Petrol Tank Brackets

rednorton · Dec 21, 2013

I have come across what I think to be an unusual problem. The petrol brackets on my '70 750 (original owner) with 22,000 miles on the clock have broken off, first one side then the other. I had them welded back on but they broke off again, separately.
Okay, crummy weld job is possible but could there be any other reason for this occurrence? My local mechanic has never seen this happen before. Maybe front wheel/drum is not round? I had it trued with new Avon's and Dynabeads. It seems to ride smooth and the tires show no wear pattern that would suggest not being balanced. Any input would be helpful.
Happy Holidays to all

Rohan · Dec 21, 2013

Don't specifically know 1970 brackets, but the later tanks had large foam pads glued up underneath the tank, above the frame backbone.
This took some of the load, and vibration, out of the tank and brackets.
Does this bike have any such foam pads under the tank ?
Are there any marks under the tank that show metal-to-metal contact ?

Are these tank brackets stock.
Any chance of a pic. ?
Always best to question everything, and assume nothing...

Front fork action can give the bike a pounding.
Do your forks move freely, and feel well damped ?

rednorton · Dec 21, 2013

It's possible that the foam is hard and less forgiving . I will try to post some pics on Sun. Thanks

DogT · Dec 21, 2013

I would suggest that you are probably not supporting the tank enough with the pads on the center tube. I had one wing break off recently, because of precisely that problem. I then made some padding with Zorries (flip flops) which seems to be a good consistency for the pads. The object is not to have the tank supported by those wings, but the wings just keep the tank from moving around. I also fabricated an aluminum plate under the wings to support it even more, just in case. And while I was at it, I added an aluminum L bracket for the coils. Other thing to do is not hunker down on the nuts that hold the tank on but add some lock nuts so you can also get rid of those hateful nylocks.

Matt Spencer · Dec 21, 2013

10 / 10 Mr T , discussion here tank-pad-t12516.html .

you put two big bits of mouldy licurish

in the roof of the tunnel . :twisted:

Or some people use high density foam rubber ,

IF the tank sits on comfortably , the nuts pull a little tension onto it , so it stays put . The weight ( Fuel ) is transfered over a large area to the Top Tube , so loads Not concentrated .

batrider · Dec 22, 2013

In the picture the tank is too close to the bracket and vibration will kill it. The rubber buffer needs to be thicker or more of them added. The stock ones are not that expensive and are black, not blue too.

Some people use a muffler mount instead of the rubber washer stackup.

Russ

DogT · Dec 22, 2013

If what you think is the blue tank right on the black bracket (wing), it's really a piece of the blue zorrie that's a replacement grommet from the old hard black round ones. I bought blue zorries to match the paint. So, no, the tank is not resting on the wing. I purposely spaced the tank above the wing and added zorrie grommets to fill the void. The consistency of zorries is great, and it doesn't seem to harden, at least in the few years I've used them, and you can buy 2-3 pair for about $1, lots less than buying the spacers from a Norton dealer for cheapo Luddites like me.

Dave

batrider · Dec 23, 2013

No it's the sharp corner of the black bracket right against the tank (thin area). I have a small divot out of my yellow tank right there because the rubber washers had compressed and let the tank get too close. The tank will vibrate and touch that metal bracket. You need maybe 3/16" clearance at the minimum.

I can see the Zorrie sandals clearly....

concours · Dec 23, 2013

DogT said:
If what you think is the blue tank right on the black bracket (wing), it's really a piece of the blue zorrie that's a replacement grommet from the old hard black round ones. I bought blue zorries to match the paint. So, no, the tank is not resting on the wing. I purposely spaced the tank above the wing and added zorrie grommets to fill the void. The consistency of zorries is great, and it doesn't seem to harden, at least in the few years I've used them, and you can buy 2-3 pair for about $1, lots less than buying the spacers from a Norton dealer for cheapo Luddites like me.

Dave

There is also a need for a special shouldered grommet to keep the stud centered in the hole, preventing metal to metal contact on the hole. I got them from http://www.mcmaster.com/#vibration-damp ... ts/=pxuhcb

lomaxcm · Dec 23, 2013

Tuned in to learn more. On the 74 commando I had and the 73 commando I now have, there was no way to center the tank studs in the holes. The studs are on the inside of them and moving the tank forward or backward makes no difference. I do have rubber bumpers on top and on the bottom of the mounting however and good padding under the tunnel.

Marc

DogT · Dec 23, 2013

I have the tank pushed back as far as I can because if I don't the stanchions hit the tank at full crank. There's always some trade offs on these early bikes I've found and I try as best I can. If the grommets/mounting studs were centered in the wing holes, the stanchions most certainly would hit the tank. Remember, I have the early bike that has the small turning radius. I haven't had any problems with the reflector bracket rubbing the tank, yet.

concours · Dec 24, 2013

DogT said:
I have the tank pushed back as far as I can because if I don't the stanchions hit the tank at full crank. There's always some trade offs on these early bikes I've found and I try as best I can. If the grommets/mounting studs were centered in the wing holes, the stanchions most certainly would hit the tank. Remember, I have the early bike that has the small turning radius. I haven't had any problems with the reflector bracket rubbing the tank, yet.

Soooo, that's how they came stock? pushed back in the hole? And if a mechanic got in a hurry, left the tank centered by habit, dentage? Ouch. ALL early bikes? or just your SS?

kommando · Dec 24, 2013

My tanks are pulled back also to get clearance, so the stud is nearly touching the hole, this is a 74. I use pads under the tanks so the tanks rest on the pads before the rubber buffers on the front studs touch the brackets. As doing up the studs the nut pulls the tank down compressing the pads, undo the nuts and the tank goes back up as the pad re-expands

concours · Dec 24, 2013

kommando said:
My tanks are pulled back also to get clearance, so the stud is nearly touching the hole, this is a 74. I use pads under the tanks so the tanks rest on the pads before the rubber buffers on the front studs touch the brackets. As doing up the studs the nut pulls the tank down compressing the pads, undo the nuts and the tank goes back up as the pad re-expands

Interesting. My '74 centers in the bracket holes, 1/2" clearance to the tank at full lock. Variations, I guess.

DogT · Dec 24, 2013

I don't know if all early bikes are like mine, I've really only experience with mine, so I can't generalize. But I can say mine has always been like this, it may just be factory differences and I got a tight one? I do know the fork stops changed in 71 and it may have been because of this issue, don't really know.

The clearance between my carbs and the front air box must be tighter too, because there's no way I can get the filter rubbers on without taking off the carbs.

Dave
69S

kommando · Dec 24, 2013

Interesting. My '74 centers in the bracket holes, 1/2" clearance to the tank at full lock. Variations, I guess.

It left the factory as an Interstate, must put that back on to check, but with a Roadster tank (a MK3 one by the paintwork) and 2 Interplod tanks the tank needs pulling back.

Petrol Tank Brackets

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