Ed

[Builder65]

Hi all,

I have a 72 ossa mar mark1,

in 2017 I acquired the bike,

I renewed the gear oil and from that point onwards my clutch sticks,when cold and to re-release it I need to rock the bike back and forward,my question is what is the correct oil I should be using for the gearbox/clutch,

thank you for your response in advance,

Ed

[feetupfun]

The properties of different oils do make a difference to the issue of the plates not wanting to separate but the underlying cause is that the friction plate pads can act like suction cups against the steel plates. The proper fix is to roughen the finish of the steel plates to help break the vacuum and to remove any grooves in the basket fingers. Grooves there can hold the plates together when the clutch has load on it.

For a temporary improvement, use the lowest viscosity oil that will also provide enough lubrication for the chain. If it was a racing motor, the primary chain would not enjoy it if you use ATF but for trials use, ATF is usually OK for lubrication and is very good at breaking the vacuum seal.

There are also name brand low viscosity gearbox oils that will work well for this issue and questions like yours usually get lots of suggestions for which oil is the best.

OSSA primary drive casings retain some of the old oil during an oil change so if you want to get rid of all the old oil, an easy way is to loosen off or remove the clutch cover to drain the remainder out.