Oil Pipe Fittings for 1920 2 3/4hp - what sizes please?

[pvn06]

Hi Folks,
I know this sounds like it should be simple, but I would like to check with a couple of owners of 2 3/4hp bikes before proceeding.
I am trying to make the oil pipe unions and fittings for a 1920 2 3/4hp model, this has the petrol/oil tank of the type that has the dripfeed eyeglass at 45 degree and the oil pipe fittings to the taps running vertically through to the bottom of the tank (see photo of my bike attached last week . . . obviously still in build phase!) - this shows on the original Douglas catalog as part 1215D.

I believe the threads on the bottom of the oil dripfeed unit are 7/16 x 20 tpi (not a BSP thread, surprisingly).  The thread to the bottom of handpump on the tank is standard 1/4BSP (this being 1206D).  Then the original two piece crankcase oil pipe Non Return Valve (404D) is 1/8 BSP on the end that accepts the oil pipe from the drip feed.

I am trying to confirm what bore and outer diameter of copper pipe was used  on the oil pipe - both from hand pump to drip feed, and then from drip feed to one way valve (if different).  Because the one way valve and drip feed threads are different, it is not as straightforward as I expected .. . but am just about to make the nuts to fit the dripfeed (i.e. 7/16 x 20 tpi), so don't want to setup for these until I know the correct original copper pipe diameter/brass union fitting that would fit through these nuts.

Also, if enough interest and these not commercially available elsewhere, I might make a bigger batch for our online catalog Douglas section.

Likewise, I am also looking at petrol taps and was looking to get a batch of 1/8" BSP taps (which is the thread type going into the petrol tank) and 1/4BSP outlet, which I will then manufacture stainless filter units which screw onto these, to look like the original Douglas type taps - 1185D.  I believe the output thread from this filter unit was also 1/4 BSP - but don't have an original, so if anyone can confirm this was the outlet thread and possibly supply me a good quality closeup photo of an original item, I would be very grateful.

If any of you have an interest in these parts yourself, please email me at paul.norman@racingvincent.co.uk and I will consider writng the CNC programs to manufacture a batch for sale.

Many thanks
Paul
www.RacingNorton.co.uk

[douglas1947]

Hi Paul,

I had the same thread problem on petrol tank pipe connection to level the  petron in the tank on my S6.

I think it is special to Douglas.
But the (newer)   UNF 7/16" - 20 will fit!!!

Michael

[cardan]

I think it is special to Douglas.

Hi Michael,

Special to Douglas - nah. They would have chosen 7/16-21.5 or something equally bizarre

20 tpi gets a pretty good run on British bikes. It was a cycle thread (BSCy), mostly used in sizes around 7/16, 1/2 and 9/16. UNF will fit, but there is a different thread angle. Beware using UNF nuts early Douglas axles which are BSCy 20 tpi, but hardened, so the UNF nuts are prone to seize on the thread.

Last year I indulged myself and bought a complete set of "ultra-rare BSCy 20 tpi taps and dies". When they arrived they were no such thing, instead UNF in the sizes that overlap and UNS in the others. Hard to get good help - or good taps and dies - these days.

Cheers

Leon

[Hutch]

Hi Paul,

The 1092D pipes I have are 1/4" diameter nickle plated copper tube. The thread on the oil drip feed pipe 1224 D is 7/16 20 TPI but looks like it is whitworth form - I will confirm tomorrow. I will also check the bore and diameter of an original oil pipe from the oil dripper to the one way valve on the engine for you when I get a chance. I guess you may also want some dimensions of the soldered on fittings on the 1092D?.

Cheers

Ian

[pvn06]

Many thanks for your replies - but particularly thanks Ian . . . seeing that original pipe was just what I needed to see - I had come to the conclusion yesterday that 1/4" OD was most likely, but did not want to take a guess.  I already have copper reels size below and 5/16" for different pipes and breathers we make for Norton singles - but will probably buy a reel of this as well.
I am assuming then that the output pipe from the dripfeed (which has the same 7/16 x 20 union as you show in your photograph) is the same as well (unless of course anyone knows different!).  Good stuff and thanks for this.

And Michael/Leon - thanks as well, and yes you are both right .  .. frankly I was surprised to find the thread was 7/16 x 20 (particularly as we manufacture slightly later Manx Norton primary chain oilers from the same original manufacturer and they have a similar sized nut which is BSP) - but am sure that will turn out to be the Whit or BSC form.
On that subject 7/16 x 20tpi is a common Norton engine bolt size, so it is one of the standard threads we work with.  I do have taps (and will use one for making these nuts in stainless), but for the CNC machine will also use single point carbide thread cutting tips.  However BSC thread form now virtually obsolete and no one makes single point tips with BSC (60 degree) profile, only 55 degree Whit.  Therefore for a lot of the special male threads I use Whit profile but with Cycle TPI and double check fit on both male/female.  This is just a reality of modern CNC machining.  Checking threads on original fasteners (and lots of modern made classic bolts!) . . . I find a large variation in original tolerances anyway - some of the modern mass produced fasteners I have found have a 'more than generous' tolerance!

Best wishes and thanks for your help . . . will update with a couple of photos when have got something made
Paul
www.RacingNorton.co.uk

[pvn06]

By the way Ian . . . you mentioned fittings dimensions at the end - yes please if not too much trouble, any info is useful, but can possibly work it out if I have too.  If I can get commercially available fittings then great, but if not will have to machine them.
thx
Paul

[Hutch]

Hi Paul,

I finally got a chance to look at the oil pipe that I have that goes from the drip feed to the one way valve on the engine and alas it looks to be not original fitment for a 2 3/4 hp. It is 5/16 diameter and not a relatively direct path from the tank to engine as in period pictures I have looked at. It came it two separate job lots of 2 3/4 hp parts and it did fit, so I assumed it was the real-deal......unfortunately not.. Looking at period pictures and the parts guide and it looks to me, as you also surmised -  to be 1/4" copper pipe.

Find attached the dimensions of 1092D.  Tt would be great if another forum member can measure theirs to confirm ?

I have the fitting on the oil dripper as 7/16"-20 tpi  Whitworth form and the Oil pump end as per Chris's excellent thread guide -

https://www.douglasmotorcycles.net/index.php?topic=1102.0

, that is G 1/4" -19 BSPP (Whitworth thread form).


I did the drawing in a hurry, so if anyone finds anything amiss, please let me know and I will update it.

cheers

Ian

[cardan]

Hi Ian,

Good info, but are you sure the 7/16-20 thread is "Whitworth form" and not BSC? 7/16-20 is listed in the cycle thread standard (60 degree thread angle), but is not a standard Whitworth thread (55 degree thread angle).

Leon

[Hutch]

Very good question Leon,

I measured it twice with my old Stalwille thread guages and even held it up to the light to see the gap, but maybe I cannot pick the difference between 55 and 60 degrees with my eyesight ?(highly likely!) I took a picture and blew it up for comparison. I will see if I can take a better one and blow it up some more and actually measure it somehow.

Note the Stalwille guage has 20 G 1/4 on it which is strange because I looked on the web and noticed that G 1/4 BSPP is listed as 19 tpi in a few places....strange. Some more investigations to do as usual.

I wasn't 100% sure and that is why I asked for some other forum members to measure theirs - hopefully consensus will be found and I'm more than happy to stand corrected. Yet again we are being "amused" by Douglas's funny threads! :-)

Other than that I'm not sure what else to do. I did try a 7/16 -20 BSC form nut on it and it did go on ok, maybe a bit tight, so maybe it is all a moot point anyway?

Cheers

Ian

[eddie]

Ian,
       If that is an accurate thread gauge, I would hazard a guess that the gauge is 20 tpi but the fitting is 1.25mm pitch. As you say, 1/4BSP is 19tpi, but it is larger in diameter at .518".

  Regards,
                 Eddie.

[Hutch]

Eddie,
Great suggestion - I didn't think of that and of course a 1.25mm pitch gauge was right in front of me!! I thought you could be onto something as maybe Douglas got some metric machine tools as part of WW1 reparation? So I dismantled my thread gauges and tried again. The 1.25 mm pitch is close  and over 6 or so threads it would probably be close enough. So a M11 x 1.25 thread would be a possible option.

To my eye,I still think the Whitworth form fits slightly better than the metric one and I think it would take something like an optical comparator to be able to accurately measure what the thread actually is.

So we have 3 options - maybe I mark up the drawing to say what the 3 options are and let Paul decide which one he wants to make! :-)

I still have to look into why the 20 tpi Whitworth gauge has G 1/4 marked on it ......

cheers

Ian

[cardan]

I still have to look into why the 20 tpi Whitworth gauge has G 1/4 marked on it ......

Because the only BSW thread which is 20 tpi is 1/4".

Leon

[Hutch]

Leon,

Further investigations have revealed that I believe you are correct and the thread is indeed BSC. As usual I overthought the problem and didn't see the most likely solution. I measured a couple of other 7/16-20 threads found on a CW - the hub axles and kickstarter and my thread gauge matched them pretty well, tho'maybe not exactly and thought that Douglas, although prone to have their own thread (with Whitworth form) would not have bothered with that for a size thread that was fairly common with taps and dies readily available. So probably the gauge I used is not very accurate and this combined with the fact that it is difficult to discern between 55 and 60 degrees means that it would have been unlikely I could have picked it anyway with the equipment I had at hand. The simplest solution is usually the correct one.

I did learn something in the process tho', that is how close (or is not close?) M11-1.25 is to 7/16"-20......

So I have updated the drawing and thanks for picking up my foh-pah.

Cheers

Ian

[Hutch]

oh and I confused the hell out of myself looking at hydraulic fitting thread guides....time for a beer and a good lie down....

[pvn06]

Hi Folks,
First of all . . . many thanks to everyone for contributions on this . . . but particularly to Ian for taking the trouble to give great photos and details - many thanks and apologies for not replying to you sooner, but were a great help.
Actually - I had already started writing CNC programs for some of the fittings before the updated drawings came in . . . a case in point is that I first wrote a program for the brass ferrule to the bottom of the hand pump, without looking closely and realising that the hand pump does not have a standard conical union as with most other BSP fittings (and later fuel connectors) . . . I soon found out though when I offered the conical union up to the bottom of the pump!
Never mind, a revised program for a second batch was not an issue, and I am expecting to use the conical batch somewhere along the line when I get round to fuel pipes.

Anyway, the short and tall of it is that the last few weeks spent making batch's of all the parts (alongside the normal day to day Norton parts business).  I have not quite finished the listings on the catalog yet, but most parts are available to buy (discount for Ian though!) individually or as a set.  Apologies that some of prices not cheap - but writing CNC programs for small batch's of specials is very time consuming.  The union nuts I have ended up milling in imperial hex from round stainless bar.
Copper pipe batch's also made, but not finished yet.  Not really planning to get them plated for sale - as individual customers may want to tweak shape to their own model which would remove plating. 

Email me for more details if you have questions or queries over what done so far: paul.norman@racingvincent.co.uk

The item listing not fully done yet . . . but will post it in the Commercial section of the forum very shortly.
best wishes
Paul
www.RacingNorton.co.uk