Have the vehicle on center stand on a horizontal surface and then open the inspection hole.
Using a 18mm spanner or in some old models you can use a coin since they have a slot for easy opening
You will now have access to primary chain, insert a rod or screw driver to lift the primary chain to check tension.( Note do not put your finger in if the engine is running )
Insert a screw driver underneath the primary chain
Lift to check for at least 5-6mm or 1/4" slack
You can use a normal ruler which has both mm and inch measure ( Borrow the tool from your school goer ). 5 - 6mm or 1/4th of an inch is the slack recommended
If you decide to tighten the primary chain then remove this main bolt using a 18mm spanner rotating anti clockwise.
Now oil may start oozing out from the case. To get better access you can press the brake lever and lock it in that position
Unscrew brake lever stopper bolt to desired level
Remove or loosen the foot peg using a 14mm spanner
Now you will have more access to the primary chain cover.
Pop open the primary chain cover. Oil will flow down, collect the old oil in a tray.
You need to first loosen the locknut
Use a 11 mm spanner to loosen the lock nut
Use the same 11mm spanner to turn the bolt anti clockwise to increase tensioner height
Check for slack again. Adjust till satisfied
Put cover back and tighten the main nut. Inspect and decide on changing the gasket of the cover. Take care of the pin that slots thing together.
Use a funnel to pour oil
Pour any SAE 20W40 oil or use transmission fluid on non electric start motorcycles
Pour oil slowly
Until oil drips out of the drain plug at the bottom
Wait for excess oil to drip out
Plug the hole with the drainer bolt
Tighten using 11mm spanner or with screw driver
Close the inspection hole, do not forget the copper colored gasket
Tighten using 18 mm spanner
Tighten using 11 mm spanner or with screw driver
Put back foot peg and tighten the nut using 14mm spanner
Release the brake lever stopper screw and adjust as per your seating position and ergonomics.
Inspect all nuts and bolts for tightness. Wear a helmet go for a test ride and adjust vehicle as per riding style.