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Chassis Restoration

Module by: Andrew R. Barron. E-mail the author

The Seven S4 (Type 60) chassis is actually comprised of a tubular structure reinforced by two sheet steel side panels that are spot-welded along the side and underside of the chassis. Once the chassis was stripped it was clear that here were signs of corrosion of the side lower tube below the sheet panel. Removal of both panels (Figure 1) showed only surface corrosion at this location. However, one of the upper side tubes was significantly corroded in the region of the engine bay and this had led to a 1/2” length hole. In addition to chassis lower tube the front box section had corroded resulting in the destruction of a significant portion of the lower half (Figure 2).

Figure 1: A view of the right hand side of the bare chassis.
Figure 1 (graphics3.jpg)
Figure 2: Underside of front box section before media blasting showing significant corrosion.
Figure 2 (graphics4.jpg)

Three of the four bolts holding the two steering rack clamps were readily loosened; however, the last (forward right hand side) sheered-off (Figure 3) and will have to be drilled out.

Figure 3: The front box section and steering rack mounting brackets (A) showing the single bolt (B) that sheered off while removing the steering rack.
Figure 3 (graphics5.jpg)

Repair of chassis

All chassis repairs were undertaken by Lucas Racing and Restoration (Houston, TX). In order to ascertain whether there was any additional damage hidden by corrosion, the chassis was cleaned by Custom Coatings (Cypress, TX) using media (alumina) blasting (Figure 4). Importantly, the bronze welding used on the chassis showed no sign of damage due to either age or the fire (Figure 5).

Figure 4: The bare chassis after media blasting.
Figure 4 (graphics6.jpg)
Figure 5: An example of the bronze welding used in the chassis construction.
Figure 5 (graphics7.jpg)

As expected the front box section will have to be replaced (Figure 6). Happily, the only damage due to corrosion in the steel tubing appeared to be in the upper right side tube, the lower left and right sides. In addition, it was found that one of the upper engine cross members was cracked.

Figure 6: Underside of front box section after media blasting for comparison with Figure 2.
Figure 6 (graphics8.jpg)
Figure 7: The upper right side tube showing a hole due to corrosion.
Figure 7 (graphics10.jpg)

Repair of side tubes

The first issue was to make a jig to ensure that the chassis frame remains straight during repair. As such it was found that there was a slight bend in the chassis frame that will be straightened during repair. The small sections of the right side upper and lower tubes were repaired by cutting out a small area from the damaged face (Figure 8) and welding in a replacement section (Figure 9 and Figure 10). A similar process was used for the engine upper member (Figure 11).

Figure 8: FIGURE. Schematic of the process for repair of the upper tubes.
Figure 8 (graphics11.jpg)
Figure 9: The upper right side tube showing the repair section in comparison with Figure 7.
Figure 9 (graphics12.jpg)
Figure 10: The lower right side tube showing the repair section in comparison after welding, grinding and painting with primer.
Figure 10 (graphics13.jpg)
Figure 11: The upper left side engine brace tube showing the repair section after welding, grinding and painting with primer.
Figure 11 (graphics14.jpg)

The lower left side required two separate sections to be replaced either side of one of the body-to-chassis threaded bobbins (Figure 12). One small section was removed in a similar manner to done for the upper tubes (Figure 8) then a new piece of steel welded in-place. The second, larger, section was cut out completely rather than just one face of the tube. Furthermore, it was cut at an angle rather than at 90° to the tube (Figure 13) in order to provide larger welding area. The finished section is shown in Figure 14.

Figure 12: View of lower left-hand side chassis tube showing removal of the section aft of the chassis-to-body bobbin.
Figure 12 (graphics15.jpg)
Figure 13: Schematic representation of the repair of lower chassis tube.
Figure 13 (graphics16.jpg)
Figure 14: Finished repair lower chassis section. N.B. The chassis is upside down and thus viewed from below.
Figure 14 (graphics17.jpg)

Repair of front box section

The front box section is almost completely corroded and needs to be replaced. In addition, this is a good time for it to be strengthened so that it can be used as a front jack point. The complete lower part of the box was cut away and a replacement section made from 1/8” steel plate. Before the lower section is welded in place a brace is welded to strength the box (Figure 15). Once the lower section is welded in place the sides are straightened and then welded to the new metal (Figure 16 and Figure 17).

Figure 15: Schematic of the reinforcement (shaded) added to the front box section.
Figure 15 (graphics18.jpg)
Figure 16: View of the underside of front box section (viewed from the front of the chassis) after removal of the old metal and welding in the lower plate. Compare with Figure 6.
Figure 16 (graphics19.jpg)
Figure 17: View of the underside of front box section (viewed from the rear of the chassis) after removal of the old metal and welding in the lower plate. Compare with Figure 6.
Figure 17 (graphics20.jpg)

On the upper side of the box section the seams were bronzed to ensure that no water ingress could occur and cause a repeat of the corrosion that was present.

Steering rack mount

As shown in Figure 3 one of the four bolts holding the steering rack clamps had sheered-off. Given that the nut is welded to the lower side of the mount, and it was found difficult to remove the bolt or replace that one nut, it was decided to replace the whole top of the bracket along with new nuts (Figure 18).

Figure 18: The replacement steering rack mounting brackets. Compare to Figure 3.
Figure 18 (graphics21.jpg)

Chassis brace

At the rear of the chassis the inner seat belt and axle locating link are attached to a removable brace. The points where this is bolted to the cross member were strengthened (Figure 19).

Figure 19: Strengthening of the brackets on the rear cross member.
Figure 19 (graphics22.jpg)

Fabrication and attachment of new side panels

The original side panels were made from thin steel, and since they were damaged by the fire (Figure 20) it was necessary to replace the panels. However, it was decided to upgrade the thickness of the panel for added strength.

Figure 20: The outside of the two chassis panels of the Lotus Seven S4 after removal from the chassis. The panel from the right hand side of the car (A) shows more external corrosion, while the exhaust outlet is shown in the panel from the left hand side of the car (B). Note that the lower edges of the panels are facing each other.
Figure 20 (graphics23.jpg)

New panels were cut from 18 gauge steel using the original panels as templates. The new panels were welded to the repaired frame by drilling a 3/16” hole in the panel and TIG welding through the hole. This resulted in a spot-welded look, but with a greater strength. The finished panels are shown in Figure 21 - Figure 23. The original panels were sized such that when the edges were folded over the chassis rail, they did not meet the edge (Figure 24A). The new panels were sized such that the edges matched (Figure 24B). Prior to welding the side panels, the chassis and panels were sprayed with weld-through primer to ensure that corrosion does not occur under the powder coat.

Figure 21: The chassis ready for powder coating, viewed from the front.
Figure 21 (graphics24.jpg)
Figure 22: The chassis ready for powder coating, viewed from the right hand side, and showing the new side panels.
Figure 22 (graphics25.jpg)
Figure 23: The chassis ready for powder coating, viewed from the rear, and showing the new side panels.
Figure 23 (graphics26.jpg)
Figure 24: Schematic representation of the alignment of the side panel with the lower chassis tube in the original (A) and replacement (B).
Figure 24 (graphics27.jpg)

Cleaning and powder coatings

Once the chassis frame was repaired and the new side panels were welded in place the whole chassis was cleaned by media blasting and powder coated semi gloss black (Figure 25 - Figure 31). Powder coating was performed by Custom Coatings (Cypress, TX).

Figure 25: Powder coated chassis viewed from the front.
Figure 25 (graphics28.jpg)
Figure 26: Powder coated chassis viewed from the right.
Figure 26 (graphics29.jpg)
Figure 27: Powder coated chassis viewed from the left.
Figure 27 (graphics30.jpg)
Figure 28: Powder coated chassis viewed from the rear.
Figure 28 (graphics31.jpg)
Figure 29: Powder coated engine bay viewed from the left (intake side of the engine).
Figure 29 (graphics32.jpg)
Figure 30: Powder coated engine bay viewed from the right (exhaust side of the engine).
Figure 30 (graphics33.jpg)
Figure 31: Powder coated chassis brace and the rear cross member.
Figure 31 (graphics34.jpg)

One of the advantages of media blasting and powder coating is that the original frame number became visible (Figure 32). The number GE-031 indicates that the chassis was produced by Griston Engineering.

Figure 32: View of the frame number stamped onto the right hand side scuttle.
Figure 32 (chassis number.jpg)

Resources

  • Lucas Racing and Restoration, 10030 Talley Lane, Houston, TX 77041, USA Tel: +1 713 462 0068. www.lucasracinginc.com.
  • Custom Coatings, 16219 Dundee, Cypress, TX 77429, USA. Tel: +1 281 813 0119.

Bibliography

  • Lotus Seven Register (www.lotus7register.co.uk).
  • D. Ortenburger, Legend of the Lotus Seven, Mercian Press (1987).
  • J. Coulter, Lotus Seven, Amadeus Press (1995).

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