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cr250 2t in 09 crf 450 frame?

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ok so I've been throwing the idea around of putting a cr 250 smoker in my 09 450 frame. I've been trying to a little research just to figure out what kind of mess im looking at getting into and can only find info about cr 500 af conversions in 450 frames. I am a fabricator/machinist by trade and part time mechanical engineer student so I have no worries about being able to make it work.

 

So I guess what I would like to know is if anybody has done this with a cr250 to a crf 450 and has tips or thoughts how it will work out? really any help or feedback will be greatly appreciated thanks

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people have done it, Its more for doing something cool and looking updated. I find the 02-07 cr250 frame/chassis was far superior to the 09 crf450 handling in every way.

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people have done it, Its more for doing something cool and looking updated. I find the 02-07 cr250 frame/chassis was far superior to the 09 crf450 handling in every way.

Owned an 09 & now own a 10 CRF450r model.  The chassis can be improved & is pretty good by getting the suspension balanced & sorted out.  I agree the 02-07 is a better option, but the OP is probably going for a more updated look.  I'd also believe the suspension would have a different affect with the lighter 250 2t motor transplant.

 

Here's a good example of it here.

  http://www.thumpertalk.com/topic/1019526-cr250-afs/?view=findpost&p=10719852&hl=06+motor

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just a guess but... stick your 250 motor into the 450 frame with the swing arm bolt in, line the sprocket up with the chain slider then check to see if the swing arm will still fit or need shims or cutting have your frame level and tilt the motor so the Honda logo on the case also is about level then check to see how the pipe lines up -you probably need to make new or relocate mounts.

as for the air boot try the250 one that came with your motor,usualy mounting a thin piece of aluminum on the front of your airbox alowes for locating the air boot whar ever it needs to be(might need a thicker shim). when you have those basics coverd bottom and front motor mounts and a head stay would be in order.

get on it and you could be riding it by lunch time lol

I built a few bikes like an 04 crf450/500 and a cr250/500 the most recent was putting a kx125 motor into a kx100 frame for my short wife

every build is different take your time and plan ahead do some mockup

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Ok thanks everybody for the feedback been great help i havent gotten a 250 motor yet but am working on it hopefully i can find one soon and get started

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Why exactly do you want to do this? I'm not trying to be an ass or anything, just wondering what the intentions are. I love 2 strokes just like all the guys here but that 450 motor will kick ass too. Did it go kaboom and now you want to ride without spending thousands on a rebuild? It will be sweet, but I'm not sure it will add up cost wise.

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The notorious 09 fuel pump took a dump along with just having a baby my spending limits on parts has went down considerably, like zero lol so ive been thinking about tryin to sell the still near new motor/other parts i wont need and getting myself a decent 250 then transplant the motor mainly just because i think itd be cool and i used to have a cr 250 that was a blast to ride i just couldnt ever get comfortable with it an i think it mostly had to with the fact it had a giant oversize tank on it an was top heavy as hell but now i have this 09 an really like the way it feels and i have pretty good suspension set up goin an im hoping with some minor changes to it after the transplant ill have myself the bike of my dreams and it wont cost an arm n leg to keep maintained

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The notorious 09 fuel pump took a dump along with just having a baby my spending limits on parts has went down considerably, like zero lol so ive been thinking about tryin to sell the still near new motor/other parts i wont need and getting myself a decent 250 then transplant the motor mainly just because i think itd be cool and i used to have a cr 250 that was a blast to ride i just couldnt ever get comfortable with it an i think it mostly had to with the fact it had a giant oversize tank on it an was top heavy as hell but now i have this 09 an really like the way it feels and i have pretty good suspension set up goin an im hoping with some minor changes to it after the transplant ill have myself the bike of my dreams and it wont cost an arm n leg to keep maintained

Makes sense to me! Obviously you won't have fitment issues with a smaller motor, the bear will be getting it all to line up. I'm not sure if the "Y" of the frame will have to be moved. But other than that it should just be some engine mounts, and get the airbox in there. Good luck!

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Makes sense to me! Obviously you won't have fitment issues with a smaller motor, the bear will be getting it all to line up. I'm not sure if the "Y" of the frame will have to be moved. But other than that it should just be some engine mounts, and get the airbox in there. Good luck!

Thanks and hopefully line up wont be to bad with a full machine shop at my disposal what im now starting to worry about it is how its going to affect the center of gravity with it being a smaller motor thanks for pointing that out i wasnt thinking of that yet got the wheels turnin now now i need to find me a motor and get this thing goin

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the newer 09-12 crf450 frames seem to like the lighter 2 stroke motors.  MPS does those swaps.  Also service Honda.  MXA had a video of one posted at Glen Helen. 

 

just remember you will have to figure a way around the in-tank fuel pump and mount a normal petcock. 

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The yoke will have to be moved up to allow room for the exhaust port, also the cr250 cases are a bit bigger then the cr500 cases so you have to deal with that. Lastly just try and keep the "Honda" logo on the side case as even as possible this will keep the crank on the same plan (same goes with the sprockets) as the rest of the bike and you'll have zero to no vibrations (The last point I made I did not grasp to fully when read but alot of guys have pointed it out on there builds) lastly go to bannedcr500riders.com they have alot of info and would be glad to help

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the newer 09-12 crf450 frames seem to like the lighter 2 stroke motors. MPS does those swaps. Also service Honda. MXA had a video of one posted at Glen Helen.

just remember you will have to figure a way around the in-tank fuel pump and mount a normal petcock.

Awesome i hope it does and already on top of the tank issue i was lookin at that one last night i thinkin a 3/16 piece of ally and cut a new gasket but ill have to wait on makin it till the motor is in an airbox on so ill have the carb height and were ill be able to then put the petcock

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