yesterday I tried starting my 56 M20 and it had wet sumped about 2 pints of 50! but I persisted and after 50 kicks or so it started, I made a quick exit out of the garage as the resulting smoke cloud enveloped the whole street!
P.S It feel like trying to kickstart a bucket of porridge if it has wetsumped
I haven't got round to plumbing my WM20 as yet, but would it be worth investing in one of these jobbies, or are the wet-sumping issues discussed in this thread uncommon?
Scorp.
email (option): wm20atscorpionvideo.net
P.S It feel like trying to kickstart a bucket of porridge if it has wetsumped
Thanks all for the replies so far! Lots of things to test and mess around with.
Your description of kicking a bucket of porridge does seem to be how it feels so it might be that you are right with the wet sumping idea.
Just thought i'd add that I did get it going a few weeks back for about 30 secconds a couple of times but it ended up just dying out and fuel leaking out of every joint in the carb. I was told this was most likely down to the needle and jets so replaced those. Since then I cant get anything more than a few coughs on closed throttle...
email (option): martynhillyard@msn.com
I've got an anti wet sumping valve on my bike like the one you've shown Sporp. It works really well and screws into the crank case so it's as near the pump as possible. I doubt anyone would notice it if I didn't show them. The good thing with a 16H is it has an oil pressure indicator so I can see the oil is flowing straight away.
You can see it in the picture in the crank case on the top oil line
email (option): horror@blueyonder.co.uk
Hi Martyn...There are two main factors that can affect the engines inclination to wet sump...
1)Anti Drain Valves...
The M20 engine has two anti drain valves to prevent wet sumping. One is a spring loaded ball fitted into the timing cover and is situated 'downstream' from the oil pump..
When the engine is started pressure from the pump lifts the ball off its seat in the timing cover (at approx. 7psi) and allows oil to be supplied throughout the engine...
To access this ball and spring remove the hexagon headed fitting on the timing cover...It is unlikely the spring has ever been replaced, so if you are unsure of that get a new one. (the ball and spring come from C&D Autos as a kit for a couple of pounds)...
When refitting place the ball into the cover until it is sitting on its 'seat'..Then using a parallel punch and hammer, give the ball a light tap to seat it into the casing..then replace the spring and fitting. It is easier to do this with the cover removed...
The second anti drain valve is in the oil pump..The steel 'base plate' of the pump has a small tubular extension that extends into the sump from where the return side of the pump picks up oil. This tube contains a ball, loosely held in place by a small wire clip. When the engine is not running the ball falls onto its seat and a combination of gravity and the weight of the oil behind it keep it on its seat...There is no spring...
To access the ball you will have to remove the oil pump and partially disassemble it by removing the two bolts that hold the pump together. This will release the end plate..Remove the retainer from the tube and the ball can be taken out...Check that the ball is not rusted or damaged and that its seat inside the bottom of the tube is also good...Once this has been established carry out the same procedure to 'seat' the ball and reassemble the pump..Note the pump itself should turn freely by hand...If it is tight it will require attention, but that is another subject. Replace the pump into the cases...Ensure you have spring washers fitted under the pump retaining bolts and do not go too mad tightening them. Screw them in all the way and then give them a 'nip' to finally tighten them....
2)Replace the pump gasket as part of the work described above....
Most BSAs of this type will wet sump if left standing for lengthy periods..However, you should be able to leave the bike for weeks without real problems if everything is correctly set up. When contemplating remedial work follow the 'golden rule' and start with the simplest job first..then test. If there is no improvement then move on to the more involved work ...
My own opinion is that it is best not to use an aftermarket drain valve in the feed side of the system and I have explained my reasoning on the subject more than once in previous posts on the subject...You may be able to search and find these previous posts....Ian
Many thanks all for this great advice!
Lots to try out, have started by removing the timing cover ball bearing. Have cleaned that now and replaced. The spring seemed quite weak but ran out of time so I replaced it all and will see if it makes any difference. If not I will most likely order the new parts and do the oil pump.
email (option): martynhillyard@msn.com
I use a good anti-wet sump valve and it works great.
On one bike it is an in-line type, and on the other one it is the screw-in type.
I must say that it does scare me, and I always take a look into the oil tank
To see that the return line is spitting back, and also once or twice when I am
waiting on traffic lights, usually.
The problem was that I could never get to a point of the bike's own valves
work good enough. It always drained.. 
A manual tap was not an option, as I would forget it closed one day and kill the motor,
Or, I will make sure it is opened all the time when riding..
I just thought of another option:
Isn't there a way to fit a hard, oil-resistant rubber ball, or a copper ball which should do a better job?
Any thought?..
I found this site:
http://www.nemb.com/product/other_materials.php
Noam.
email (option): noam10@gmail.com