Dear All
What make & grade of oil is best for my Commando gearbox?
1973 750cc Commando Interstate
Thanks Neil
Synthetic 75w90 seems to…
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I would go for the thinnest…
I would go for the thinnest EP on the grounds that the plain bushes need the oil to flow well.
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Opened the can of worms again
Actually, I think our Nortons rarely run so many miles that choice of oil matters. Though some oils give smoother gearchanges.
I believe it was Mick Hemmings who attributed rust on the gearchange plate, springs and screws to a clogged breather hole.
Some early GL-5 synthetic oils where not friendly to yellow metal bushings.
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Gearbox oil
Have to agree with the Mickey Hemmings comment, my gearbox breather hole was blocked by solvoautosol and every metal part above the oil line including nuts inside the first cover were solid rust. The parts behind the inner cover were fine. Having checked and replaced the rusty parts it runs very well on EP90.
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Synthetic 75w90 seems to reduce gear and bush wear, e.g. Millers Oils TRX Synth 75w-90 Fully synthetic gear oil
https://www.opieoils.co.uk/p-60227-millers-oils-trx-synth-75w-90-fully-synthetic-gear-oil-gl-4-gl-5.aspx - other makes and suppliers are available.
Most important thing seems to be to change the oil regularly, especially if there's any sign of water (usually via the clutch cable and breather hole).