Yes I know, I have to ask just about every step of the way. I need to remove the tank in order to examine the wiring on my 1965 B40F. I have taken the two nyloc nuts and the metal strap off, and the tank appears to be loose both at the back and at the front, but something seems to be holding it in the middle. Peering up underneath I see foam, wires, and a plastic tie, but don't know if that tie is holding it, and can't think how it could be. Don't want to tug too hard on the tank if something is holding it. Could it be? Phil (novice.)
You have taken the fuel pipe off the petrol tap haven't you?! (Yes, I had to learn somehow too...)
Yes, even I didn't miss that!
Probably rubber-foam holding it down. Sit on the bike and pull slowly away from the yokes, it will come off.
Centre nut under the rubber bung in middle of tank.
See illustration below whuch show the centre assembly unber the rubber bung.
I don't think mine is like that - I undid two nuts holding a strap under the tank near the front.
You should have a rubber bung in the top of the tank, pull it out and have a look.
As said, providing you've got the correct tank on the bike, it just sits down on to three rubber buffers fitted to the frame. The tank centre bolts then stops it pulling off.
Okay thanks - I guess being as I took off two nyloc nots holding a metal strap, my tank must not be standard for a B40?
The metal strap is a standard feature, prevents damage to tank by flexing. It does not hold the tank in place.
If there is not a hole with a rubber bung in the tank, suggest you post a photo.
Got the tank off eventually. You were all right, of course, it was a single bolt and the two nuts I undid weren't holding it to the frame atall. I still had trouble getting it off but eventually it came free. The main problem was that I am an idiot! - why didn't I look under the rubber grommet until advised to - twice - by Julian?! I am really enjoying all this but it's not doing a lot for my self-esteem! The frame where the tank was sitting is still covered with foam rubber, wires, etc at the moment.
Not sure why there is foam on the top tube. The tank should sit on 3 rubber buffers; one at the back fixed above the top tube and 2 at the front fixed to a cross bracket. The tank tunnel should not come into contact with the top tube. I can't really see from the pic whether you have the front cross bracket and it looks as though you don't have the rear rubber buffer fitted.
I've got a rubber button from the back. It's a bit worse for wear - seemed to have string wound round the smaller diameter - don't know why. Might get a new one I think. Also a flat piece of rubber a few mm thick and about an inch or so square - not sure where it fell from when I removed the tank. And of course the metal strap which has two rubber buttons - but as discussed that's not holding the tank in place. Not sure about the cross bracket, I'll have a look tomorrow. Fingers crossed. I guess I'll take all the foam off for now anyway so I can get a proper look at everything. Phil (novice.)
The picture shows the frame for a C15. The three rubber buffers push into the holes in the rear bracket on the top tube and into the cross bracket under the front of the top tube. When sitting on these buffers, the tank is very stable and its tunnel does not come into contact with the top tube.
The arrangement for the B40 is similar but instead of a front cross bracket being welded to the frame, the bracket is bolted to the frame via two horizontal brackets welded to the frame as shown. It sounds as though your's might be missing the cross bracket and the tank is resting on the top tube at the front?
Here are my tank fastenings etc with the foam rubber removed. Looks fairly standard, I hope? Don't know why all the foam rubber.
The centre bolt set-up doesn't look quite what I expected. You'll see on the photo there is a rubber bit which the centre bolt pokes through. A penny washer sits on top of the rubber bit, then a spring washer, then the nut. Is that how it should be? Doesn't look quite like the drawing, does it? The nut was only tightened against the rubber, so just felt spongy rather than nipped up against anything more solid. Is that really how it should be?
The squarish bit of sheet rubber fell off from somewhere when I removed the tank. Any idea where?
Phil (novice.)
There needs to be a larger diameter plain washer between the nut and the rubber so that the rubber expands in diameter and gripsmthe tank when nut tightened.
There is the one on the second photo, what I call a penny washer, almost as big in diameter as the rubber. That's okay, isn't it? But the rubber bit isn't the standard rubber bit, is it? It seems to have a hole in the middle which closes up when there's nothing filling it. Phil (novice)
It's good news that you've got the right brackets - it's difficult to know why he used all that foam rubber?
The tank is held in position by the shaped rubber bung (40-8085) inside the tube down the middle of the tank. The idea is that this is compressed by tightening up the nut so that it expands outwards to tightly grip the tank tube . There should be two spacers on the centre bolt. The lower one with a washer between it and the rubber bung is there to give the correct height for the bung inside the tank tube. The other spacer then goes inside the bung and is slightly shorter than the thickness of the bung. When you do the nut up it should tighten up against the two spacers and the two washers above and below the bung to allow it to be adequately compressed. Unfortunately, since the assembly rarely survives in its original form, it always seems to be necessary in my experience to rejig it so that it works correctly.
I don' think mine is anything like the arrangement you describe - as you'll see for the photos. Phil (novice)
Is it possible to take a picture showing all the separate bits you have including the bolt so that we can see what you might be missing? If you place a ruler alongside the bits, we can then see whether you've got the correct length of the bolt and spacer(s).
Here's a picture of the set up for the tank on the C15 I am restoring which should be identical to your B40. The bung is an old one and will be replaced and the longer spacer needs to be reduced by 5-10mm in length to fit the bolt (and the washers aren't the correct ones). As you can see, the shorter spacer is much shorter than the depth of the bung which allows it to be compressed by the nut.
Here is the set-up on mine. The rubber was a stiff push fit into the hole (straight hole through tank) and appears to be a rough cut home-made job? I can see that with the orthodox set up the top nut tightens, and squeezes out the rubber, until the nut hits against the top spacer. But with mine it appears to be just tightening onto the rubber? Anyway, any thoughts on what I've got please? I'm thinking maybe I need to get it as per AWJDT's.
Phil (novice)
PS AWJDThumper's photo is much clearer than my fuzzy one - any idea why? Is mine simply short of pixels?
All the bits are available from Burton Bike Bits which is where mine recently came from. Only problem was the larger spacer is too large and will need to be trimmed down to the correct length.
Thanks. What is the correct length?
Phil you have the wrong rubber.
Yes, I think it must be something a previous owner made. I'm going to try to get a proper one.
You can see from my pic that the two spacers are about 1" and 2" long. The shorter one is fine but, for everything to properly fit on to the bolt, I will need to shorten the longer one by slightly more than 1/4" - this is despite buying all the correct bits from BBB. Your long spacer might be ok but I can't really tell from your pic if you don't have the correct bolt as in my pic. If not, I would buy the correct one from BBB.
Thanks very much.
AWJDT's photo of parts, and the explanation of how the arrangement works, seem very clear. But the drawing kindly shown by AWJDT shows a rubber sleeve(41-8020). What is that for? Also, I notice there are more washers on the drawing than on the photo? As always, any advice is much appreciated. Phil (novice)
PS Will spring ever arrive?
I think the parts drawing is a bit confusing. If your tank has a simple tube down the middle then the arrangement shown in my pic and Julian's earlier drawing are correct. However, some tanks had a small cup in the top of the tank tube and a tubular bung was designed to fit in this cup and was pulled down by the nut on the end of the fixing bolt - it wasn't designed to expand like the shaped bung in my pic. The parts book picture appears to show both means of fixing the tank.
Thanks AWJDT and Julian. Any comments re the extra washers?
Having just looked at the parts books again, they are a bit confusing to say the least. The parts book tank picture I originally showed was for a 1965 B40 and seemed to mainly show the original (pre-1961) cylindrical bung arrangement but with the 1961+ shaped bung also shown. However, the 1965 C15 parts book extract bellow gives the proper fixing bolts line up and all the required washers. Not sure why the B40 parts book for 1965 had not been fully updated.
Be prepared to fettle the parts to fit your bike. New parts often fail to fit as well as we would wish them to.
The below diagram, which shows the earliery tank fixing method does show the position of the washer 29 5655 - which is shown in AJWDThumpers illustration- as being over the bolt but under the frame bracket.
Yes, I take your point, Julian. So looking at AWJDT's 1965 C15 extract, it appears there is a (plain?) washer below the tank bracket, and one just under the bolt head? Phil (novice)
No, sorry, one between the bolt head and the bracket, and one between the bracket and the spacer? Phil(novice)
One either side of the rubber, one either side of frame bracket plus a spring washer under the nut is how I read the books.
You need large washers either side of the rubber to give sufficient contact area for compression, essentially, between the long spacer underneath the rubber and by the nut above. The small spacer then limits the amount of compression of the rubber before the nut fully tightens down against the two spacers. The extra washer is needed between the frame bracket and the bottom of the long spacer simply to spread the contact area. You could use a modern Nyloc nut above the top large washer or a plain nut and lock washer as per parts diagram.