Crack in lowered floor pan

[Tony C]

Just been under my SV and while glancing about noticed a girt big crack in the drivers side lowered floor pan. The crack is in the lower bend and begins adjacent to the rear inboard seat rail bolt and extends rearwards to within about an inch of the rear of the pan where it has then begun to head across the rear inboard corner.

 

I've grounded myself until I can fix it. Probably rivet a doubler across the bend on the outside, having stop-drilled the crack - I don't particularly relish the idea of de-riveting it, so will try for an in situ repair first.

 

I'll let CC know tomorrow. It's probably a one-off, but wouldn't hurt to check yours, as it's not something one would think to inspect during regular maintenance.

 

I "only" weigh 92kg and never drop into the seat, but lower myself elegantly, so I'm thinking the bending process may have work hardened it - the crack (in the floor pan) 😬 is in the area of greatest load.

 

BRG Brooklands SV 😬 It seems that perfection is achieved not when there is nothing more to add, but when there is nothing more to take away. (Antoine de Saint-Exupery)

[k80rum]

Sorry to hear about this Tony, but it's lucky you spotted it

 

Something to bear in mind for those who are considering lowered floorpans - your theory certainly makes sense re the bending process.

 

 

 

Darren E

K80RUM Superlight R #54

 

 

[Tony C]

Just informed CC (James) of the crack and also spoke to Bruce at Arch, who immediately offered to weld it up FOC - good ol' Bruce

 

I've spoken to the welder at work and he can weld it up or weld-up an angled full length patch to be then rivetted on the outside.

 

When I've removed the underbody seal and done a more detailed inspection I can better decide which repair to use.

 

This'll teach me to keep trying to get completely airborne at the top of the hill on the way home from work

 

BRG Brooklands SV 😬 It seems that perfection is achieved not when there is nothing more to add, but when there is nothing more to take away. (Antoine de Saint-Exupery)

[Tony C]

Close inspection shows the crack to be 12" long with jagged edges at the rear. When removing the drivers seat there was evidence (couldn't get the nut off without a great deal of swearing) of contact between the rear inboard seat runner bolt end and the third planet. I seem to remember an almighty BANG when flying across a dip in the road two-up about a year ago, but thought it was the rear towing eye again - it was a bit bent. I'm guessing the impact generated the crack which has been propagating ever since.

 

There is also quite a bit of fretting corrosion on the inside of the seat pan where the bolts go through the seat runners - particularly at the rear inboard bolt.

 

I plan to stop drill the crack, hoping I get its ends (unfortunately the real ends of the crack may be invisible even with a magnifying glass) I've seen quite a few stop drilled cracks that just propagated around the hole. Then rivet a doubler on the outside.

 

BRG Brooklands SV 😬 It seems that perfection is achieved not when there is nothing more to add, but when there is nothing more to take away. (Antoine de Saint-Exupery)

[Tony C]

Obviously not my lucky day 😔

 

While closely inspecting existing crack with magnifying glass to identify ends of crack for stop drilling, I've noticed the lowered floor pan is also cracked in approximately the same place on the outboard side too

 

I guess I can use one of the two welded doublers I've had made-up, intending to put one on either face of the known crack, on the inboard crack and one on the outboard crack.

 

Although there IS evidence of the inboard rear seat rail bolt making contact with the road - it's not bent, just abraded - I still think the work hardening the floor pan gets when it's bent through nearly 90 degrees during manufacture didn't help and caused it to crack rather than bend.

 

If I rivet the doublers to the outside I can at least closely monitor the floor pan from the inside for further deterioration. I suppose I should accept the inevitable and order a new floor pan - it's just the thought of having to close all those steel rivets again makes my arms ache 🙆🏻

 

BRG Brooklands SV 😬 It seems that perfection is achieved not when there is nothing more to add, but when there is nothing more to take away. (Antoine de Saint-Exupery)

[CageyH]

Get yourself an air powered rivetter

Works a treat on stainless rivets.

 

Only dead fish go with the flow....!

[Paul Deslandes]

Wouldn't it be easier and cheaper to get the folded seams/cracks all TIG welded? I don't know much about welding but I'd have thought it would be stronger than the original and save all the hassle and you could get it done in-situ. Either that or let Bruce have a look at it to if he'll replace it foc.

 

 

[Tony C]

Apparently, welding aluminium is not at all straight forward - heat dissipation is not even. I could get it welded in-situ, but as the pan is rigidly located this will give rise to some strange stresses.

 

The seat pan is bowed laterally across the two rear seat rail mounting bolts and that is where the crack is centred on the outboard side. I drive with the seat positioned full aft so the load is concentrated in that area. I’ll try to engineer suitable strengthening across the two rear holes by using riveted doublers, hung from the side of the lowered pan; if I can spread the load into the surrounding structure my 🙆🏻 should be safe.

 

BRG Brooklands SV 😬 It seems that perfection is achieved not when there is nothing more to add, but when there is nothing more to take away. (Antoine de Saint-Exupery)

[Tony C]

If anyone's interested: I've finished making the doublers to rivet to the cracked lowered floor pan. I'm going to use two sheets of Aluminium, one inside and one outside - NS4 H6, 14 gauge (2 mm) obtained from Merlin Motorsport. I used this spec for no other reason than that was what was available, but it has taken the bending beautifully, with no visual signs of stress. The two pieces are both the length of the seat runners + a bit and full width, bent up at either side; this section when viewed from the rear ____________/.

 

Once I've checked for best rivet spacing I can start drilling and riveting.

 

With a total of 6mm thickness it is over engineered, but shouldn't give any further problems

 

BRG Brooklands SV 😬 It seems that perfection is achieved not when there is nothing more to add, but when there is nothing more to take away. (Antoine de Saint-Exupery)

 

Edited by - Tony C on 23 Mar 2007 20:10:12