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Excessive oil consumption (again).

My WM20 (actually M21 now) has started using horrendous amounts of oil. At a rough estimate it's about 70 miles per pint.
Apart from the problem the engine runs OK.
The engine puffs a bit of grey smoke occasionally, usually when revved. But surely there'd be more smoke at that rate of consumption if oil were getting past the rings?
It's not wet sumping, & oil isn't getting into the chaincase.
I've extended the breather pipe to exit behind the chaincase & when parked after a run there's a smallish (size of a large coin) oil puddle.
I've cleaned the breather which looks OK but I don't really know how to judge this.
Can someone offer help?

Re: Excessive oil consumption (again).

You definitely have a problem to be loosing so much oil....Assuming you don't have a serious leak somewhere it is either being burnt off in the cylinder, passed through the breather or a combination of the two...

There could be a problem with the crank case breather depending on the details of the flap valve you have fitted...There was more than one version.....To pressurise the crank case the flap valve would need to be stuck in the 'closed' position. Earlier pattern valves were still able to pass some air/oil even when 'closed' so on the principle of starting with the easiest thing I'd look there first..

Next is the condition of the bore/rings/piston...When was the last time any work was done here? Wear or damage to any of the components could cause a problem...General wear and/or broken/damaged rings could result in increased oil consumption and pressurisation of the crank cases..

If the crank cases are being pressurised oil will be forced through the breather..There should never be a 'puddle' of oil produced here....Just the odd spot and some 'misting'.

An M20 with good compression will bear an average riders weight on the kick start initially when on the compression stroke, slowly 'giving way' as gas passes the static piston rings under the effects of the pressure....If the engine has low compression that could point to a problem....If your engine has been together for a long/indeterminate time I'd be inclined to take the top end off and check the condition of the piston/bore/rings and, while you're at it, valves and seats....Ian

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

Re: Excessive oil consumption (again).

Ian
Thanks for the reply.
The compression feels OK, as you describe it.
I'm not sure about the crankcase breather. Mine has an internal thread with a piece screwed down inside. This piece has cutouts to let gas pass. There are no moving parts. What's there looks in good condition & is clean. Oddly, it didn't leave its usual puddle after this run.
An identical run today gave the same consumption.
It continues to blow very little visible smoke, some on starting when cold & when the throttle's blipped hard.
I'd have thought that much oil being burnt in the combustion chamber would've produced a smoke trail to rival a steam locomotive?
The bottom end of the engine has done about 35000 miles. The top was done a couple of thousand ago, the valves more recently.

Re: Excessive oil consumption (again).

If you take the breather valve off and risk blowing and sucking. If the valve is working? You should be able to blow through it from the engine end but not suck. Or you can connect a piece of petrol hose to the breather pipe and do it that way.

Did you have the barrel rebored? Did the piston ever nip up during running in? Ron

email (option): ronpier@talk21.com

Re: Excessive oil consumption (again).

The breather valve consists of the body with the fitting screwed into it as you describe...However, under the screwed in fitting, and retained by it, there should be a Tufnol disc...This is the moving element of the valve. When the piston is on the downward stroke it pressurises the air within the crank case. This pushes the breather disc off its seat and vents the air to atmosphere...
As the piston passes BDC and starts to rise up the bore it then creates a partial vacuum in the crank case and this pulls the breather disc back onto its seat which seals the crank case and reduces the amount of air drawn back in by the rising piston...

Rons description of how to test the valves operation duplicates this effect....

Although the valve is small it's operating at high speed...At 3000rpm for example the valve will be operating 50 times per second....In reducing the amount of air being moved by the piston on every stroke and the resulting pressure generated, the valves action minimizes what are described as 'pumping losses' or horsepower wasted in moving air...

It might be an idea to run your breather pipe via a rubber hose to an oil catcher bottle and then to take the bike for a ride to try and determine whether you are in fact burning oil or pumping it from the breather....Ian

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

Re: Excessive oil consumption (again).

Well folks, I've got a bit to digest here.
Ron, the bore is +60 & has never nipped up. It was run in slowly. I get the idea of sucking through the valve but it won't be necessary because without the disc Ian mentions there's no impediment to gas flow at all.
So all this time the bike's run with a faulty crankcase breather. I've always regarded it as a bit heavy on oil (nothing like what it is at the moment) & this may be why. I'll have to locate one of the Tufnol discs I need & fit it.
And Ian, a good idea to fit an oil catcher, an excuse to polish off another can...

Re: Excessive oil consumption (again).

Email me off forum if you want...I can probably find you a spare tufnol disc...Ian

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

Re: Excessive oil consumption (again).

I took the bike for a 40 mile run with a catcher bottle & even with the faulty breather valve it only pumped out a small amount from the crankcase, maybe 5ml.
So all that oil's going somewhere else, time to look upstairs. There are traces of unburnt oil in the exhaust, but I still don't understand why if the oil's getting into the combustion chamber it isn't burning blue-grey.

Re: Excessive oil consumption (again).

If it's not coming out of the breather and there isn't a major leak, then apart from evaporation there's only one place it can be going...smoke or no smoke.. :dash: :stuck_out_tongue_winking_eye: ....Ian

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

Re: Excessive oil consumption (again).

Just a thought... Is there any chance that someone is winding you up ? Can anyone else access the bike when you are not around ? The amount of oil you are talking about should be more than a blue haze.
I remember years ago being asked to sort out the poor fuel consumption on a Mini 1000. I couldn't find anything wrong with it.When we got to the bottom of the story someone was "borrowing" the car during the day. Could someone be draining a bit out to get you worried.

Re: Excessive oil consumption (again).

My guess, if the bike is not burning the oil which you would see, it's pumping in to the primary and leaking out. When you park the bike after a ride, how big a puddle of oil is under it?

Re: Excessive oil consumption (again).

Jon, Bruce & Ian
Thanks for the thoughts.
No, there's no chance of someone winding me up, at least about this. The bike's locked up in a fairly isolated rural area, and I've made the consumption measurements immediately after the rides so there's no possibility of interference. And I've checked for leaks into the chaincase. I drained it & ran it dry for one test run, nothing in it at the end.
I still haven't discounted the possibility of an electrical short between my ears but can't see what that might be. And if there aren't any serious bottom end leaks it must be coming out the top.
The only idea I've come up with about that is the possibility of oil being forced up a worn exhaust valve guide & being swept out of the combustion chamber before it can burn?
I'm no great shakes mechanically & will be getting a pro to look at the engine, hopefully early next week.

Re: Excessive oil consumption (again).

Bob
Jon, Bruce & Ian
Thanks for the thoughts.
No, there\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\'s no chance of someone winding me up, at least about this. The bike\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\'s locked up in a fairly isolated rural area, and I\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\'ve made the consumption measurements immediately after the rides so there\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\'s no possibility of interference. And I\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\'ve checked for leaks into the chaincase. I drained it & ran it dry for one test run, nothing in it at the end.
I still haven\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\'t discounted the possibility of an electrical short between my ears but can\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\'t see what that might be. And if there aren\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\'t any serious bottom end leaks it must be coming out the top.
The only idea I\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\'ve come up with about that is the possibility of oil being forced up a worn exhaust valve guide & being swept out of the combustion chamber before it can burn?
I\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\'m no great shakes mechanically & will be getting a pro to look at the engine, hopefully early next week.
The tailpipe should be visibly dripping with oil, based on the consumption you’re seeing... It’s possible that a worn intake valve/guide could allow oil to be drawn through into the combustion chamber, but the quantity described would show itself by a massively coked and dripping exhaust system. The same result would occur if this large amount of oil was passing through the exhaust valve/guide.

Quite the puzzle!

email (option): teladelujo@msn.com

Re: Excessive oil consumption (again).

Years ago when I had my standard M20 rebored for it's new O/S piston, it nipped up even after some considerable miles of running in. The bike soon started and ran again, but it had lost some compression and was using an awful lot of oil. There was no tell tail smoke screen, and when I removed the barrel for inspection, the piston had been damaged by the nip up where some of the aluminium side of the piston had been pushed up forcing the rings into their grooves. I think your answer will be to inspect the barrel and piston and get the bore to piston measured by an expert with proper measuring micrometers. Ron

email (option): ronpier@talk21.com

Re: Excessive oil consumption (again).

John & Ron
Thanks once more.
The exhaust pipe is indeed very black & sticking the finger in the pipe reveals quite a bit of carbon deposit & oil as you say.
The barrel will come off & be examined properly.
As I said I'm not great mechanically & wouldn't trust my judgement when it comes to clearances, etc so the professional mechanic will get the job.
Interesting, Ron, that you've had one that didn't smoke too.

Re: Excessive oil consumption (again).

Well, investigation reveals a metallurgical failure in the linerless +60 barrel. There seem to be some porous spots allowing gas to pass, especially around the gudgeon area of the piston.
So the plan is to fit a liner back to standard size, new piston & gudgeon.
Good thing this is happening in our winter.

Re: Excessive oil consumption (again).

The bike's back home again & now has to be run in. The barrel's been fitted with a liner about 3mm wall thickness & standard bore.
The previous piston's in horrible condition. Gas had been passing on both sides around the gudgeon, & had scored a groove in the piston & cut through the oil ring, the little end bush was also distorted & the piston had been chattering in the bore. I didn't pick up on any noise that may've made. Running in at about 35 is quite pleasant, perhaps I should get a Veteran. Can someone give me the money for it please?

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