1934 external oil pump.

[saluki42]

Hi I've been happily re-machining the oil pump chamber plates for my 1934 model Z pump, which came fully dismantled and badly damaged in a box,  but have hit a puzzle. The top, pressure feed, chamber is easy to understand but the lower scavenge one doesn't make sense as it stands. Does anybody have a drawing or sketch of this lower pump that shows the internal drilling for the oil passage ways as my one may have been modified in the past. I think I can see what they have done but would appreciate confirmation before I accidently starve the oil tank as the return isn't working.

Any advice would be gratefully received.
Chris

[Ian Hand]

Hi Chris,
I am rebuilding a Z1 750 engine at the moment.  I can pull the pump apart and post some photographs if you have not got an answer yet.  There seems to be very little information available for the Z model. I have 2 of them. One of them I restored 40 years ago and it has been very reliable and well used since. I recall spending a lot of time on the oil pump and with a cold engine I still get 15 PSI on the guage, dropping to 10 when the engine is hot.  From memory. Just to make sure we are on the same page....is this the pump you are talking about.

[saluki42]

Yes that's the one Ian. A previous owner of mine had butchered the wrong filling into the top pump chamber which is I believe the delivery side of the pump and had damaged the other lower chamber which I think is the scavenge / return section. I've machined two new pump chambers and drilled the oil galleries as near to the original as possible the thing that was confusing me was one of the drilled holes seemed to join the delivery chamber the the scavenge chamber meaning it wouldn't function anywhere near correctly, this chamber having 3 holes visible on its sides. Two of these holes now appear to need blanking off having been used purely as drill access. One hole opposite side to the pipe connection just I think gets plugged externally whilst the other on the long side seems to need a special plug machined blocking a section of the cross hole and keeping the two chambers apart.

A bit of a long winded explanation but does this sound right to you.

Regards
Chris

[saluki42]

Hi again Ian, just looked at you photo again and have another question for you. Your photo shows a pipe connection to the upper pump chamber, presumably the feed from the oil tank, but doesn't show the return to the sump. Is this connection on the same face as thi inlet just on the lower pump section?

Chris

[Ian Hand]

Hi Chris,
Yes the return line is on the same face as the feed line. The feed from the tank to the pump also has an on/off tap to prevent the crancase filling up with oil. 

[Ian Hand]

I will dismantle the pump today and take a series of pictures. Your explanation is quite clear, but my memory of what the various plates looked like when I did the first pump 40 years ago is not up to speed.  I also believe the Douglas engineers might have been prone to minor changes on the run with this model. There are some little differences between my two bikes that lead me to think they may have been struggling with getting things right.  More tonight.  Are you anywhere near Suffolk ?

[Doug]

Basically the same oilpump on the ohv engine. In the case of the ohv the upper stage is the scavenge and the lower the feed.



-Doug

[Ian Hand]

That looks like and interesting engine.  Here are the pictures I took today after dismantling the pump. Not a lot of wear in the plates or gears so I just gave each plate a polish on an optical flat with 1200 wet and dry and re assembled it.  I will run a pressure test on it before I re fit it.  The plates are laid out in sequence and if you imagine tipping them up so the right hand side is uppermost they go together with all the holes aligned correctly.  (First angle projection in draughtsmanspeak.)

[Ian Hand]

More pictures,I don't seem to be getting them uploaded all in the same post.

[eddie]

The above photos appear to confirm something I was told many years ago regarding the oiling on Z and Z1 models. It would seem that the capacities of the feed and return pumps are the same - this is unusual. On most dry sump machines, the return pump is normally 50% larger than the feed (to ensure that the crankcase doesn't get (and remain) flooded with oil. One of the photos shows the oil feed banjo on the pump to have some sort of adjusting screw and locknut - could this be an afterthought to restrict the oil feed in order that the return pump will cope, and keep the crankcase 'dry'?

  Regards,
                Eddie.

[Doug]

I was told the same thing when I was using 1934 OW1 on the road in the late eighties. The 1935 Endeavour uses the same pump and some in the LDMCC had even gone to the trouble of making a new scavenge stage half again taller to give it a 50% increase in capacity over the delivery stage. However I have to say I never had any problem with it not scavenging completely as monitored by watching the return at the standpipe outlet inside the oil tank compartment. It had plenty of other problems, but that was not one of them! Once it cleared the accumulated oil, it would start to blubber and spit as it scavenged all the oil and started to suck air. And had no trouble keeping that up, cold or hot. So yes, there does seem to be something that prevents the delivery stage from delivering at full capacity, such that a scavenge stage of the same volumetric displacement - though theoretically a bad design - worked in practice. Part of that is that it does develop about 10psi pressure on the delivery side, so there is a restriction against delivery that the scavenge side does not have to contend with. I am not sure what the pressure is on the scavenge side, but I cannot imagine the pressure on the head of oil to lift it back up to the top of the oil tank is that much.

-Doug

[saluki42]

Thanks for the advice from you all and especially the photographs they will be really helpful in getting my pump together and working properly.

As usual the forum members bend over backwards to help

Chris

[Ian Hand]

In reply to Eddie's comment YES, the feed line has a banjo fitting with an adjustment system. Mine was set about halfway down the threaded needle valve.  There is also a tap on the feed line which should be turned off if you are  leaving the bike in the shed for a week or so. My hand change Z1 will wet sump in a week if this tap  is not turned off.  So far, in 40 years I have not failed to remember to turn it on again !!!!  There was also an earlier comment about cracking in the timing cover/inlet manifold casting due to over tightening the 4 main through bolts.  Mine has that too !! so yesterday I was a welder.  All good now, but thanks for the advice, I would  have missed that as the cracks were only "hairline" but would open up when the 4 nuts were tightened up.

[eddie]

Yes, the cracking of the timing cover can be caused by overtightening of the securing nuts, but more likely to be caused by the incorrect  sequence of tightening the nuts on the crankcase through bolts. The 2 crankcase halves AND the primary chaincase should be clamped up BEFORE the timing cover is fitted. That way, the timing cover nuts only perform the task of securing the timing cover. The wrong sequence not only overloads the timing cover, but may lead to the cam followers, etc. being poorly located, and possibly moving in the crankcase (along with the outrigger plate for the cams - the usual result being a snapped off oil feed post!!).

  Regards,
               Eddie.

[saluki42]

Thanks to all of you for your help with this issue pretty certain I have enough information to proceed now.

Thanks again
Chris