Honda Monkey 2021 Owner's Manual page 58

Maintenance Fundamentals
Cleaning and Lubricating
#
After inspecting the slack, clean the chain and
sprockets while rotating the rear wheel. Use a dry
cloth with high flash-point solvent. Use a soft
brush if the chain is dirty.
After cleaning, wipe dry and lubricate with the
recommended lubricant.
Recommended lubricant:
Drive chain lubricant
If not available, use SAE 80 or 90 gear oil.
Never use petrol or low flash point solvents for
cleaning the drive chain.
A fire or explosion could result.
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Avoid getting lubricant on the brakes or tyres.
Avoid applying excess chain lubricant to prevent
spray onto your clothes and the vehicle.
Crankcase Breather
Service more frequently when riding in rain, at
full throttle, or after the vehicle is washed or
overturned. Service if the deposit level can be
seen in the transparent section of the drain tube.
If the drain tube overflows, the air filter may
become contaminated with engine oil causing
poor engine performance.