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retaining screw for Ewarts fuel tap sliders

I had a wee excitement on my '55 Dommie a few days ago - I pulled out the slider, and it came out in my hand.  Spilling lots of petrol.   Oops.  Thumb on the hole, find the escaped tap, and shoved it in.  The retaining screw had escaped. 

Temporary fix was to move the retaining screw from the reserve tap so that the main works properly, and put duct tape and a zip tie to hold the reserve tap in place.

This is the tap slider, I need some retaining screws:


1 Can I buy some spare screws anywhere?

2  What is the thread on the screw?

3  My bike gives around 3 miles before reserve runs out.  Is there an easy mod to give a more useful 10-20 miles on reserve?



you may have to buy an old worn out tap to get a screw. The nose of the screw is reduced in diameter to fit the plunger slot,and Its very close tolerances.  To increase reserve I think you will have to remove the filter,extend  the tube and fit a longer filter which I have seen on the internet. Carefull with the plunger,if its the extended nose slotted type they are very rare and not availiable although I have a few spare if you are stuck.I also need a screw for my spare tap,they are too easy to damage if overtightened and get lost if loose!. Its worth the trouble though with a combined main and reserve, ,as they are an original fitting and with a good cork last very well.


Paul and Robert,

I have a motley collection of Ewarts taps in poor condition, but a couple have the retaining screws, so I can measure up the thread tomorrow, both the long nose and ordinary type.

Have a look at Classic Motorcycle Spares, although several taps with reserve are out of stock.

My early Model 18 has an Enots tap fitted which has a reserve lever.  The main supply connects to a tube in the tap that extends 35mm above the base fibre washer, so will provide a larger amount of fuel for reserve.  New Enots like this are not so easy to find.

On my Slimline tank I've used a modern tap with a reserve, but this only gives about 10 miles, which isn't really enough now that smaller petrol stations are closing down.



I've measured and drawn the retaining screws for the standard and the long nose types of petrol tap.  Both have 36 TPI threads that are 0.138 inch outside diameter, which seems an unusual thread but is also used on the Enots petrol taps; can anyone provide any more details of this so that I can try and buy a tap / die?

I've added a photo but it's not as clear as I would have liked, I'll have to get a tripod out and light it better!



That's a very useful contribution, Philip.  I think mine needs the short screw.  I also have an incomplete spare tap, lacking the screws....

I rang an engineer friend who thinks that the thread is 4BA:

4BA:  0.66mm thread pitch, 3.60 mm OD,  38.480  threads / inch,  0.1417" OD 

He has some 4BA cheesehead screws and is thinking of making one or two of the Ewarts screws for me..... Method being to grip the thread section in a lathe, turn down the shank, part off




Tonight I've tried 4BA screws in the tap body and they are a tight fit, but will work.  I think you only need to reduce the end that fits into the slot for it to work.  I'm not sure why the diameter is reduced by the screw head.

You really need a Model Engineer with a nice small lathe to do work like this.



That reduction by the screw head is because the end threads can not be to full depth, so causing binding.  It's good engineering practice.

Did you try both 36 and 38 tpi thread gauges on your sample? 

Assuming that 4BA is correct, if the screws are too tight, a similar tap in the body will sort it out.

To turn a 4BA cheesehead into a suitable fixing screw is just a matter of turning the reduced diameters and parting off.  I have sent my friend the drawing by email and he has offered to make me one or two tomorrow.



hello Norton had Race taps fitted with a long leaver Both my Norton's have them  as standard , Ewarts taps  were for BSA  Triumph and Light-weighs  Motorcycles   Real Norton have Race taps yours  Anna J 


Ewarts  taps were fitted to  some Bracebridge St Nortons  from new. Over the years and models a number of changes were made. To some its important to keep as many standard parts as possible. Sometimes the extra trouble in refurbing the old parts is well worth it as replacement pattern stuff can be of very poor quality often made in inferior metals .When I rebuilt the wreck of my 99DL I could not find a new combined main and reserve that would do the job  so I rebuilt the original Ewarts , lots of leaky corks later I found a quality cork that has lasted for years. You cannot beat Quality, but its not easy to find it. I would be  very happy to buy 3 screws for the long bodied Ewarts with the slotted long plunger. I still have a few of these rare plungers spare for members who are stuck without one or damaged, they still will need new cork as 50 years dry storage has not helped.

Dear Anna,

It's not the case. The Workshop manual describes a knurled knob , pulled out for normal running and a hexagonal knob for reserve. When two taps are used, either can be used for reserve and will supply 5-8 miles of running.


I am fairly certain that the two-plunger Ewarts tap on my '55 Model 88 is original.  You have to pull the main tap for flow, and the hexagonal reserve tap for the extra - but it seems to last around 4 miles before it too runs out.

Thanks to Phil Ham's drawings and photos, I am now the proud owner of a pair of newly made screws for my Ewarts fuel tap, made from stainless 4BA cheesehead screws.  The head is larger and fatter than original, but hey, it's a new screw which fits, and made very promptly as a present.





I've been out to the garage to re-check the TPI of the screws and found that my thread gauge jumps from 36 to 40TPI, so couldn't confirm this.  As the screw only has a small length of thread it's not easy to measure the TPI.  But thanks your input the 4BA screws fit perfectly.


I have a spare long nose Ewarts tap but no plunger, please can you tell me how long it is?  The normal (shorter) ones are just under 1" or 24mm long.


Whilst we're discussing petrol taps can I ask about the Enots type tap?  A couple of these taps (no reserve type) have a filter gauze that screws into the tap body, rather than the usual fiddly solder fixing.  Now, this thread is either 36 or 38tpi but measures 0.249" or 6.32mm on the OD.  So this seems to be a 4BA thread with larger diameter!  Can someone enlighten me?



Hi Phill, The long plungers are 40mm overall including knob, the tap will be stamped "UK PAT.758264&ABROAD. If you dismantle to fit a new cork take photos as the reserve brass slotted section can be fitted in the wrong alignment. Some of these taps were fitted with an extra long shaft which leaves the knob well away from the tap. If you are rebuilding the tap I would try to increase the reserve tube as It does not take you far. I have a suspicion that when in the normal position fuel can seep by so you are running on reserve before you know it!.If you will confirm that the tap has the above pat no I will find you a plunger.   BOB.


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