This isn't the original tank for my 1954 M33, but is it a genuine BSA tank or a pattern copy? It certainly doesn't impress, as:
[photo 1] the left side is a quarter of an inch further forward of the right and the rear mounts are not centred.
[photo 2] The tunnel for the frame tube isn't parallel sided and the tap does not sit square.
[photo 3] the rear mounts do not lay flat upon the frame mounts; it isn't possible to rise the front of the tank to make them align as the top yoke is in the way.
[photo 4] side view, it seems to be an earlier than 1954 tank.
So is it a real one or a pattern?
You may have seen these photos before in my topic asking about the front tank mounts.
All the copies I've seen have been Indian and that tank looks too old. If it's a copy it must be a helluva old one or it or it's had a very hard life. It looks very like the tank from my 1948 rigid framed ZB32 Competition. The badges on the tank would also indicate that's for a rigid or early plunger frame up to 1953.
Originally there would be a rubber support between the frame mount and the tank with another rubber underneath it which may help make up for the misalignment with the frame mount. I don't think the alignment with the frame mounts is that great on mine either but not so bad as yours.
I had my tank off recently to solder the top seam behind the steering head where it had split. I didn't notice any irregularities, but then I wasn't looking for them. I reckon your tank is probably genuine.
My 1955 BSA C11 has the similar golden BSA Badges on the front of the tank.
However any of the M33 tanks from India only have a clip for the plastic BSA Round Badges.
The C11 tank has different cutouts on the bottom, so would not be an option.
Looks like you are stuck with what you have, although a new paint job would improve it considerably.
It also needs rubber mounts and proper bolts, all of which are available on Ebay.
Thank you, chaps.
Quote from: Derek996 on 04 May, 2026, 14:08 I had my tank off recently to solder the top seam behind the steering head where it had split. I didn't notice any irregularities, but then I wasn't looking for them. I reckon your tank is probably genuine.
I'd not noticed the irregularities until recently, when I tried getting to the bottom of why it's such a struggle to replace all the bolts. I've had to solder my tank in almost the same place.
The previous owner reckoned the tank was from a B31 or B33, as the M33 tank has a pipe running under the frame top tube, joining the two sides of the tank. It being a 'B' tank rather than an 'M' might be why the rear mounts are not parallel.
So it looks like BSA tanks were not the most precisely made ones in the World, oh well.
Quote from: scifi on 04 May, 2026, 22:07 Looks like you are stuck with what you have, although a new paint job would improve it considerably.
It also needs rubber mounts and proper bolts, all of which are available on Ebay.
Oh, the paint job! Whoever painted it did a fine job except that they were a stranger to surface preparation; after a few really hot days the tank expanded but the paint didn't. It now comes off with a fingernail!
The plan is to get the rear mounts sorted, then sort out the front mounting ears which are not too straight and the holes too big.
I have an A series and a B series and never noticed any accuracy issues with those tanks, or any previous BSA tank. Not easy to mess up when the tank halves are pressed out on a 10 ton press, unlike when sitting cross-legged on a dirt floor and armed only with a small hammer.
Quote from: Rog1 on 05 May, 2026, 00:18 The previous owner reckoned the tank was from a B31 or B33, as the M33 tank has a pipe running under the frame top tube, joining the two sides of the tank. It being a 'B' tank rather than an 'M' might be why the rear mounts are not parallel.
I agree that it looks like a B31/B33 tank.
my B31 tank has a bolt fixing in the middle, not saying its correct mind.
Having just got a chain guard from India that will shortly be on its way back I can say the welds on that tank are far too good for it to be a copy. I may be older or off another model but I think that was made in the UK.
Quote from: rustyboots on 06 May, 2026, 18:59 my B31 tank has a bolt fixing in the middle, not saying its correct mind.
Rog1's tank is from a rigid or plunger framed model which has two mounting points to the frame lugs at the rear and forward facing lugs on the tank on each side of the steering head that a bolt goes through. The swinging arm frame tank, which I guessing yours is, has a single bolt through the centre of tank and a crosspiece on the underside, attached across both sides of the tank near the front.
I think there are subtle differences between the M and B series frames, which is why the rear mounts on my tank are at an angle to the rear mounts on the frame.