Steering Arm routine bring up

[Ruairidh Dunford]

Paul - your car is a work of art, lovely!

[Zetomagneto]

Sometimes see "belt and braces" safety brackets on similar lines. However if the arm fails at the shoulder instead of at the more usual radius may be of limited assistance.

Very much less likely to fail now, the arm is effectively triangulated, there will little or no deflection of the arm itself.

[Duncan Grimmond]

What a treat! Thanks for those pics.

[Paul N-M]

What a treat! Thanks for those pics.

Thanks Duncan and Ruairidh.

[Dave Wortley]

Not had a failure but very large crack on my Ruby years ago. Also got hit by a large Zephyr on the offside front on my way to work which broke the arm into 2 pieces and the glasslike kingpin into 3 pieces It looks as though the arm already had a crack in the internal rad. I have 3 or 4 arms with deepish cracks taken off cars over many years. A friend had a slow speed complete failure and ended up off the road but no damage to car or passengers. Some cracks in internal rad and one in the spigot corner on my steering arms.

[Zetomagneto]

My take on JM's design.

Paul,superb engineering, I just love seeing the skills and innovation put into these cars, a real inspiration.
Big 7 front axles have my vote too, I have one for my car

[Bob Culver]

I have recounted before how my father broke a steer arm about 1950. He was uncommonly late home and I can still recall my mothers concern. He was rounding a sweeping suburban corner at a brisk 30 mph when the car went straight ahead, struck the generous gutter at an angle and continued until the car stopped violently at a crossing bridge. The engine was running flat out and the horn sounding. The free drop arm had cut the wire and opened the throttle. It was the biggest thrill of his life (no desert war service)! Just afterwards the Comet incidents brought metal fatigue to general attention. Although a small country town a local engineer had an early machine. He ran earthworking machinery and reckoned the testing paid for itself many times over during overhauls.We became very crack conscious and had a lot of parts tested subsequently. I later acquired a quantity of fluid which with a magnet works on small local polished areas. I have since detected cracks in several Seven arms, stub axles, front axles, axle keyways, cranks. And on other cars; arms, kingpins, gearbox thrust washers, conrods. And stubs on several trailers. The latter a worry. A lost trailer wheel is a huge danger and often the trailer overturns and crashes the car.

I suspect most who have experienced and survived promptly quit Sevens, even if the car remained serviceable.

[Ruairidh Dunford]

I am thankful that there appear only to be a handful of such failures - the few instances above are certainly the only ones that I have any knowledge of.

I crack test all of the components listed above before fitment and almost all are absolutely fine.

If this were a serious defect I consider that we would be reading actual reports about this particular failure on a monthly, if not weekly, basis from a plethora of sources.

Crack testing kits are a useful addition to the garage kit - easy to use and cost effective, they will give piece of mind quickly after which choices can be made between another original or a first class replacement.

[Alan]

The reason I asked the question in the first place is that there appears to be a need among certain forum members to portray our cars as fragile, unreliable and dangerous. In truth, they are none of these and such an attitude is not helpful to anyone thinking of taking up seven ownership, or even using the one they already have.

[Ron Hayhurst]

Of all A7 components, whether deemed fragile or not, the steering arm has for many years been one whose condition needs to be  checked. The problem of cracking and its solution was well described in A7CA Mag 2004B. This can be seen on line at A7 Components web site where the article is reproduced. I would strongly suggest any viewer of this thread who has not yet picked up this article to do so now.
At around 2000 when this was a hot topic, about twenty steering arms were located in the Bristol Club Spares Shed and were carefully examined for cracks. All but two were shown to be cracked when subjected to magnetic particle inspection -i.e. it is not always easy to spot by cursory examination. The racing fraternity have been hot on this for years. It is subject to scrutineering. No used steering arms are now sold out of the Bristol shed. 

The point about fatigue cracking is that the component continues to give "normal service" while the crack propagates. If you are lucky, as happened with the failures experienced by a few BA7C members, it will finally fail under the stress of slowly going lock to lock when parking. Not so lucky if you are hairing round a corner and hit a pothole!
Thank you Bob for again raising this thread. The topic needs airing now and then if only to bring it to the attention of those who are new to austinneering.
Ron