FROM
http://theoildrop.server101.com/ubb....=000006
If you like your bike, I strongly recommend not using a conventional car oil, synth or not.
In bikes that DO NOT share the gear box, you can get away with this longer and some synth's will work better but still there is limitations involved . There is many who has the shared gearbox and this is where trouble will begin.
Failures due to lubrication is seldom obvious and doesn't normally happen just overnite. This type of wear is over a long period of time and I seriously have doubts that you can point lubrication as the culprit since the wear is at minimal amounts and takes awhile for it to appear and most failure will appear to be due to just normal wear. In a lot of cases, this would be true, but not all.
The reason so many can run a car oil is that they are using a heavier wt oil that provides better hydrodyamic properties in turn it takes longer to squeeze out between the parts thus providing an adaquate protection, with the exception of startup, this is good and this is why so many can get away with it. In the older days, harleys and such used the heaviest wt (50wt normally) which did exactly what I descibed above.
Now with the newer multiviscosity oils, the base oils are thinner, they rely on VI improvers to maintain the viscosity(good things about synth's) and they DO SHEAR down to the LOWER viscosity under demand.
OK, let me explain.
50wt oil cannot shear down to anything but a 50wt therefore it will not flow any faster than a 50wt thus maintaining a layer of oil under load longer.
a 20w50 is a 20wt oil with VI improvers that expand when heated up to operating temps to ACT like a 50wt oil, and when put between two surfaces that squeeze together, these vi's will compress back down momentarily to the 20wt and this WILL squeeze out FASTER than a straight 50wt.
What does this mean as for protection? If an oil takes longer to move, then it takes more or longer time for the pressure to move it, thus a layer of oil is still protecting the parts. So figure, 20wt-moves faster than 50wt. 15wt moves faster than 20wt and so on.
NOW, this is where the antiwear/antiscuffing additives called barrier additives such as moly, zddp and such come into play. When the shearing takes effect(and I can assure you it does with newer mutivisc oils) The barrier additive is coating/bonding on the surface and is what is known as the LAST LINE of DEFENSE for wear protection. This coating will handle anywhere from 15,-500,000 lbs of pressure depending on the barrier additive used and quanitiy. This is the main difference between M/c oils and convention OTC oils for cars. Cars are having to REDUCE this additive to maintain manufactures requirements for EPA concerns and this makes the oil an undesirable thing for bikes.
If you watch, most air cooled engines used a straight wt oil, (just FYI, a straight 30wt is thicker than a 20w50 since thats a 20wt with vi's). VW's, Harleys, generators,lawn equipment and such all used straight wts back then. Not so much now adays obviously but alot of these air cooled engines now have water/oil coolers incorporated which changes the whole process of how the oil maintains its hydrodynamic properties.
I myself have a small harley sportster and I use the Schaeffers 20w50 in the engine, and a specialized gear oil in the box which all of my lubricants that I use on there has moly in it for the barrier additive. The difference is the Schaeffers uses a high barrier additive that will provide the added protection over any of the conventional OTC oils including any of the synth's. This is also true with redline and amsoil's non api series 2 and 3000 oils.
So in my opinion, you think your doing yourself no harm running a conventional OTC synth or otherwise api certified oil, then more power to you but remember, the only one it hurts is YOUR pocketbook and not mine as the old saying goes, pay now or pay later.
