The importance of crack testing

[Stuart Giles]

hi stuart,

i notice the oilway is probably at 90 degrees.

it that a pheonix crank, or another modern crank.

thanks tony

Tony, well spotted there. it is an Austin A35 crank from an ex race motor. but this problem was solved by Marc and the chaps at Phoenix:



I have also found an appropriate use for an A7 crank that failed Magnaflux. This is mounted on the gable of my main workshop; although I suppose I could have a problem if there happens to be anything more than a stiff breeze....

[Bob Culver]

Hi Tony
 
Your kitset seems remarkably effective. What do you use for magnet? Although powerful magnets in speakers, microwaves etc, large horseshoe magnets not now common
 
It is good of you to check parts. Many known seriously cracked parts must get passed on. I purchased a seemingly good crank from a person well versed in Sevens; suspect they knew it was cracked. Such parts can waste a lot of time and money for many down the path.
 
With the likes of trailers often wish I had never looked as cannot then sell with conscience.
 
I dont have much faith in non magnetic systems. Any attempt to clean the area tends to close the fissure. However it is unlikely a dangerously cracked steer arm would be completely missed.
 
The traditional method was to soak in kero, dry, strike sharply a few times, sprinkle with French chalk (or baby powder). Usable on pistons. Heating of soaked parts often effective. (Noted NZ mechanic late  Ralph Watson describes how multiple  cracks appeared in 1930s Alfa GP crank when left to dry in the sun. Colleagues have observed the same  with Ford 10 steering arms!)
 
What is the typical charge for commercial testing? For a crank presented clean should not take more than ¼ hour including any paperwork so L70 seems a lot. I have found paint stripper removes varnish type deposits.
 
Fifty years ago for about £2 I purchased a gallon tin of the fluid used commercially. I guess it is just iron dust or oxide in kero. With a hand magnet there is a technique and it will only clearly indicate cracks on polished parts but where suspect areas are known this not a problem. I have picked up cracks in Seven and Jowett steer arms, con rods, Seven and trailer stub axles, Seven cranks and rear axle keyways, Jowett kingpins and gearbox thrust washers. Only a few drops each time. If I was in UK could distribute many bottles!
 
(After my father broke a steer arm about 1950 we later took the whole front components to a local firm who had equipment. At 100,000 one stub axle was similar Tonys but more ominously through the tubular wall instead of through the back plate. Cars here were subject to a lot of corrugated roads. The firm  maintained their own fleet of earthmoving eqpt and reckoned the detecting gear paid for itself immediately. They demonstrated at a small local show. Washers had been clamped on a screwed rod and ground off perfect. All clearly showed. )
 
If I welded all my cracked cranks end to end would not need the gable.

[Geoff Halstead]

Thanks for the interesting post Tony.
I've only used the spray time and that was in the '70s when building my Kent race engines.
Been busy sorting compressor air cooler and water trap hence delay in responding

Geoff - Plus hospital visit.