What Gearbox Oil For KX 250?

[Chokey]

Agreed.I always thought the shear thing was a crock.In automotive applications,standard transmissions are spec'd with different fluids depending on the manufacturer.Some use ATF,some synthetic gear lube and some 10w30-and it rarely gets changed over the life of the vehicle unless you're changing a clutch.

Viscosity shear is a real issue with our trannies, because of the much higher rpms our engines turn. Most cars spend the majority of their lives between 1500-2500 rpm, and they have much taller gear ratios so the tranny components are spinning more slowly.

I have known many riders over the years that have done UOA testing, and the general consensus is that in our trannies most oils will no longer be in spec after as little as four hours of race useage. And contrary to popular belief, many synthetics are no better at resisting molecular shear than high quality dino oils.

[ford832]

Viscosity shear is a real issue with our trannies, because of the much higher rpms our engines turn. Most cars spend the majority of their lives between 1500-2500 rpm, and they have much taller gear ratios so the tranny components are spinning more slowly.

[/quote]

Interesting.So what then is responsible for oil breakdown on a machine that runs an hour or two at a higher rpm vs. one that runs thousands of hours at a lower rpm given that in an auto application it would also be moisture contaminated for most of it's working life?Loss of wedge at higher rpm or something I'm not seeing?

[Chokey]

One of the biggest factors is friction, both between the gear teeth, and within the oil itself (lubricants, like any fluid, have internal friction that manifests as resistance to flow). Friction increases exponentially with rpms, so going from 1000 rpm to 2000 rpm is four times the friction, not twice the friction.

[ford832]

I've heard it described as an oil molecule being like a spider such that the "legs" interlock but in time the "legs" get sheared off and therefore don't bind together as well.It's a good way of picturing it though I'm not sure how accurate it is.

[helfrick15205]

if you are like me and dont want political debates and just answers i would use the trial and error method. find out what works best for you.  every one has their favorite brand and weight but you have to work with what you can get witch is going to be less and less because we are a dying breed. motorcycle shops around where i live dont even carry pre mix so i have to mail order every thing.

[helfrick15205]

almost forgot kawasaki has the recommended oil

[helfrick15205]

i have a 98 kx 500 and order the kawasaki oil

[mxaniac]

For years I ran a motor oil and changed it often.  Then I had a bike that had smoother clutch engagement and shifted better with Maxima MTL.  Since then I just always use MTL.

Clearly a motor oil can work for a gearbox or you wouldn't have a zillion bikes out there that share the tranny, clutch, and gearbox oil.  That said some of the characteristics of a gearbox oil (i.e. high contact pressure) will differ from something like a motor oil that might favor anti-foaming additives.  Is the minimal gain achieved by using a gearbox oil worth the cost?  Likely not but I'd rather my kids and I didn't have a DNF either.

[TMKIWI]

That doesnt look like a 2 stroke.

[Kodackamera]

If I may, as a side note do be aware that if the engine uses an oil for both wet clutch and transmission, that using some oils designed for car engines may well use certain friction modifiers which could reduce the clutches friction in an undesirable way.

Example. Typical 10w40 which is designed with (fill and forget) average 4 stroke car driver Joe Bloggs in mind, or John Doe if you're in USA.