Austin Seven
Matt adds some strength to his Seven’s chassis
Last month I finished up with the bare chassis blasted, painted and with loose rivets replaced with nuts and bolts to restore it to factory strength. Factory strength, however, becomes insufficient when additional forces are put through the chassis from improved brakes, increased cornering speeds and, generally, anything else that will set my little two-seater special apart from a saloon pottering down country lanes. There is myriad advice available in the various publications
I’ve been reading since the project began with regard to strengthening the various weak points, however after a conversation on the phone with Ian from Oxfordshire Sevens, I loaded the painted chassis into the back of my MGB GT (yes, it did fit!) and hit the road south to his workshop in Launton, near Bicester.
Ian’s worked on enough Seven specials to know the weak spots, so could offer plenty of thoughts on how to keep my frame rigid. John Haynes’ publication recommends welding a plate along the bottom of the Seven’s channel chassis – as does Bill Williams’ Austin Seven Specials bible, however Ian disagrees. ‘If you know anything about metallurgy, you’ll know that simply boxing in the bottom of the channel with flat plate will still allow the box section you’ve created to twist under stress. You’re much better off inserting a second channel inside of the chassis at strategic points and welding this in, to ensure the frame keeps its shape.’ These strategic points – from the rear engine mount to just behind the bracket for the brake cross shaft on both sides as well as the centre beam along its whole length, were marked on my chassis with chalk pen before Ian went on. ‘You’ll also want to fit larger bolts to hold the radius arm pivot on – 3/8in should do it – and also weld strengthening ribs to the brake cross shaft brackets as these can twist under duress.’
Steering strength
Finally, Ian said that improvements to the way the steering box and brake pedal was mounted would be essential for safety. ‘From standard, the steering box and brake pedal on the Ruby bolt to the side of the chassis through just one skin. You’ll need to weld cross-tubes into the chassis and allow them to be bolted through the whole
frame. If you end up racing this car, you’ll be hanging onto the steering wheel for dear life, exerting considerable lateral forces on it while cornering. You don’t really want it coming away in your hand, do you?!’
Back to the shed
I returned home with a plan and ordered some 2mm steel and tube, pre-cut to suit my needs. Once this arrived, bending up the channels and welding them in didn’t take long at all, with the biggest headache being welding up the steering box holes and re-drilling them to give the column a rake more suitable for a sports car. Before long, I had a chassis ready to build on, so that’s just what I did. Starting with the rebuilt and modified springs, which each received a fresh set of brass bushes, reamed to size, I began to build the rolling chassis up from the pile of refurbished pieces now cluttering up the shed. The front axle bolted to the transverse front leaf spring via its original hangers which cleaned up well and displayed little wear before I fitted my new double friction damper along with a pair of billet aluminium drop links – both upgrades from Oxfordshire Sevens.
The front swivels were next and went back together with the kingpins and spacers that came off just a few weeks previously. A second check with a DTI gauge revealed that them to be free of play and good to go.
The rear axle and torque tube dropped on, the latter’s support having received a new Metalastik bush, before the rear dampers, too, could be loosely fitted. My original arms had been powder coated, but the damping itself will be done with another modern day upgrade – using a centre nylon bush and a pair of spring plates either side of the arms, and a modern composite friction material between the plates and chassismounting bracket. I’ll set them up properly in due course, but for now they’re on and the chassis is really starting to come together.
The next task will be to fit the brakes. I’ve already built up the rear backplates with their original adjusters and cable-operated cylinders, and the fronts will follow after a session of cleaning up on the Clarke rotary wire wheel