Author Topic: Oil pump from 1936 Douglas 250  (Read 4984 times)

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Offline RolloTurner

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Oil pump from 1936 Douglas 250
« on: 13 Aug 2010 at 14:14 »
I have just taken my oil pump and the sight glass assembly to pieces on my '36 Aero 250 in order to clean it all up and remove dead beetles and wot nots. When removing the screw from inside the sight chamber on the top of the timing case a spring and ball bearing were revealed. Trouble is that the only way to reassemble seems to have the ball bearing blocking the exit hole for the oil. Is there supposed to be a ball bearing and a spring acting to impede the flow of oil out of the sight chamber? is there supposed to be a ball bearing here at all?
Thanks
Rollo

Offline Doug

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Re: Oil pump from 1936 Douglas 250
« Reply #1 on: 14 Aug 2010 at 02:26 »
Rollo,

Yes there is supposed to be a ball and light spring. From the 1932 handbook: "A further ball valve is situated between the sight feed body and the timing cover to prevent the sight feed filling while the engine is stationary."

It is really only needed in case the oil from the tank were to bleed past the first stage of the oil pump. It would then pass on to the sight feed, and flood it as described. The second stage of the oil pump draws from the sight feed, and provides the requisite vacuum to lift the ball from its seat and allow the oil to pass into the sight glass. 

-Doug

 

Offline RolloTurner

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Re: Oil pump from 1936 Douglas 250
« Reply #2 on: 14 Aug 2010 at 08:12 »
Thanks Doug for your ever helpful answers. And I was afraid that was the way it was supposed to be. I removed a quarter inch ball and (broken) spring from the timing cover after removing the screw in the sight feed. Now I come to put it back together I find the screw in the sight feed actually engages with the quarter inch ball before the screw can secure the sight feed to the timing case so there is no room for the ball to move at all even if I could put the spring back. Since the hole in the securing screw seems to be plain when I would have thought it should be shoulderd to retain the ball internally I am a little baffled. Any further advice, or am I missing something really obvious here - which I have a sneaking suspicion must be the case?
Rollo

Offline Doug

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Re: Oil pump from 1936 Douglas 250
« Reply #3 on: 14 Aug 2010 at 14:29 »
Rollo,

Yup, 'fraid so.

I pulled the sight feed off an engine this morning to check. Confirmed 0.250 inch ball that sits over the hole in the timing cover plinth. The spring stuffs up into the drilled recess in the sigh feed body. The spring is a tapered coil. Measurements the I got were:

0.660 inch free length
0.156 inch diameter at small end
0.260 inch diameter at large end
0.011 inch diameter wire
3.5 active coils

So a very light spring. Not that it does a lot of work, so how on earth did it manage to get broken? I did not check the hole in the sight glass body, but presume it to be 1/4 inch, so that the large end of the spring was a friction fit. It acts that way. I dare say any very light spring would work, though finding a tapered one would be nigh impossible these days. A straight cylindrical spring would need to be a good clearance in the hole, as you do not want it to drag and hang the ball up. You could tweeze the closed ends to modify the diameter, a little larger and smaller to get a good fit in the hole and against the ball. There is no reason the spring needs to taper over its entire length. It just look nicer that way.
Good luck!

-Doug

Offline RolloTurner

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Re: Oil pump from 1936 Douglas 250
« Reply #4 on: 15 Aug 2010 at 07:30 »
Thanks Doug. No idea really how the spring got broken but it was a monumental struggle getting the fixing screw out and I suspect it got chewed up in the threads or something.
I must confess to being puzzled because my ball bearing wont go back like it came out. As you say it sits in the timing chest plinth sort of covering up the oil hole (which I assume is the exit for the oil) but the hollow fixing screw will then not screw in all the way as it hits the ball. Now it clearly was in all the way when I took it out as the sight glass was not rattling around on the timing cover like it is now because the hollow fixing screw will not tighten the sight glass to the timing cover because it is obstructed by the ball which then cant move . Is there some magic afoot or should I make up a shorter hollow screw, and whilst about it put a shoulder in so that any new spring I fit will have something to but up against. Reckon a biro spring could be about right?

One thing still puzzles me a bit. If the oil exits the sight glass through this hollow screw, spring and ball bearing wouldnt the ball obstruct the outflow? What would both push the ball up and permit the outflow of oil? This very simple piece of equipment has me absolutely baffled!
Rollo

Offline Chris

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Re: Oil pump from 1936 Douglas 250
« Reply #5 on: 15 Aug 2010 at 07:36 »
Hi Rollo
   The taper spring that is described by Doug sounds like the taper spring and 1/4" diameter ball sets available from LDMCC Pre-war Spares that are used in the crankshafts of 2.3/4hp and 4hp models.   Chris.

Offline Doug

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Re: Oil pump from 1936 Douglas 250
« Reply #6 on: 15 Aug 2010 at 11:08 »
Rollo,

Oh you are going to like this, it really is a simple solution. The ball and spring are to block off the other hole! It has to supply slight resistance to oil flowing into the sight feed. As you point out there would be no reason to stop it from flowing out, and as you discovered no room to fit it under the hollow screw. So place the ball over the rear hole, and the spring up into the cavity drilled in the sight feed leading to the flow adjustment needle valve. (I could have made this a little more clear in the previous post.) 

Sounds like you might be in luck if the LDMCC stocks the spring.

-Doug

Offline RolloTurner

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Re: Oil pump from 1936 Douglas 250
« Reply #7 on: 15 Aug 2010 at 11:27 »
Well I'll be ******! I could have sworn the ball and spring came out the other hole on disassembly - so much so never thought of any other place. How idiotic can i be! Many thanks and thanks to Chris pointing out the similarity between this spring and the one on 2 3/4 Douglas I might catually get a working pump and sight feed! Many thanks to all and apologies to eveeryone else for having to endure my stupidity. Doubtless I will find other impondrable as I go through!
Rollo

Offline Tazmantic

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Re: Oil pump from 1936 Douglas 250
« Reply #8 on: 19 Sep 2020 at 12:24 »
Tagging onto an old thread again as this is the same bike the drip feed has decided not to work today no matter what i do.....

its always been a bit slow to start dripping (unlike my other bike that is instant) there is oil coming out the oil feed pipe, oil is returning to the tank, and if I remove the sight glass an pour oil in there it gets sucked out but the feed just wont drip today......

Offline Tazmantic

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Re: Oil pump from 1936 Douglas 250
« Reply #9 on: 19 Sep 2020 at 14:17 »
Removed drip pot, cleaned and reassembled, all working ok now can only presume the ball bearing got stuck..... how many drips a min should it be?

Thanks

Offline Tazmantic

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Re: Oil pump from 1936 Douglas 250
« Reply #10 on: 19 Sep 2020 at 19:03 »
Think ball is now stuck open as the sight glass keeps filling up  :(

 

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