A7 Plunger fuel tank

[A7restore]

I am havining problems finding a tank to fit my 1953 A7 plunger. I purchased a tank from India, nice tank, fitted on bare frame. However when I fitted the engine in the frame the tank fouled the top of the engine and would not sit lower enough to fit the mounting bolts. Also the nose of the dual seat hits the top of the tank.

Does any body have pictures and measurements of a correct tank so I can find one which will fit

Thank you

[muskrat]

G'day A7.
The A7 tank is smaller in volume than the A10, all the tanks I've seen on ebay from India are A10. The rear mounts should be slotted not a plain hole.
The tank for you is 67-8047/17. A google of the part # didn't find any but a google of "BSA A7 fuel tank" found a couple of 2nd hand ones https://tinyurl.com/39z32572 https://tinyurl.com/8chyjt5k The only new one doesn't have the screw holes for the badge and the under side looks wrong.
This one has the holes but the under side looks wrong and is raw https://tinyurl.com/nhs87436
Good luck.
Cheers

ps: click the link "Muskys plunger" below.

[A7restore]

Hi Musky.

Thanks for the reply. I had a look at the link to a picture of your bike. Absolutley stunning I hope mine is as good when I finish.

The tank in the advert looks right I will have to check what the postage is back to blighty

when I bought mine it had the wrong tank welded to the frame. somebody had wanted to convert it into a chopper so they weled a little tank to the frame and covered every thing with half a ton of filler.

I've attached a photo of my efforts so far.

[muskrat]

G'day A7.
"Absolutley stunning I hope mine is as good when I finish." Ha, don't look too hard I'm more into go than show.
Yours is coming along. It is a shame what some people do.
Cheers

[Minto]

Hi Musky.

Thanks for the reply. I had a look at the link to a picture of your bike. Absolutley stunning I hope mine is as good when I finish.

The tank in the advert looks right I will have to check what the postage is back to blighty

when I bought mine it had the wrong tank welded to the frame. somebody had wanted to convert it into a chopper so they weled a little tank to the frame and covered every thing with half a ton of filler.

I've attached a photo of my efforts so far.

Thats looking very nice indeed. Its a shame the tank doesn't fit, it looks grand.

[Swarfcut]

   It looks as if the mountings are simply WRONG.

  '53 Frame featured a brazed on prop stand lug and a rubber mounted thro' sleeve at the front, to take the tank mounting bolt. This tank has a slotted front mount. At the rear, the tank mounts themselves are rubber bushed, with a through bolt going through the frame lug. This is hardly likely to be reproduced for today's market. A bit of make do and mend seems to be par for the course with a lot of these tanks.

  That tank is lying too low at the front, and should be closer to the steering head. Plenty of pictures on the web. Moving the tank forward will solve the seat problem.

 As for buying an Indian Tank, for UK buyers there are now a good few UK dealers, and with the variable quality, getting some sort of redress for a wrong'un is far easier than trying to get sense out of some outfit halfway around the world. They may cost a bit more, but you'll sleep easier...

 Swarfy.

[JulianS]

This service sheet explains further the rubber mounts mentioned by Swarfcut.

[A7restore]

Thank you for your help, much appreciated. As a stop gap solution I have found an old A10 plunger gold flash tank. A abit dented but it fits correctly with the correct mountings to house the rear rubber bushes. my plan is to make up a jig  from this and use it to refit the mounting brackets In the correct postion. I did try a tank from a UK supplier and that had exactly the same problems with the mounting brackets.

As I understand the first pungers and rigids did not have the rubber mounts at the rear, these were introduced because the weld/braze of the rearmounts tended to fracture from vibration. I may be wrong and if anybody could clarify this situationthat would be helpful.

[Ted_Flash]

My 1950 frame doesn't have scope for rubber mounting at the front.  The tank I use has scope for rubbers at the rear.  However - I have bolted it up solid at both ends, and it's been fine for 18k miles (and the bodge is invisible to the naked eye). Only flexibly mounting one end seems like a recipe for cracking.

[Swarfcut]

   Thanks to JulianS and the archive word of mouth you can see that any original rigid or plunger BSA manufactured  tank, "rubber or not" will fit, because the front and rear mounting centres on the frame are the same. So you can have any of the various combinations of front and rear mounting styles and it will fit. However, as Ted notes, the longevity may be compromised with one end fixed and the other end free. Both ends free or both ends fixed would be the way to go by experience.

   Original fitment was solid mount front and rear. With the increasing power output and no doubt greater vibration with the move to shortstroke engines, isolating the tank to some degree could be considered progress of some sort.

    Some  BSA tanks have provision for a bracing bar across the underside of the tank towards the front. Part 67 8085. This appears in the 1950 catalogue. Is absent from my combined '49-'53, reappearing in the '54-'57 It's a simple length of flat bar. That's what those two surplus downward pointing studs are for...

 Swarfy.

[Rex]

My bike proves that it's not quite as simple as that though. Solid mounts (through stud) on the front, and circular mounts (presumably for rubbers) on the rear, but those circular mounts and the frame through hole aren't concentric at all.
I made up  solid brass bushes for the rear and did some off-centre turning to drill the mounting holes off-centre to allow the tank to be fitted.
As I understand it my A7 Star Twin should have a smaller tank fitted (this is likely an A10 tank) though it's always good to tell the rivet counters that this slightly larger tank was intended for Paris-Dakar use...

[Swarfcut]

 Rex. My take is that to avoid this situation, later tanks were made with a slotted front mount. The parts catalogue still illustrates a hole rather than a slot, where shown,  but unmolested original examples were made with slotted front mounts, (I've got two) which also makes assembly that bit easier. From a styling point of view the tank ends up close to the steering head.

 Swarfy.

[Greybeard]

Rex. My take is that to avoid this situation, later tanks were made with a slotted front mount. The parts catalogue still illustrates a hole rather than a slot, where shown,  but unmolested original examples were made with slotted front mounts, (I've got two) which also makes assembly that bit easier. From a styling point of view the tank ends up close to the steering head.

 Swarfy.

The tank on my '55 is like that.

[Rex]

Rex. My take is that to avoid this situation, later tanks were made with a slotted front mount. The parts catalogue still illustrates a hole rather than a slot, where shown,  but unmolested original examples were made with slotted front mounts, (I've got two) which also makes assembly that bit easier. From a styling point of view the tank ends up close to the steering head.

 Swarfy.

Yep, my tank has slotted front mounts too, but it still can't be slid forward enough for the rear mounts to work as BSA probably intended.