Floorpan replacement - best method?

[Fatboy]

Hi Everyone,

As I'm digging further into my Mini I'm finding a lot of bodged previous repairs (such as plated over rust etc), and the floorpan seems to have a fair amount of rust, plus a lot of plates down the outer edges.

Given that every plate I've remove so far has has old rusty metal plated over behind it, and that I really want to do the best job I can, I figured that proper replacement panels is the way to go, and that a replacement floor is quite probably justified (such as here).

Only issue is I'm not sure how best to go about this - previously I'd not been worried abut the shell distorting as I cut bits off, due to the large bolt-in multipoint rollcage, but obviously removing the floor means removing the roll cage - how should I go about bracing things?

I was thinking perhaps box section bolted in the door apertures and between the bulkhead and rear seat base, but a bit of advice would be most welcome!

Cheers,

Fatboy

Edited by Fatboy on Tuesday 8th December 22:03

[Cooperman]

If you can lift the car quite high and support it under the sub-frame towers and the rear sub-frame back mounting points with no risk of it moving and all support points taking the load equally end-to-end it will not distort, especially as the big cross-member will still be in-situ.
It's a big job to change the complete floor and most people find that the 'tunnel', which is like a central spine, is OK, so you can renew the floor in 4 separate pieces. the only difficulty comes with the part of the floor under the transverse cross-member if that is rusted badly. In such a case a complete floor can be the answer. It is not so much a difficult job, as a long and dirty one with loads of welding. Still, that's minis for you!
If you are going to do the sills as well, then you must either put the car in a jig or weld steel cross-bars across the door apertures to prevent twisting, then just cut them off afterwards, grind back and finish.

[Fatboy]

Thanks Cooperman,

I will be replacing the sills as well - it had some new sills last time, and it looks to me that the people I paid to do it just stuck some new sills over the old rusty ones, so they'll have to come off as well.

I dread to think what might be under the crossmember But as I want to add some reinforcemenr plates to the back side of it for moving the seat mounts, I might as well have it out to check!

I'll weld a couple of 3mm 20x20mm box section in the door aperture - is it worth welding another couple between the B pillars to stop it moving that way?

[guru_1071]

fat

plenty of bracing and measure it all first, during and after.

also, like pete says get it nice and high, support it well on four axel stands and make sure its level both ways with a sprit level before you start cutting.

below is an example, bit of overkill for you, but i was replacing both inner wings, sills, door posts, scuttle etc etc.

by the time it was all chopped out there was no strength left around the bulkhead area at all



this frame is designed so it will come out and can be (has been) used again on another car, it was also strong enough to get a jack against it to push the toe board out (was bent)

[cpas]

I would do either the cills first with the floor in situ or the floor firt with the sills still there - but not both at the same time!!! This also leaved datum points. As previously said, if the floor is done in 4 sections, then the remaining 3 sections will help maintain the strength.

[guru_1071]

cpas said:

I would do either the cills first with the floor in situ or the floor firt with the sills still there - but not both at the same time!!! This also leaved datum points. As previously said, if the floor is done in 4 sections, then the remaining 3 sections will help maintain the strength.

how do you do a floor without removing the sills - if the floor is rotten the sills will be as well

the sills weld to the floor - they need to be out the way to get a complete floor back into the shell.

the only 'correct' way to do a floor (as oposed to just using 'floor-pans' to repair the small sections) is to remove the sill and floor then replace with either a full floor, half floors or the sill/floor combo that goes to the first flute on the floor pan.