J.A.P. 5 Filler cap problem

Dad's fuel tank's Filler cap does not fit. Its a J.A.P. tank and a J.A.P. cap but across the peaks of the tank threads is 1.86" and the peaks of the cap threads are the same 1.86" (Help needed)

HI Tom,

Just checked four JAP tanks and OD is approx 1.86". However, what you say doesn't ring true. If the OD of tank thread is 1.86" then ID of filler cap thread should be somewhat less as peaks of tank thread would sit inside troughs of cap threads.

Maybe need to get to work with wire brush and needle files>

Tony think you got it wrong way round. Cap drops on, obviously the wrong cap where do I find the right one. 1.86" is about (allowing for error) 1 and 7/8"

OK, got it - thought you meant it would not go on.
Not sure I have a spare cap but will have a look later.

Hi Tom,

Sadly all the caps I have are attached to tanks so no spares. By way of interest, I tried the cap from my Villiers V engine and it's exactly the same so maybe they are a standard size. Could yours be off a motorcycle?

I am not sure, It has the J.A.P. emboss on it and obviously does not belong to the tank.
this is our first engine so we lack knowledge.

this is a before picture

Hi I/m almost sure on the JAP 5 I have the oil filler cap and fuel tank cap look the same maybe try swapping them or at least give it a try
good luck Tom

The oil cap is definitely the oil cap in this case.

Reckon you have a Petter tank, put a photo up of the tank and underside of the cap...

Both sides of cap.



Tank.



And a stamp mark on tank.

tony RA wrote:Hi I/m almost sure on the JAP 5 I have the oil filler cap and fuel tank cap look the same maybe try swapping them or at least give it a try
                                           good luck Tom

Dad tried the petrol cap on the oil filler thread and its the same, so maybe it is the wrong tank.

Tony you may need the correct oil cap if your two are the same.

Getting desperate now almost finished except cap fit!!1

Help.

I'm also not convinced that it's a J.A.P tank. Either keep looking for a tank with cap or, if you want to keep the cap try Franks Tanks - see Suppliers.
Good luck.

Petter A1 with JAP cap. I reckon there's a lot of pick and mix going on

https://i.ebayimg.com/images/g/o~cAAOSwIKlff3Am/s-l400.jpg

I have several brass caps 1.84 inch ish internal. One is marked Petter A1. Any good ?

Done!! Swapped some Land rover bits for a smaller J.A.P. tank with Cap, it was ceased on.  but when it was released it fit Dad's tank perfectly.

Excellent news!