21 replies to this topic

[Cooperman]

I have to fit a new battery box to a Mini and I am considering bonding it in with a suitable structural adhesive.

My feelings are that this will be an ideal way to do this and it will be structurally sound as well as easier than a lot of welding. It is the bottom of the battery box which is corroded, so the top edges/flange is in good condition. All that needs doing it the old box cutting of, the edges linishing back to paint-free metal and the adhesive applying to the new box. Then just drop the box in with some weight in the bottom of the box to provide contact pressure during curing of the adhesive.

Has anyone else done this?

[nicklouse]

Don’t think it would fulfill the MOT regs as it will be in the prescribed distance from the subframe mounts which if I remember correctly requires original means of attachment or be fully seam welded.

 

saying that it would work.

[MiNiKiN]

I think (if we factor out MOT-requirements) this is a sound way to do it. I'd use windscreen adhesive, just make sure you correctly prep the surfaces (primer).
 

I doubt this is a structural area, and even if, the windscreen adhesive will provide the necessary bonding and connection.

 

This leaves the question if the MOT-terster will notice your "bodge" - give it a try and prepare a good reasoning for your doing.

[Cooperman]

An MoT test station will not be able to discern the structural bonding in place of the welding. The battery box is not considered as a structural requirement. How would an inspector know it has been structurally bonded and why would that cause it to fail? The flanges will be as original and standard. They are not allowed to put a screwdriver under the mounting flange to try to prize the battery box off of the boot floor and even if they did, it would not move. It will all be painted as well.

Personally I don't think it is an MoT issue at all.

[nicklouse]

 

Personally I don't think it is an MoT issue at all.

But if any of the join for the battery box is within the prescribed area of a load bearing area, suspension/subframe mount/seatbelt mount etc then an Adhesive is not permitted. 
 

correct they can’t start digging around and if they can not be 100% sure they can only advise the presenter of the car that the repair is of an questionable method but they cant fail it.

 

I am only stating info that can readily be found on the appropriate web pages.

[sonscar]

The box could fail under battery securely fitted.I agree no one will know and it could actually be better than original.
An MOT tester told me that using the 30cm of any load bearing part meant that there was a small area of the roof which was not affected on a mini.Of course discretion is used extensively?,Steve..

[Vanman20]

We use adhesive to bond some panels on at work but it's a 2 part with an activator,much stronger than a windscreen adhesive.

If it were my car I'd weld it

[Maccmike8]

Lots of cars are bonded wholly or in parts. 

 

I think you should try it.

[Cooperman]

I fully intend to.
As a former aerospace design engineer I cannot see how structurally bonding a piece of secondary structure can be in any way unsound.
Unless the tester took a sharp chisel and hammered it between the flanges of the battery box and the boot floor how would he know. Even then he would find it hard to separate the join and would seriously damage the floor and the box in doing so.
How would you establish that two surfaces had been bonded rather than welded? X-ray inspection might indicate bonding.
Next time I do a Mk.1 rear light conversion I fully intend bonding the adaptor panels in place. The edges of jointed panels are usually seam-sealed and then painted.
Modern structural adhesives are fantastic if used correctly.

[sonscar]

Cars that are bonded are designed to be and presumably a quality process is in force.its a battery box after all.Steve..

[Cooperman]

I have considered how the dynamic loads are applied and they are compressive and shear loads and thus ideal for bonding secondary structure. There is no tensile loading.
I believe that using modern adhesives the outer sills could also be bonded on and would be as strong as if they were welded
I don't intend to try this but having seen the poor quality of some welding I would love to see some test pieces done and tests carried out.

[Maccmike8]

Good man. I look forward to your verdict.

[Cooperman]

Loctite Epoxy Bonding Compound has an ultimate shear strength of c.3000 lb/sq.in.
It is a 2-pack adhesive and is seen as an alternative to welding.
If an MoT tester failed a car because the battery box was so bonded I am sure Loctite would support the owner.

[GraemeC]

Support the owner with what?
The MOT requires it to be of the original construction, so welded. Not of a suitable alternative construction (that may even be stronger).
Loctite can’t help the owner to prove it meets the MOT requirement because it doesn’t. Even if it is a more modern approach that could be considered better.

So yes it will no doubt be undetectable to the tester (as are sills rebuilt with chicken wire, newspaper and filler). It may be far superior in terms of strength to a welded battery box, however it is technically against the rules.

Edited by GraemeC, 17 April 2021 - 08:12 PM.

[Cooperman]

Do you know what, I don't really care so long as my cars are safe and I can have confidence in them.

To me using a professional structural adhesive for fitting the battery box makes so much sense I shall definitely use it in the knowledge that the result will be stronger than normal plug welds used to replace those boxes and will be corrosion resistant.