YZ125 MX bike convert to track-worthy bike?

Just tossing aroudn an idea - i noticed someone has posted some pics of a YZ450 and CR450 that were done up as vintage road race bikes and it caught my eye.

I've got a YZ426 supermoto that i made street legal, and its fun as a supermoto, but i also just picked up a '94 YZ125 for cheap and in pretty good condition with some goodies on it.

I was curious if I were to convert it to a road race bike if it would get me around the track even half as fast as the popular RS125's etc.

I've had my '00 R6 and '04 ZX10 on the local track a dozen times, but i never felt good about pushing them hard especially after 2 crashes on the R6. The times i've had my supermoto on the track however its been balls-to-the-wall w/o worries even after i crashed it at about 80. Thats what i'm looking for but in a light, road race style bike (a knee dragger not a tire slider) and thought this cheap YZ125 might be the ticket to some fun.

I also think it will force me to learn to ride faster instead of rlying on the power of my ZX10 or even the power of the big thumper (the 426).

What all would be needed to get the bike in shape? 17" wheels i suppose, but what else? Some clipons, SS lines and oversized brakes, Shorten the forks? shorter spring for the rear shock, stiffer, and or a completely different shock? Sportbike forks maybe? Spacers in the stock forks somehow?

i'm open to criticism, suggestions, and cool pictures of others who have already tried this and succeeded or failed.

BTW, i LOVE making and converting things, even if in the end it costs just as much as buying a ready-made RS125. I'de rather build it.

I have a lathe and a mill at home for any machining needs.

I'm all ears!

 

The bikes i'm referring to:

 

I'll chime in a bit
I have owned 125 GP bikes and 125 MXer's

The MX engine has more torque and revs less.
They get hp in the low 30s. GP engines are about 40hp
stock. The MX engines are also a
lot heavier. GP engines are so light they are like toys.
Gearing is very different on the two.

My guess with gearing it will be difficult to get much more than 100mph
with an MX motor. Now with money anything is possible.

GP125s can go over 120mph. First gear feels like it good from
0-60 mph

I'd say you are pushing it.


I love that honda project you posted. I have a CRF450 I'd love to do that with. Anybody know that owner or have details.

 

I like it too but would rather mount some RS250 bodywork on it or some TYGA NSR250 bodywork on it.....pretty cool. If you find out what was done please forward me the info or link.

 

It's funny that this thread is going because I was thinking about those same photos today. I believe I may have seen them somewhere else, I can't remember. I believe that the honda was seen on a AHRMA site or some such vintage site. Any one with any info on the bikes please chime in.

 

I think the YZ # 57 belongs to Kevin Brown and the CR #14 belongs to Kevin Keys. That is according to the results from Daytona this year with AHRMA. Hope this helps.:up:

 

got it off of CMRA website that referenced the WERA website as the original posting.

lol.

i'm not looking to compete in a race - just to have some fun. It sounds like i'de be a little slower than stock RS125 bikes. Thats cool.

Our local track - i can only reach about 130mph on my ZX10 on teh front straight... about 120 on my R6.

I made it to 80mph on my YZ426 but i was running 10 secs slower than my sportbike times. Sounds like if the YZ125 would do 80 on the front straight, i coudl hold corner speed a lot higher than on my motard (still stock MX suspension) and knock off those 10 secs easily.

I'm looking to learn how to ride instead of twist the throttle. make sense?

but mainly i'm looking to have fun on something that wont cost a fortune to maintain or repair after a crash.

 

I was thinking about it too after seeing that CR450R. I thought about using a CR250R.

IMHO unless you get some hella deals on suspension work etc., you're going to end up piling enough money into the project to buy a well prepped and decently "spared" GP 125.

And I know which one I'd rather ride.

 

come-on somebody has to have some info on that yz450....it looks kinda like a tz250 tank....i think my yz450 might have a new future!!!!

 

Well can you always get a pre95 rs125 whcih aren't to expensive, but parts are getting scarce these days. Great for a trackday bike and you can carry some real coner speed, i dont think even a very tricked out yz125 road racer like what your talking about could really compare to a rs125, just my own opinion . You could always just restore a rs125 or get crazy and biuld a gp-mono

 

Metrakit makes what they call the Pre GP125 which uses a 125cc Husky MX engine.

http://www.cycleimports.com/acatalog/PRE_GP_125.html

There was a discussion about it a few moons ago on this BBS.

http://forums.13x.com/showthread.php?t=123876

In order to convert the YZ, you'd need the 17" wheels (yes, I am Cpt. Obvious ), drop your triples down, attach clip-ons under the upper triple, run a large front brake setup, stiffen/slow down (or replace) the front suspension, internally limit the rear suspension travel (like the dirt trackers do), and possibly install shorter dog bones to lower the rear.

And then, if you want to get fancy, start looking at mounting bodywork. Or not. There are plenty of budget racers that don't run full fairings.

That's all IMHO. I'll let you know towards the end of the year once I've done some mad science to a '84 TT600 I am about to lay my hands on.

 

Thanks for the honest answers guys.

From my perspective, i love doing things that are different. I already have a bike, and going out and purchasing yet another bike, well... i think i owe the girlfriend 1 good street bike for her to ride before i buy a 4th bike for myself lol. Plus, i cant imagine having over $1500 in the whole bike when its done...

A friend who races 636's is actually purchasing an RS125 here shortly. Hes already way faster than i am on our local track, but is getting the 125 to learn how to go even faster. Hes pretty good with suspension, and seemed interested in helping figure that part out on this project if i try it.

I've got access to a large lathe at work to shorten the inner fork tubes.

I can make my own dog-bones for the rear, and i'm not scared to try to modify the rear shock, or simply replace it with something else.

I have a friend that vacuum bags his own carbon fiber body work for his BMW cycle and has copied many other stock fairing parts for other bikes, including fenders and whatnot. I'm sure we can come up with some body work. He does fiberglass also (cheaper )

I'm not looking to make the fastest bike out there. Maybe not even competitive. I just wanna do something where i have fun building it, its different, and people walk up to me and go... WOW - what is that? Did you make that?

That puts a grin on my face

Any other suggestions please, keep them coming.

 

The gearing is going to be a problem unless you can fit a large CS sprocket. The large CS sprocket may interfere with the SA pivot.

The long wheelbase is going to be a detriment. The longer the WB the more you have to lean the bike to go around a corner at a given speed. This is why GP 125's have such a short WB and part of the reason they corner so well.

The thing may vibrate like crazy and strew bits of motorcycle around the track causing extra work and disallusionment.

 

And and of all the people on the WERA BBS, this man would know.

'Sup old fart. Hope you're not hurting too bad.

 

Oh, I don't know...this mxer seems to work pretty good!

 

Yup, I guess it's your boy? I saw him flying around Tally in April. :up:

As a mini, I think it's a sound idea. A bigger bike presents itself with other issues though. It's not that it's impossble but I think the hassle might be bigger than the reward.

One thing that is cool is those rear sets. How was that fabricated?

 

Oh I know, I just couldn't resist LOL The rearsets are OEM GSXR. Going to Tally next weekend? If so, cya there. Tdub

 

What kind of suspension adjustments or modifications had to be made?

 

The bike started off as a DTX (MXer converted for dirttrack) bike. The suspension has been lowered and revalved. I do these conversions on 65 to 500cc MXers. Tdub

 

I bought an ATK 260 [ with spare motor :up: ] when I was building my RS250/Rotax 257 SOS/Clubman bike. I kept having thoughts of lowering the ATK and having a 2stroke super motard pavement bike but then I would see the RS chassis'd bike sitting there and say "naaaah".