Aluminium Fuel Tank Fitment

[BarryC]

Given the present shortage of supply of steel fuel tanks, for expediency  I am considering using an alternative standard size aluminiun tank (said to be with thicker alu side plates)..

I am aware there have been some failures with stress cracks on alu tanks (tank being a structural member), particularly at the side lugs - from flexing/ vibration, but have been advised that various methods of 'anti-vibration' are common to aleiviate/ reduce the risk of fracture. These vary from expensive purpose made fitments (believed to be based on rubber sleeves) to simple insertion of nylon / fibre washers with/ at the bolt fixing points (tank to body),

Could you please advise youe experiences, if these fitments are necessary (normal road use), and methods (where/ how placed) if/ which addition is beneficial. There seems to be debate both ways (e.g fitments may reduce the structural rigidity/ intended).

Thanks in anticipation

BJC

[Keith66]

Hi Barry and all

Its an interesting question.

I have also read that Ally tanks suffer from cracking using the standard install method of the original steel tanks, due to that being a hard bolted "structural" member.

But quiet how structural?

If anyone goes Ally on flexible mounts do they loose an apprciable amount of structural integrity due to that big steel box being missing or is it  pretty negligable.

I can see the engineering logigic behind the argument but have no idea myself and as i'm looking at repairing/refurbing my original steel or buying a new tank it would be great to have some feedback before Barry and I have to take the plunge one way or another.

Cheers

Keith

[Motorsport Mickey]

Barry,

Our cars are pre safety designs. No crash structures, no deformable stress tested wings sills or inner tubs, there is no documented engineering calculated figures and no sacrificial testing of part and completed shells and cars.....what do you want us to tell you ?

These cars with chassis and single skin tubs and bolt on wings have hardly ANY resistance to crash and flexing being boxes which even when welded were only spot welded, (except certain limited areas) which is why extra seam welding helps the rigidity greatly, and the petrol tank finished in steel and secured in the traditional fashion is one of the only stressed units on the car that can offer ANY resistance to the cockpit lozenging into various shapes.

I've raced a TR4 and it was fitted with a steel fuel tank fitted in the standard manner because my engineering background says steel is much more amenable to compressive and twisting forces than alloy, any flexible mount of any magnitude to be of use will impinge into the stressed benefit of the tank and reduce it's affect but other than my subjective judgement that the steel tank will offer considerable better stiffening affect than an alloy tank that's all I can say.  

Stuart who has completed many of these TRs in rebuild may have other information and thoughts on it, and has reported failures on the mounting lugs, but I doubt anything categorical or official is available upon effect on stiffness other than a seat of the pants reaction to a car equipped thus.  

Just to focus the mind we do have instances recounted by Alec Pringle (search box)  who lost a few friends because of a fuel tank rupturing in accidents (steel) and my choice is to fit steel because the weakening of the Alloy tanks strength and resistance to cracking on mounts is unable to be qualified.

Mick Richards    

Edited June 7, 2019 by Motorsport Mickey

[Drewmotty]

If you fit an alloy tank a firewall will stiffen the area and help reduce any load on the tank lugs. 

[Waldi]

I think any tank in our cars is pretty flexible  (but steel ones will be stiffer if made from same thickness). The side walls will act as a “membrane”, sort off. But on the other hand, the body is not stiff either, so the tank will help increasing overall stiffness to some (limited?) degree; no data to back that up, just my feeling/judgement.

What can improve stiffness more (but only in one plane) and more important, safety, is a properly installed firewall, and that is what I will do, for both reasons.

Back to the alu tank: If we agree there is movement in the body, the alu tank and especially its fittings should be designed such that this movement will not rupture the welds (and potentially lead to fuel leakage!). Just a plate welded with fillet welds perpendicular to the side of the tank would not be ok for me. The devil is in the detail.

Waldi

[stuart]

The Revington tanks have rubber ferrules to mount on the fixing bolts which sort of insulates the tank from body flexing a bit.

I find the best way to stop flex through the shell when I build the shells is to use at least three times the amount of spot welds as original for a start and then I always seam weld the "A" and "B" posts down to the sills and around the front and rear decks to the inner wings as well as seaming and spot welding the sill end caps and the seat belt mounting plates at the bottom of the "B" post. Seam welding the main floor mounts also. This stiffens the shell up a lot and also allied to a firewall as well. Obviously if your going to build a cage into it then that will also help but a standard roll bar will go some way to helping.

My 4a took a hard side swipe from a 4x4 a few years ago and it bounced off the "B " post on its way down the side and I only had to replace the outer panels as it hadnt moved any of the main structure as that was built like that.

Stuart.

[PodOne]

Just to add to Stuarts list if replacing the sills is to extend the downward floor outer sill up to be sandwiched between the inner and outer sill so in effect you have three tubes running the length of the sills. I also found adding a flange to where the bulkhead meets the flat panels under the front wheel arch made a big difference in reducing twist to the front inner wing's and seals up a muck and rust trap (mine was rotten). I also have seam welded the floor pans.

Given the above comments I have a steel tank but while the shell is bear is it worth adding a fire wall now if so I have a few questions;

1) Can this be 1mm metal sheet welded in?

2) Or is Ali sheet pop riveted into place better?

3) dose it need to be removable to allow for future maintance?

Lastly anyone got any pictures? 

Andy    

[BarryC]

Thanks everyone for the useful comments/ observations.

2. Structural - it is appreciated there is no doubt that introducing additional stiffening to the body (by welded plate (firewall benefit), welds, / bracing etc.) is the way to go, especially during a re-build process. A more major task when (as mine, and posibly Keith's) is post re-build i.e 'on the road', (additional safety benefits of the former still primary and understood).

1. Anti-vibration; stress/ impact reduction - given there are many 'alu' tanks already (irrespective of the pro's & con's) in use out there I was interested in forum members or associates actual experience with installed 'alu' tanks; the method(s) utilised (if or not) of reducing stress risk (e.g at fixings); success rate/ performance or failure to date, source of supply (tank / fixings, impact reduction elements). This is not intended to be interpreted as a formal 'survey' - just for personal consideration/ assistance.

Hope this assista Keith also.

Cheers

BJC.

 

 

0

[Waldi]

Barry,

I have no aluminium tank, but several on this forum have reported experiences with them, good and bad.

One of the active members is selling some, maybe he and others will comment.

As for the fire wall:

I forgot to install one earlier, and will install one by pop-riveting, combined with a good temperature resistant adhesive, so it can withstand a fire for some more time (minutes probably).

For stiffness reasons, welding would be (a bit) better, but my main reason for installing one is safety (fire retarding),  and riveting will make future access to the tank and its components much easier.

When you want to go the welding route, I think it should be spot welding, because if welded with weld seams, the accumulated shrinkage may deform the rear deck.

Regards,

Waldi

[BarryC]

One additional related question :

Fuel Tank - On (Moss & Rimmer) parts diagrams there is a felt strip - Rear Top & Rear Bottom. What is the purpose, where/ what  does it fit to,  and is it ACTUALY needed (presume is as it is shown) ? Seems to be missing on mine.

Thanks

BJC.

[rcreweread]

Waldi/ Barry

Not sure if it was me you were referring to in your post, but I was able to get a really good deal on alloy fuel tanks from Alicool some time ago and have been making their tanks available to fellow club members for a couple of years now, not as a business, but as a means to helping other members and enthusiasts. As far as I can recall, I have never had any problems reported to me about cracking or leakage.

Alicool have been manufacturing alloy tanks for a reasonable period of time.  As I understand it, the two partners in the business used to work previously for one of the other main alloy tank manufacturers, before setting up Alicool. Between them, they have many years of experience in this field.

I have queried the issue of cracking with them on several occasions, and they have told me they are genuinely not aware of any of their tanks cracking in all their years of manufacturing - they are concerned about these reports as it creates, in their view, an unfair reputation for alloy tanks in general. There is no question that there are some very poor quality tanks out there, probably emanating from China, which have been known to crack.

There has even been some speculation that one of the main TR suppliers switched their tank supply to a poorer quality item, not that long ago, and have suffered quite a few quality issues as a consequence. This could explain why Alicool suddenly started being asked about this issue on a much more regular basis.

I am not an expert on alloy fuel tanks, nor am I a dyed in the wool supporter of Alicool, but I know the quality of their work and I am inclined to believe them about the reliability of their tanks - as far as I am aware, they do not advocate  the need to provide any sort of anti vibration mounting - to do so would seem to negate any structural strengthening even an alloy tank can provide .

I am sure they will be happy to answer any concerns  people may have so why not contact them direct  - www.alicool.co.uk

Their tanks genuinely appear very well made, and the welding on them is top quality (some of the best I've ever seen) so I have no qualms about their quality and am quite happy to use them on my own restorations.

Barry - just seen your latest post - the felt strips fit horizontally along the back face of the tank behind the boot board - they do have a habit of trapping moisture thereby exacerbating corrosion so I would be tempted to replace them with some form of inert, non moisture absorbing foam

Hope this helps

Cheers

Rich

[Waldi]

Hi Rich,

yes now I recall, it was you:)

Hope your tanks find a good home.

Regards,

Waldi