I am sure this has been posted before but found on the web - written by Ray Crenshaw
Someone found one of these SC-500 things, still alive; I thought the
vigilantes had killed 'em all, but I reckon oversights happen. I wrote this
to warn him not to try teaching his wife to trail ride with it... unless the
insurance premium was current. I never really finished writing it though...
not that you'd notice any difference if I had...
jrc in...
S -outh
C -arolina*****
The SC from SC
Well, I hope your friend doesn't have one of these, but... there was a
Yamaha SC-500 MX bike. I know this because I actually raced one and may be
the only known survivor. It was twin-shocked, high piped, silver tanked
(with black accent stripes), fast as stink on swamp mud, peaky and
obstinate. And those were its good points. The SC-500 was equipped with
Yamaha’s earliest attempt at electronic ignition and the ignition timing (if
you could call it that) would make a strobe light wander across the face of
the rotor in such a manner as to make those “Route 66” TV show guys seem
like a couple of stay-at-homes. Detonation is often the result of this kind
of ignition enigma, and if you thought you already knew that, you may not
know real detonation.You could rev the SC and watch its timing advance from idle to around 4,000
Rpm's, then all of a sudden it went haywire. The timing would actually jump
around all the way from after top-dead-center, to waaaay back before TDC,
then back to waaaaay after again. The SC shop manual recommended large doses
of Dramamine before checking the timing, such was the vertiginous swing of
its mark. My buddy (who, aptly enough, was named “Buddy”) adapted all sorts
of gadgets and switches to make the timing come out right. Yamaha had a new
ream of service bulletins waiting every Monday morning at the shop, and
Buddy used every one of them. He had a different setup every week, each one
"guaranteed to fix it". One week he had installed a Mini-Enduro headlight
switch/horn button combo and told me to“Crank it on high-beam and race it on low... “Or was it the other way around?
Oh well, it ain’t just my advancing age; I never could remember back then either. I also could never tell the
difference in how it ran, it just detonated no matter where the switch was.
And Oh Man! Did it detonate. You know, maybe this was the secret to it's
prodigious power...The above ignition problem fomented, even nurtured, the most destructive
case of rattle in all of motorcycling. It even got worse when rolling off
the throttle! I've backed off on the face of a killer jump (an entirely
accurate topographic assessment when considering the SC’s 3.5" rear wheel
travel) only to have that wretched beast clang out in the throes of vicious
pre-ignition and stand straight up... for a long time! Now, let me fill some
of you young'uns in on Detonation (notice the capitals). And I mean REAL
detonation. I'm not talking about a couple of flaccid little "dinks" like
your new breast-fed CR-250 would cough up when it tried to spit up some of
its precious $6.00/gallon race fuel… No, I'm talking mid-battle,
death-rattle, kill the cattle, pinch the saddle,
tombstones-in-the-crankcase, Ten Seconds Over Tokyo, Katy-bar-the-door (and
duck!) explosions. Did I mention that these ominous noises were
serendipitously accompanied by what felt to be a two-fold power increase? We
Americans have been known to launch Tomahawks over smaller explosions than
those the SC doled out of its vicious top-end. And remember… all this
occurred with the throttle off!This dangerous but crowd-stimulating behavior made the end of every
straightaway a rollicking game of Russian roulette… but with all chambers
full. There’s simply nothing that builds excitement among the huddled masses
nearly so much as the sight of a fast racing motorcycle that occasionally
speeds up when the throttle is released. I know it got my attention.I don't know what the SC-500’s top speed was but there was a sand track in
Augusta, GA that had a front straightaway that would have done Daytona
Speedway proud; its far end actually disappeared into a distant haze among
the towering pines. Richard Petty refused to run his Hemi there because he
said they:"Didn't carry that kinda gearing in the MOPAR spare parts truck".With a decent run out of the sweeper and onto this straight I could tap the
foul SC completely out in 3rd third gear, even with the slightly higher
gearing I liked to run, which was one tooth larger on the countershaft
sprocket. Friends, I don't mean "near the top", I mean it wouldn'ta revved
any higher if I'd pulled in the clutch. I never touched 4th with this
gearing setup; I was young and brave but I loved life. Let me put it to you
this way;"If you ain't never been tapped out on a properly set up desert sled, you
ain't never been this fast in bumpy dirt."I don't mean to brag here, but I've seen what passes for a "moto-cross"
track in the years since those days, and they now think that if they get
twenty feet off the ground with their 12 inches of supension travel that
they should get some kinda trophy for their braveness. We had guys like that
back then too; they oiled our chains between motos and brought us Gatorade.
Kids nowadays honk lustily around in the mid-range of their pristine CR's
and pat each other on the back to tell themselves they're going fast. Bah!
Men used to ride.This prodigious speed allowed by the above straight made that 25-foot wide
moto-freeway look more like a thread-the-needle job... with the sewing
machine still running! I still remember the first time I decided to try
holding the SC’s throttle open all the way down that rutted piece of real
estate they called a straightaway. As I reached the end, still in one piece,
and prepared to apply the brakes, I could almost swear to you that I saw, in
the corner of my eye, an exit ramp capped with a green sign saying “Tupelo,
Mississippi” looming large on my left. Coulda been a mirage, but more likely
something a bit more sinister. It was an omen!The SC would attain such incredible velocities on that Augusta moto-cross
track that me and the SumoYama would often lap all the way up through 2nd
place... all because of what Mr. SC could do on that one front straight. I'm
willing to say that if it wasn't fully 65 mph, then it wasn't far from it,
and for all I know it could have been more than that; the dirt does have a
way of warping one's sense of speed. If I just wanted to brag about this I
would have done it 25 years ago... the SC would get so fast that the
motorcycle-crazy Augusta race fans (3 or 4,000 per race, remember those
days?) would run back from the fence when I came in front of the
grandstands. When the SC rattled and went sideways people jumped to safety.
Yes, I said jumped. During one particularly lurid episode I actually saw the
crowd as it performed this daring and death-defying leap of faith.While tapped-out in 3rd gear and waiting for the SC’s tormented engine to
explode, I had missed my line, the only good one, on the fast jump near the
flagstand. I was soon checking the Northern skies while travelling
south-southwest as I was immediately thrown sideways, in the air and at
terminal velocity, and “terminal” was sounding like just the kind of
velocity I had attained considering the imminent demise assured by my
present predicament. With my feet off the pegs and the throttle wide open,
my entrance was grandly trumpeted by the SC-500's tortured mating call...
"RATTLE-CLANK-CLANK", it had done it again. This event’s unfortunate timing,
both situationally and ignitionally, had placed me sideways on the face of a
60mph jump with 40 horsepower more than I’d bargained for, and had pitched
the front wheel straight up, and me 90 degrees to the right. I was still
young enough to believe I could hold on and save it. I didn't fall, but it
was the God of Abraham and gyroscopic forces that kept me, not skill. I was
so sideways I was looking directly into the eyes of the idiots at the fence
who waited too late to jump this time. As it is now obvious to me, I will,
in the interest of both clarity and humanitarianism, reveal to you that this
blood-curdling scenario was most surely supervised by Angelic professionals.
I also feel compelled to inform you that no life forms were injured or
mistreated during its transpiration… with the possible exception of me. I
must also sing the praises of the personal freedoms afforded citizens of
this great country as regards those areas of life, liberty, and the pursuit
of not being impaled by out-of-control teenagers on dirt bikes. They managed
to get clear with not a moment to spare. And you may also rest easier
knowing that this section of fence was well clear before the next time I
came around, and remained so for every other lap that I ever raced there."Fool me once, shame on you..."I don't want to get too hyperbolic here but I hear an awful lot of young
riders (of which I was one when I rode the SC) talk about how much faster
they are now than we were then. Well, let me say this about that; there’s
not much you can do to a modern 250 CRKXYZRM that would allow it to even see
the rear fender of one of these SC-500 demon-encrusted beasts on a long,
lonely straightaway. Now triple-jumping the length of a soccer stadium…
well, that would be a different matter, and I gladly remove my hat in
reverence for the surely reduced mental faculties of any who are so disposed
to such behavior.The Augusta track was a typical sand venue; the bikes would almost disappear
in the scoops and whoops up the straights, including the front one that I am
speaking of. I touched every 20 feet or so if I got a clear run at it. I
never had to use the SC's 4th gear at any track I raced, and that was a Very
Good Thing Indeed as I'm not sure I had the biological ancillary spheroids
to go any faster than the velocities an up-geared SC-500 was capable of...
even when constrained to 3rd.I am looking back and am truly glad to still be here. I won't bore you with
the time the throttle stuck open... at the end of a fast straight... heading
for the barb-wire fence... that kept us out of the 15-foot deep ditch...
next to the highway... You wouldn’t believe it anyway. I know I wouldn’t
because I didn’t then...... and I was riding the devilish device at the time!Owww! Gotta go, my knee hurts;
Ray Crenshaw in SC (USA) 25/May/98
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