Technical Information · issue 18 of 2005
New STIHL BT 121 earth auger
IssueTI 18/2005
Full text
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STIH)
Technical Information 18.2005
New STIHL BT 121 earth auger – Series 4313
Contents
1. Technical description
2. Specifications
3. Service accessories and special tools
4. Repairs
5. Spare parts
TI_18_2005_30_01_01.fm englisch / English USA
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1. Technical description 2.2 Fuel System
The new STIHL BT 121 earth auger is an improved Carburetor: All position diaphragm carburetor with
modification of the prior BT 120 C and will replace it limiter cap on the H-screw
in the product line.
The most significant change is the new, quadruple, Standard limiter cap setting on the H-screw
vibration-suppressed handle frame. The substantial High-speed adjustment
reduction of vibrations allows you to work more screw H Open 3/4 turn
comfortably with less effort. (max. to stop)
The newly developed, large padding also enhances
comfort of use. Low-speed adjustment
screw L: 1 turn open
The STIHL Quickstop® auger brake comes
standard as with the BT 120 C.
The engine and transmission are identical to those Basic service setting (without the limiter cap on
of the BT 120 C. the H-screw)
The users and possible applications are the same High-speed adjustment
as for the BT 120 C: screw H Open 1 3/4 turns
. Agriculture and forestry Low-speed adjustment
. Landscaping businesses, tree nurseries screw L: 1 turn open
. Municipal agencies and road construction
companies
Fuel tank capacity: 1.35 US pt (0.64 l)
. Vintners and fruit farms
. Manufacturers of sports facilities and sports
equipment Fuel mixture
The fuel mixture is the same as for all STIHL
two-stroke motors.
2. Specifications
2.3 Ignition System
2.1 Engine Ignition System: Electronically controlled
STIHL single cylinder two-stroke engine Spark plug
(suppressed): NGK BPMR 7 A
Displacement 1.88 cu.in (30.8 cm3) Bosch WSR 6 F
Cylinder bore 1.38 in (35 mm) Electrode gap: 0.020 in (0.5 mm)
Piston stroke 1.26 in (32 mm)
Power output to ISO 8893 1.8 bhp (1.3 kW) 2.4 Gear
Idle speed 2,800 rpm Model: Two-speed cylindrical
Max. motor speed without gearing
auger 12,300 rpm Gear ratio: 47.5 : 1
Max. spindle speed: 190 rpm
Weight without auger 20.7 lb (9.4 kg)
Max. torque
(drill spindle): 79 Nm
Lubrication: STIHL gear lubricant for
brushcutters
Amount of grease: 6 oz (first time filled)
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Technical Information 18.2005 Page 3
2.5 Earth augers
The following earth augers are approved:
Item Part name Part No. Remarks
1 Earth auger; 1.6 in dia (40 mm), 27.4 in (695 mm) long 4404 680 2004 1)
2 Earth auger; 2.4 in dia (60 mm), 27.4 in (695 mm) long 4404 680 2006 1)
3 Earth auger; 3.5 in dia (90 mm), 27.4 in (695 mm) long 4404 680 2009 1)
4 Earth auger; 4.7 in dia (120 mm), 27.4 in (695 mm) long 4404 680 2012 1)
5 Earth auger; 5.9 in dia (150 mm), 27.4 in (695 mm) long 4404 680 2015 1)
6 Earth auger; 7.9 in dia (200 mm), 27.4 in (695 mm) long 4404 680 2020 1)
7 Shaft extension, 17.7 in (450 mm) long 4311 680 2350 1)
8 Planting hole drill; 10.2 in dia (260 mm) 4404 680 1900 1)
9 Planting auger, 6 in dia (150 mm), 20.6 in (525 mm) long 4311 680 2515 1)
10 Chuck for augers from 5/64" to 1/2" (2 to 13 mm) 4311 680 4010 1)
Remarks
1) See replacement parts documentation for individual parts
3. Service accessories and special
tools
3.1 Service accessories
Part name Part number Use
Set of carburetor parts 1129 007 1062 Repairing the carburetor
Set of gaskets 4134 007 1050 Repairing the engine
Grease (225 g tube) 0781 120 1111 Oil seals
Gear lubricant (225 g tube) 0781 120 1118 Gear lubrication
Dirko HT red sealant 0783 830 2000 Crankcase/auger drilling gear sealing surfaces
Standard commercially Cleaning crankshaft stub and cone on flywheel
available CFC and HFC-free
solvent-based degreasing
agent
3.2 Special Servicing Tools
No new special tools are required for the BT 121
earth auger. The special tools needed for repairs are
listed in the repair instructions for the BT 120 C and
FS 120.
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4. Repairs
Specific national safety regulations and the safety
instructions in the User Manual must be observed
when starting the machine.
The repair instructions for the BT 120 C (drilling
gear) and FS 120 (motor) can be used for repairs.
4.1 Repair times
The repair timetable for the BT120 C can also be
used for the BT121.
4.2 Serial number
The machine number is clearly visible on the right
side of the auger on the fuel tank (see arrow).
5. Spare parts
A separate illustrated parts list is available for the
BT 121.
© ANDREAS STIHL AG & Co. KG, 2005 Technical Documentation
D1/MTK-sc
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Extracted from the manufacturer's 2012 service catalogue. Most of these PDFs embed fonts with a shifted character map, so the text above was recovered rather than copied — read it as a faithful but imperfect transcription, and treat the page image above each block as the authority where the two disagree — the figures exist only there, because they are vector drawings that text extraction cannot keep.