RG500 Transmission Oil Philosophy

The RG500 is the only 2Smoke motorcycle I know of which uses gear oil to lube some of its crank bearings.  The four center main bearings are lubed with oil from the gearbox.  The mains are all ball bearings, as are the transmission shaft bearings.  So oil which works for the tranny bearings will also work for the crank bearings.

The tranny also has lubrication requirements for the gear teeth.  After all, wherever there are moving metal surfaces lubrication is required.  Millions of 4Stroke motorcycles which share engine and transmission oil have demonstrated that engine oil can also work for transmissions.

Suzuki recommends using 4Stroke engine oil in RG500 transmissions.

The problem with using engine oil in trannys is the meshing action of the gear teeth shears the engine oil molecules into little pieces.  Think of oil molecules as being strands of spaghetti which get between the gears so they never directly touch each other.  Cut the "spaghetti" into short bits and the gears have more likelihood of direct contact with each other.  That is why gear oil was invented.  Gear oil has stuff in which allows the long molecules to survive the gear teeth shearing action.

As far as Gammas go the problem with gear oil is the stuff which prevents molecular shearing of the gear oil also limits the oil's lubricity with respect to the ball type bearings in the crankshaft.  Oil which is really good for gear teeth is not so good for the ball type bearings used in the RG500 crankshaft.

RG500 crankshaft bearings are expensive to replace.  Also lots of work splitting the cases just to get to them.

I used to think only of the tranny's requirements.  Especially with respect to the dreaded 2nd gear clunk Gammas are famous for.  Putting really heavy gear oil into a Gamma can make the clunk go away.  However, the crank bearings pay the price by being under-lubricated.  Heavy gear oil just cannot flow around ball bearings in a crank spinning 10,000 RPM.

Meanwhile, oil which is really good for the crank can also be really good for the tranny.  For a while.  Using engine oil in an RG500's tranny means the gears will merrily shear the long molecules in fairly short order.  The solution to that is to change the oil frequently.

Changing tranny oil frequently is less work than replacing crank main bearings.  My experience with using heavy gear oil is I have to replace my center crank bearings every time I have to replace pistons.  I know of  other Gammas which have had frequent tranny oil changes which have the crank bearings last through multiple sets of pistons.

So here's what I've come to about Gamma tranny oil: use straight 40wt engine oil and change it every 800 miles.