Bolt Holes on bottom of Fuel Tank

[67Survivor]

Can anyone tell me what the hole on the bottom of each fuel tank next to the outlet pipe is for please? The tanks were already removed when I purchased the car, and I am finding that a few pieces seem to be missing. The obvious answer is that it is a drain of some sort. Does it take a regular bolt, or a drain valve of some sort? Do I use some sort of sealant on the bolt as well? Any info would be great. I did try to attach a photo, but.... anyways....
Thank you,
Rob

 

[hartmandm]

I am re-doing the interiors of the fuel tanks on my Series V right now. Those holes are drains. There are drain plugs with flat head screw tops. Picture is attached. You should have a hole in the rear quarter panel bottom, so you can insert a screw driver through the hole to loosen the drain plugs and drain the tanks. I haven't removed the drain plugs on my tanks. I drained the fuel tanks at my fuel filter, which is the near the balance pipe outlet. That left some fuel sitting in the tanks still, so I stuffed a rag in each outlet pipe opening when removing the tanks.

I plan to do the interior tank coating with the drain plugs in place. I figure that will result in one less possible leak point. I just don't see that I will be using those drains in the future.

Mike

 

[67Survivor]

Thank you very much Mike. I don't see why I would ever drain the tank there instead of disconnecting to center pipe from the metal line under the car. a couple of bolts should do the trick.

 

[67Survivor]

I stand corrected, a couple of bolts won't do the trick....
Can anyone tell me what the thread pattern is on these drain plugs? I have tried both imperial and metric in fine thread and neither seem to fit. The closest seemed to be a 10MM fine. Is this possibly a "Whitworth"? At this point, I am thinking a couple of welded up holes would do the trick...

 

[hartmandm]

It looks like it is 28 tpi. It measures 0.390" where it exits the hole and 0.392" at its end. I would expect it to be tapered to create a seal. So it should be a tapered pipe thread. A guess is British Standard Taper Pipe Thread. Wikipedia has a size chart. https://en.wikipedia.org/wiki/British_Standard_Pipe

1/8 size looks like a candidate:
Size - 1/8
TPI - 28
Decimal Major - 0.383
Decimal Minor - 0.3372

Hopefully someone familiar with pipe threads will chime in to confirm or refute the guess here.

Mike

 

[67Survivor]

Wow Mike,
Thank you for all of your effort. My first stop today was a plumbing supplier as I expected they would have a something tapered to fit. We tried what they had listed as a 1/8, but it was too big for the hole. I'm guessing that a British 1/8 might have a slightly different threading. I could retap for a more standard size, but welding it over is one less potential leak point.

 

[oLD lIMEY]

Dose my 64 S3 have those bolt/plugs in the bottom of the tanks? Reason I ask is I have a gas smell after sitting in the trunk area but can't find any leaks in any of the piping and wondering if it's them. Thanks.

 

[hartmandm]

Probably. I think the left tank remained constant from series III to V. Check if you have the access holes under the car.

Have you checked the 3/8" rubber vent pipe condition?

Mike

 

[Fastback]

BSPT plugs

Here's a possible source for that plug:

http://www.discounthydraulichose.com/9030T_British_Pipe_BSPT_Hex_Head_Plug_p/9030t.htm

Currently have my tanks out for a cleaning at the local radiator shop, but can't figure how to attach a photo for another view. Need to shrink it down somehow...

 

[oLD lIMEY]

Probably. I think the left tank remained constant from series III to V. Check if you have the access holes under the car.

Have you checked the 3/8" rubber vent pipe condition?

Mike

Yes I replaced it with a temporary plastic line with no improvement

 

[oLD lIMEY]

Yes I replaced it with a temporary plastic line with no improvement

Will also check for access holes. Thanks for the reply.