13 replies to this topic

[jpf]

I vaguely remember reading or seeing somewhere about a 917 that was built using magnesium tubing for the chassis. I seem to remember that there was a problem with cracking of the frame, and so they pressurized the tubing, and had a gauge in the cockpit showing the tubing pressure. When the needle started to fall, the chassis was in trouble ...

... now I don't know where I read this, but it sounds just crazy. Does anyone have any memory of this? Am I mixing up more than one story?

[tyjak]

I'm not sure about the 917, but the 908 had fittings on the aluminum frame tubes that would be used to pressure test and check for cracks.

[wsshores]

The tubes were pressurized to check for leaks because they were designed to carry oil. In the interest of reliability, the Wyer team bypassed this and used regular oil lines.

The 1971 Le Mans winning Martini Racing 917 of Marko and van Lennep was the magnesium-framed car.

[Gary Davies]

The memory's letting me down... I hope someone can find/recall the comments Frank Gardner made about the gas filled tubes!

[JacnGille]

Originally posted by Vanwall
The memory's letting me down... I hope someone can find/recall the comments Frank Gardner made about the gas filled tubes!

http://forums.autosp...t=Frank Gardner
Post #2
The Search function is your friend.

[Gary Davies]

Thank you, JacnGille. Exactly wot like I wuz after!

[LOLE]

The story about the pressurized tube frame of the Porsche 917 is correct.
German 917 driver Kurt Ahrens told me this.
This system is still used in aviation to detect cracks in the structure. An example of this is the tubular tail structure of the French Alouette 2...

[URY914]

I have a picture of the Brunn 908/3 that shows the air valve nipple on a frame member or at least that what it appears to be. Open up this link and hit the "all sizes" incon on top of the picture. The valve is just about dead center in the shot.

http://www.flickr.co...57604677247211/

[jpf]

Thanks, great info. I tried searching here for "magnesium" and "917" but no dice. I think it was the Gardner quotes that I had seen before.

I can imagine pressure testing the frame periodically as a matter of maintenance, but the implication that it was used as a real-time measure of chassis strength is hilarious to me.

[Stephen W]

Originally posted by jpf
I can imagine pressure testing the frame periodically as a matter of maintenance, but the implication that it was used as a real-time measure of chassis strength is hilarious to me.

Not so funny if you were driving at over 150mph at the time the gauge sank to zero & the red light came on!

[Bumblyari]

From Paul Frère's 'The Racing Porsches' on the development of the 908:

"On the occasion of the preliminary practice at Sebring, another interesting idea was tried out and finally adopted: the aluminium tube frame was fitted with a valve that made it possible to pressurize it. Where necessary, the frame tubes were drilled so that air circulated through the whole frame. After assembly, the frame was put under pressure and the pressure drop, due to inevitable small leaks in welds, was recorded against time. This made a quick subsequent check for any cracks very easy, the frame becoming suspect as soon as the pressure dropped appreciably faster than originally"

[Formula Once]

Gijs van Lennep recently admitted that he only found out after the race that he drove the magnesium car. He did not care about the risk at the time as 'all those cars would easily catch fire in those days anyway. The 1971 Le Mans winning chassis is still owned by Porsche, but Gijs says they can not run it as they fear the thing would just evaporate when they start up the engine...

[Ren� de Boer]

The 1971 winning car was present at the magnificent "Porsche Rennsport Reunion" in Daytona last November and Gijs would have loved to drive it, but it couldn't be used for the reason outlined in the post above, so he had to make to with a 917 CanAm Spyder, which wasn't bad either...

[Gene]

Hi, I just wanted to jump in here with something that might be of interest to this thread.

About 10 years or so ago Carey (Carey Adams Engineering up in High Wickam) asked me to do a bit of engineering sleuthing that turned out to be pretty interesting. Jonathan (now chief mechanic at Red Bull) and Norm Hossak were reproducing a 917 chasses for Richard Piper. The problem was they knew the chasses were constructed from a 70 series aluminum which is not supposed to be weld able, at least by any practical method that can be done in a shop. What I found out was they were made of 7020 rather that 7071 which is very weld able. Some further digging, we went to the supplier who supplied the original of the tubing to Porsche. They found in an old dusty bin, tubing left over from Porsche’s original order. So the reproductions were fabricated from the exact tubing used on the originals.

As far as the chasses themselves, there were 2 threaded locations, one for a filler valve and the other for a pressure fitting. According to Norm, they would pressurize the chassis and waited an hour or so and check for any loss. If there was, the chasses were pressurized again in a tank of water and they looked for the bubbles that showed where the cracks were. The other thing that impressed all of us was the lack of quality of the welding. Everyone looked like they used a whole stick on it. That combined with the “Us” in what was supposed to be a roll bar for the hinges for the rear engine cover and I was pretty horrified that Siffert and Rodriguez actually drove these thing over 200+ at Le Mans. Those guys had a lot more guts than I have!!!