[Art_NJr]

Originally Posted by HAMSHOG

To add another "learned" item, I was talking to some bikers on another forum and was told that they use the 75-90w gear oil in the primary. I may give that a try.

As long as it's got the additives for a "wet clutch" you'll be fine.

Also, to make lubricant with a really wide range, like 75-140, you have to use a LOT of additives. The theory is that the gear oil acts like a 75 cold but a 140 hot & to do that you start with a 75 & put in a lot of additives to make it "act" like a 140 hot. Oil (conventional or synthetic) doesn't "wear out" but the additives sure do & heat breaks 'em down quick.

A chemical engineer I worked for explained it like this - the molecular structure is like a licorice stick or a DNA molecule - twisted. As the oil heats up, those additive molecules start to unwind & get longer - they'll twist back tighter & get shorter as the oil cools down. But if the oil gets too hot, the molecular structure just falls apart & you can't put it back together again.

And the more additives you use, the less time the oil will last. That's true with anything - engine oil, primary fluid, trans fluid, whatever. Lots of gimmicky stuff on the market & lots of fancy lab tests to make you think it's the greatest thing since sliced bread. But as I said, when you take the engine, transmission, whatever apart & measure the parts with a micrometer, you'll soon see what works & what doesn't.