Can you tell me what gearbox oil is recommended for the 1967 650 ss.
EP90 is what in the book?
Your wisdom is needed please?
In the late sixties, new oils evolved rapidly so oil recommendations changed.
The instruction book says engine oil SAE50 but also SAE 30 probably for winter use. A few years later the same gearbox fitted in the Commando should have transmission oil SAE90, which have about the same viscosity. After that, multigrade SAE 75W90 became available.
I believe that a 75W90 transmission oil is your best choice. If you often use the 650SS on very long journeys, say more than 30,000 miles per year, it could be important with oil selection. Most of us would not notice the difference in wear.
I use a fully synthetic 75W90 gear oil.which according to the data sheet is friendly to all metals used in gearboxes.
Great thanks for the advise.
I have used fully synthetic oil in my gearbox for the last 10 years. It is pricey but I was informed that it does not have to be changed yearly. So averaging 3,000 miles each year I rode for five years before changing it. No problem. Another 5 years later and I found that the stainless drain bolt had welded itself to the gearbox casing and nothing I did would allow it to turn.
To get the gearbox out meant removing all the transmission and lifting the engine. Plus removing the exhaust system fuel tank, battery box and oil tank. On reflection it would have been easier to lift the engine/gearbox cradle out as one unit. I have gone back to using castrol EP90 in the box.
My experience similar to Phil, tried all the fancy synthetic lubes but the Quaiffe cluster runs really sweet on various EP80w90 or Castrol Classic EP90 mineral oils. Changed every couple of years 4-5000 miles EP90 at present
I have used EP 90 because I have a few gallons!. My understanding is that the gear design does not need EP oil and that ordinary monograde is normally sufficient . I do think that the plain bushes in the gears are the main wear point and that they last better with thinner oil that gets where its needed,so 75/90 may be a good bet. Also condensation and rust can be an issue in damp climates so regular oil changes or an oil with anti rust properties would help.I can imagine that Tuned ,raced 750/850 /920 motors need better protection. Whatever I do, the selector parts in the outer cover get rusty. When I had to do an impromptu box strip in the IOM campsite to rectify an upside down KS pawl (no laughter at the back please!) I was surprised to find Grey sludge mixed with the wet grass in the bottom of the box.
"I found that the stainless drain bolt had welded itself to the gearbox casing"
Rather than abandon the 75w90 synthetic, I'd suggest abandoning the SS plug. SS/aluminum has a bigger galvanic voltage than steel/aluminum.
I'd instantly use TefGel, loctite PST or 567 as in the marine industry where this is an especially big problem.
This is also a problem with aluminum calipers where the bleeders are improved with copper plated steel to reduce the galvanic voltage even more.
SS bleeders can eventually cause a problem especially with hygroscopic.brake fluid.
I have used valvoline 75W90 Syntec for a long time and love it. easy smooth shifts even if brutally cold.
I doubt there is anything wrong with any of the modern gearbox oils when used in the AMC box,some say some oils will attack the bushes, but this occurs when the oil gets very hot. Some of the modern oils foam like mad when in use, but still work fine.
With the current price of EP 90, I doubt there is much difference in price, and suspect that the syntec Dave uses may even work out cheaper it changed less often.