Hi,
I'm not a metalurgist, and I've not been a racer for eons, so my offering
is more along the lines of a "lint picking session"... but to answer
the principle question: why do hubs break? I'd have to say "for a lot of
reasons".
Have the cornering forces increased? Well, in a word: yes. Think about it
- have lap times changed since these cars used to race?? Yes. _If_ you
can find a track that hasn't changed. But tire compounds are stickier,
suspension settings generally tend to be quite a bit harder than they
used to be - something's gotta give somewhere.
But wait - there's more. Even when your car can slide, there are plenty
of big forces on your little GT6 hubs... the metal will twist a little
bit each time you stress it. Eventually, you can develop stress cracks at
the surface, and if these pieces are stressed further - they will fail.
There's also the bigger problem (at least from my perspective) of
determining the lineage of your parts. Take for example that pesky hub
that someone heated cherry red to take apart... I can't say with
authority that such a process doesn't change the temper of the part, but
my best guess is that it has to effect it somehow. If you're lucky, you
get to see the cracks on the surface - if you're not lucky - well then
you'll know how good the part is eventually.
If you want to be sure of the integrity of the parts - get 'em x-rayed.
At the very minimum crack test the parts that get stressed the most on
some sort of regular basis. Your local welding supply store will have the
stuff you need to check for surface cracks.
But basically - things wear out. And when in doubt - replace.
Now, a quote (from memory, so forgive me if I'm slightly off-base here)
from the TR6 competition prep manual suggests replacing the TR6 rear hubs
every _four races_. I'll bet this was suggested because that's how many
races they would see before the all important bearing end-float would go
into the "critical range" and likely fail if run any more, but Kas could
probably provide some insight there. On TR6's, one of the failure modes
is that one of the bearings will spin in place when the bearing end-float
gets excessive, and this will score the axle stub and form a nice little
place for cracks to start. And I further know that Spitfire axles are not
made any more betterer (!) than big Triumphs - so I'll bet bearing
end-float is real important and more important when they fail (the
bearing spins, for example) you're wrecking the axles.
The GT6 (and Spitfire) parts - being smaller and lighter, are probably
just as prone to problems if things get "out of whack" regarding bearing
end-float and torque spec and the like.
Bottom line - if you don't want to ball your car up, you need to check
this stuff on a very regular basis.
And do as I say, not as I do. But I'm not a road racer, so a failure in my
persuit would likely be less "life threatening" (well to me anyway,
apologies in advance to any cone pickers should my car ever suffer an
axle failure) than a road racer's might be. By way of example - if you
doubt your car would be able to go full tilt through Road America's
"kink", you're probably not doing enough preventive maintenance to get
your confidence level where it should be.
Hmmm. I'm overly wordy today. Sorry for rambling. X-ray your hubs, please.
rml
-------------------------------------------------------------------------------
Bob Lang Room N42-140Q | This space for rent.
Consultant MIT Computer Services |
Voice: (617)253-7438 FAX: (617)258-9535 |
-------------------------------------------------------------------------------
|