Tapping a new thread for Petrol taps

[Duncan R]

Hi All,

My Indian replica tank has dodgy threads on the tap holes. I thought that maybe the 3/8 BSP to 1/2 BSP reducers might fit but the holes are too small, I have no idea what the threads are, I currently have Indian made petrol taps fitted and want to fit the BAP taps. Can I just buy the right size drill and 3/8 BSP tap to re-thread the wholes? I have looked on the web for the tap and found a 3/8 BSP x 19 but I noticed that they list "second" and "Bottom/Plug Taps" Do I need just the one tap to do this? Many thanks

Duncan

[iansoady]

Normally a second cut tap will be fine for this type of job as it's an open ended hole. The plug tap is only needed for a blind hole so you can get the thread right to tye bottom.

[Duncan R]

Hi Ian,

Thank you - Me being an engineering numpty wasn't sure if I needed a set of taps for the job or just a single cut. Once I have the drill and tap I am going to ask my local bike tech to do it.

Regards

Duncan

[orabanda]

Duncan,
There are two types of BSP threads:

BSPT (British Standard Pipe Tapered)
BSPP (British Standatd Pipe Parallel)

The tapping drill sizes are different.

BSPT is designed to seal on "wedging" (metal - to - metal contact WITH a sealing medium; 569 loctite is best). Previously we would have used teflon thread tape.

By contrast, with BSPP thread form the thread retains the fixture (bush or tap), and a sealing washer (traditionally fibre or copper; now a days metal backed viton washers are available), seals the petrol (or oil) in. The tapping size is slightly larger, and the fitting will spin in easily, until it bottoms out against the washer. Both surfaces must be smooth and parallal, and free of scratches, paint, etc.

A BSPT tap has a distinctly tapered appearance, whereas a BSPP tap has is "straight" (parallel thread form).

If you run a tapered tap too far into the hole, the fitting will be too loose, and will probably leak. Usually, tapping 2/3 depth of the tap will be good. It is recommended that the hole has a tapered reamer run through it before tapping, but you can get away without doing this.

Richard

[Duncan R]

Hi Richard,

I think I will need BSPP, the reducers were supplied with sealing washers and they don't look tapered. I will confirm with the mechanic before ordering the tap. As he only deal with Ducatis he hasn't got any imperial taps.

Thank you

[bsa-bill]

The guy I bought my Indian tank off, supplied badges taps and reducers so the reducers are available, 1/4 inch (gas thread) comes to mind but the pathways linking  the cells in my mind don't always arrive at the correct cupboard these days

[Duncan R]

Hi Bill,

Its a long story with my tank, I bought the bike in India and the original tank (don't think it was original BSA) fractured around the centre whole. The dealer I bought the bike from gave me a new(?) tank with the taps already fitted, me being a complete noivice with Brit bikes didn't pay much attention to the taps or the fact that there was no fittings to bolt the metal strap to at front of the tank. It did come chromed and painted and it hasn't leaked or gone rusty inside since 1996. The reducers I bought were to 1/4 not 1/2 as mentioned before.