Stihl MS 661 User Manual

5MS 661, MS 661 C-M
2. Specifications
2.1 Engine
MS 661, MS 661 C-M
Displacement: 91.1 cc
Bore: 56.0 mm
Stroke: 37.0 mm
Engine power to ISO 7293: 5.4 kW (7.4 bhp) at 9,500 rpm
Max. permissible speed (with cutting
attachment):
1)
13,500 rpm
1)
Idle speed: 2,800 rpm
Clutch: Centrifugal clutch without linings
Clutch engages at: 4,080 rpm
Crankcase leakage test
at gauge pressure: 0.5 bar
under vacuum: 0.5 bar
2.2 Fuel System
Carburetor leakage test at
gauge pressure: 0.8 bar
Operation of tank vent at
gauge pressure: 0.5 bar
Fuel: see instruction manual
2.3 Ignition System
Air gap between ignition
module and fanwheel: 0.30 (+ 0.05 / - 0.10) mm
Spark plug (resistor type): NGK BPMR 7 A
BOSCH WSR 6 F
Electrode gap: 0.5 mm
2.4 Chain Lubrication
Speed-controlled oil pump with reciprocating piston and
manual flow control
Standard / Uprated
Standard
Uprated
(with pin driven home)
Settings for oil delivery rate:
min.:
max.:
max.:
7.0 (+/- 2.8) cc/min
at 7,000 rpm
14.3 (+/- 2.5) cc/min
at 7,000 rpm
18.9 (+/- 2.5) cc/min
at 7,000 rpm
1) The engine reaches its maximum RPM and maximum power after the break-in period (5 to 10 tank fillings) –
do not make any changes to the high speed screw (H) during the break-in period.

Stihl MS 661 Specifications

General

Displacement	91.1 cc
Chain Pitch	3/8"
Engine Power	5.4 kW
Fuel Capacity	825 ml
Chain Oil Capacity	360 ml
Guide Bar Lengths	90 cm