My M20s been laid up for a few months while I've been sorting out other projects. A nice little puddle of oil has since deposited itself under the engine (looks like it's coming from around the inside of the primary tinware, but it's hard to be sure until I drag it all out for close inspection).

Now, this might be an obvious question, but can the M20 wet sump enough to actually push oil from the engine breathe while the engine ISN'T running? Presumably, it can (seeing as the oil tank is a few inches above the breather). What I'm really asking, I guess, is whether this actually happens in practice, or whether the oil pump design makes this unlikely.

The bike has wet sumped a few times following a few weeks of inactivity. But it's never pushed it out through the breather (not as far as I know; it just smokes a little until it clears). If it pumped oil with the engine running and crankcase pressure forcing it out, I'd understand. But as I said, with the engine off, can oil be forced out through the breather by gravity alone?

It's not a desperate issue. I just want to get things clear in my head for when the snow thaws and I can get down there to work. Any thoughts/views welcome.

email (option): dannydefazio@sumpmagazine.com

Hi Danny...That wouldn't really be possible. Although the breather is below the level of the oiltank the crankcases would have to be completely full of oil for it to make its way out through the breather valve.(which is at the top of the crankcase.)
The anti drain valve in the timing cover and the one in the base plate of the oilpump SHOULD prevent wet sumping but we all know the system is not 100% effective over a long time period...even if in sound condition.
And of course there are leakage possibilities from both the primary chain cases and gearbox...particularly if you are careful to maintain the correct level in the latter....Ian

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

Hi Ian, thanks for that. It clears my mind a little. I suspect the primary chaincase is the problem, but I'll clean it all down when I get a chance and will check levels, etc. I just wanted to rule out the breather. It's a pity we can't have colour-coded oil. It's not always easy to tell which is which. Maybe it's time I invented coloured particles that you mix with the oil and which shows up on ultra violet light or something. Think it's worth the trouble?

email (option): dannydefazio@sumpmagazine.com

Adding some liquid food dye wouldn't have any effect on the lubricating qualities of the primary and gearbox oils...and the engine oil is usually black anyway...but don't use sunset yellow...you will risk your M20 becoming hyper active!! ...Ian

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

I was thinking of scraping some garlic into it and seeing if that works. I've got four bikes in the garage, three of which are in the habit of marking their territory (and all use different oils). I think the UV/food additive/garlic idea might have some potential - unless someone out there has a reliable method of tracking down leaks without lengthy inspection. What I really need is a decent workshop where I can put the bike on a ramp and study it in comfort. But my "workshop" facilities, such as they are, are more spartan and primitive.

email (option): dannydefazio@sumpmagazine.com

I don't know how the drive side mainshaft is sealed on the M20, but on the Norton there is no labyrinth seal and simply a drain from a chamber in the crankcase boss.

A Norton of this period becomes externally incontinent as soon as the oil is up to main bearing height. Later models with an oil seal don't normally show that the're full of oil.

Even if the M20 has a seal (and I appreciate that it is a thoroughly modern motorcycle when compared with a 16H), if the seal is no longer 100% then it could start to fill up the primary.

Val Page took care of that potential problem on the lavishly equipped M20...there are not one, but two oil drain holes between the main bearings on the drive side that return any accumulated oil to the main crankcase...Ian

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

Ian, does this mean that M20s can wet sump and fill the primary chaincase - perhaps overflling it until it leaks? Or am I misunderstanding something here? I'd always thought M20 primary chaincases were completely separate. The point you made about the drain holes "opens" things up a little (it sounds like the same system as fitted to, say, my T140)

email (option): dannydefazio@sumpmagazine.com

I hate to think what you'd like to do to the guy who owned it before me who had it laid up for about ten years.



But it hasn't been exactly idle for that long. I've just not been riding it. Instead, I've had it running on the spot and doing all kinds of calisthenics to help it stay in shape. It seems to have lost a great dollop of oil over a period of maybe two weeks. I was at first blaming it on my Triumph. But the fresh evidence said otherwise.

email (option): dannydefazio@sumpmagazine.com

I'm guessing the drain holes are here?



How much space is there inside the crank cases for oil?

email (option): robmiller11@yahoo.co.uk

I deleted the last post as it didn't make sense!! .
Rik is correct about the drain holes..they are obviously there to drain the oil when the engine is running, not idle. I didn't think that one through very thoroughly.!!
If either of the drain valves is not functioning oil drainage to the sump could be fairly rapid...and various people have noted their M20s dropping a fair bit of oil after a short 'idle period'.
When full the oiltank holds 5 pints...I don't know how that relates to crankcase volume but I would imagine that if the entire contents were dropped it may well reach the level of the main bearings.
There is no oil seal as such on the drive side so if that were to happen then I suppose it could find its way into the primary chaincases.
Saying that, I have never known that happen and M20s are not known for it.
It may be that as the level in the oiltank drops there is an insufficient 'head' of oil to force what is a fairly viscous fluid past the valve(s).
A sensible course of action would be to ensure the anti drain valves are working (how often does the spring get replaced in the timing cover valve?) and to start the bike up periodically during a long 'lay up'to scavenge the crankcase....Ian

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

Yes, that's where they are Rob...Ian

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

After I left my WM20 standing for a long time it lost all the oil in the tank down to the gauze filter. The bike started with a bit of effort, but after running it for long enough for the pump to scavenge the sump out the oil tank was only half full.
I took the bike out for a ride to find the clutch slipping badly (it had previously been ok). I drained over a pint out of the primery chain case, and when I took the dome off the clutch I found oil on the plates.
My thinking is that oil either runs past the main bearing as it stands with a full sump, or maybe when the engine is started crankcase pressure pushes it past. The oil level then gets so high in the chaincase that it gets along the shafts or around the bearing into the clutch.
Does that sound likely to you experts?

email (option): Gasboy@btinternet.com

Danny.
When I was trying to find the source of oil leaks on my Commando I would thourghly wash the suspected area off and get it clean. Then sprinkle or blow talcum powder over the suspected area. Any leak can easily be seen in the talcum powder.

email (option): Gasboy@btinternet.com

Well there you go...that proves the point that if all the oil drops into the crankcase it will find its way to the primary chaincases. All the more reason to attend to those anti drain valves and start the bike occassionally!!.....Ian

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

Hi Peter, thanks for the tip. Best one I've heard in a while. Only, one of my Triumphs is leaking so much these days that I think I'll need to use sawdust.

email (option): dannydefazio@sumpmagazine.com

Have had problems from kicking a WDM20 bike over without trying to start it whilst in the garage. As the oil is still cold as engine not started it does not let the ball bearing in the oil pump sit properly on its seat and will leak substantially. Since I stopped walking past and kicking it over a couple of times have not a problem with oil leaking. John

email (option): ukcarbs@hotmail.com