Navigator tank thread size

I think I have an orriginal  lightweight  main and reserve  tap.  I will check it.   Smaller than 1/4 bsp  possibly 1/8 BSP  a fine thread , I have some BSP dies  in the cold dark dungion that is the garage that should allow me to check the thread.  If correct  tap is in good working condition with filter and for sale. Other posts say the tank thread is 1/8 BSP .  Which is nearly 10 mm  18 tpi . BSP is hard to follow as it links the  inner flow size to a thread I think.   Totally confusing.

The following information is from the revised 2020 DSNs. Via Dale Middlehurst.

Chapter 38 - TANKS & TINWARE

Primary Chaincase Drain – Bolt 067630  1/4” BSP 1/2”  Also fits oil tank 3/8” x 26

Oil Tank – Feed Union  193791” x 20 5/16”  L4/292, 25348

Oil Tank Pre 1965 - Return Union 22148  1/2” x 20 5/16”  19380 Low Pressure Rocker Feed

Oil Tank Post 1965 - Return Union 067923  1/2” x 20 1/2” High Pressure Rocker Feed

Oil Tank - Drain Plug 13765  1/4” BSP 1/2”  Also fits oil tank 3/8” x 26

Oil Tank – Bottom Studs 5/16” x 26  5/16” x 261”

Oil Tank – Top Fixing Bolt  22475  5/16" x 26 1”  Needs sleeve, washers & nut

Petrol Tap 1/4” BSP

Phil,

Robert is correct. The tank feed on a lightweight Norton tank is 1/8 BSP. On Dominator I believe it is 1/4 BSP as you indicate and confirmed by Dave M in the Dominator Service Notes. It rather limits the choice of tap for lightweights.

Peter 

Hi Phil,    The tap lower thread does  look  like  1/4" bsp  , so the notes are  probably  still  correct (sort of) , but unlike a Dommy tap  which also has  this same  lower thread   the lightweight tap has a 1/8 bsp upper thread into the tank.  It caught me out  when I went through my  "taps on the brain phase ". The Tap patent number stamped on the side is the same for both taps  , that encouraged me to buy one.   The lower threads could also  be 7/16" bsf  to fit  the  pipe union ?  , I have always assumed them to be bsp  , I will know later  , I have just cleared a mates garage of "stuff" ,I now have everything  possible  and improbable ,including a  hundredweight of  new possibly aircraft fittings ,  Would be great if they are  Spitfire! , might barter my way into a free flying lesson.  Lots of  "stuff" in boxes marked  Mortar and Sten , so it was a bit like "Danger UXB"  exploring dark spaces !.

Hi Adrian,  I doubt you will be able to do what you are suggesting..  You can either get the right tap  or  if there is enough metal in the tank boss you could do what I did to a poor Ducati .  Drill out the tank thread  (was 10mm)  and re-tap with a 1/4" bsp tap  and then you have a choice of petrol taps . The tricky stuff is getting a straight hole/thread in the tank  and not  using enough force to loosen the boss or buckle the tank. .  I did it all freehand and it worked ,but they don't call me Bob the  bodger for nothing !.

BSP parallel , I got a pair of BSP taps from Tracy Taps .  Means I can use  Norton suppliers  who post the same day and  accept goods back if faulty.  Support your  trusted people  and they may be there when you need them.    I still have the right petrol tap though.!!.

I just assumed that as the Navigator tank  looked so similar to the Dommie version then the threads would probably be the same.  Now I know better. Somebody needs to produce  a Lightweight Service Notes Book.

Hi Adrian. 

Pipe taps are based on the internal diameter  of pipes, this is so that the flow capacity of the pipe can be calculated. It does refer to the out side diameter but to a British standard for pipe  fittings.

Hope that makes sense.

Peter Fairbank. 

The Noc shop lists a non reserve tap for the lightweights   . It states it has a 7/16 thread for the tank ,   Understandable  but I suspect thats an error , should be 1/8 BSP   and probably is.  Much safer than tank surgery.

Could anybody tell me the thread size of the screws holding the Norton badge to the Navigators petrol tank.

After fruitlessly looking at  lots of lightweight photo's from way back I have to conclude that  lightweights were fitted with several types of fuel tap  , mostly Ewarts  some with a reserve ability (250's?) ,some with an outlet at 90 degrees . I think that all had the small 1/8" BSP  thread in the tank that visually looks like  about 1/4 " very fine thread  ,just to confuse.  Perhaps Andy S.  knows  more?.

Hi Adrian. Well spotted.

Cheap or not, this looks ideal. I found that one problem is the presentation of the lever. A straight BSP thread seals when the sealing washer is compressed, not when the lever is handily presented to the rider.

Your choice looks to come with a generous elastomeric sealing washer, so should give you a better chance of making a seal and presenting the lever where you want it.

Please tell us how you get on with this.

I can confirm that the Lightweight does not have any residual fuel in the right hand side of the tank when it runs out. Fortunately a mobile phone, a spare tank of fuel in the garage, and a willing wife sorted me out.

Happy riding

Peter