Technical Information · issue 31 of 1995
Air filter system with compensator; decompression
Model 026 chainsaws from machine number
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Technical Information
31.95
Model 024, 026 Chainsaws - Series 1121
&RQWHQWV
1. STIHL 026: Air filter system with compensator (air filter, carburetor, carburetor box cover),
Decompression valve (cylinder, shroud)
2. 026 oil pump (service note)
3. Chain brake (stronger brake spring)
1.=======Air filter system with compensator,
decompression valve
Model 026 chainsaws from machine number
X 32 252 039=will come with a newly developed
air filter system and decompression valve. The
filter system considerably improves particle reten-
tion and, together with the compensator, helps
extend filter service life many times over. This
permits very long periods of operation and thus
reduces maintenance costs. The decompression
valve helps bring about a considerable increase in
133TI004 KN
starting comfort.
The assemblies and parts affected by the
modification are described below.
1.1======Air filter system with compensator
Benefits and features of the new air filter:
• Much larger filter area
• Filter fabric made of two-ply polyamide
(instead of wire mesh)
• Integrally molded baffle (no longer available as
separate item)
• Redesigned and optimized choke shutter
• Inner half of filter with connector for
133TI005 KN
compensator
• Retaining lugs for the carburetor box cover
• A "felt" filter is available in place of the
"flocked" air filter Original New
version version
)Technical Information 31.95 - Page 2
The connector on the metering end cover of the
new FDUEXUHWRU projects into the inner half of the
air filter. This connection between the clean air side
of the air filters and the outside of the metering
diaphragm produces the compensator effect.
The FRPSHQVDWRU keeps the fuel content in the
air flow constant at all times, irrespective of how
dirty the air filter is. The mixture cannot become
over-rich and it is no longer necessary to change
133TI006 KN
the setting of the high speed screw as contamina-
tion of the air filter increases.
The new carburetor box cover=has been designed
so that combustion air is no longer drawn it at the
top (through the gap), but at the bottom (between
the carburetor box cover and tank housing). 2
The carburetor box cover is secured to the air filter
with a twist-lock lever (1) which turns through 90°. 1
The original wire mesh prefilter has been replaced
by an integrally molded plastic screen which is
sealed off for summer operation by cover (2). fo
133TI007 KN
To change over to winter operation it is necessary
to remove this cover and fit it in the slot at the
bottom of the carburetor box cover (see arrow).
This causes warm air from around the cylinder to be
drawn in along with cold air. Carburetor box cover 1121 140 1904
1.2===Decompression valve
The decompression valve releases the compres-
sion in the combustion chamber during starts and
thus reduces the effort required to pull the starter
rope and enhances operator comfort. The valve is
opened manually and closes automatically as soon
as the engine begins to fire.
The shroud now has an opening to accommodate
the decompression valve.
The area around the opening is raised (see arrow)
to protect the decompression valve from accidental
contact.
A cover 1122 084 1405 is fitted between the
cylinder and shroud to help prevent the ingress of
dust and dirt.
133TI008 LÄ
)Technical Information 31.95 - Page 3
1.3===Parts availability
The original versions of the air filter and carburetor
box cover remain available as replacement parts.
The original end cover is supplied with the new
replacement carburetor 1121 120 0650 for use in
026 saws without compensator (and for the 024).
Only the new versions of the shroud and cylinder
are available. If they are used for a machine wit-
hout decompression valve, the opening must be
sealed with the cap 1122 084 7100 provided and
133TI009 LÄ
the tapped hole for the decompression valve
sealed with the plug 1122 025 2200.
The cap and plug are therefore included in the
scope of supply of the new replacement parts.
1 Cap 2 Plug
1122 084 7100 1122 025 2200
1.4===Service note
Air filter system, carburetor
The component parts of the new air filter system
(air filter, carburetor with connector for compensa-
tor and carburetor box cover) may only be installed
in model 026 saws from machine number
X 30 976 775 and only as a complete assembly.
Tank housings with a new (lower) tank vent (see
TI 06.95) were installed for the first time from this
machine number, and this provides sufficient
space for the extra width of the new air filter.
The carburetor’s high and low speed adjusting
screws are sealed with LOCTITE 221.
In the event of repairs to a carburetor with compen-
sator cover, the adjusting screws must be cleaned
thoroughly before installation and recoated with
fresh=il`qfqb=OONK=Do not apply LOCTITE to
the first two to three turns of the thread - under
no circumstances may adhesive get into the
carburetor!
Correctly sealed adjusting screws tend to be a
little difficult to turn.
Decompression valve
The decompression valve can be removed and
installed with a standard deep well 13-mm socket.
Tightening torque 14 Nm (10.3 lbf.ft).
To carry out the pressure test on the engine, we
recommend that the decompression valve be
removed and the tapped hole sealed with the
plug 1122 025 2200.
Important!=fn case of repairs, remove the decom-
pression valve before fitting the locking strip
(to block the piston).
The new repair kit 1121 900 9004 and new intake
air preheating kit 1121 007 1044 are available for
models 026 with the new air filter system.
)Technical Information 31.95 - Page 4
1.5===Summary
133TI010 LÄ
Parts of original version
133TI011 LÄ
Parts of new version
)Technical Information 31.95 - Page 5
Item Part Name Original New Rem.
version version
1 Air filter; 1121 120 1611 1121 120 1617 1)
Air filter "flocked"; 1121 120 1612 --- 1)
Air filter "felt"; --- 1121 120 1618
each of above includes items 2 - 6:
2 Baffle 1121 121 7001 --- 1)
3 Slotted nut 1121 141 8300 1124 141 8300 1)
4 Spring 0000 997 5505 1121 124 3000 1)
5 Choke shutter 1121 121 2900 1121 121 2905 1)
6 Split pin 2x10 9395 825 1090 --- 1)
7 Carburetor; 1121 120 0606 1121 120 0650 2)3)
including items 8 to 10:
8 End cover 1113 121 0800 1121 121 0810 1)
9 O-ring --- 9645 945 7485
10 Round head screw 1106 122 7400 1121 122 7101 1)
All other parts as before
11 Carburetor box cover; 1121 140 1902 1121 140 1904 1)
including items 12 to 19:
12
13
Prefilter
Cover ---
1121 124 0811 ---
1121 141 2900
1)
14 Self-tapping screw B2.2x6.5 9099 021 0160 --- 1)
15 Twist lock 1121 141 2300 --- 1)
16 Lever --- 1130 141 2300
17 Helical spring 0000 997 1335 --- 1)
18 Detent 1121 141 2100 --- 1)
19 Self-tapping screw B3.9x16 9099 021 2790 --- 1)
20 Cylinder with piston; 1121 020 1208 1121 020 1209 2)
including item 21:
21 Plug --- 1122 025 2200
All other parts as before
22 Decompression valve --- 1128 020 9400
23 Cover --- 1122 084 1405
24 Shroud;
1121 080 1608 1121 080 1609 2)
including item 25:
25 Cap --- 1122 084 7100
All other parts as before
Special accessories
Intake air preheating kit; 1121 007 1027 1121 007 1044 1)
including:
Carburetor box cover 1121 140 1906 1121 140 1907 1)
All other parts as before
Repair kit (ElastoStart); 1121 900 5002 1121 900 5004 1)
including item 1
Modification to be introduced from machine number X 32 252 039
5HPDUNV
1) Original version of part remains available as spare
2) Original version of part no longer available from factory
3) End cover 1113 121 0800 included in with new carburetor for use in machines without
compensator
)Technical Information 31.95 - Page 6
2.=====026 oil pump
Before installing a new oil pump and when
servicing the saw, check lubrication of the pump
piston and replenish it as follows if necessary:
• Pry the plastic plug out of the pump body
• Apply a little grease to the piston control face
• Refit the plug.
3.=Chain brake
A higher strength version of brake spring
1121 160 5500 will be installed from machine
number X 31 103 922=to further optimize operation
of the chain brake.
6XPPDU\
Item Part Name Original New Rem.
version version
1 Brake spring 1121 160 5500 1121 160 5500 1)
Modification to be introduced from machine number X 31 103 922
5HPDUNV
1) Only modified version of part available from factory
Last Technical Information on models 024, 026: 06.95
Waiblingen, June 29, 1995 Andreas Stihl - D1/MTK-sc
© 1995 Andreas Stihl Technical Documentation Page 2 of 6
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