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Re: 1942 BSA M20 oil type

Ambient temperature is a factor, but don't confuse SAE 40 with 90EP as they are similar in viscosity; Extreme Pressure oils with hypoid additives are more recent. 40w will be fine in both unless you're riding in the Western Desert.

Re: 1942 BSA M20 oil type

I am in the western desert. I live in Arizona temp today is 102F. What weight would you suggest

Re: 1942 BSA M20 oil type

I am in the western desert. I live in Arizona temp today is 102F. What weight would you suggest I i

Re: 1942 BSA M20 oil type

Only use ordinary engine oil in your gearbox. As you are in a hot climate, use SAE 50 in both. Ron

email (option): ronpier@talk21.com

Re: 1942 BSA M20 oil type

50W motor oil is fine in the gearbox but I prefer 90W gear oil. If you are going to be touring on your M20, then stick with motor oil so you don't need to carry both types.

I have also used 140W gear oil many times and it does not leak out as fast in hot weather. Those riding in the UK don't see temperatures over 100 degrees and don't really a heavy oil. I have ridden my M21 in 118 degrees and the 140W did work better but not a good idea to use if you live where it gets to freezing in the winter.

Re: 1942 BSA M20 oil type

Just remember EP90 dissolves bronze bushes, but it's ok I have the replacements.

Mark

email (option): pes.sales@btconnect.com

Re: 1942 BSA M20 oil type

Mark Cook
Just remember EP90 dissolves bronze bushes, but it's ok I have the replacements.

Mark
Yes, some EP oils will attack bronze but not all will. And even the ones not recommended for use with bronze will only cause problems at temperatures of over 300 degrees F. If your gearbox gets this hot you have bigger problems.

If you are worried about this, read the EP oil bottle and it will state if it is safe for bronze. The EP oil I use says it is safe for all yellow metals. The bike I have had the longest is a 1958 Triumph TR6 and it has been running on EP 90W oil for 37 years that I have owned it. I bought it from the widow of the original owner and it had EP oil in it when I got it. So 66 years now and the gearbox bushes are still original.

My M21 has been using EP 90W for the 32 years I have owned it without issue.

And finally late 1960's Triumphs when they went to bronze shifting forks, the service manual says to use EP 90W.

Re: 1942 BSA M20 oil type

I've drained gold paint from Mercedes truck gearboxes that have been run on EP90 Bruce.
Not all bonzes are made of the same ratios of elements.

Mark

email (option): pes.sales@btconnect.com

Re: 1942 BSA M20 oil type

Mark Cook
I've drained gold paint from Mercedes truck gearboxes that have been run on EP90 Bruce.
Not all bonzes are made of the same ratios of elements.

Mark
Yes EP oil can sometimes cause problems. But again, the bottle of oil will state if it is OK to use with bronze. The brand of gear oil I use in all of my Brit bikes says specifically on the label "it is safe to use with all yellow metals". Some other brands of EP oils make no mention of this and should be avoided.

Re: 1942 BSA M20 oil type

I forgot to post this. The oil is made by a company called Sta-Lube in the USA and may not be available in Europe. There is nothing special about it and other companies make similar oil.

From their website

GL-4 Hypoid Gear Oil has low pour points and high temp properties to provide lubrication over a wide temperature range. This versatile lubricant contains anti-rust and anti-wear EP additives to provide the corrosion protection in drives and hypoid gears. It is not corrosive to copper, bronze, or other non-ferrous alloy bearings and bushings.

If touring I don't use gear oil as I don't want to have to carry another oil and use 50W motor oil. But still have to carry ATF for the primary!

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