19S gearbox oil

The manual recommends Castrol XL (SAE 30) for winter use, and Castrol XXL (SAE 40) for summer use in both engine and gearbox. Similar grade oils from another manufacturer could be used.

Morris Oils (with a NOC discount) do a classic gearbox oil. Some of the modern gearbox oils are thought to a bit hard on bronze bushes so the classic gearbox 90 would be the way to go if you have any concerns. I have used both SAE 50 engine oil and EP 90 in my Norton gearbox which has now clocked up 220,000 miles and still works just fine.

I seem to remember reading somewhere that the viscosities of gearbox oils and engine oils are measured differently and that EP90 equates to SAE40. Maybe Charles Bovington may care to enlighten us.

Previously howard_thompson wrote:

I seem to remember reading somewhere that the viscosities of gearbox oils and engine oils are measured differently and that EP90 equates to SAE40. Maybe Charles Bovington may care to enlighten us.

The original recommendation of Norton's was for a 40 grade engine oil in summer and a 30 grade engine oil in winter. There is confusion because the numbering systems for engine and gear oils are different. A 30 grade engine oil has a kinematic viscosity at 100 C. of from 9.5 to 12.5 cSt., a 40 grade has a range from 12.5 cSt. to 16.3. Gear oil 80 goes from 7cSt to 11 ,85 from 11 to 13.5 cSt and 90 grade from 13.5cSt to 18.5cSt.. So there is a lot of overlap between engine and gear oil grades. There is concern that some gear oils contain additives harmful to bronze / copper components like our bushes and thrust washers. GL-3 and GL-4 oils are not a risk, according to supplies. Both Miller and Castrol offer GL-3/4 gear oils which have a viscosity grade of 80/90. These should be suitable for all year round use.

Finally there is no certainty that the monogrades no sold will not corrode Copper or bronze.

GL5 oils when first introduced attacked bronze bushes, but if you read the Glacier Bearing design engineers handbook this only happened above 100 C, plus after a few years GL5 was reformulated to remove the offending chemicals. A pre unit bikes gearbox is never going to get its oil above 100 C anyway, I have been using GL5 EP90 in my Commando gearbox since 1984 and its only issue was the layshaft bearings steel ball retainer disintegrating which had nothing to do with the oil,