Petrol tank filler neck thread size ?

[african imp]

I restored a real wreck of a Seagull for a chap in Pretoria, the engine had been laying around in a farm for decades, the petrol tank had the neck of a cars radiator fitted, plus a large hole around it.

I imported a spare tank from SOS for that motor , wanting to re use the damaged tank I then had an engineer turn a solid brass filler neck up for me.

He made a great job of it, the filler cap was a perfect fit, right now it is not, was there another filler cap thread used, have I swopped the caps over?

None of the other caps I have here will fit, that includes the alloy one off the 102 series motor I have just refurbished.

Any ideas please?

[Nudge]

the filler cap was a perfect fit, right now it is not, was there another filler cap thread used,

As far as I know there is only one thread for seagull fuel caps. I think it is 8 TPI 55deg.(I will have to check)

Did the cap fit before you soldered it in? Or did you braze it in? If it was brazed in did it get squashed out of shape.

[african imp]

Thanks on the info.

The cap was a perfect fit when collected from the engineer.

Then later on I found that none of the caps I have on the various British Seagulls I have will fit.

It was not fitting when I gave the brass turning and a spare cap to a friend who was asked to straighten the ends of the bashed in tank out.

I asked him NOT to fit the brass inlet but he forgot !

All of the tank was cut up, ends off etc, then and after straightening , the ends were soldered on as was the brass filler neck, so no brazing.

The man is a marine engineer of many years, he actually designed ships in his later years.

He also had the tank painted by a pro paint shop.

[Nudge]

It looks like the thread is too fine. Did you give him the correct cap to measure off? Or did you tell him the thread? If you gave him the cap then go back to him and let him fix the problem.
If you told him the thread and it is what you told him then it is your problem!

[african imp]

The cap I gave him had the brass fitting made to fit it, when I got them from the engineer both were a perfect fit.

That is why I ask, was there another thread that was used?

Did I fit that cap to another Seagull that I restored?

Its gone now of course!

is the correct thread and pitch 8 TPI 55 degrees?

[Nudge]

The thread is 1-1/4 7 TPI 55deg.... I have just had another look

[african imp]

Nudge, thanks,

The tank and a spare plastic screw in cap is now with the engineer, he will sort it out when he is at work next week.

When I mentioned 8 and 55 he said that will be correct, so possibly that is where the issue is with the caps that I have in stock, the one I gave him originally was that thread ?

[african imp]

Some more pictures of the tank that came in with one Seagull restoration.

The round hole with the two cut outs had been brazed over the hole with four sides, I think an angle grinder and a disc cut those out?

[african imp]

The same tank, now restored, not quite perfect but rather better than when it arrived?

[AusAnzani]

The same tank, now restored, not quite perfect but rather better than when it arrived?

WOW, you got that nice and straight!

Excellent work.

Regards,
Spiro