Design And Build.

This week, the final assembly on the front hubs and the knocking-in of the kingpins would see a major part of the chassis schedule put to bed. That all went without a hitch and I was happy to see that there was almost no play present in either side. Then I put the nearside kingpin cap on – fine – and the offside cap…. Blast! That wouldn’t go on because the root of the steering arm fouls the cap and to get the steering arm out of the way, I have to dismantle everything again. I remember thinking that it was a dopey bit of design and that I should remember this little ‘gotcha’ when I was re-assembling the hubs; I should have written it down.

Nearside hub and brake cylinder

This is the nearside front hub which demonstrates the brake cylinder set-up. The cylinder itself has a capacity of just over 20cc so, although I’ve yet to read up on the form, I’m guessing that a master cylinder of about 50cc should be adequate to operate both cylinders with a bit to spare. It’ll be interesting to see how they behave because, as they’re clutch slave cylinders, they have a larger capacity than a normal brake cylinder and so might be a little be slower – or softer perhaps – in operation; pure speculation, I haven’t a clue but I’ll find out soon enough.

And, still on the subject of wheels, I’ve been wondering what to do with the spare. Originally I imagined that I might be able to tuck it out of sight behind the seats somewhere or, failing that, the more traditional position – hang it on the back. The former takes up too much room in the cockpit – the hood mechanism and Miss X’s wardrobe take priority, and the latter spoils the line so it looks like I’ll be strapping it to the side – the nearside in this case because the handbrake is the feature on the offside. I did this on the Austin Special by constructing a pillar with a hub welded in the centre and then secured the top and bottom of the pillar to the floor and upper longeron with one-piece brackets. I carried the load to the opposite longeron by means of a tube running across the cockpit. It was a rather neat solution and I think I’ll do something similar on the Hillman.

Austin spare wheel carrier

I think it’s one of the best bits on the Austin.

Austin spare wheel carrier 2

Fortunately, on the Hillman, just eyeballing where everything might fall, it looks like I’ll be able to utilise the bracing between the firewall and the windscreen pillar post to anchor some sort of fandango that’ll do the job. It’ll have to be a fairly robust affair as a wheel weighs a ton. I’m hoping that the cross-brace falls in the right position and that the line of the wing won’t be compromised – if it is, I’ll just have to design and fabricate something to get the wheel in the right place.

Spare wheel position

And you’ll notice I’ve drawn in the seat position. I wasn’t able to get hold of the actual Avro drawing for the bucket seat but, I have in my paperwork a copy of the relevant page of the Schedule of Parts for the 504k. The seat is illustrated and I’ve been able to source enough basic dimensions to work up a sketch.

Avro seat dim's

The high sides of the seat made me feel very secure, especially when in the height of summer, I had to get across the country in the middle of the day and we were being shoved from pillar to post by the thermals. The sides are probably a bit too high for a car seat but a compromise between this and the Bentley seat, I think, is going to be just the ticket.

Maybe ‘Design and Build’ is a bit high-falutin’. ‘Cut and Fit’ is probably nearer the truth.


9 comments on “Design And Build.

  1. Grant says:

    Nothing looks neater than a side mounted spare wheel, or two, which are bang on the centre-line of the firewall. Easily achieved on a special by running a stout tube right across the inside of the firewall at the appropriate height, well fastened, with the ends cranked forward a little to hit the center-line. Fit the wheel mounting gubbins of your choice and you’re done. Easy, simple and a styling success!

  2. Thanks Grant; I hadn’t quite got to the cross-tube idea which is the simple and tidy solution. The only snag I may hit is the height and length of the engine but, as you suggest, cranking the tube to align the wheel is the fix. The important thing is to distribute the load as effectively as possible – which the cross-tube does. That’s saved me some thinking time; excellent!

    • Grant says:

      It helps considerably if your firewall is a slab of quarter-inch (engine turned) aluminium plate strongly angle bracketed to the chassis, as on 30-98, Delage DI etc. these brackets also carry the sloping footboard and the body bolts up firmly to the firewall. Make all body mounts through the chassis spring loaded to allow for chassis flex and use a strip of insertion rubber ‘twixt body and chassis. No racking, no damage and no squeaking!

  3. I know it’s cast but, I was looking at a Bentley scuttle/firewall the other day and thinking along the lines you suggest. The only difference would be that the bulkhead would be fabricated rather than one solid sheet – the set-up won’t allow it. I can do the engine-turning but I want to be careful not to over-decorate. Is a spring loaded chassis mount much the same as a spring loaded engine mount – a couple of springs and some washers to float the flange?

    • Grant says:

      Whilst Bentleys are an admirable car they were somewhat over-designed, over-engineered and were very costly to build so probably do not set not a particularly good example for the semi inpecunious special builder who is trying to mate parts of different cars together in such a fashion as it looks as if it was done in a factory, and that ain’t easy!
      Do avoid too much engine turning, it can look a bit ‘girly’. The E/T on my 30-98 firewall and dash had been mostly polished away over the decades and I liked it like that. I know a chap who has now had his DI Delage for 55 or so years and when he subjected it to the “big” rebuild (it had had many small ones) he engine turned every piece of alloy in sight, and on a DI that’s quite a lot. He did NOT respond at all well to questions as to how long it had taken him to E/T inside the crankcase…
      Your body mounting bolts, and you won’t need many, should be 3/8″ by long enough to do the job. Coachbolts are probably best as long as they are galvanised and well driven in to set the square shank in the timber – use some grease to retard the effects of corrosion. Under the chassis flange use a penny washer, a short stout spring around one inch long with at least a 7/16” bore, another penny washer and a nyloc nut. Finish with a quick spray of invisible paint (satin black from a spray can) and you’re done!

  4. asciimation says:

    I don’t know if it’s any help but I always liked the look of these seats which were in a Lagonda at last years Roycroft meeting here in NZ:


  5. Thanks Simon, that’s more or less what I’ve got in mind – just a bit more padding I think as it’s a long way to Monaco…
    And Grant, thanks for the confirmation of the sprung body bolt arrangement – I’ll go with that.

  6. renaud says:

    I was wondering how you will bleed those front brakes?

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