Hello.

I want to change oil in my M20. Now I have a 20-50W Multigrad oil in it. I am thinkig to go to this one SF/CD SAE 40 - it`s that correct oil for a M20 1940?

BR, Mitja

email (option): mitja.peterka77@gmail.com

Hi, I use Castrol sae50, especially for oldtimer motorcycles.

Do not know where you live. I live in Holland and just order it online. In a beautiful vintage looking 5 liters can.


Regards, ramon

email (option): Noahlevi6@hotmail.com

Me too!!

Gulf has introduced a line of classic oils that are somewhat better priced than the ever lovely Castrol. "Gulf Classic SAE 50" would be the appropriate for our bikes. Comes in a nice 5 liter retro tin can.
Mind, I have not tried it myself yet.

Thanks for the answers. I live in Slovenia (Slovenija) so in the sommer we have 30 - 35 Degrees Celsius. So it is quad hot. I was using the 20-50W and I must say everything was OK, but I read on diferent forums that the "original" oil is a SAE 40. In the gearbox and chaincase I have a SAE 40.

BR, Mitja

By the original ratings a 20-50 has the viscosity of a 20 grade oil and the 'mechanical protection' of a 50 grade.

All ok if you have a nice watercooled motor.

These older iron engines do seem to feel and sound better on a 'straight 40 or 50.

I have a friend (B50 & T100 rider) who restores VW campers ... it seems they have eventually re-discovered that these also run better on a straight 30 or 40 grade oil - a handy source of straight oils.



One thing though - some motor oils can effect the clutch - JASCO rated oils are designed for wet clutch', but i know of no 30/40/50 grade JASCO rated oils ....

The Silkolene 40 or 50 i tend to use, dos'nt seem to upset a Norton clutch.

I've use Morris Oils straight and multi grade oils for different applications for years...Ian

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

The best oil is the one you put in yesterday and will change tomorrow.
In reality, the cheapest nastiest supermarket oil will be better than what the M20 ran when new.
Thicker oils will reduce the amount of engine noise so your "engine will run better " and be more inclined to coat the inside of your engine rather than the outside of the engine.
Too thick and it will start to rob the engine of its lack of horsepower.
Over the years I have run mine on
Penrite HPR 30
Penrite HPR 40
BP Coarse + 30
Valvoline 20W 50
Shell Rotella deisel 30W 40
Western oil deisel 20W 50
Western Oil 20W 50
and now use 30W Lawnmower oil

Over the 18 years I have run this bike I have noticed almost no difference in the operation of the bike and the most noticable difference was the oil consumption.
I get my oil in 44 gllon drums so it costs very little ( 25% of the shop price ) thus loosing a bit is no probles as is REGULAR OIL CHANGES.

It is a source of perpetual mirth to me tha ownes will agonise you ages about which is the ultimate oil for their bikes but steadfastly refuse to do the most important thing, CHANGE THE BLOODY OIL.

There are 10 rules for a long & happy BSA ownership.
1) Change the oil at the required time intervals
2) Change the oil at the required milae intervals
3) change the oil 1/2 way through the regular service intervals.
4) change the ol again because you can not remember when you changed the oil
5) Change the oil before you lay the bike up for winter
6) Change the oil when you put the bike back into service after winter
7) change the oil mid winer
8) Change the oil before you go to Normandy
9) Change the oil after you ge back from Normandy
10) hange the oil just for practice in changing the oil

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

And change the oil a lot while it's running in after a rebuild... ...Ian

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

Was reading an article in a Velo Mag that the 24Hr 100mph world record set by a Velo 500 was run on a 20/50 grade oil which surprised me.

Yep, whatever oil you go for ... change it very regularly.