Author Topic: The EW duplex oil pump described and illustrated  (Read 10484 times)

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Offline Doug

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The EW duplex oil pump described and illustrated
« on: 26 Nov 2005 at 04:43 »
There have been some recent queries about the EW oiling system.  The following is a description primarily about the system used on engines after YE6418, fitted with a duplex plunger pump.  These engines can also be identified by the fact the timing cover has two oil line fittings rather than one. 

First, a view inside the timing cover with the pump in place:


Larger view

The oil enters via the lower of the two fittings, and exits to the sight glass via the upper fitting.  This is handled by the first stage of the pump 'A'.  The lower portion of the pump is the second stage 'B', it lifts oil from the base of the timing chest and pumps it to the quill feeding the end of the crankshaft, which would thread into the tapped hole 'C'.   

A closer view with the pump removed, with the drillings indicated.  A fuller description of what goes on follows further below, when the pump itself is described.  For now it suffices to mark out the location of the drillings in the timing cover.


Larger view

And then we get to the pump proper.  This is quite a long description, so you will need to refer back to the image several times.


Larger view

On the right is the complete duplex pump 'A' as seen before with the worm 'B' that threads onto the end of the crankshaft.  On the left is the reverse side of the pump, with the parts dissembled. 

Following the path of the oil, we start at the port 'C' where the oil enters the pump, supplied by the pipe from the oil tank tap.  This corresponds with the hole indicated by 'IN', in the previous picture.  The plunger, 'I', raises the oil to the next higher port, where it flows via gallery 'D', to return by the other pipe up to the sight glass.  This corresponds to the hole indicated by 'OUT' in the previous picture.


For the oil to get from port 'C' to gallery 'D', it has to force its way past the piston valve 'E', help down by a spring and cap 'F', situated in the top of the pump body.  This one-way valve also serves double duty as a bypass valve.  Since the plunger pumps the same amount of oil with every stroke, yet the sight glass only allows an adjustable but small fraction of that to enter the engine (under normal conditions!) the rest of the oil has to be provided with a place to go or a hydraulic lock would result.  (This would not jam this particular pump, or strip the drive gear.)  If the bypass valve 'E' lifts a bit further, the oil is allowed to pass out a port near the top of the pump bore, and return via gallery 'G' to the inlet port of the pump. 

If the gasket between the pump body and the inside face of the timing cover were breached at gallery 'D' or 'G' the full output of the pump would enter the timing chest directly, rather than having to pass drip by drip through the sight glass.  This would cause an oversupply of oil to the engine's timing chest. 

So that is the first stage of the pump, to pump oil to the sight glass.  In the sight glass the oil has to pass through a restriction controlled by an adjustable needle valve.  Then it drips through the sight, and drains via a tube by gravity and enters the engine by a non-return valve at the base of the front cylinder.  The ascending pistons help draw the oil into the front cylinder through the valve, and it splashes and frolics about the bottom end, lubricating both the cylinders.  Some oil mist passes out of the crankcase through the hollow cam spindles, lubricating the cam wheel bushes.  Early engines also had a non-return valve between the crankcase chamber and the timing chest (seen on YE2173), but this seems to have been dropped later on (seen on YE13343.)  On the later engines I am not sure how the oil was expected to easily get to the timing chest.  By the time of the A31 engine (1931 350cc, updated EW), they had a timed rotary breather situated behind the crankshaft pinion that de-pressurized the crankcase into the timing chest and provided a generous passage for oil. But that has a different pump and oiling arrangement, to suit a re-circulating system.   

The next role the pump has to play is when (by whatever means it gets there) the oil level builds up in the base of the timing chest.

The siphon 'H' sucks up this oil into the bottom portion of the pump bore.  There is a hole in the bottom of the pump plunger 'I' at the location indicated by 'J'.  When the plunger descends, the oil flows up through the center of the plunger as indicated by the dotted line, past a one-way ball valve inside the plunger.  It exits via a hole in the side of the plunger (not visible), into the annular groove at 'K'.  This leads via a short angled drilling to the gallery 'O', which communicates to the quill feeding oil to the end of the crankshaft via another drilling in the timing cover. 

The drive gear 'L' spins freely on the plunger, which has a peg screwed into the side of it (just above the letter 'I'.)  A face-cam on the drive gear bears on this peg, depressing the plunger once per revolution of the gear.  This same peg projects through a slot in the pump housing, allowing the plunger to reciprocate axially, but not rotate.  Other Douglas plunger pumps have a cam-slot that, providing positive plunger displacement in both directions.  On the 350cc EW duplex pump, the face-cam only provides positive displacement in one direction only.  Spring 'M' serves to return the plunger. 

So the second stage (crankshaft feed) of the pump is by positive displacement by the cam.  The first stage (sight-glass feed) of the pump is by the spring returning the plunger.  So the return spring M needs to be stiffer than the spring in the bypass valve.  Which does not seem to be the case in this illustration, but I have no way of knowing if these are the correct, original springs; being a bit of a grab-bag of odds and ends.  (If anyone has dimensions of the original springs, i.e.: a working pump, I would appreciate hearing from them.)  Tab-washer 'N' is really a thrust washer to stop the drive gear from wearing into the soft aluminum pump housing. 

One final word about the non-return/bypass valve in the upper, first stage of the pump.  As just mentioned, it is a bit of a balancing act between the bypass spring and the plunger return spring.  Clearly the plunger return spring needs to be the stronger of the two.  Otherwise the plunger will be unable to lift the non-return valve, and no oil will pass other than that which bleeds by the valve (it is not a very close fit in the bore.)  The plunger will ascend till it traps the oil between itself and valve 'E' and then it will just stop.  The drive gear will continue to rotate, but the peg on the plunger will no longer be in contact with the face cam till it rotate far enough to again depress the plunger down.  This is why a hydraulic lock in the first stage will not strip the drive gear. 

If the spring in valve 'E' is too weak, it may bypass oil too readily rather than force it up through the needle valve in the sight glass. 

Then the valve 'E' could be stuck.  If stuck down, it would be the same effect as too stiff a spring, preventing the plunger from obtaining full stroke.  If stuck up, it would not perform its non-return function, and the oil would just oscillate back and forth in gallery 'D' without being pumped anywhere.  Another, but remote possibility is it can move a little, but not enough to act as a bypass valve.  This could occur if the wrong spring was fitted, and it became coil bound before the valve could fully lift.  On maybe the valve just hangs up part way up the bore.  Regardless, the pump will then try to pump all the oil through the sight glass, and develop as high a pressure as the plunger spring will permit. 

The EW oiling system is a total loss system.  That is, it never returns the oil from the engine to the oil tank.  While it does pump oil up to the tank, this is only so it can pass through the sight glass under the rider's observation.  So all oil that enters the engine must exit some other way.  Some works past the piston rings and is burnt up in the combustion process.  Most riders find quite a bit escapes though the drive to the magneto!  And every other joint and orifice is a contender for an oil leak. 

A high level of oil in the crankcase will cause over oiling of the cylinders.  As previously mentioned, it is not clear how the surplus oil is supposed to easily get over to the timing chest on the bulk of EW production, where it is next needed.  Other models just had a large hole drilled through the back wall of the timing chest into the crankcase chamber.  But once in the timing chest, there is a stand pipe projecting up from the bottom that limits the oil level to just above the teeth on the lower cam wheel.  The excess oil is led off to drip on the primary chain.  This also acts as the breather for the timing chest.  Blocking this pipe to stop a source of an oil leak or over oiling of the primary chain will lead to oil blowing out the other joints of the timing chest. 

The later 350cc engines with the rotary breather valve (excluding wet-sump types) do not have an overflow pipe.  To vent the timing chest, they instead had a pipe from the top of the timing chest that carried oil mist over the top of the crankcase to lubricate the primary chain.  They were also a re-circulating system, so the oil above the level required to lubricate the cam wheels is sucked up and returned to the oil tank.  But that is a another story. 

And yet, that is not all there is to say on the EW duplex pump!  The illustration of the oiling circuit for the duplex pump as shown in the 'Running Instructions for E.W. Model Douglas Motor Cycles' contains an error.  This shows the fittings for oil-in and oil-out of the pump reversed.  This incorrect illustration can be further identified by the sub-description 'As fitted to all Engines from No. YE 6418'.  What I gather to be a slightly later publication, 'Care and Maintenance of the 350c.c. E.W. Douglas' shows a redrawn illustration of the duplex system that has the correct oil line connections.  The sub-heading on this illustration reads 'As fitted to all Engines from No. YE 6450', rounding up to leave eighty two owners misguided!  But at least show the oil lines hooked up properly! 

I think the error in the illustration came about due to the fact that when Douglas switched from the gear-type pump fitted to engines up to YE6417, they designed the duplex pump to utilize the existing timing cover with the minimum of alterations.  The oil line from the sight glass branched and fed both the non-return valve in the base of the front cylinder and the oil pump.  Originally the one and only fitting on the timing chest was the feed in to the top of the gear pump.  The oil then exited out the bottom of the gear pump and went to the crankshaft quill via drillings in the timing cover, the pump only fed the crankshaft and perhaps helped form a vacuum to draw oil through the sight glass.  With the duplex pump an output to pump oil to the sight glass had to be arranged.  The existing (now upper) fitting became the pump output, and a lower fitting added which became the feed in to the pump.  This role reversal made the circuits in the plunger pump somewhat simpler to arrange.  But is seems the illustrator got mixed up or miss-informed about the change. 


Larger view

I have not seen an example of the EW geared pump, so my mark-ups are speculation, but the illustration in the handbooks show the gears positioned and oriented as indicated in the above illustration.  Note too the continuation of the bronze insert that once supported the non-driven gear of the pump.  The other bush is for the inlet cam spindle; the oil pump was driven directly off the end of the inlet cam.  The redundant bush became a well to connect the drilling between the added fitting and the duplex pump.   

Addendum: A picture of the earlier gear-type pump has turned up, and is shown below with the oil routing to the crankshaft quill.



-Doug

[Add image of early style gear oil pump. 14Jun15 -Doug]
« Last Edit: 15 Jun 2015 at 00:12 by Doug »

Offline Clive

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Re: The EW duplex oil pump described and illustrated
« Reply #1 on: 29 Nov 2005 at 20:01 »
Hi Doug,
Another EW owner , i went through the oiling system saga about 10 yrs ago when i started my re build , the bike has been on the road 5yrs now and covered some 3000kms so i am assuming the mods i made to the system are working.i am still running cast iron pistons as i think the clearances required for aliminum ones to work correctly allow too much blow by and defeat the breathing system which i have modified as well.
So will start with the breathing as you correctly discribe ,i went a step further and added a breather to the timing chest in the same position as the B31 ,3/8  copper pipe leading over to the primary chain termanating with a Royal  Enfield breather the flat ended neaprene pipe which allows air out and not in .Works very well and the engine stays very clean. As we now have another oil supply to the primary chain in the form of a mist from the breather so i re-routed the timing case drain to under the rh foot board !!! the bike stays very clean even after a 100km run which i did on the 20th of this month and won first Vintage.
On to the duplex pump , mine was in very bad condition with the springs having rusted away so i never really knew the correct spring strengths !! By trial and error i relized the top pypass spring must be weaker than the bottom force spring in fact my top spring is quite a weak one and functions quite well.
The bottom of the pump the crank feed i could not get to work properly untill i hit upon the idea of a foot valve in the bottom of the syfon tube i still cant see how it can work with out one . Surely as the plunger decends the oil would be pushed back out of the syfon tube or is that the ball valve or plunger base is a greater diameter than the inlet hole in the sypon tube and only some gets pushed out and enough goes past the ball for it to work.. Any way mine has a 1/8 ball and hair spring to hold it in place ,it pumps oil hot or cold which is more than can be said for the top half which needs constant adjustment , cold it pumps like mad with the adjuster nearly right done but needs to be opened up as the engine warms up there must be too much wear in the pump housing. Has any one ever tried to o ring these little pumps to give them another lease of life
Anyway for what its worth thats my experiances of the douglas duplex pump .
The EW is a great little bike and i could talk about it for hrs.
Regards
Clive Hallam LDMC 2896

Offline shuswapkev

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Re: The EW duplex oil pump described and illustrated
« Reply #2 on: 30 Apr 2014 at 11:08 »
doug

 thanks heaps for the oil pump dissertation.....really is a big help...i cant imagine how hard they must have worked to get something like that designed and working..a lot of longdays and nights...
makes the later gear pump  look like a breeze...  was hopin i could adapt or make one...but from the looks of that...i better start lookin for one...... i  have the 2 oil fittings

the advert section...did think of that..after i pushed ..post...

Offline Doug

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Re: The EW duplex oil pump described and illustrated
« Reply #3 on: 30 Apr 2014 at 12:01 »
The main complaint with the gear pump was that it relied solely on vacuum to lift the oil from the oil tank the few inches to the oil sight glass positioned on the top of the petrol tank. From there gravity took over. Any miniscule air leak in the pipework up to that point would diminish or destroy the vacuum, and so the oil supply. Douglas provided kits to the dealers to convert the earlier gear oil pump to the later duplex plunger pump.

-Doug

Offline shuswapkev

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Re: The EW duplex oil pump described and illustrated
« Reply #4 on: 04 May 2016 at 09:56 »


  my oil pump springs are much different than in the picture...my top hat spring is very light...and the lower spring looks to be twice the length of the one in the picture...

any specs available on this...??   easy enough to measure a  spring...  put a dowel in your drill press chuck...a scale on the drill table...spring under the dowel...push down 50%....and read the weight...  I do this to measure valve springs....I I don't have the specs...for that spring...use that to make sure all near the same..

Offline Robert

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Re: The EW duplex oil pump described and illustrated
« Reply #5 on: 15 Mar 2018 at 03:46 »
I have just dismantled my 1927 EW350 pump and all seems to be original and measured the springs and suction tube ball check valve.

Plunger Main spring. (pushes the plunger up)
Free length 1.5"
O.D.  .350"
Wire gauge .030"

Top check valve spring
Free length 1."
O.D.  approx .330"
Wire gauge .012"

Suction pipe check valve. (yes there is a ball and spring in there)
Ball O.D. .154"
Spring free length 1"
O.D. .200" (smaller bottom coil to press against the ball)
Wire gauge .007"
Note: this spring would work better if smaller dia. say .150" to .180" as it binds in the tube and jams up and is that fine most people do not realize it is in there.
Hope this helps.

 

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