-100
J-125
J-175
J-225
SPARK
TESTER
J-100
J-125
CRANKSHAFT OIL
SEAL STARTER SLEEVES
set ignition timing and to lock piston at bot-
tom dead center for easy removal of starter
pawl assembly.
C. Oil Seal Starter Sleeve - use on crankshaft to
protect oil seal when removing or installing
back plate or crankcase head.
D. Large Wrist Pin Drift - use to remove and in-
stall wrist pin in piston.
E. Vibra-Tak - used to check RPM's of engine.
F. Ring Compressor - used to compress rings
when installing piston in cylinder.
G. Wico Test Plug - used to test magneto.
BALL
RETAINER
REMOVER
J-175
FLYWHEEL
KNOCKOUT
J-225
VIBRA-TAK
CLUTCH PLATE
RIVETING TOOL
TIMING GAUGE
AND FLYWHEEL
HOLDER
Figure 5. Special Tools
3. 2 sPECIFICATIONS
J-125-H
J-175-H
J-100-H J-125-V
J-175-V
J-225-V
Horse Power 2. 25
1. 8
2.25 3 4
Piston Displacement 4.71
4. 71 6. 206 7.95
Compression Ratio 5.5-1 5.5-1
5.5-1 5.333-1
. Cyl. Head Compression 80-85
80-85 85-90 85-90
Recommended Spark Plug
UJ-12
J-11-J J-11-J
J-8-J J-8-J
Stroke
1.500
1.500
1. 750 2.000
11

SECTION Ill - SERVICE DATA------------------
3. 3 SERVICE TOLERANCES AND CLEARANCES
Cylinder Bore
Piston Skirt Diameter
Piston Ring Width
Piston Pin Diameter
Piston Pin Bore in Piston
Piston Pin Bore in Rod
Crank Pin Diameter
Crank Pin Width
Conn. Rod Bore
Conn. Rod Crankpin Width
Spark Plug Gap
Mag. Point Gap
Timing in Degrees B. T. D. C.
Timing in Inches of Piston Travel B. T. D. C.
Piston Skirt to Cylinder Clearance
Maximum Wear Tolerance on Cylinder Bore
Maximum out of round Tolerance
Piston Ring End Gap
Piston Ring to Land Side Clearance
Piston Pin Clearance in Rod
Conn. Rod Clearance
Conn. _ Rod Crankpin Side Clearance
a. J-175-V .0935
b. ( .00
2)
J-175-V
( . 003)
* Needle - Bearing Used.
3.4 TORQUE DATA
Head Bolts -180 inch pounds all models
Connecting Rod - 70-75 inch pounds all models
J-125-H
J-100..,H
J-125-V
2.0015 2.0015
2.0010 2.0010
1. 9970 1. 9970
1. 9965
1. 9965
.0905 •0905
.089
.089
• 50025 . 50025
.49975 •49975
.5003 . 5003
. 5000 • 5000
·•50125 • 50125
.50075 • 50075
•6245 • 6235
• 6240 • 6230
.817 •817
•812
.812
• 627 . 627
• 626 • 626
.808 .808
. 800 •800
.035 .035
.020 .020
30 ° 30°
.125 .125
.004
.004
.005 .005
.002 .002
.0015 .0015
.005
.005
.010 .010
.0035 .0035
.0055
.0055
.0005 .0005
.0015
.0015
.0015 . 0025
.003 .004
. 004 .004
.017 .017
All other bolts or studs in aluminum. Not to exceed 180 inch pounds .
12
J-175-H
J-175-V
J-225-V
2.1265
2.2515
2.126
2.2510
2.1240 2.2480
2.1235 2.2475
a•
.0625 .0925
•0615
.0935
• 50025 • 50025
•49975 •49975
•5003 • 5003
•5000
-5000
• 5008 • 687 *·
• 5015 • 688
•7485 •7503
• 748
.7500
.938
• 568
.933 • 563
•7525
.9403 *
.07530 .9399
.929 .555
.921 • 550
.035 .035
.020
.020
28° 27°
.125 .125
.002 .003
.003
.004
.002 .002
.0015 •0015
59-.005-.013
.005
60-.052-.060
.013
.004
.002
b. .006 .0035
.0005 Needle
.0017
Bre:s•
.0030
Needle
.0040
Brgs .
.004 .008
.017 .018

SECTION IV - MINOR OVERHAUL INSTRUCTIONS
4.1 GENERAL INFORMATION
When an engine is not operating properly, a minor
tune-up or overhaul is necessary to bring it up to
good performance.
For a minor tune-up check as follows:
A. Fuel mixture in tank.
Check and clean fuel line and connections
and see that fuel is flowing to carburetor.
B. Check ignition for adequate spark.
If necessary, refer to Magneto Overhaul,
paragraph 4.2.
Check for correct spark plug. ·Clean plug
and adjust points.
C. Check air cleaner, carburetor and linkage.
Clean air cleaner thoroughly.
Adjust carburetor, refer to paragraph 4.3 .
If performance indicates a dirty and slug-
gish carburetor, refer to Carburetor Over-
haul, paragraph 4.3.
D. Check compression by slowly engaging
starter. Throttle should be open when
checking compression.
NOTE: On rotary mowers, do not make
compression check unless cutting disc is
removed.
If compression is low, refer to Section V,
Major Overhaul.
E. If excessive carbon is indicated by slug-
gish operation and inspection of spark plug
opening and muffler, refer to Section V,
Major Overhaul.
F. Tighten all external nuts, bolts and screws .
Clean engine thoroughly.
For minor overhaul of engine refer to the follow-
ing:
Magneto Overhaul, paragraph 4.2
Carburetor Overhaul, paragraph 4.3
Fuel Line and Tank, paragraph 4.4
Adjustments, paragraph 4.5
Starter Overhaul, paragraph 4.6
4.2 MAGNETO OVERHAUL
To overhaul magneto disassemble engine as follows:
A. Remove automatic rewind or gyro starter
by removing the screws that fasten it to
the flywheel. housing. See figure 6.
B. Remove screws from flywheel housing and
high tension wire clip and slip off housing.
On some models the fuel tank is attached
to the housing and must also be removed.
This requires disconnection of the fuel
line and carburetor linkage., See figure 6.
Figure 6. Disassembling Engine
C. Remove spark plug and insert flywheel
holder . special tool (figure 5) in opening.
Turn flywheel until piston is at bottom
dead center. Screw in stud of special tool
until it locks piston, then tighten lock nut.
D. Use a 5/ 8" socket wrench on nut of start-
er pawl assembly and remove assembly.
See figure 7.
E. Screw flywheel knockout nut on crankshaft.
Pull up on flywheel with one hand and with
the other hand tap nut sharply with a steel
hammer. Flywheel will snap loose from
crankshaft. See figure 8.
NOTE: Never strike crankshaft directly
with a steel hammer. The knockout nut
must be used to prevent damage to threads
and bending the crankshaft.
13

SECTION IV - MINOR OVERHAUL INSTRUCTIONS-----------
figure 7. Removing Starter Pawl
figure 8. Removing Flywheel
Breaker points, adjusting and timing magneto.
14
A. Remove cover plate and gasket from stator
assembly for inspection of breaker points
and adjustment of magneto.
B. If breaker points are dirty or corroded,
dress them with a point file. If burned,
pitted, or badly worn replace both points.
To replace points, remove the connection
stud nut, connection stud and contact clamp
screw. Be certain to clean points after
dressing by drawing a piece of hard paper
such as card stock between points.
C. If the points are badly pitted replace the
condenser.
D. The flywheel requires no recharging as
the magnets used in it are made of Alnico
which retains its magnetism indefinitely.
E. Check all soldered connections. Resolder
if necessary. Check breaker spring and
mechanism to be sure they are in good
operating condition.
F. Test the ignition coil and condenser if
testing equipment is available. To remove
coil and condenser refer to J, page 15.
G. The only lubrication required is supplied
by the cam wiper felt. Install new felt
when servicing magneto. Place a small
amount of soft grease on felt.
H. Reset breaker point gap as follows:
Turn crankshaft until the breaker arm
shoe is on the high point of the cam.
Measure the gap with a feeler gage. The
opening should be . 020 inch. If points
need adjusting, loosen adjustment screw
with screw driver and move breaker plate
for correct setting. Tighten screw and
recheck gap. See figure 9.
I. Retime magneto as follows:
Use timing gage (special tool) described
in paragraph 3.1, subparagraph B. For
timing, bring piston to top dead center.
Run the long bolt against piston top. With
nut against spark plug shell, back off nut
two full turns. Back up piston and run
figure 9. Adjusting Magneto Breaker Points

------------ENGINE SERVICE MANUAL
long screw in until nut is tight against
plug shell. Bring piston back up against
long screw and it will be in correct tim-
ing position.
Loosen two fillister head screws holding
stator plate and move plate until points
just begin to break. See figure 10. Tighten
screws. Recheck timing gage setting and
position of points for correct timing.
J. To complete disassembly of magneto, pro-
ceed as follows:
1. Remove flywheel key from the crank-
shaft.
2. Remove two fillister head screws hold-
ing stator plate assembly to magneto
back plate. Remove magneto and pull
high tension wire through back plate.
3. Remove cam positioning ring from
crankshaft. This can be done easily
with a screw driver, being careful not
to damage keyway. See figure 11.
4. Remove four screws securing magneto
back plate to crankcase. On J-100 and
J-125 engines, place oil seal sleeve
(figure 5) over threaded end of crank-
shaft. Use tape to protect threads on
other engines. This precaution will
prevent cutting oil seal when remov-
ing back plate. See figure 12.
NOTE: Exploded views of each type of
Jacobsen eng - ine are shown in Section V,
Major Overhaul. All parts are num-
bered in the order of disassembly. To
disassemble, remove parts in sequence
of index numbers.
Figure 10. Timing Magneto
Figure 11. Removing Cam Positioning Ring
Figure 12. Removing Magneto Baclc Plate
Reassemble magneto and engine parts.
A. To reassemble parts that have been re-
moved to the magneto back plate, refer
to the exploded views in Section VI. Re-
assemble in reverse order of the sequence
of index numbers.
15

SECTION IV - MINOR OVERHAUL INSTRUCTIONS----------
B. The following important items are listed
to help reassembly:
Be sure high tension wire is pushed through
hole in magneto back plate.
Be sure smaller diameter of breaker cam
faces upwards when installing.
Be sure magneto breaker points and tim-
ing are adjusted properly.
Be sure key is inserted into crankshaft
before flywheel is installed.
Be sure nut on starter pawl assembly is
securely tightened.
C. Check operation of engine after assembly.
4. 3 CARBURETOR OVERHAUL
Remove and disassemble carburetor. Refer to the
exploded views in Section V for disassembly pro-
cedure of carburetor that applies. All parts are
numbered in order of disassembly.
16
A. Remove fuel line from inlet on carburetor.
See figure 13.
NOTE: If fuel line is difficult to disen-
gage, use a screw driver to pry end loose
from inlet.
Figure 13. Removing Fuel line
B. Remove wing nuts that hold air cleaner
to carburetor. See figure 14. Disassem-
ble air cleaner and clean thoroughly. Refer
to paragraph 1. 4, air cleaner.
Figure 14. Removing Air Cleaner
C. Remove four screws that hold carburetor
adapter to engine. Disengage governor
linkage and remove carburetor and adapt-
er assembly. See figure 15. On all models
the reed valve is part of this assembly.
Refer to the exploded view in Section VI,
for disassembly of carburetor and adapter.
Figure 15. Removing Adapter and Carburetor

------------ENGINE SERVICE MANUAL
D. After disassembly of carburetor, clean all
parts in a grease solvent. Air dry all
parts instead of using cloth to avoid ac-
cumulation of lint. To remove gummy de-
posits in parts , float bowl, needle valve,
idle tube, adjustment screw, etc. use al-
cohol. Remove gasket material and clean
all gasket surfaces thoroughly.
NOTE: Clean out high speed needle valve
opening with 1/ 16" drill to make sure it
is clean.
E. Inspect needle ends of idle adjustment and
main adjusting screws and inlet needle for
bent or scored tapered ends. Replace
damaged needles; do not attempt to repair
them. Make sure needle valve seats are
not damaged.
F. Inspect reed valve surface of adapter be-
fore installing. Surface must be absolute-
ly clean and reed must be installed to
completely cover intake hole and lay per-
fectly flat against the adapter. Reed is
made with a slight bend in it to apply
tension against adapter and act as an in-
let valve. Dirt or grit on surface or an
incorrectly positioned reed can cause blow
back through carburetor.
G. Reassemble carburetor in reverse order
of number sequence on exploded view.
Parts are numbered in order of disas-
sembly.
Use all new gaskets and use new packing
for main adjustment screw. Thread new
packing on main adjustment screw , with
the black face away from needle. Thread
packing far enough on screw to expose
three or four threads. Install screw into
carburetor body far enough to gently seat
needle point. Install packing nut so that
it is tight against the packing. Back main
adjustment screw away from seat 1-1 / 4
to 1-1 / 2 turns.
NOTE: Before assembling main adjust-
ment screw, the packing nut and packing
must be removed and reassembled as di-
rected above. If nut and packing are not
removed . and installed correctly, small
pieces of packing will be pushed into fuel
channels causing restrictions to fuel flow.
H. Check carburetor float setting. Use idle
tube as gage for 1/ 16 - 3/ 32 " distance
between bowl cover flange and nearest edge
of float when bowl cover assembly is in
inverted position. Bend tab on float for
correct settin g. See figure 16. If car-
buretor has a plastic float measure in
same manner , setting distance at 5/ 16",
IDLE
TUBE
Figure 16. Adjustment of Float
I. Install carburetor and adapter assembly
on engine. Install air cleaner assembly,
making sure it has been thoroughlyclean-
ed.
Adjust carburetor using the following screws:
MAIN ADJUSTMENT SCREW - Controls power
range mixture
IDLE MIXTURE SCREW - Governs idle mix-
ture at closed throttle
IDLE SPEED REGULATING SCREW - Con-
trols required idling speed
A. INITIAL ADJUSTMENT: Completelr close
the IDLE MIXTURE SCREW by turning in
without forcing until seated. Then turn
screw in opposite direction one turn. Pro-
ceed in like manner with MAIN ADJUST-
MENT SCREW except open one and one-
half full turn after first being closed. Now
choke and start engine in usual manner
and run until thoroughly warm.
B. MAIN ADJUSTMENT SCREW ADJUST-
MENT: With speed control lever set at
fast position, slowly turn MAIN ADJUST-
MENT SCREW inward until motor begins
to lose speed. Then slowly turn screw · in
opposite direction (usually 1/ Bth to 1/ 4th
of a turn) until maximum speed and power
is obtained which is then final adjustment
setting.
C. IDLE MIXTURE SCREW: This adjustment
should only be made AFTER the above
mentioned MAIN ADJUSTMENT SCREW
has been completed. Close throttle and
allow engine to idle at slightly faster than
17

SECTION IV - MINOR OVERHAUL INSTRUCTIONS-----------
normal idling speed requirements by turn-
ing IDLE SPEED REGULATING SCREW,
located in throttle stop boss, INWARD.
Next, slowly turn IDLE MIXTURE SCREW
inward until motor begins to lose speed
and miss or flutter; then turn screw in
opposite direction, usually about one-eighth
of a turn, until engine functions smoothly
and steadily.
D. IDLE SPEED REGULATING SCREW: This
adjustment is made after the above two
adjustments. Engine will be idling faster
than normal at this point. Now slowly
back out IDLE SPEED REGULATING
SCREW until desired idling speed is ob-
tained. Refer to figure 17.
IDLE SPEED
REGULATING SCREW
IDLE MIXTURE
SCREW
MAIN ADJUSTMENT
SCREW
IDLE MIXTURE
SCREW~
MAIN ADJUSTMENT
SCREW
CHOKE LEVER
(RUNNING POSITION)
CHOKE LEVER
Figure 17. Carburetor Adjustment
4. 4 FUEL LINE AND TANK
Remove and clean fuel line and tank. Refer to
exploded view in Section VI that applies to the en-
gine assembly. Parts are numbered in order of
disassembly.
18
A. Remove fuel line from inlet on carburetor
and on fuel tank. If fuel line is difficult
to disengage, use a screw driver to pry
ends loose from inlets. Clean fuel line
thoroughly with grease solvent and blow
out with air.
B. Remove fuel tank from engine by remov-
ing screws holding adapter. Some models
have additional engine cowling or throttle
linkage which will first have to be re-
moved. If necessary, release bands hold-
ing tank to cowling or adapter bracket.
Clean out tank thoroughly with a grease
solvent. If a gummy substance still re-
mains, use alcohol to clean. Be certain
to remove shut-off valve to thoroughly
clean the valve and screen. Blow air into
tank and through inlet to air dry thorough-
ly.
C. Reassemble fuel tank, adapter and cowl-
ing and install on engine •. Connect throttle
linkage if disconnect was necessary. In-
stall fuel line by pushing ends over inlet
on fuel tank and carburetor. Reassemble
all parts in · reverse order of sequence
shown on exploded views.
4. 5 ADJUSTMENTS
Ignition system - for easy starting, best perform-
ance and plug life maintain a magneto breaker point
setting of . 020" and a spark plug gap of . 035".
The following examples indicate the effects of im-
proper settings, on the magneto secondary output
voltage:
Magneto closepoint setting (. 008" to •010 ') -
results in hard starting caused by low voltage
at normal cranking speeds.
Magneto wide point setting (. 030" to . 032 ') -
may cause rapid plug fouling, intermittent
secondary voltage output or even no secondary
voltage output.
Spark plug close electrode gap (. 020" and
under) - may cause rapid plug fouling because
of bridging.
Spark plug wide electrode gap (. 040" and high-
er) - may cause hard starting because of the
high voltage required to jump the gap under
compr _ ession.
Governor linkage - adjustment of linkage for prop-
er speed control by the air vane type governor is
accomplished on horizontal models previous to 1959
as follows: (Refer to figure 18)