In a message dated 6/29/00 6:23:54 AM Pacific Daylight Time,
casalp@earthlink.net writes:
<< I am running at Thunderhill next Thursday on 22+ year old magnesium wheels
with Toyo R1s. Should I be concerned or will I be safe >>
Let me know how it goes, I have a 30 year old set of mag Minilites I'd like
to use :-)
Seriously, before doing any serious track speed I'm going to get mine
crack-checked.
Craig Carter
Fountain Valley, CA
1970 SRL311 #14100 "DAT2000"
1968 Datsun Roadster DP racecars
FYI, I attach the following, from Carroll Smith on Crack Detection & Repair:
One of the greatest fears in racing is to have some type of catastrophic
suspension or steering failure. The best way to avoid this dangerous (and
potentially costly!) situation is regular inspection and crack testing of
critical steering and suspension parts. What follows is a brief synopsis of
the different crack testing methods readily available to the amateur racer
and some considerations to think about when you find that one of your
critical pieces is cracked.
X-RAY
X-ray examination is the best single method of inspection. If taken from
the right angles and interpreted by an expert, an X-ray will show casting,
forging or welding faults, grain structure deficiencies, internal or external
stress cracks, porosities, cold shots, and any other nasty things you can
think of. Unfortunately, X-ray examination tends to be very expensive and
requires expert interpretation. Pretty much the same applies to ultrasonic
inspection.
MAGNAFLUX
...The most popular method for inspecting ferrous parts is magnetic
particle examination or Magnaflux...
ZYGLOW
For nonferrous metals the equivalent of magnaflux is Zyglow, which
substitutes a fluorescent dye for the iron particles. Most companies that
offer Magnaflux also do Zyglow, and again the cost is nominal. Zyglow
equipment is also available with the portable magnaflux unit.
Your cost for having any nondestructive testing done can be considerably
reduced by stripping all paint, oil, grease, dirt, and corrosion from the
parts and delivering them to the inspection station in a really clean
condition. I do not consider it necessary to remove rod ends from links for
inspection.
DYE PENETRANT KITS
Relatively inexpensive aerosol kits of dye penetrant inspection materials
good for both ferrous and nonferrous materials are available at most welding
supply houses and should be a part of every racer’s road kit. Follow the
instructions religiously or you will be wasting your time and building up a
false sense of security. Parts to be inspected must be really clean.
A really thorough visual inspection of clean unpainted parts under strong
light and with a good ten-power magnifying glass costs nothing and will
reveal a large number of the defects found by the more scientific methods. It
will also show up stretched bolts.
The ideal inspection schedule (budget permitting) is X-ray inspection of
all forged and cast parts when received (or new to the owner), followed by
visual and Magnaflux or Zyglow inspections every 500 to 1,000 miles of
running depending on the nature of the part. Very careful aerosol kit
inspection can be substituted for Magnaflux and Zyglow. Critical parts to be
concerned with are: hubs and hub carriers, hub carrier clevises, rack and
pinion, drive shafts, universal joints and their yokes, transmission input
and output shafts, ring and pinion units, intermediate gears, engine valves,
connecting rods, pistons, piston pins, and crankshafts. If your schedule does
not permit regular inspection of critical items, you should think about
racing less often!
Now comes the question of what to do after your careful inspection has
discovered a crack. Don’t panic – the red tag from the Magnaflux station
does not necessarily mean that all is lost! First of all, all FAA certified
stations will reject a part for any flaw. Porosity in a noncritical portion
of an upright will produce the familiar red tag, but is nothing to worry
about. Small cracks can often be ground or filed out and carefully radiused.
A cold lap on a portion of a weld can often be safely ignored or, at worst,
rewelded. The problem, as always, lies in the decision-making process. Until
you have enough experience to have valid confidence in your own judgment,
find someone to make the decision for you. Your Magnaflux/Zyglow station will
always let you inspect a rejected part yourself so that you can see whether
or not it can be saved. If the part is not salvageable, don’t put it on the
shelf. If you throw it away, you know that it will never end up on the car.
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