OzVMX Forum

Clubroom => General Discussion => Topic started by: Hoony on December 24, 2012, 04:44:19 pm

Title: Yamaha SC500's info wanted
Post by: Hoony on December 24, 2012, 04:44:19 pm

I have a mate who is collecting big bore Yamaha Mx'ers. he has Mx360, yz400, yz 465, yz490 and a few others in the collection.

The SC500 seems an oddity to me (SC model designation, not YZ or MX are they 71 era around the time of RT1's etc?) its before my time so i know little of them other than they were prone to seizure apparently.

my question is where does the SC500 come in the family? what years were they made, and were they marketed as production mx bikes or other?

fill me in on the details Yamafans

Title: Re: Yamaha SC500's info wanted
Post by: BETRIC on December 24, 2012, 05:21:30 pm

Hoony SC500's were made for 2 yrs, from 73 = SC500 (silver), 74 = SC500A (yellow), they have a 4 speed gearbox, use the same basic frame, body work etc as the MX 250/360, they came standard with a light switch power band ;D, the MX360 is better to ride.   

Title: Re: Yamaha SC500's info wanted
Post by: JAP 454 on December 24, 2012, 06:15:31 pm

Heres a couple of SC 500 shots

(http://i854.photobucket.com/albums/ab106/JAP454/Yass3-1.jpg)

Head scratching moment with a grey tanker at Yass

(http://i854.photobucket.com/albums/ab106/JAP454/WestWyalong94.jpg)

# 4 Kevin Horton on a yellow one trying to catch TH at the '94 DT Nats at Wyalong

I had a ride on an SC 500 powered Hagon at Wyalong , I took it back to the pits after a lap, bloody near uncontrollable !! nothing then watery eyes !!
Foss

Title: Re: Yamaha SC500's info wanted
Post by: Purple Dave on December 24, 2012, 09:07:06 pm

Hi Hoony.......I ran one in 1974.......I called it THE BEAST !!, however, I managed a 6th place in NSW Senior Championship at Heddon Greta.....also, every day since a bad crash at Woodlands at Temora in the same year, my left shoulder reminds me, they can BITE you. :D
(http://i396.photobucket.com/albums/pp45/triumph51/HeddonGreta1974-2_zps515ec77b.jpg)

Title: Re: Yamaha SC500's info wanted
Post by: Purple Dave on December 24, 2012, 09:11:09 pm

Amaroo Park 3-Way ( Central, St George and Fairfield ) winner 1974.... ;D
(http://i396.photobucket.com/albums/pp45/triumph51/AmarooPark1975.jpg)

Title: Re: Yamaha SC500's info wanted
Post by: Purple Dave on December 24, 2012, 09:32:15 pm

I think they were developed for the American market, to be used in Desert races like Baha.....just start at one side of a desert, get it into top gear and hold on until you reach the other side......no handling required !!.....they got that right.......they didn't HANDLE !! I also rode it at Oran Park....with 19 tooth engine sprocket and specially made 39 tooth rear sprocket, it wasn't a bad mount.  8)

Title: Re: Yamaha SC500's info wanted
Post by: TooFastTim on December 24, 2012, 09:37:37 pm

There was a write up on rec.motorcycle.dirt about the SC500 many years ago. It was one of the funniest articles I have ever read on the 'net. Sadly I don't think anybody kept it.

Title: Re: Yamaha SC500's info wanted
Post by: TooFastTim on December 24, 2012, 09:52:24 pm

Here it is (from https://groups.google.com/forum/?fromgroups=#!topic/rec.motorcycles.dirt/6D6QCEehXXQ (https://groups.google.com/forum/?fromgroups=#!topic/rec.motorcycles.dirt/6D6QCEehXXQ). There's a great yarn about the TM400 there too). You may change your mind about the SC after reading this

"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"

Title: Re: Yamaha SC500's info wanted
Post by: firko on December 24, 2012, 10:06:14 pm

I've had three of the fat buggers, one in a Champion flat track frame and two stockers, both silver '73 models. The SC moniker stands for SCramble as some marketing hot shot at Yamaha figured that the bike would make a good flat track TT bike (sometimes called scrambles in the US) and/or desert racer. Unfortunately the bike came pretty close to being a great thing but it was let down by details like piston distortion problems, a pretty abrupt power curve and godawful handling. All of the engine's weak points can be fixed however, as can some of the shortcomings of the chassis (actually, much of the frames dodgy handling is caused by the weird power characteristics of the engine)....Edgar Phipps built an engine with a new sleeve that decreased the 90mm bore to 89mm using a much lighter yet stronger Honda CR500 piston. He also removed the balancer and fitted a 5 speed from, I think a DT250. That engine is now housed in Edgars ex Firko Champion flat tracker but it's so powerful and torquey Ed had to add hefty gussets to the swingarm to prevent it twisting but it didn't seem to help all that much. The stock pistons tend to crack around the gudgeon area which causes a lot of distortion and the bikes reputation for siezing however I never siezed one and to my knowledge neither has Edgar so we must have been doing something right ;D.

The advance curve on the ignition is all wrong but can be sort of sorted by fitting the ubiquitous external flywheel DT400 cdi or, like one of mine had, a points ignition from a DT360. Yamaha was aware of the problem and released Technical Bulletin No 348 for the 73 sc500 that suggested adding a small condenser (has a Yamaha part number) that controlled the spark advance curve and made the bike a little more ridable. My Champion and the other CDI equipped SC I owned both had this mod done by previous owners. The flat tracker actually had two condensors wired into the system with a toggle switch between them. To start it I'd flick the switch to the left which somehow advanced the ignition a tad for easier starting. One downside to this little home made mod was that the bike would sometimes start in reverse, causing lots of laughter as I'd zoom off the line backwards.

I have a soft spot for the much maligned SC500. If Yamaha had put a bit more effort into sorting the engine's shortcomings it could have been a really good thing. I've long had this little idea to fit an SC500 engine(with all of the fix up mods) to an MX250/400B roller to see just how good a bike it could have been if Yamaha had taken it seriously. I'd love to see someone do it or even better fit one to a YZ-250/400D roller, I reckon it has the potential to be the killer pre 78 class weapon. It's a hell of a better bike than the gnarly old Suzuki TM400.

Title: Re: Yamaha SC500's info wanted
Post by: OverTheHill on December 25, 2012, 11:02:01 am

shouldn't be getting sidetracked as xmas dinner awaites so without reading other comments till later--my take on the sc500 was [is] they were 'way' over square with the 360 [70mm] stroke & about a 90mm bore, [compared to 80mm for the 360] i had the mx250 & boss tim gibbes had the 500. Same bike basically but what a difference a different motor made. i couldn't ride the 'pig' in a 'proper' mx but borrowed it on the odd occasion for a fast & flowing grassy TT [miniature TT we called them] & loved it for that type of going.--BUT, in the year they came out our Hugh Anderson [of road race fame--& top MXer] actually won the NZ champs from [our fast] Ivan Miller on the Suzuki latest model that year. Never forget that day--sc's just can't go that fast, memories aye!! Merry Xmas, Morley Shirriffs in little ol NZ, hot n muggy today. ps, think ivan's bike was the RN400 which was 'worksy', might be wrong but more praise to Hughie if so.

Title: Re: Yamaha SC500's info wanted
Post by: bazza on December 25, 2012, 11:31:30 am

The electrics were different on the 2 years and made HUGE difference to power and smoothness

Title: Boxing Day Street Races wanganui NZ
Post by: OverTheHill on December 25, 2012, 11:55:15 am

not sure how to start a new subject so butted in to the sc500 one sorry & re-wrote the subject. Wanganui Boxing Day Road Races are on the net 'free' as good as Grant from 'Ctas' can do it, sitting on top of a roof in the sun [or rain tomorrow] pointing his camera at the bridge where they come down main straight [street], will be as good as he can do so don't complain as things may play up a bit--good keen man though. Is a live chat room too if ya want, & hope it all works out as it's a free service, think he's doing the jet sprint the next day with my boss tim gibbes manning the camera for grant. Tim is doing the live laptiming boxing day & they sort off work in together. just had a google practice & put in [ctas] which is grant collingwoods business & think it was second one down [on google here] which says [ctas live timing & video], you'll find it. Otherwise the 'nzsbk' site should have a link or [tim gibbes track timing] etc etc. ctas is easy though. All the best, Morley Shirriffs nz. ps, 60 years this year for the street race, 57 or so on the same track & two or 3 in other areas of town for some reason in the early days. by memory the famous Randy Mamola started there as a 16 year old on a TZ i think, i remember the day well.

Title: Re: Yamaha SC500's info wanted
Post by: Matador107 on December 25, 2012, 01:09:51 pm

Boxing day bike races eh. In my mind they beat the most stupid boring so called "sport" in the world.CRICKET, or how to catch melonomas, I would rather go to work. I'll check out the races tomorrow and counting down for the speedway gp, tickets, hotel, flights all done. Cheers to all.