Tensioning The Chain; Checking Chain Tension; Fuel - Stihl MS 661 C-M Instruction Manual

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Tensioning the Chain

1
Retensioning during cutting work:
Shut off the engine.
N
Loosen the nuts.
N
Hold the bar nose up.
N
Use a screwdriver to turn the
N
tensioning screw (1) clockwise until
the chain fits snugly against the
underside of the bar.
While still holding the bar nose up,
N
tighten down the nuts firmly.
Go to "Checking Chain Tension".
N
A new chain has to be retensioned more
often than one that has been in use for
some time.
Check chain tension frequently –
N
see chapter on "Operating
Instructions".
28

Checking Chain Tension

Shut off the engine.
N
Wear work gloves to protect your
N
hands.
The chain must fit snugly against
N
the underside of the bar and it must
still be possible to pull the chain
along the bar by hand.
If necessary, retension the chain.
N
A new chain has to be retensioned more
often than one that has been in use for
some time.
Check chain tension frequently –
N
see chapter on "Operating
Instructions".

Fuel

This engine is certified to operate on
unleaded gasoline and STIHL two-
stroke engine oil at a mix ratio of 50:1.
Your engine requires a mixture of high-
quality gasoline and two-stroke air
cooled engine oil.
Use mid-grade unleaded gasoline with a
minimum octane rating of 89 (R+M/2)
and no more than 10% ethanol content.
Fuel with a lower octane rating may
increase engine temperatures. This, in
turn, increases the risk of piston seizure
and damage to the engine.
The chemical composition of the fuel is
also important. Some fuel additives not
only detrimentally affect elastomers
(carburetor diaphragms, oil seals, fuel
lines, etc.), but magnesium castings and
catalytic converters as well. This could
cause running problems or even
damage the engine. For this reason
STIHL recommends that you use only
high-quality unleaded gasoline!
For further details, see
www.STIHLusa.com/ethanol
Use only STIHL two-stroke engine oil or
equivalent high-quality two-stroke
engine oils that are designed for use
only in air cooled two-cycle engines.
We recommend STIHL HP Ultra 2-Cycle
Engine Oil since it is specially
formulated for use in STIHL engines.
Do not use BIA or TCW rated (two-
stroke water cooled) mix oils or other
mix oils that state they are for use in both
MS 661 C-M