Lambretta Gearbox Oil Change
A two stroke engine lubricates itself in two separate ways. The gearbox, clutch, and drive is lubricated by standard gearbox oil. There is no oil pump. Instead, the gears running in the oil manage to pass enough oil around the gearbox to lubricate it properly. Gearbox oil in a scooter should be changed about every 3000 miles with new ST 90 gear oil, which is the same as SAE 30 motor oil. For some reason oil manufacturers have different viscosity definitions for motor oil vs. gear oil. This is a constant cause of confusion when buying transmission oil for your scooter. If in doubt remember that oil for car engines is crankcase oil and oil specifically for scooter transmissions is gear oil. Below are directions for any Lambretta series I through III.
Tools - You will need:
It is a good idea to run the bike awhile so the oil will get hot and flow much more easily. Place the bike on its kick stand on level ground and remove the right hand panel. Find the lower of the two large allen head cover caps noted as (1) below on the chain case cover. Please note that the bike in the picture also has the rear right footboard removed but this is NOT necessary to change the oil.
Place an oil pan directly below the cap and unscrew it in an anti-clockwise direction to remove the plug. Be careful not to lose the small sealing washer around the outer rim as this can be reused if necessary, although it's best to replace it altogether. This plug also contains a small magnet which attracts any small metal pieces that are loose in the oil. It should be cleaned when removed.
The oil should immediately flow out until the gearbox is drained. Once drained, refit the oil drain plug and tighten carefully. The plug is only meant to seal against oil leaks so go easy! It is very easy to strip in the soft aluminum casing. If possible use a new felt washer to seal it rather than reusing the original.
Be sure the bike is relatively level and locate the second chain case allen head cap (2 in the photo above) and remove it. This second small hole is simply used to see when the gearbox is completely filled with about 1 1/4 pints (0.7 liters) of oil.
Find the filler hole and remove the large 21mm bolt with a domed cap and a small breathing hole. This is on the top of the chaincase near the main exhaust mount (see below).
I use an attachment that screws onto a standard quart size bottle of oil to fill up my bikes. I found it at my local Kragen auto parts store. It keeps things clean, is easy to use, and is relatively inexpensive. Start filling the gearbox until the oil reaches the upper sight hole.
Once this is done, refit the upper sight hole allen head cap bolt with a new felt washer and tighten down the filler bolt. Take the bike for a spin and once things get hot, make sure there are no leaks. Lastly, please dispose of your oil responsibly. It can be extremely harmful to the environment if simply dumped. Most recycling centers will take it for no charge.