KX500 powered RGV250

[dickytoo]

There has always been talk, and it's surfacing again, of people throwing big singles inton small 2 stroke sports machine chasis. I always wondered at the sense in this. The factory V-twin smoker of an RGV for example, makes more power and is a hell of alot smoother than any XR500 lump.

Ten years ago I actually owned a similar beast. A 1989 RGV250, fitted with a monster of an aircooled, 5 speed KX500 single. The engineering was performed by Damon at Cycleworks and to be honest, it was a bloody nice job. He built the expansion chamber and exhaust system, a steel engine cradle and welded in a block of aluminium between the frame spars as a top engine mount.

The bike had been converted for racing and had alot of spares eg: barrels, pistons, crank and a shitload of gearing. It had been owned by the late Stu Ploughman and he'd only raced it once when exiting Coke at Manfeild, it developed a nasty tankslapper then promptly threw him on his head. Stu decided this might not be the bike for him and I swapped it for a wrecked RGV I'd just totalled.

Having no room for a kick start, we were forever pushing this fucker up and down the road trying to get it to go, once running, the neighbours were running for cover. It was THE LOUDEST bike I've ever heard, and VIBRATE! FARRRKKKK! I used to do numerous testing runs up and down the Wainui Coast road, not sure what I was testing but Jesus was it good fun. The bike had been dynoed at 53hp, about the same as my previous RGV (on the same dyno) but it had about 6 times the torque. It was geared for the moon and was a bit of a mission to get rolling.

Once rolling, you had to try to remember to change gear as the bastard strained ahead then promptly ran out of revs, begging for another gear. Tachos are for poofters. It was fast. but dangerous. Not alot of thought had gone into weight distribution and a hastily fitted steering damper only helped a bit. All in all, the bike ran flawlessly.

Right, time for my first ever race meeting. Clubmans for the first time suited so we traiklered the beast to Manfeild, unloaded, waited till everybody had started their bikes so as not to look too conspicuous, then start pushing. We pushed the fucken thing around for hours, would it go? No way! Disgusted and dijected, we loaded it on the trailer and returned to the safety of the Wainui Coast road. Unloading the piece of shit, I thought I'll give the bugger one last shot. Started in about 2 meters! WTF???

1 month later, it's time for the next round. Start the bike in the morning before we left (6am) just to make sure and we're off. Get to the track, bike starts! Yay! Out for the first practice, two laps and in and doing quite well, the fucken thing seizes into Coke. Push it back to the pits and a then VERY young Fizzerman gets stuck in. Pulls the motor down, new barrel, gaskets, piston and ring. About 30 seconds before the call for the dummy grid.

Out I go, nice and carefully on the warmup lap and grid up for the start. All of a sudden, the bike's starting to creep forward, I'm still hanging onto the clutch. Look down and the clutch cable is holding on by one strand and gettin longer. I ramp up the revs a little to stop from stalling and the rear wheel starts to spin, the cable lets go completely and I'm sitting on a start grid, 15 seconds before the start, doing a big phat static burnout. I contemplated kepping it going 'till the start but wasn't sure how slicks would enjoy such abuse. Absolutely wrecked, I shut it down and pushed it to the inside of the track.

I only rode the bike once after that day. In a fit of clear thinking, I thought I'd take it to work at Ngauranga, I lived in Naenae at the time. Rode to work, no worries, coming home, there's five cops on bikes sitting at the weigh station on Hutt Road. I'm riding a slick shod, noisey as fuck, race bike. Didn't know about runers at that stage so I stopped when asked. To the cops credit, he didn't give me a ticket. He did, however, ban me from riding my bike on the road and made me push it home. Every 10 minutes a car would drive past keeping an eye on me. Took fucken hours.

I sold the beast soon after that to a guy in Taranaki I think. Saw him do a warm up lap at Wanganui that year on it and haven't seen the bike since. Strange.

That bike actually belonged to a friend of mine. we built it up from scratch using an old aircooled KX500 engine. We ran it in the nationals in the formula 3 class one year. we had quite a bit of problem with the gearbox and no money to fix it. I've got some good pics of the bike including some of the development work at home.

when it ran, it was very fast but we also seized a few pistons as well. And it was a bloody nightmare trying to push start it. The wheel would lock and we'd leave long black streaks. From time to time, my buddy and I still talk about our experiences with our F3 experiment.

[dickytoo]

The later ones are, yeah, but let me assure you, this bone shaker was air cooled.

The reason the motor was air-cooled was because the rules at the time didn't allow you to use a water-cooled engine, although they were available at the time and would have been more reliable.

[pete376403]

"Streetbike" back in the days when edited by Geoff Seddon, had a feature on an RGV (parallel twin version) powered with a BSA Lightning motor. Looked very neat and the article said it went very well too. Big motors in small bikes = mostly good.

[F5 Dave]

You must mean RG 250, all the RGVs were by name & design ‘V’s.

PB had some other old leaky brit nail in an RGV ages back.

Desert racers of the time had all sorts of grief with their big MX bikes as you did have to hold them flat out. Many simply reduced the compression ratio, but the real problem is the MSV (maximum squish velocity) & lowering the comp helps in other ways but not here. Twin sparkplug heads (& no I don’t mean TS400, both have to work) were an advantage reducing the spark lead, but some experimented with variable machining of the squish area.

[Motu]

Interesting about the twin plug head Dave - some Nissan CA20 engines were twin plug,the early ones used points and a 5 deg stagger,with a baseplate like a motorcycle or single dist rotary.Later ones with electronic ign fired the plugs together,the last of them were computer controlled and dropped the exhaust plugs out under certain condtions.

The reason they didn't stagger fire the electronic igns is that they had extended the burn time,that was the whole point behind the twin plugs,to keep the fire going.The biggest drawback with CDI is the very short burn time,and that's why it will never be used in production cars....I wonder if an ign system in these big bore 2 strokes with a good long burn time would solve any combustion issues....has it been tried?

[NordieBoy]

Big motors in small bikes = mostly good.

Check out the SuperMoto section of VisorDown.
Supermoto_Spike is putting a CR500 engine in a Derbi 50cc supermoto frame

[Brian d marge]

Check out the SuperMoto section of VisorDown.
Supermoto_Spike is putting a CR500 engine in a Derbi 50cc supermoto frame

No Froggen wayyy I want one ...foget everything I said bfore ,,,,This is the one I want ,,,,
Video footage???any out there

Stephen
Who now has new goals in life.....

[F5 Dave]

My old C20 with the Jap A series copy only had single plugs. Was a lot better when we added my mate’s home made transistor module onto it. Problem was it would run just fine until one day it would refused to start, and then you’d have to open the contacts up a bit (by eye), felt just fine until the points wore against the cam & kept closed. That cam would always get a bit dry. (Not sure what a CA20 is, probably don't care, I'll keep the HiAce).

I digress. The twin spark was just to reduce the length the flame had to travel over such a big cylinder. The staggering idea is interesting too but newer CDIs allow a longer burn time then the early ones. While the longer burn time will def help cold starting etc at low revs, at highish revs I doubt there would be any influence & the detonation is the problem that causes the issues.

[White trash]

That bike actually belonged to a friend of mine. we built it up from scratch using an old aircooled KX500 engine. We ran it in the nationals in the formula 3 class one year. we had quite a bit of problem with the gearbox and no money to fix it. I've got some good pics of the bike including some of the development work at home.

when it ran, it was very fast but we also seized a few pistons as well. And it was a bloody nightmare trying to push start it. The wheel would lock and we'd leave long black streaks. From time to time, my buddy and I still talk about our experiences with our F3 experiment.

Hey I wouldn't mind meeting up some time dickytoo and reminising about this cool machine, although, you sure it's the same bike? As Damon led me to believe he did all the engineering on it.

It's one of the fondest motorcycling memories I have riding that bike when it went well.

[Kwaka-Kid]

haha wiiicked read!!
i always wondered about a 2 stroke 500 single in F3.. theres an idea, however 53hp? why the low hp and how much torque did it have?

from a '79 XR500Z you can get at least 70hp, and does a 4 stroke not generally have more torque? (Always interested in this stuff!)

[Brian d marge]

.I wonder if an ign system in these big bore 2 strokes with a good long burn time would solve any combustion issues....has it been tried?

MSD ignitions ..cant quite remember the name I deal with the Australian place ,,,Anyway ... they do a multi discharge ignition ...which basically fires the cdi a Gazzilion times a second ,,,,Not that expensive actually ....but then I have always had a soft spot for points ,,,so Wayy to expensive for me

Stephen

[dickytoo]

Hey I wouldn't mind meeting up some time dickytoo and reminising about this cool machine, although, you sure it's the same bike? As Damon led me to believe he did all the engineering on it.

It's one of the fondest motorcycling memories I have riding that bike when it went well.

yeah, damien did the frame and exhaust for it but it was a concept my buddy dreamed up. i left the top bolt loose (the one that ties the head to the frame) and the vibration snapped the cross brace on the top of the frame. My buddy said the vibration shook his hands from the handlebars!!!

i also remember trying to transplant the ignition system from a KX250 (which just happened to be handy) when our original black box blew up. i tried to repair it but one of the components (some sort of transistor) was a one of and i couldn't find a supplier. i tried quite a few suppliers, even overseas. eventually we gave in and bought a new one from the big K. The 250 ignition ran but the timing advances was all wrong.

I was looking at some pictures last night from when we first built it. brought back from fond memories.

That same bike is on sale in dannevirke for $1K at the moment.

i'll be down at taupo on sunday, hopefully. my buddy is riding a green zx9r number 73 (we used to be number 71 but every body seems to have that number at the moment).

[sugilite:Me]

Heyya All, I'm the crazy guy that dreamed the KX500/RGV up.
I still stand by the concept, so yeah I'm still crazy.
The guy that bought it off me got a very cool ignition for it, so that was sorted.
Heres a few of my favourite yarns concerning the bike.
Originally it had a aluminum frame cradle, and this combined with Dickytoo deciding the top engine mount was way to heavy to use made for a mind numbing 1st and last lap! Thank God it was a practice day, I was sharing the track with a porshe at the time, as I came down the back straight the alloy cradle fractured and it vibrated so much that even Margret Thatcher would of achieved orgasm, hell multiple orgasm's even! My hands literally started opening by themselves! It belatedly dawned on me to pull the bloody clutch in and stop the show! After that, we had a steel cradle made and it took care of a lot of the vibration, now I know that will raise the eyebrows of those that had it after me lol

Though Daiman built the exhaust and fitted it into the frame Dickytoo did a lot of work on it too. With the limited budget, things were tough!

The 1st time I took it racing was at the Masterton street circuit. I remember taking it down the straight waiting for it to hit the power and I blew a bite sized chunk out the piston, spat every bit into the exhaust, I guess I was expecting a bit much from it...poor thing, it was not it's fault that I'd just stepped off my FZR100 proddie racer lol
We bored the keihn carb out from 38mm to 40mm. It ran much worse, moral of the story is NEVER bore a oval shaped carb throat lol
From there, it only got better.
We fitted another 38 off my KX250 mx bike and it went much better, said 250 also donated ignition and other goodies hehehe.
Anyways, we took it down south to the Ruapuna round of the nats. On the Friday I qualified around 15th fastest, that night Dickytoo fitted the 2nd RGV disc brake and fabricated a airbox for it complete with crude ram air! what a difference!!!
Saturday Morning I qualified 2nd fastest, only a fraction of a second behind Tony McMurdo on only the 3rd lap of practice!!! unfortunately it lost 3rd gear on the 4th lap lol. Hell who needs 3rd anyway, shifting from 2nd to 4th still kept most of the hordes behind me, though we decided against racing it as other gears were getting pretty suss too. Turned out to be bent selector forks.
I notice it was written elsewhere here that the handling may have been suss due to weight distribution, the only comment i can make is it handled bloody well when ridden at class lap record pace ;-)

Unfortunately I never got it to Wanganui, I reckon it would have kicked butt there!

So, why do I still have faith in the concept? Well, On my KX500 Supermotard bike I've lapped Manfield at a 1:18 flat, and that is with my slow cast iron liner barrel on, at least 7 to 8 hp down on my nikisil barrel, so it's safe to say I'd crack a 17, now thats on a motard bike with all the aerodynamics of a brick, so imagine what a water cooled motor in said rgv chassis with a ram airbox would do!

The weird thing is, I moved from Wellington out rural 25km's from Dannevirke, and what do I see in the local garage...said bike! The guy was running it without the airbox. I told him to run it, but as yet, it is still sitting in his garage, go figure!
The bike was actually being raced at the Taupo race just run. It was a 1st time racer who had borrowed the bike, so that would of been fun for him....hmmm, wonder if the current owner would lend it to me for Wanganui...Would need to fit the airbox 1st though!

I toyed with the idea of buying it just to torture Dickytoo with, but figured he had enough of a job keeping the ZX9R going! I'd better keep on his good side, as he has just about single handedly turned the ZX9R from a heap of steaming crap into a bloody great racebike. We will be at Puke this weekend #73 :-)

[T.W.R]

heres the RGV/BSA lightning that pete347? was talking about: it was a RGV(M) with a 650 A65 lightning taken out to 820cc with some norman hyde goodies. 75hp & 140kg

the others are a KR-1 with a HRC race kitted XR600 & a RGV with a blueprinted RG500 ( 115hp ). there was a bloke in england in the mid 90s building them to order & he couldn't keep up with the demand! it would be an easy job doing it with the likes of a RG400 etc

[Ivan]

Sounds fun I have always been tempted with the idea of a huge 2 stroke motor likethat running in the Honda RS125 Chassis I reckon you would cut 1:15's round Manfield small AeroDynamic Purpose built race chassis bloody good brakes would be lots of fun Knee Slider burning out turn 1 YEAH