Cr 500 supermoto/roadrace

What bike is that?

 

ktm 250sx.

 

Yeah, that changes things quite a bit...500 vs. 250 is no comparison.

 

If a 500cc 2t single would work, eveybody would be doing it. 60+ hp in a super light motor.

 

Explain the large batch of reliable 500's on supermotojunkie.

Bottom line is, with certain tuning and work, it can be reliable. the 500 was the only two that amazed me, It'd keep compression through anything, and would stay dead reliable. Just always a bitch to start.

 

I rode mine on the road with no problem. Kart tracks would be fine too. WFO at Road Atlanta.....good luck.

 

With big trucks pulling a long step hill , you have to watch the pyrometer because of heat that will eat the piston etc . When things heat up, you need to shift down so the engine is not lugging & things cool down . I think that is what happens to MX 2 -strokes in road racing because of the much higher gearing . My CR500 never has fouled plugs , but the RD250 I had would.. when it sounded like it was , reving it up would finish it off most of the time ... shifting up a few gears & holding it wide open would lean it out then clear the plug up . I would like to buy one of those high modified , high HP CR500 engines . I have a 86 & a 87 CR500 that are mildly modded .

 

huh?

 

Doesnt the liquid cooling help stabilize the engine temps??

 

Heat was never a problem.
It's the big heavy piston that is moving very fast for a long time.

 

Large batch? I don't think so, I've been on SMJ for a few years.

And most if not all of these boys ride them on go cart tracks. Not road racing tracks. Different ball game.

In fact, the only person I know for a fact roadraced a MX 500 with some sort of negligible success is Dr. Rob Tuluie, on a custom framed CR500 racer. And he's not exactly your average bike builder or club racer.

http://www.motorbyte.com/mmm/pages/bikebuilders/tulda12_96.htm

Quote;

Tuluie moved to Minnesota this past season and raced the Tul-da at a couple CRA meets at Brainerd International Raceway. BIR has an extremely long and fast front straight and first turn. Racers must hold their bikes wide open up the mile-long straight and through Turn One, and the Tul-da did not like it. It siezed three or four times. Tuluie is still considering ways to fix this problem.

 

I seem to recall a guy racing a CR at Portland International with OMRRA in 1990 or so. As I remember, he did pretty well.

 

I did trackdays on mine all year on a 2.2 mile RR track with out any issues. Only issue is that it tops out at 105mph about half way down the 1/2 mile straight. Never run out of gear anywhere else. It starts 2nd kick everytime and I've never even checked the plug. Dead reliable as far as I'm concerned. It currently has 15/39 gears. I can still go 16/36, but I'll have to grind the case to make the 16 fit. That should give me about 112mph. As it is, I eat up SV's in Intermediate and can even hang with some of the 600's with slower riders. I lose ground on the straight, but by the time we come back around I've made a pass or I'm at their heels, even with the 105mph top speed. These bikes are so fun to ride. Just do it!!

 

Sweet bike! :up:

 

I raced a KX500 in a honda hawk chassis... as someone said earlier, if it was easy, everyone would do it.

I'm not trying to stir the pot of the CR500 vs. KX500, but I believe the KX500 motor is superior to the CR500 for RR applications for many reasons.

1st: it has Nikasil bore and aluminum cylinder, which means its expands at roughly the same rate as the piston. Seizure is a problem with these machines. The heat generated in these things is enormous. You'll want to add radiators so that coolant temps do not exceed 130deg F. Any hotter, and you'll need much more piston clearance...which can lead to cold seizure while warming up. I ran a GSXR1000 radiator and oil mixure of 25:1, which is also what most shifter kart guys run.

2nd: The bore and stroke of the KX500 (86mmx86mm) is much more efficient than the CR500 (I think its 89mmx79mm) at building RPM. Its unlikely that anything other that a heavily modified CR500 would ever rev past 7000rpm... while a stock KX500 with a good pipe will rev to 8000rpm

3rd: Transmissions: I never had an issue with the shift forks or falling out of gear with the KX500 motor, but I hear that its a common problem with the CR's. Also, the gearing of the KX500 motor is better for top speed. With a primary reduction ratio of 2.538 and a fifth gear of 0.791, 130mph top speeds are possible. Trying to find NOS wide ratio tranny kits for the CR500 that haven't been made for 10 years is almost impossible.

4th: The powervalve system: The CR500 doesn't have an exhaust powervalve, which, when coupled with its inability to rev past 7000rpm, means you have a very narrow powerband. Miss your shift, or exit too slow and the motor will just wheeze. The KX500 has a powervalve and pulls extremely well from as low as 3000rpm, all the way to 8000rpm.

Whichever motor you choose it will needs to be balanced. I had my setup for a balance factor @6500rpm. At idle, the motor literally rattles your eyeballs, but above 4000rpm, she's very smooth.

 

wow!!! lots of input from all !! thanx to all of you , but sounds like alot more wrenching than racing ???thanx again,pj

 

Alot less wrenching than I ever did on my 525SMR, and I never even ran the KTM at a track and was still doing oil changes and adjusting valves like crazy. Not to mention it being 5x more expensive when the motor finally goes.

 

CR500 road racer

I've been road racing a cr500 for about 15 years now. In all of this time i've only seized the bike twice. Both times it was my fault. Not the bike. My current bike is a highly, highly modified 99 model. It has beaten quite a few TZ250's not to mention endless amounts of 600's, 750's and 1000's. However, this bike performs very well with riders who have a lot of experience. Newby's would probably either crash it, blow it up or be intimidated to the point of hating it.

 

Just a few points.
Ever heard of the Le Touquet Beach race? CR500s won this race many times...long sand HP robbing straights. These motors can achieve over 80HP and rev to 8000rpm with the right porting and pipe. As far as the lack of a powervalve, in the case of the RR application, the lack of would be a benefit IMO.
Small meaningless correction...the KX500 was never Nicosil OEM. It was plated, but not with the Nic process. It is easy to sleeve the CR cylinder with an aluminum sleeve and Nicosil.
The Rotax 250 "kart" motor was used in several motorcycles with several displacements...very fast!
Tdub

BTW, 7044 very nice looking bike!!

 

Well said Tdub. You obviously are familiar with these wonderful bikes!