8 replies to this topic

[Durknp]

Has anybody every used rectangular box section to replace their sills? I understand this must be bit of a blasphemy to some but they must be inherently stronger than the regular three piece sill structure. Any thoughts would be appreciated.

[Tupers]

I think any box section large enough to replace the inner and outer sill in one go would be significantly heavier than the original structure. It would also be tricky to weld to the existing structure without modifying it.

 

Ultimately I don't think any gains in rigidity would be advantageous unless it was a competition vehicle in which case you would have a roll cage which would do the same job without adding unnecessary weight. 

[Ethel]

By being a Monocoque, as opposed to having a chassis, the Mini got rid of box sections.

 

The sills also have the advantage that they are pre stressed in the process of fitting them.

[69k1100]

The sills are box sections. You could seam weld them if it makes you feel safer. And I struggle to see how they are pre stressed? I'm assuming you mean under tension? in which case there would be no way to Ricky them and rusty cars would twist and bend when the sills rot out.

[Ethel]

I don't think you can pre stress rust, but they do "spring" when you relase a whole edge, if they're not too rotten.

 

The sills do form box sections, but not in the sense  I think dirk meant. They aren't square, they're profiled to turn the whole body into a torsional box.

[Cooperman]

As Ethel says the sill structure is designed to take out both torsion & bending loads as part of the monocoque body-shell.

You would need a good degree in structural automotive design to be able to calculate whether a revised design would be acceptable and would also possibly need an IVA test afterwards as it would be a mod. to the basic structure.

If you need new inner and outer sills the best option is a complete ready-to-weld-in sill sub-assembly from M-Machine. It fits really well. Superb value for money at around £70 and highly recommended.

[nicklouse]

Remember there is a curve in the side of sill.

[Durknp]

Thanks for all the replies. I think cooperman is right from looking at it further. It is probably easier to just buy a pre made sill to first groove and replace that way. I just thought for the price of a similar size box section you could put that in instead but it would ruin the shape and make fitting the door step difficult. Plus the legal side of things would be a pain. It was a silly idea I think. ha.

[Cooperman]

I did used to consider adding a 1.5" x 1.5" x 1/8" stiffener along the inner sill at its top edge where it welds to the door step and carrying this right through to the front inner wing and rear heel board on rally cars to add to the side impact strength and general lower strength. But I decided it was unnecessary as the box section sill is very strong (when not rusty) and it would simply add weight. The roll cage takes a lot of loads when fitted correctly on competition cars.