I drained about sixty galons of oil from the M20 this afternoon (sump and primary case). I checked the anti-drain ball (still there) and gave it a tap. Whether it makes a difference remains to be seen.

However, something changed a long-standing minor wet sumping problem into a more serious event. Usually, I get a small wet sumping problem if I don't use the bike for a couple of weeks.

Anyway, a friend said he had a theory that heavy grades of oil are the culprit. He's of the view that thick oil, by its nature, prevents the ball from seating, whereas a thinner oil has less resistance.

I haven't an opinion either way, but does anyone else have views on this? And what's the thinnest oil that can safely be used in the British climate (I'm referring to a low or non-detergent oil)?

email (option): dannydefazio@sumpmagazine.com

Balderdash!! (is that how it's spelt?)

When an M20 engine starts (eventually...if the oil has dropped) the anti drain valve is lifted off its seat when pump pressure reaches 7 PSI...so pretty much instantly really. Anyway, I guess that means the spring exerts just under that much pressure in the opposite direction. So I don't think oil grade would affect its performance. Dirt/carbon particles, a badly seated ball or a weak spring are more likely causes of leakage I would think.
On average I would say most M20s have the spring replaced about once every 50 years so at £1.50 for the ball and spring from C&D Autos it is well worth doing to help things along.The thinnest oil I would recommend would be a 20/50 multigrade...Ian

Thanks, Ian. I think I'll invest in a new ball and spring - even though Russell Motors might well have fitted a new one when they rebuilt the engine - or had it rebuilt (that was before my ownership).

I'd rather run it on a multigrade if possible - just so I can have the same oil for all my bikes. Can you recommend a specific one?

email (option): dannydefazio@sumpmagazine.com

Danny, just do a google search for Classic 20/50 oil. Castrol do a low detergent grade for pre 1980 cars/bikes. There are other make available from Halfords and others. Personally I use a straight 40 all year. Ron

email (option): ronpier@talk21.com

Morris's also do a good 20/50...You can pretty much go with any 20/50 that doesn't have too much detergent, they will all be suited to the M20...All oils are produced to a British standard at the end of the day and there isn't really any 'bad stuff'.
As with many things it is a case of which 'expert' you believe, some will say you should run a monograde with a roller big end, others say a 20/50 is more suitable. Over the years I have done a lot of miles on all types and can't define any real differences in actual use.
Ian

Have a look at this site Danny

http://www.castrol.com/castrol/sectiongenericarticle.do?categoryId=9014107&contentId=7027099

It tells you what oil is for what type of engine. Personally I wouldn't use a 20/50 in a big single. I would use 40w or 50w. I use Rockoil 50w cus I ride my OHV Nortons quite hard and they get hot..!

http://www.rockoil.co.uk/cm/products-and-solutions/motorcycle.html

In fact I have spoken to Mick Hemmings about what oil to put in a Norton Commando and 40w is now what is recommended. I trashed a Commando engine in 2000 miles from a rebuild (cam, followers, rings etc)and my engineer put it down to the wrong oil (and yes I did run it in). I was using Valvoline 20/50. So after another rebuild, I now use Rockoil TRM semi synthetic (graded as 20/60w) It's excellent and sticks like sh*t to a blanket

email (option): horror@blueyonder.co.uk

Thanks for all the suggestions about the oil. I'm pretty much already using these products. Low detergent. Castrol Classic 10/40 (or thereabouts). Rock Oil. Straight 40W. Etc. I think I'm going to shift everything (except my BMW Boxer) to a Castrol Classic 10/40 or 20/50. The simplest thing to do, I guess, is just not worry too much and change the oil more often. I'm just tired of having half a dozen oil containers with varying amounts cluttering up the garage and trying to remember what went where.

email (option): dannydefazio@sumpmagazine.com

I was using Halfords Classic 2050 in my Matchless G80s. It was green like Duckhams used to be. Are Duckhams still in business and do they make it for Halfords?

i think at one time duckhams owned halfords they might still

Duckhams oils were bought out by Castrol quite some years ago,you occasionaly see old stock for sale.

There you go..as I said it's all down to which expert you believe.
I've run my BSA singles..(M20/21s,M33s,Gold Stars,B31/33s etc,) over the decades on all sorts of oil. Just 2 of those many bikes have done nearly 190,000 miles between them.
I've run them standard, substantially oversize, heavily tuned, off road, on road and with sidecars..and all have been driven hard at various times. I've fussed over some and badly neglected others.
To date I've never siezed one, run a main bearing, worn out any cams or knocked out a big end..its the reason I ride a BSA. I've always used either straight 40 or 50 depending on prevailing temperatures/ seasons or 20/50...no particular make and both cheap and expensive.Currently I'm running on Morris's straight 40 as I got a good deal on a quantity, before that it was 20/50. I don't even think about the subject much as I've never had any problems relating to it..and surely EVERYTHING on the market today at least matches and probably exceeds the specification of the oil originally used?....Ian