Has anyone used any modern gear oil, Royal Purple, Lucas, etc in the M20 gear box? I have read the labels and they claim to be safe for bronze, brass, etc. I don't want to damage my gear box but running smoother and quieter would be ok. It seems to be difficult to find gear oils that don't have some synthetic blend these days. Any suggestions would be appreciated, both my M20s are getting serviced tomorrow if I can find a good gear oil.

Syncro cones are made from sintered brass.
Thus every car gear oil made for the last 40 years is safe for a BSA gearbox.

The only ones to avoid are truck gear oils which still use a lot of sulphur to take the extreme loads.
What you need to worry about is all the flogged out holes which now have clearences big enough for ep5 grease to leak out.

email (option): bsansw1@tpg.com.au

Thanks Trevor I just did not want to use the wrong oil, I am on it this morning. Thanks,Jim

Question:
Does Mobil 1 Synthetic Gear Lube Corrode Yellow Metals?
Is Mobil 1 Synthetic Gear Lube LS 75W-90 gear oil OK to run in Harley Transmissions? The big buzz on the internet chat rooms is that it corrodes "yellow" metals, such as brass and copper. Is this true? Please answer THIS question.
-- Michael Carravetta, Janesville, WI

Answer:
Unless the transmission specifically recommends an API GL-5 fluid for your transmission, it should not be used. GL-5 gear oils are designed for gears that require a high level of EP (Extreme Pressure) additives to protect gear teeth under extreme stress. Unfortunately, these same additives can be very aggressive toward “yellow metals “and are generally not recommended where copper, brass and bronze components are used.

The above is a Q&A from the Mobil Oils website...

I don't claim to be an expert on the subject but the above would indicate oil selection should be approached with caution...

In the past I have found a question to the customer services dept. will often produce the required information on particular products...Ian

email (option): ian@wright52.plus.com

With the low mileages these bikes do, corrosion is a bigger problem than any wear factors.

Like Ian, i always understood that EP oils would have ago at any brass components - attacking any zinc in the metal

A true bronze would not be attacked in the same way.

I have found that gearbox oils are very forgiving, running everything from AFT to SAE 140 in everything from Villiers/Yamaha/Triumph/Norton etc. etc over the years usually racing but also in my road bikes.

I would not even use a 'gearbox' oil, just whatever engine oil you are using. Just use oil when you should and grease only when specified, in a gearbox.



As for Mobil 1 - i was sponsored by Mobil when it first came out - i lost over 500 rpm from my top-end @ Brands-hatch in my Triumph - when i stripped the engine the pistons looked like suede, absolutely matt !!!
The Mobil 1 went in the van after that, it was 10 years later before i tried synthetic again in the TZ.
After 6 months running my crank builder refused to do anymore cranks if i used synthetic - i swapped to 'R' and my crank rebuilds went out to every three year !!!!

I'm not a fan of synthetics in old bikes.

I have been running Non Detergent SAE30 and can't seem to find a SAE50 non detergent. Do you think the 30 is heavy enough for the purpose?

Short answer NO. Use Castrol GP50 still available all over the place. Just Google it for sources.

or you add something like WYNNS or STP.

Don't laugh .... when i raced the BMW outfit (with some considerable success) Gerrards corner @ Mallory Park was an absolute killer on my big-ends, despite serious baffling/etc. in the sump.

I changed the big-ends between practice and 1st race, then again in the lunch break!!!
In desperation at one event i threw some WYNNS into the oil (mineral) and job done!!! Yes the oil pressure sagged as the 'G' force hit the oil, but the bearing held up wonderfully. Eventually more professionally solved by dry-sumping the engine.

Before the BEAMISH i threw some into the NORTON oil as the pressure was low and the 3HW not sorted - i'm still running her and promising a rebuild as soon as 3HW is finally sorted.

The Castol GP50 is not easy to find in the US for some reason. It seems almost all motor oil has some modern and unwanted additives . That is why I have been purchasing what is call lawnmower oil, non detergent for my old bikes. For some reason even that is hard to find in a 50 weight . Don't want to beat a dead horse so to speak but if anyone on this side of the pond has a good answer I would love to hear it. I'm using 30 in the motor but thought a heavier weight would work best in the box. Thanks again for all the input,

What about oils for older Harleys?...There might be something suitable there...Also try agricultural suppliers...Older tractors and other machinery run on suitable grades...

BSA recommended engine oil for the gearbox, not a specifically gearbox oil..I've run on SAE40 for decades without any oil related gearbox problems...

How about this on e bay USA.... 381245366491 ....Ian

email (option): ian@wright52.plus.com

Ian,
Your brilliant! I forgot about my local farm store, they stock a SAE40 non detergent, a 90 weight gear oil for old [1940s]tractors GL1, and Lucas Classic motor oil. I'm off to the farm store.
Cheers, Jim

Just use what ever engine oil you use, it's fine. OK, it may leak out of the starter bush and the main shaft but as long as there is some in there it won't complain. and neither do I after 47 years of doing so.
Richard

I agree, a key thing to remember with the M20 is that as standard it has no seal at the drive end of the box...This can lead to a rapid loss of oil, particularly if the field stand is used regularly...

I would recommend that the level be checked every 300-350 miles to ensure the oil level does not fall to a level whereby the sleeve gear bushes may be compromised by lack of lubrication...

At gearbox overhaul the fitment of a sealed gearbox main bearing is a must to reduce this rapid loss...The bearing number required is 6207 2RS, 2RS indicating two rubber seals...

Remove the seal from the side of the bearing that will be innermost before fitting...Ian

email (option): ian@wright52.plus.com