Floorpan

Section VII Fitting the Floor Pan

Warning:- Before carrying out any modifications to the standard design seek written approval from the Kit Designer. Use only high quality materials and fasteners and lock all threads. This applies particularly to Safety Critical items such as Brakes, Steering & Suspension Components.

Before starting read the note on Side Panels at the bottom of the page.

With the Chassis upside down, ensure the Handbrake apertures are on the correct passenger side (on the " offside " when the chassis is upside down) and more or less central. Once the Rear Suspension is bolted in place the Floorpan can be secured. I used Rivetwise 4.8mm St St Rivets Part No. SSD 62 SSBS x 60 off into 5mm holes. Note:- Before you fully rivet the floorpan in place it may be a good idea to fit the Handbrake/Seat 1" x 1" cross angle and the 40mm x 40mm Rear Cable angle. The position of the front angle is set by the rear handbrake hole and the rear angle by the Recaro seat runner mounting hole pitch. If fitted now they will not conflict with the floorpan rivets and a much better job can be done with the chassis upside down, they will also ensure the floor stays flat when the Tunnel and Rear panel go in. (Read the Handbrake section first)

This is where a lot of builders seem to come adrift as 4.8mm stainless steel Pop Rivets are very hard to set by hand without proper tooling. Drilling stainless steel is not easy as it has the property of " work hardening " even a centre pop will harden just the spot you wish to drill. Next is the drill. Long whippy drills from your local DIY are a waste of money. Use a Metric Cobalt Stub Drill with a 135 Deg Point. (3.3mm dia for the 3.2mm Part No.DSE-20130H pops & 5mm dia Part No.DSE-20197C for the 4.8mm pops) These can be obtained from J+L Industrial Supply at approx. £2.50 each. (Phone 0800 66 33 55)

Another very useful riveting aid is the "Cleco Sheet Metal Holder" This is sold by Aircraft Spruce in the USA but I am sure there must be a UK supplier. When you open the Aircraft Spruce site go to Tools then Sheet Metal Tools, the Cleco holders are the fifth item down. These are in effect "removable" pop rivets. Drill one hole and pop a Cleco in using the special pliers (these pliers are essential ) and drill the next hole. Pop a second cleco in etc. When you have drilled a dozen or so holes, take out a Cleco and pop rivet. Repeat for all the holes. Ensure perfect alignment. Also very useful for welding etc.

If you are fitting the Sierra 5 speed box the chassis & floor pan may need to be trimmed. See the Video.

Trim off the plastic film where you will rivet, but leave it on the rest of the pan, removing in the final stages of build. Once you are 100% sure the floor pan is in the correct position, recheck it twice as this is a one way ticket. Trim off the excess floor material (approx. 3/8" each side so that the edge of the pan is EXACTLY in line with the outside edge of the Chassis Tube. Watch out for the curves in the chassis. Run a file over the cut edges as they will be razor sharp. (When working with sheet metal always wear gloves as you can easily get a nasty cut, a pair of gloves is provided in the kit .) This enables you to determine the exact centre line of the Chassis tubes as they are now 19mm in from the edge of the trimmed floor pan (assuming 38mm tubes). This is vital as an off centre drill will wander and break. With a centre punch & a pair of dividers mark off your rivet holes at 3" (75mm) centres. Using a G clamp close to the drill position, drill thro' 3.3mm with the Cobalt Stub Drill. Due to the previously mentioned work hardening you MUST keep up a continuous cut. This is done by keeping the drill perpendicular, apply heavy vertical force and drill quite SLOWLY. Say 100 rpm. Use of a cutting oil such as Gold Spot keeps the temperature down. Once the drill skids the surface instantly work hardens and you have had it. Repeat using the 5mm Cobalt drill at the same speed. After drilling ensure there is no swarf between the chassis & the floor pan as this will be trapped by the pop rivet and may cause a loose joint. See using a drilling jig in Section XII

You may at this point wish to inject some Waxoyl etc. into the chassis tubes, this is essential in the case of a Mild Steel chassis but no so important in the stainless steel version. A thick SAE 90 oil may be best as it will flow just to where the water will collect. Robin Hood have recently advised builders to drill 3mm drain holes at chassis low points to assist in the drainage of trapped water. (Be advised that holes also allow water in, so use rubber plugs.)

Setting the 4.8mm rivets is easy, use a Lazy Tongue Riveter. These tools have a mechanical advantage of approx. 50:1 & will set up to 6.4mm rivets with ease. The tool tends to jump as the heavy rivet shank breaks so use a piece of hardboard with a 12mm hole to stop it jumping onto the floor pan. The this sheet dents very easy. This can be held in position with the G clamp.

After riveting peen the floor pan down and over onto the tube using a rubber mallet or rubber faced dead blow hammer. The small gap can be sealed with mastic if required.

My floorpan turned out to be too long and it is difficult to shorten once the car is turned over and the Propshaft tunnel is in. This is only a minor point, but this ledge will collect dirt and muck. The Floorpan should be the same length as the fitted Propshaft tunnel sides.

All the above is a bit long winded but will achieve 100% perfect results with a minimum of aggravation. So far I have used only one drill of each size on the whole of the car. The shank of the drill is beginning to wear out !!

Side Panel Note. When you come to fit the RHSC's side panels, much later in your build, you will find that the lower fold is too low. The side panel needs to be a snug fit over the top tube and the lower tube + floorpan. It is a good idea, before you turn the chassis over, to mark off the correct position of the fold and get this sorted and trimmed NOW. It is far easier to do this with the chassis inverted. See Section XX Exterior Panels.

Showing the cutaway needed for the 5 speed gearbox.

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