Author Topic: Petrol tank mounts A7 plunger  (Read 516 times)

Online Rex

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Petrol tank mounts A7 plunger
« on: 18.09. 2018 12:59 »
Hi all. My A7 plunger is getting to the stage of mounting the petrol tank. The front mount is just a long stud with nuts and is different to the parts book pic. Not a problem I can replicate that, but the rear mounting originally had rubber bushes around a trumpet-shaped steel spacer and it's all missing. Drags show no stock so I'm after suggestions for anything I could use in it's place. I'm leaning towards making the steel components on the lathe in conjunction with rubber bushes in the rear tank mounting holes, but at (seemingly unavailable) 17mm od even that won't be straight forward. Has anyone got around this issue with non-standard parts?

Online Greybeard

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Re: Petrol tank mounts A7 plunger
« Reply #1 on: 18.09. 2018 21:33 »
Hi all. My A7 plunger is getting to the stage of mounting the petrol tank. The front mount is just a long stud with nuts and is different to the parts book pic. Not a problem I can replicate that, but the rear mounting originally had rubber bushes around a trumpet-shaped steel spacer and it's all missing. Drags show no stock so I'm after suggestions for anything I could use in it's place. I'm leaning towards making the steel components on the lathe in conjunction with rubber bushes in the rear tank mounting holes, but at (seemingly unavailable) 17mm od even that won't be straight forward. Has anyone got around this issue with non-standard parts?

I lost the spacers so hacksawed off some lengths of thick-walled steel tube that was in my scrap box. As for the bushes; I'm lucky in that my originals are still ok. What about pieces of rubber hose?

Maybe self-amalgamating tape https://en.wikipedia.org/wiki/Self-amalgamating_tape could be moulded around a suitable rod and left until it 'amalgamates' to form a bush. You'd have to figure out the right outer and inner diameters to allow for compression when pushed into the tank lugs. I have no idea how strong it would be though.

I have a spare plunger style petrol tank that has slotted flat ears at the rear; no provision for rubber bushes; https://drive.google.com/drive/folders/11mmW4Ax3wuJjMyvVMDS6jyU9D-Bq5QYp?usp=sharing

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A Distinguished Gentleman Riding his 1955 Plunger Golden Flash

Offline cznorbert

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Re: Petrol tank mounts A7 plunger
« Reply #2 on: 08.09. 2022 09:48 »
Hello Gentlemen,


I would like to get a clear picture of the fuel tank mounting, and I would like your help.

On my 1949/50 A7 plunger bike I have absolutely no rubber parts between the tank and the frame, picture of the tank attached

I'm afraid the vibration will crack the tank.

I have looked for a part for this at known distributors, 65-8326 bolt, but it is too thick to fit in the bushing of the frame with the 67-8108 and 67-8109 rubber and metal spacers in one.


can you help me, how did the factory imagine to mount the tank?

Thank you very much

Norbert



Online RDfella

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Re: Petrol tank mounts A7 plunger
« Reply #3 on: 08.09. 2022 09:59 »
On my rigids (similar to your bike) the front of tank is mounted solid to frame with a long bolt. The rear has 1/4" flat rubber between tank and mounting lug, and same underneath. Obviously a large washer (thick enough not to distort - mine are 1/8" and square) is required underneath that. I cut my rubber pads from suitable sheet - agricultural merchants stock it.
'49 B31, '49 M21, '53 DOT, '58 Flash, '62 Flash special, '00 Firestorm, Weslake sprint bike.

Offline Swarfcut

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Re: Petrol tank mounts A7 plunger
« Reply #4 on: 08.09. 2022 20:29 »
Norbert. Your frame is the early type with no rubber mounts used. Sorry to say your tank is a solid mount as standard, the parts you list are for the later frame and tank. They called it progress.

  Mitch's link above shows detail of this later mounting.  The later frame has a larger hole at the front (20mm bore) into which the pair of rubber sleeves 67 8108  and metal bushes 678109  are pushed in from each side of the frame. The tank front then tightens down onto the steel bushes, isolated from vibration by the rubber sleeve. At the rear the later tank has rubber bushes (not shown in the parts book) but the same metal bushes. These mount onto  a through bolt, but in fact a length of studding/threaded bar and  nuts and washers works better. and gives scope to align the tank centrally and keep it there. Not for the purists. The 49/53 & 54/57 Parts books also shows two different rear mounts, for the two different tanks. In short any combination of frame and tank can be made to fit, the basic fixing points are the same. You can end up with  no flexible mounting, flex at front and back , or flex at either end depending on the tank and frame types.  This reiterates the sentiment of the BSA Service Bulletin above.

  Some Tanks have provision for a bracing bar between each side of the tank underneath at the front, often missing, it's a simple metal strip onto a couple of downward pointing studs. Designed to keep the two halves from flexing.

 Use spacing washers between the frame and the tank front mounting to avoid strain on the tank as you tighten everything up.

 Swarfy.

Offline cznorbert

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Re: Petrol tank mounts A7 plunger
« Reply #5 on: 09.09. 2022 12:32 »
I understand and thanks for the info

very unusual for me, vibration is not good for the tank

I'm afraid of leaks, I'll have to look into how I can get a flexible connection between the frame and the tank

thank you very much for your comments