250r to Crf450r?

[Golden Joker]

( I didn't know what forum to put this in so I am posing it here.)


Hi everyone,


My dad and I are gonna be starting a new project this spring and we thinking about buying a cheap 250r then changing it to a crf450, sorta like dana creechs old atv. And if the 250r already doesn't have all the aftermarket goodies we will put them on.(extended a-arms, tires, axle etc) We are gonna make this becuase I have heard the 250r frame is really good for mx and with a high performance 450 engine in it, I think it would be extremly good in mx. I may be wrong!

I know that it takes a lot of frame modification for the 450 engine to fit in, but I do not know specifically what to do so I need help!

My dad knows tons of stuff about engines and cars, motorcycles etc.. but does not really know how to fit the 450 engine in the 250r, so I am asking you to help us.

Give me all the info you know about this kind of atv etc...

Also, give me some instructions or something on how to do the mod. I have heard that some people cut the 450 silencer becuase its too long and will hit the brake caliber or something. Is that true?

p.s. If my dad and I decide do go through with this project what are some good mods for the crf 450 motor, besides an aftermarket exhaust?

[Narly R]

Well there is tons and tons of info that you will know, but there is also a lot on this site. I would recomend (if you wanna do it right) to get a aftermarket frame, walsh is money isnt an issue, but there is lonestar also. Talk to John Arens, he can help you get a frame modded and fixed if you want to get a r frame and mod it.

Might find some helpful info here:http://www.exriders.com/vbb/search.php?s=&action=showresults&searchid=774560&sortby=lastpost&sortorder=descending

I built this bike, and wont ever do it again. You have to re-do everything, and maybe its just my bike, but its hard to keep together. Defently get a bigger radiator whe you do it. Talk to PWR for that. You have to custom bend the pipe, i bent the header in a little, and had to do a lot of work with the silencer. The rear brake caliper will hit it. Try to go with a CR500 rear linkage setup if possible. One thing that makes things hard it the engine is so tall, make sure your gas tank doesnt hit it. And get a shorter kickstarter lever. I just used the stocker, and welded 2 of the pieces that connect the kick starter, and the shaft that goes into the engine together to make it stick out farther. You have to make it clear the frame. For water pump cover, and rear brake mounting stsytem get ahold of American Dream Motorsports (if you go with aftermarket frame)... the list goes on and on. I would also recomend not getting a used engine. Look for a whole bike that hasnt been used, and use the engine, and part the rest out. I have a stage 2 cam, and Wiseco higher comp. piston for more power, I think you can do something to the vaulves also, but thats about it, besides boring it out.

Are you leaning towards a aftermarket frame, or stock r frame?

[Golden Joker]

i am leaning towards a stock frame. I'd rather to work to that then buy a whole new frame.


Is it easier to fit a yz426 in then a crf450?

p.s. does your crf handle good and is it pretty powerful?

[Tommy 17]

have fun trying to get that motor into a 250r frame... its just to tall... it fits into a 400ex frame pretty easy thou...


the only 250rs u see with crf motors are aftermarket frames...

[SRH]

Originally posted by Tommy 17
have fun trying to get that motor into a 250r frame... its just to tall... it fits into a 400ex frame pretty easy thou...


the only 250rs u see with crf motors are aftermarket frames...

word :p i t hink walsh sells a removable frame rail to put a crf motor in a r frame ...or if you can come how raise that area of the frame...i cant see throwing a crf motor in a stock frame anyway...its not going to stand up to something nearly 2 times the power when its over 16 years old... it will for a lil while but your throwing your money away...id go with a aftermarket frame if your serious about building something...do it right

[Narly R]

Like SRH said, a stock frame wont hold up. If you are going to build a race ready crf bike, a aftermarket frame is just part of it. I do belive the 426 is easier to put in r frame, I dont think they are as tall. The only diff between a walsh and any other frame is the removable upper frame rail, so you can rebuild the top end without having to take the engine out, and walsh stuff is super good quality, but I can still change my piston in my lsr frame without taking out or loosning the engine.

My crf is really powerful, but I still want more power....:D It handles very well, has LSR DC-4 swinger and a-arms, and elka longtravel all around. Handles superbly! If you HAVE to go with the stock frame, an ex frame is way easier, make sure and talk to John Arens! He will help you (if you modify a stock r frame).

What excatly do you plan on doing to, and with this bike? j/w

[QuadRacer041]

Originally posted by Tommy 17
have fun trying to get that motor into a 250r frame... its just to tall... it fits into a 400ex frame pretty easy thou...


the only 250rs u see with crf motors are aftermarket frames...

tru dat tru dat

[beerock]

Originally posted by Tommy 17
have fun trying to get that motor into a 250r frame... its just to tall... it fits into a 400ex frame pretty easy thou...


the only 250rs u see with crf motors are aftermarket frames...

yes this is so true, even the radiator from a trx 450r wont fit in a 250r frame, I measured the R frame and the trx450 frame and the 450 frame has a good 3-4 inches higher for the radiator AND the motor. You cant use a cr500 link setup with anything other then a purposely built frame like a walsh or laeger. My suggestion is gusset the frame and instead of putting all that effort and money into a crf motored R frame. Build a new R motor. New 88 crank, big bore cylinder possibly stay with a 310 or 330 for reliability. have the cylinder ported by someone that may give you a edge over all the ct, esr cylinders. if you do this youll be walking away from the 4 bangers EASILY.

The R is still king so dont kill it.:macho

[Golden Joker]

meh, screw this, i'am just gonna get a yfz450 or 250r!