2004 ZZ-R 250 (EX250H) Race/Track build

[Dangerboy]

Hi everyone!

Would this be the best place to start a build thread for my race bike?

It's going to be a aluminum twin-spar framed '04 ZZ-R250 with an extreme emphasis on weight reduction.

I created a couple other threads already but I'm an old racer, CSBK/AMA Pro who now has kids racing in the mini club and I wanted to build a bike I can race there as well as play at the big tracks again.

25 years ago now I built a ZX-6(D) that looked almost identical to this bike so this is a bit nostalgic too. I still have my old racing wire diagram I made for the ZX-6 that basically is a total loss simple harness which gets rid of almost everything electrical on the bike, even most of the connectors.

The rules I'm running with allow a lot of modifications but many stock parts do need to be retained;

I cannot swap the carbs but I can modify them.

I have to run the OEM main frame but can cut off tabs. (The subframe is removeable on the ZZR250)

I have to keep the rear swingarm unmodified (This is unfortunate)

Engine has to use OEM heads, cylinders, cases. I can do whatever to them that I like though, (I could swap the crank to the 300 but I'm going to leave it)

Besides these rules it is pretty much wide open. I've already stripped the bike down to the chassis and I almost forgot how much satisfaction comes from unbolting weight from a bike!

This bike will not have a subframe, rather the tail with be two pieces that are composite and the one will simply attach to the aluminum main frame. I suppose you could consider the front portion the subframe. This is how I prepped the ZX-6 and a 6R all those years ago... I may have a aluminum fuel tank made and make a composite dummy tank to save more weight, this will be something that will come later in the build for sure.

The wheels, brakes and front suspension will be TZ125 for now. I've been considering other forks with a little longer travel but I have these here so I'm going to run them. Triples, clips ons, and rear-sets all custom CNC'ed in house (I own a CNC company, I specialize in complex 5 axis milling, 3D scanning, molds for composites, etc) I have a buddy with a GSXR1000 Ohlins rear shock (Not TT-X) I may grab and get readjusted for this bike.

I still have the carbs from the ZX6R that I put the Yoshimura "MJN" (Multiple Jet Nozzle) jet kit in. One went missing but I still have three and I'll hoping with some tweaking these could be made to work very well with the OEM carbs. They were amazing on the 600! They were quite an innovation.

I was considering running some larger high compression pistons and such in the engine but I think I'm going to just run ceramic coatings and other coatings in the engine instead. On the 6R we saw some pretty impressive gains with the coatings alone and these mods help with reliability instead of reducing it. DNF's are no fun. I'm going to leave the cams for now and see how it goes with tuning alone.

a 300 slipper clutch will be swapped in, and I'm hoping to get the proper ECU to make the most use of the engine with it's original components. I was reading the EU machines had more advanced timing? It has been ages since I ran something that wasn't fuel injected with fully programmable everything so any tips on what has worked for you guys would be great!

Engine will be running total loss ignition system with flywheel replaced or machined as required. All electrical components besides ignition will be removed with an easy to swap out lithium battery used. (This was also done on the old 6D but lithium batteries were not as common then and I used a small 4AH lead acid back then). The engine side covers (likely) will be custom milled, as they are a little damaged from the previous owner's crash anyway, and the rules say the covers need to be strengthened or protected. I can integrate UHMW-PE sliders into the covers this way and improve crash worthiness and keep the weight down at the same time.

I'll start posting photos soon of how this is progressing and also post some weights of parts as they compare to the OEM to monitor how this bike's "Diet" is coming along.

I raced RS and TZ GP's for a few years as a side class and then in the minis I put CR/YZ85 two strokes in them and I'm looking forward to seeing how this bike feels once it's ready. The GP's are in the 150lb range and handle amazing (of course) but they are a bit cramped and require a lot of constant attention to keep them going well. Once you get used to bikes in their weight class though anything else seems like heavy barges.

I have an older AIM Mychron 3 Gold system with Gyro for gauges and data logging, I'll likely toss this on and maybe even add wideband O2 sensor so I can use it with logging to help carb tuning at the track. I hate to add the weight but it's pretty light overall and the data is always helpful.

Last... Exhaust. I am in search of the right exhaust header for this project and I couldn't find anything titanium out there which surprised me. Thin-wall stainless I suppose will have to work but I don't know what is still being made that works well on the ZZ-R. Things like the centerstand, bodywork and passenger pegs no longer apply to my application so I'm hoping any system that used the EX250 engine will work?

I made a thread specific to this exhaust query, any feedback on this would be very welcome. Many of the tracks I run at are sensitive to sound so I will be running a longer silencer as needed. I think I have a Muzzy can from a FZR600 (Might have been a 400?) I could repack and fit up if needed? The header is the challange right now.

If Muzzy pipes are no longer being made and they work well and someone has one they would be willing to lend me I can scan it as a starting point to get something mandrel bent for this project and beyond.

More to come! Any and all feedback is welcome and appreciated!

[Dangerboy]

Designing the triple for USD forks.

Here is the ZZR OEM scanned assembly:

[Dangerboy]

Here is a bit more progress on the bike.

As you can see, the TZ chassis and geometry (Shown with recommended sag set for the bike) is shown (Green chassis) and the ZZR (Blue chassis)

Even though the bikes have different rake angles the trail is almost identical between the bikes. The overall fork length is so much longer on the ZZR that it isn't really feasible to use the TZ fork on the ZZR. I do think the KTM WP fork would work well though but I need to get a set to determine for sure.

Next I will be getting scan data from the engine itself to determine the exact sprocket location and model in the swingarm linkage to calculate what swingarm angles will work to permit raising the rear a little to steepen the steering head and then change the fork offset to keep similar trail numbers.

[Mohawk]

Have a look here for slipons https://dan-moto.com/collections/gpx250r

[Dangerboy]

Progress of putting the motorcycle into CAD is coming along very well! Everything from engine porting to intake and exhaust components will be much easier to produce accurately this way. More interesting development to come!

[Dangerboy]

Since my last post I picked up a basketcase Ninja 300. Think "Red Loctite" = "Missing & Mismatching bolts" + "Stripped threads" + "Rattlecan paint over decals" + "all wear on rear brake disk only". It only started to look useable again once it was a bare frame and engine. Speaking of which I'm not going to use the 300 chassis and it came with a Alberta clean title and keys which are matched to all the locking parts so if anyone is looking to fix up a salvage title bike for the street or something please let me know I'd sell it all together.

Just some observations between the older ZZR250 and the Ninja 300. First the quality of the ZZR is much higher.

The ZZR has a much larger front brake disk that is fully floating.

The ZZR has a 37mm fork like the 300 but uses threaded caps instead of that circlip retaining approach used on the 300. Unfortunately the ZZR uses a dual rate fork spring whereas as far as I can tell the 300 spring will be almost exactly right for my overall weight once the bike has been lightened. It's early to say if if the springs are the same dimensions overall, but spacers will take care of the difference either way.

My main large storage disk in my scanning PC just died so I have to get the data recovered to show more progress on the Scanning/CAD side of things.

Today I'm focusing a bit on what I'm going to do about the fork. The bad news is the CSBK Lightweight class rules say I have to keep the triple clamps stock, and the stock lower clamp is very heavy. The good news is the ZZR fork is very lightweight, and I can swap another 37mm conventional fork as well if I find something that will work. I would rather find something that is already a proper cartridge rather than retrofitting a kit. The Ninja 300 fork bottoms don't clamp the front axle either, whereas the ZZR does, which increases the rigidity of the whole front end.

Anyone have any suggestions for forks I should consider if I decide to swap them out? The threaded tops of the ZZR makes putting in a cartridge "kit" that is listed for the Ninja 300 or similar a bit of a gamble as I know some parts will need to be changed to suit the top and I can't confirm if the bottom is identical until I pull both apart. I've read the damper rod bolt is M8 on the ZZR250, I haven't checked if the 300 is the same or not. I know the brake caliper mounting location is different on the 300 due to the ZZR having a larger front disk.

At minimum at least the 300 has the slipper clutch and bottom end I wanted for the 250 project engine. I'm not sure if I'll use much else.

More to come!