Which oil... gearbox

If using common 90wt mineral gear oil - go for the GL6 spec.

For top line synthetics look at Redline, Royal purple, Lucas, amsoil, vavoline & Castrol

When I read through Comnoz’ oil tests, Bel Ray synthetic v twin oil seemed to come out on top IF you want clutch friendly oil (ie in a unit Triumph twin). Current thinking for me is that the Bel Ray synthetic v twin oil will become ‘standard issue’ in my ‘shop’.

As most modern motorcycles use the same oil in engine and gearbox, I’m wondering if the Bel Ray oil would be good in a gearbox?

Alternatively, over on the 961 forum, this was recommended: https://www.harley-davidson.com/store/quart---formula--transmission-and-primary-chaincase-lubricant and reading reviews on it, many claim it smoothed out their HD boxes a lot. Perhaps this would be good in a Norton box?

Are there any long term tests of owners using ATF in the gearbox?

Some gearbox oils are not brass friendly. Others are. I use a 50/50 mix of dino and syn, both brass compatible. Don’t know why but based on rec of hotshot rebuilder of stnd and auto transmissions

As for migration to the chain case, I suspect that use of the side stand is a factor. I cut my side stand lug off decades ago and consequently I use the center stand exclusively. I have never had an issue with oil migration

The Glacier bearings engineers design handbook refers to GL5 oils and recommends not using GL5 oils with high sulphur content if the oil goes over 100C. So a none issue in Commando gearboxes as they run cold being separate from the engine, Glacier reconfirmed this to me in the last 6 months.

Alan I have never had a good view of a monkey’s arse , are they common where you live .... while I do have a clutch rod seal nut installed , I never had a problem before the install , did it in case I overfilled the gearbox , which I was told was a possible cause of the gearbox oil migration .... sittin’ here scratching my head trying to picture a monkey’s arse ....
Craig

xbacksideslider said:

As for migration to the chain case, I suspect that use of the side stand is a factor. I cut my side stand lug off decades ago and consequently I use the center stand exclusively. I have never had an issue with oil migration

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I guess the side stand could be a factor but I use the side stand almost exclusively and only use the CS if I'm doing some work and have never had any migration. Wouldn't overfilling the gearbox be the most likely cause?

Re that, when filling mine I remove the level plug (bike on Centerstand) and add gear oil till it starts dripping out of the plug fitting. I let it continue to drip/weep from the fitting. When it stops, I install the plug. So the gearbox level on my bike is at the base of the level plug fitting.