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Douglas 2 3/4hp Induction Pipes and Nuts - Anyone know any old tricks?

Started by pvn06, 02 Oct 2020 at 20:23

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Hi Folks, hope you all well,
Here is a question for those of you that may have tried to replace your grotty old induction pipe nuts on your Douglas 2 3/4hp models (and I assume similar age 4hp and later EW models):

I am just in the process of sympathetically 'restoring' the induction pipe and Amac carb for my own Douglas 2 3/4hp . . . and need a second opinion (I use the word 'restore' in inverted comments, because actually it is more a case of cleaning carefully, making sure nothing is badly amiss and replacing washers and fasteners where too far gone - the one I am intending to use is in the photo below and came with the original bike project - it looks to be a wonderful time warp item - heavily covered in old dirt and oil, but looking like it had been sat in the corner of a workshop for the last 80 years - and both carb and pipe have that wonderful paint that looks like it may be WWI WD).

I actually have 3 different induction pipes- but two of them I think may be early pipes that came from WWI dispatch bikes - as both of these had dark green WD paint (in my own experience, darker than that found on WWII WD items).  The one I want to use came with the Amac carb attached and both looked original and unstripped - lovely.  However both induction pipe nuts to the cylinder head are very grotty - and I would like to replace these with re-manufactured items, along with the similar thread exhaust nuts.

The issue is:  on these early induction pipes, one side looks to have a collar soldered (silver soldered?) onto the induction pipe, while the other side looks to have a similar collar, but it is tight fit only - with some form of heatproof gasket, which I assume was to allow some movement with expansion when tightening both nuts to the cylinder heads.
On the induction pipe I am intending to use (carefully cleaned, and the WWI paint lacquered over to protect it), I have already removed the 'loose' collar, but the other collar is a bigger issue.  I can see that actually the copper induction pipe has been planished over the collar - and then I assume soldered.  On the second WWI induction pipe (with primer tap) I can see this planishing over of the copper more clearly. 

My question is to anyone more experienced with these induction pipes than me: Is there any generally accepted way of getting the collar off, on the side where it is planished, so that the grotty induction pipe nut can be replaced?
Looking at it logically, the only way I can think of doing this is to linish away the end of copper pipe that has been planished over the steel collar, then heat up the collar and tap off when solder melted.  However, this would mean that the pipe would be shorter on that side and although I could solder the collar back on - I would not be able to planish more copper over without shortening the length even more.  I am not sure it makes a lot of difference if copper is planished over - but dont want to do so in ignorance, if someone out there knows a better way?
I have heated up the collar (as shown in photograph) to try and tap it off the planished copper - having first linished the copper end flat, to remove knocks and make it thinner, byt can tell that the effort required to force the collar off the copper is likely to damage the induction pipe - which I definitely do not want to do.  By the way, in the photo the weird material around the pipe is a fireproof cloth welding fingerguard, held in place with gaffertape - which is keeping a lot of the heat off the original paint.
I have even considered making a new induction pipe nut (see other photo) and then carefully 'slit sawing' it and pulling apart enough to get it round the current collar (i.e. in situ), then close it up afterwards and put a touch of braze on the new stainless induction pipe nut . . . but this seems a bit too much of a bodge!

Thought it just worth asking others if they know more than me - before I make a decision and do something I can only do once! . . . if I decide to linish away the original copper planished pipe to get the old collar off and replace the nut . . . there will be no going back!

BTW - I have written the CNC programs to manufacture this slotted induction/exhaust pipe nut in stainless steel - and the first one is shown here, having just bought it in from the workshop a couple of hours ago to photograph - as you can see our cat Ringo is giving it a quick QA check!
Unlike some other parts I have made batch's of recently - I dont intend to make a commercial batch of these at the moment . . . I only had enough offcuts of Stainless billet to make enough for my own bike ..  . but if enough interest from other owners, I will get a stainless bar in, get it chopped into billets and make a batch.  If you are interested, email me on my normal email:

thanks in advance for any advice given and I will let you know how I get on regardless!
Paul Norman and

ps - final point, the photo of induction pipe with carb fitted also shows new 17/64" x 25tpi stainless steel mounting bolts and nuts.  I have just made a batch of different studs, nuts and washers and will be offering these on our online catalog in the next week or so


I've got nothing much useful to add, but could comment that your quality control supervisor Ringo there
is keeping a masterful eye on that manifold nut.
Those army green manifolds look quite impressive too.

I know this is a dumb question, but were army duggies painted all green ?
I've not really thought about this before ?
WW1 photos are all (?) b&w, and I don't believe I've seen any modern era pics of WW1 service duggies in green ??


Hi Paul,
              Looking at your first photo (with the gaffer tape), the collar on that pipe doesn't look to be original - it's much more substantial than most - they usually look to be made from copper or brass pipe with a flange formed on the end. The planishing you refer to may be an attempt to prevent total separation should the solder fail - and also a means of holding the flange in place whilst carrying out the soldering (having previously been aligned in a jig). I doubt that the flange is silver soldered (not much evidence of silver soldering on the WW1 era bikes - and probably too expensive for Mr Douglas!).
    I would suggest that it might be better to try to persude the collar further on to the pipe so that the planishing can be dressed down enough to get the flange off - probably a mandrel in the pipe and a split collar over it, then a few squeezes in the lathe chuck will get the required reduction in diameter!
    When it comes to sealing the loose collar, a Viton 'O' ring between the collar and the exhaust port will do the trick - I used an old 'O' ring from a Dragonfly inlet pipe when i was in a fix, and 20 years on, it's still doing the job faultlessly!

    Going on to EW Ron's comment about the colours of WD bikes - as far as I am aware, they had the standard colour scheme except for the petrol tank that was - to put it bluntly - a horrible sh*t brown.



Thanks Eddie,
Yes, hard to tell but you may be right .. .  although this particular pipe looks overall very original and unmolested.  In the flesh the ring does not look quite so substantial.  However, thank you for advice, and yes, was thinking of making a mandrel to hold.  Good stuff on not being silver solder, I was not sure if they were, or a softer solder which hopefully will make easier. Probably be looking at it again later this afternoon, so will see how it goes.
However, most importantly . . . you havent come back telling me I have missed something obvious!

Having gone to all the effort of making CNC programs (and half a day of adjusting programs - including breaking a nice 3mm endmill) - I would like to fit new nuts.  Incidentally - when testing thread last night - I tried first nut on 5 different heads (4 x 2/3/4hp heads and an EW head).  All but one told me the thread on the first nut is about 0.3mm oversize (i.e. loose) . . . but on one of the heads on the engine it is size on both inlet and exhaust - and the threads look in reasonable condition . .. hey ho.  Will have to adjust as I go along on the 4 for my engine!

With the WD paint . . . I am no expert, but I have looked very closely at both manifolds and they both look like original plating (worn) andl very old paint.  I also have a small WWI ammunition box with army writing on it (given to me by old friend Titch Allen 25 years ago, he used it to hold BA screws) - and that has exactly the same colour paint.  As many of the parts on the original basket case I bought looked stood up for many years - I hope it is original paint, and definitely want to keep what remains of it - even though I am sure the engine/frame are later.
I also have original Bough saddle that came with bike that (again) looked stored up for many years and leather totally dried out.  carefully leather soaping revealed what could have been names of two riders scribed in leather with ***l Engineers under names . . .. possibly dispatch riders?.  I have not fitted this seat to current project - instead having a second Brooks Junior professionally repaired by a saddle maker - a lovely job and great patina.


ps - Ron, Ringo may look like he is concentrating deeply on the nut, but in reality he is not the sharpest tool in the box (lovely though he is) .. . he is just debating if it is edible.


As a follow up to this (and in case anyone else also wants to replace nuts on similar induction pipes in the future):

Yes, this was definitely an original pipe with original ring Eddie, and the copper of the pipe was peened over the ring.  I did make an inner mandrel to keep the copper pipe supported, and an outer (split) ring which allowed me to clamp the pipe in a vice while supported - and then carefully pull back the peened copper as best I could.
However, having done so - and then using a blowtorch to heat it, in case the steel ring had also been soldered - the steel ring still did not want to budge.  After giving some thought . .. I made the decision to use a slitting disc to carefully cut the old steel ring off, as I could see that if I kept trying to get the old ring off I was in danger of damaging the original pipe, or original paint - and would rather just make a new steel ring.

So having carefully split the ring, it then came off with some gentle prising.  Suprisingly - their was no solder holding the ring on, it had just been slid/pushed on, then the copper peened over it.  Its reason for being on so tight I think was just a very tight fit and the natural corrosion of being in place for 100+ years.
So a new ring was turned down on the lathe (well . . . 2 actually - because the first one I cocked up on the tolerance and it did not feel tight enough, hey ho), and is a nice 'tap fit' onto the copper pipe, which I have lightly linished so the new ring should go on well.  I may flux and soft solder the joint when I refit it.

Last thing I did last night (Saturday afternoon/early evening - biting into red wine time!) was to have another go at a second CNC made inlet ring - having tweaked the program from the night before.  This is pretty much there now. 
So am a bit happier now.  Hoping to complete the remaining half made new stainless nuts today (giving me 5 - 2 for the inlet, 2 for the exhaust and the first trial one, which is just about usable as well) - then I can solder/planish the ring on the induction pipe and fit it to to the bike.

Incidentally, next job in this area will be to fit new cables.  I say 'new' . . . i have a small collection of 'New old stock' original cloth covered cables, so hopefully will find a couple of suitable ones for throttle and air.  By the way - question to anyone with pre 20's models, did the original cables have cable adjusters mid cable?, and if so - does anyone have a photograph of what they looked like?.  When cabling, I normally like to fit adjusters - but it got me thinking if they would originally have been fitted on a 1919 bike?

Cheers all,


last photo . . . carefully  cleaning up copper at end, ready for new ring to go on, this should also allow easily soldering.


Final post on these before I move on . . .

I did manage to get this job finished off this weekend - Sunday afternoon/evening spent final tweaking of the nut CNC progs and re-fitting ring to the 'fixed' side of inlet manifold.  See photos below.
The new ring I made went on nicely, having first tinned both the copper pipe and inside diameter of the ring.  Having tapped it on (using an old nut to do this, as of course the hole in the nut fitted nicely over the pipe), I then heated up again so the solder molten and tapped a bit more.
I cleaned up the copper pipe end after this, and did use the alloy mandrel I made up (having machined a taper on it) to flay the end out slightly, so it still goes on barrel, but should not come off in use . . . but decided against peening the copper completely over the steel ring, as per the original design . . . just in case I need to remove it again in the future.

And then finished making the new milled slot nuts in stainless on the CNC.  I even gave them a quick polish on my mops for final BS.  As mentioned, I am not intending to make a commercial batch of them yet (luckily I had some offcut billets from another job for my own) . .. but please email me if interested, and I will consider getting a bar of stainless in for the job.

Best wishes all, thanks for input Eddie/Ron,

Black Sheep

Fabulous to see you are producing some of the unobtainable items for the 2 3/4 Douglas. Anyway, here are some pictures of cables on our 1913 model O Douglas. Hope they help.


Hi Black Sheep (sorry, did not see your forename),
Many thanks for cable details - very helpful.  Unfortunately I always knew I did not have an original Douglas early type throttle/air lever assembly like yours, instead using a slightly later Bowden type.  but nice to see the knurled adjusters on the cables that end.
I did actually finish doing the throttle cables a couple of weekends ago - I had 'new old stock' cloth cables, but even though they were lightweight ones, the cables still fractionally thicker than slots in throttle lever and carb . . . but only marginal, a few minutes of careful swiss filing and everything ok. Likewise, even though outers looked lightweight (probably pre-WW2 air or mag type) I found the original nipples just fractionally too wide for original Amac adjusters and throttle/air lever housing - so had to make stainless 'reducer' ferrules - these on the old Smart and Brown manual lathe.  I always find doing cables therapeutic though - providing the wire where nipple to be fitted not soaked in old oil!

Doing front mudguard at moment at weekends, but exhaust lifter cable is next . . . and I need a special screw in housing for exhaust lifter cable into crankcase - which holds a spring on the other end.  I have one available from my spare engine, so when CNC is free (currently doing racing TT/RN bellmouths) I might write CNC prog for this one and make a small batch.

chrs and thx for original photos

Black Sheep

Was very fortunate with our one. Late father in law was only 2nd owner and he never rode it as far as we know, though a friend of his rode it in the Banbury run a couple of times. My wife inherited it and kindly allows me to ride it. It's very original and we have done very little to it. It's great fun to ride and you can put in a lot of miles in a day on it. You do learn to anticipate when riding it!


Ha ha, yes - feeling the brakes so far in the build - braking anticipation is something I am expecting to have to learn!  Interestingly - for the rear brake I was able to pick up an original 'new old stock' brake block, which still had a victorian looking sticker on it saying Douglas 2 34hp.  That bit still to fit.

Black Sheep

The back brake is surprisingly effective, unlike the front one... I need to carve out a new brake block for the back. I'm using a chunk of old tractor tyre, will see how it works. You get good at not stopping for traffic lights, anticipating the driver in front braking for no apparent reason and not quite stopping at junctions. Can be a bit hair raising.
I'm sure you will have great fun when it's up and running.


Thought you might like to see the original NOS brake block . .. with sticker (which unfortunately not make it to the build, as it had fallen off shortly after), nice to photo though


ive got exactly the same problem, i'll be making the new nuts slightly longer with a very full thread to make up for wear on head threads.
i do like that tiny linisher you have.