Chassis Crack Testing-Lola T-440

[tppj]

Morning All!

In reviewing rules from various vintage orginizations as well as SCCA, I'm not (so far) finding anything requiring crack testing for chassis, subframes, etc. Does that jive with the experience of our membership?

That said, it certainly would seem to be a prudent idea, especially on a 30+ year old car. What's the most effective way to accomplish this? Magnaflux? X-Ray?

Thanks, Tom

[beachguy12]

First off, I am not a Non-Destructive Testing (NDT) technician but I do have some familiarity with the NDT process.
For the chassis and and sub-frame dye penetrant would probably be the best method. Magnetic particle would be very cumbersom and time consuming but it would be possible. X-Ray would probably be very costly. For either dye penetrant or mag particle you would need to completely strip the parts using chemical strippers. Any kind of blasting could cover a potential defect. Based on this, it would probable be best to do this testing during a frame up restoration.
While it is possilble to do this yourself, a experienced NDT technician can quickly identify very fine defects in the visual background 'noise' present during the 'reading' of the penetrant results. An inexperianced person may only be able to identify gross defects.

[T644HU05]

Another reason the powder coating craze should be stopped.

[Ron Chisholm]

Currently in the closing stages of a restoration of a 1967 Babham BT21. After the frame was striped, I had the tubes that carry water from the front mounted radiator to the engine sonic checked for wall thickness. The lower one was fine but the upper had lost over 25% of wall thickness in places. Found several inclusions in the brazing as well.

The person who NDT the frame runs a Corvette in local vintage races and works mostly in the shipping industry checking welds. It was quite cost evective. He tested every inch in 4 places (0, 90, 180, 270 deg), when there was no interfering tube. He provided a chart of all of the measurements.

Golden Gate NDT
William Neu
925-788-6337

(San Francisco Bay Area)

[JIM McQUAIG]

When we did the frame up rebuild on my 84 VD FF we sand blasted the frame to bare . I then took it to the Fort Lauderdale Airport FAA inspection station. They placed it in a magnaflux machine ,with plenty of room to spare. No cracks found in tubes or welds . Cost was very reasonable .

[DanW]

Morning All!

In reviewing rules from various vintage orginizations as well as SCCA, I'm not (so far) finding anything requiring crack testing for chassis, subframes, etc. Does that jive with the experience of our membership?

That said, it certainly would seem to be a prudent idea, especially on a 30+ year old car. What's the most effective way to accomplish this? Magnaflux? X-Ray?

Thanks, Tom

Carroll Smith's "Prepare to Win" has a good treatise on the early tried and true inspection technologies.

Recommendations are made by the various organizations, but without much guidance. Unfortunately most of the rule makers/writers are not completely familiar with all the applications and technologies of NDI. I have the privilege of working with a PE metallurgical engineer. He advises me on the technologies to use and trained me in the use of visual, ultrasound, and dye penetrant testing for my work. Below are some non commercial links on NDI, one by my colleague's alma mater. The FAA also publishes some excellent information on NDI that is free to anyone, your tax dollars at work.

http://www.engr.sjsu.edu/WofMatE/Mat'sChar3.htm

http://en.wikipedia.org/wiki/Nondestructive_testing

Abrasive blasting, using the correct media and methods can be used to strip paint or powdercoat from a chassis without peening over a crack, or even changing the surface if desired. Sand or glass beads are not used on powdercoat. Sand heats up the plastic and makes it smear, instead of chipping off. Plastic media works well. Powdercoat shops charge about $200 to completely strip a powdercoated chassis, about $150 for paint. Its labor time, media and electric power.

I have seen soda and CO2 blasting remove paint, from a vintage aircraft fuselage without harming the surface.

The top vintage car restoration shops also go to great pains to ensure the parts' original surfaces are retained by using softer media.

I found several cracks visually with my chassis before it was stripped. I found one more on a suspect joint and a poor weld by using dye penetrant.

Ron made a great call on the Brabham chassis that used the frame rails to carry cooling water. The rust forms fastest where there is oxygen, at the top of the tube. I have seen this problem in industrial cooling water systems where entrained air gets trapped.

UT is great to verify wall thickness and thinning. There are also devices that can tell you the exact metallurgy of ferrous and non ferrous material using radiation. X-ray can reveal subsurface defects over a broad area. Tubing manufacturers use eddy current testing to detect defects, laps, or inclusions.

Most of these technologies are so widely available, the cost is very reasonable for everyone.

Regards,
Dan Wise

[10rmotor]

Another reason the powder coating craze should be stopped.

I don't know what type of PC you've had experience with, but we powdercoated all our DSR chassis a light machine gray. It was very easy to see cracks, so I'm amused at your statement. Darker colors made cracks harder to find. You just need a bright color.