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- - - - - - - - - - - - E N G I N E 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/
2
11
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/
4
11
to 1"
Expansion Hand Reamer
7/
16
11
to 1"
Dial Test Indicator
Combination Square Set
Telescoping Gauges Set
1/
2
11
to 2-1
/
8"
Inside Micrometer 2
11
to 3
11
Micrometer Calipers 0" to 1"
Micrometer Calipers l
11
to 2"
Micrometer Calipers 2
11
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 2
11
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
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