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  #1  
Old 06-06-2005, 02:06 AM
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Default 250-125 engine swap

     

anyone know if a 125 engine will drop into my '99 cr250? If so what year(s) should I look for? I got a new yz450f and I'm thinking maybe the girlfriend could ride the cr if I can get it corked.
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Old 06-06-2005, 02:16 AM
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Default Re: 250-125 engine swap

Sorry I can't really answer your question, but may I ask why you are looking to do that? Did you 250 engine grenade and is useless or did you have a major crash and write off the 125's frame?
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Old 06-06-2005, 03:59 AM
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Default Re: 250-125 engine swap

it may take a little time, but anything is possible.as long as you can get the swingarm to fit the 125 cases.you will probably have to make some sort of spacing for it. the motor mounts and head stay can be worked around if need be with a little cutting and welding...keep us posted how it goes...
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Old 06-06-2005, 06:03 AM
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Default Re: 250-125 engine swap

If the 250 still runs?? why not just take a hammer and dent the pipe in the first part of the pipe? Or just put a 14 tooth in the front with a 46 - 47 in the rear. That will tame it down, avoid manual labor of fitting the other motor, and it will give enough torque for a beginner rider to easily manage.
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Old 06-06-2005, 09:55 AM
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Default Re: 250-125 engine swap

the 250 runs great, but it's a scary bike. especially for a beginer. When it hits, there isn't any keeping the front wheel down, and it doesn't care where you are. I know a lot of parts from the 125 and the 250 are interchangeable so I was just wondering if it was an option. I know a lot of people talk about going the other way from 125 to 250 so I figure someone would have some experience here. It would probably just be easier to put in the classifieds for even swap for a smaller bike, but I do like a project every once in a while.
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Old 06-11-2005, 09:50 PM
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Default Re: 250-125 engine swap

should bolt right in as long as you get some long screws
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Old 06-11-2005, 10:03 PM
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Default Re: 250-125 engine swap

yeah I think it will bolt right in, this is kind of off topic but for the CR500AF's they use CR125 frames instead of the 250, I'll tell you why in a few after I go read the article.
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Old 06-11-2005, 10:13 PM
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Default Re: 250-125 engine swap

Since the 99 cr250 and 125 share the same swingarm, I think it will bolt in to the frame with just some minimal work to the headstay and front engine mounts.
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Old 06-12-2005, 05:42 PM
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Default Re: 250-125 engine swap

Quote:
Originally Posted by alex83
yeah I think it will bolt right in, this is kind of off topic but for the CR500AF's they use CR125 frames instead of the 250, I'll tell you why in a few after I go read the article.
Service Honda has used CR250 frames, CR125 frames, and now uses CRF250 frames. The "limited edition" was the model that used the 125 frame. The "2005" models use CRF250 frames and most of the ones before, other than the limited edition, used a CR250 chassis.
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Old 06-12-2005, 06:55 PM
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Default Re: 250-125 engine swap

Oh i read an article in TWMX about a around last year after Daytona with Pastrana on the cover, they said it was because of the Kayaba suspension, because that's what people liked best
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Old 06-13-2005, 09:12 AM
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Default Re: 250-125 engine swap

Given that the CR250's Showa suspension has been ranked as some of the best ever for quite a few years, I don't buy that explanation at all.

The CR125 frame, however, is a few pounds lighter than the 250 version, which is why they chose it for the Limited Edition model. Personally, I think they should have put Ohlins suspension on the LE model, but that's just me.

I'm using a 2000 CR250 chassis for mine.
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Old 06-13-2005, 10:17 AM
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Default Re: 250-125 engine swap

why not disconnect power valves,that will kill the hit
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Old 06-13-2005, 11:12 AM
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Default Re: 250-125 engine swap

Well that's just what TWMX said so don't ask me, something about it offered a more rider friendly package out of the box.
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Old 06-13-2005, 02:38 PM
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Default Re: 250-125 engine swap

Putting a 125 motor in it will be expensive and it will still be scary. You would probably be better off taming the 250 motor. Put a 14oz flywheel weight on it for starters. Retard the ignition timeing. This may tame it enough to make you happy, if not there is more you can do. You can remove the pv govenor and wire (or otherwise secure) the pv's shut. This will totally kill the mid-top end, but will allow it to run ok at low rpms.

good luck
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Old 06-13-2005, 11:34 PM
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Default Re: 250-125 engine swap

I haven't been able to check the thread in a couple of days. Some great suggestions, thanks. I think I'll probably try to tame the 250 first. So disabling the power valve should cork it pretty good.
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Old 06-14-2005, 06:21 AM
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Default Re: 250-125 engine swap

Yes, but you have to make sure it stays closed, keeping it open would kill the botom and make a tremondous mid-top hit.

More flywheel inertia will make a big difference as well.

good luck
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Old 06-14-2005, 10:13 AM
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Default Re: 250-125 engine swap

Leave the powervalve alone and order the heaviest flywheel weight Steahly has to offer. That will help tame it and not mess things up mechanically.
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Old 06-14-2005, 11:29 AM
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Default Re: 250-125 engine swap

Removing the linkage and locking it open is easy. Eddie Cole makes some plugs that will do it too. The problem you face then is jetting the top end as you now will have more compression as you go up in the rev range. Just something to think about, and your gf likely will not be holding it wide open for long,,but just remember that if anyone else jumps on it and finds that it doesnt have much power they are likely to hold it open and fry it.

I occasionally see someone talk about gearing a bike up to teach someone to ride,,and I dont agree with that at all. more novices kill bikes and get frustrated because they cant get rolling than over gas them. Or rather until they kill it several times and then try to get moving by over throttling etc. I have way better luck in gearing one down so they pull away easily,,most new riders and women in particular are way more throttle cautious than throttle happy,,just my two cents from teaching others to ride since 66.
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Old 06-19-2005, 07:39 PM
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Default Re: 250-125 engine swap

I think I came up with a better idea. I'm going to teach her to ride the yz450 and I'm going to ride the cr if and when I get her to ride. I hate to put her on my new bike, but it seems the best answer. Learning a four stroke is so much easier. Still a TON of power but no hit, and like you say she probably won't be much on the gas anyways. Now if only I can convince her that she only has to reach the foot pegs and not the ground to ride it.
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Old 06-19-2005, 09:13 PM
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Default Re: 250-125 engine swap

I think you're looking at this all wrong.

The girlfriend wants to ride.

This is a perfect excuse to buy a XR50 pit bike to teach her to ride on. No one says you have to sell it once she learns. A small 50 is a hoot in the backyard.
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