rmz250 hybrid?

Discussion for swapping a KDX motor in a MX frame...
cole454
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rmz250 hybrid?

Post by cole454 »

Ok so iv been reading on here and researching all night and I have not found any info on people swapping into the older steel framed KXF and RMZ 250f frames? Any info would be great, i'm looking to do this project for a friend who does not have much money to work with. He currently has a 98 kdx220 and we found a complete 2006 RMZ rolller on craigslist for $350 (steal IMO). Our goal is to get him on a bike to race this season that will be low cost with the reliability of the KDX and improved handling/suspension of the 250f. The bikes were offered as a KXF from 04-05 and RMZ from 04-06 this bike is an 06 RMZ Steel frame. I know the AF 250F's have problems with the front head stay interfering but no info on the steel framed bikes. Steel frame works better for me because I can weld it with my MIG since I do not have access to a TIG. If anybody knows anything about this swap please post away Pictures, stories, links, problems etc I just cannot find any info on such a build but I know it has to be available.
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bufftester
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Re: rmz250 hybrid?

Post by bufftester »

Biggest issue is going to be the engine cradle. The 250Fs downtube extends further down before it splits just like the aluminum frame models. This is a problem since the exhaust on the KDX exits between the rails. This is why the frame of choice would be an 99-05 KX125. For the Aluminum frames you can get prebent frame rails but I have not seen them for the steel frame bikes. If you have access to a square tubing bender you could certainly make a set. Once you get past that the other issue will be the swingarm pivot/crankcase mount. have not seen it done with theses frames mainly for the first reason. It's doable, but likely in the end it won't be a on the cheap deal. Perhaps a fiscally better idea would be KX or KLX fork conversion, and proper springing front/rear. That alone cures a lot of the handling issues of the KDX and is being raced successfully. For the same $350 you could do front end swap, rear spring, and with good shopping have some left over for miscellaneous bolt-ons (or beer!)
cole454
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Re: rmz250 hybrid?

Post by cole454 »

you are correct about the front down tube it does extend all the way down almost to the bottom. :sad: What issues do these frames have with the swingarm and pivot bolt that the other bikes don't have?
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Re: rmz250 hybrid?

Post by Tedh98 »

cole454 wrote:you are correct about the front down tube it does extend all the way down almost to the bottom. :sad: What issues do these frames have with the swingarm and pivot bolt that the other bikes don't have?

I think you are correct that no one has used a steel frame RMZ/KXF, so you would likely be the first. That means you've got the unknowns of how the tank will fit, how to handle the airbox and the little miscellaneous things. I would think you could count on having to do the same swingarm/engine modifications to make the 17mm swingarm bolt work.

Cutting off old motor mounts and welding on new ones isn't a big deal. Cutting downtubes and fabricating & welding on new ones seems like that takes the project to a new level. I trust my welding skills for motor mounts, but I would leave downtubes to a professional welder.

As long as the roller is in good shape, I agree that $350 is a good deal. If it were me, I'd buy the roller. I would then take measurements and do my best to mock things up to see how big of a project it will be to turn it into a hybrid.

If it looks like it will cost more than your friend is willing to risk on an unknown, then I'd take the front end from the RMZ and do a fork swap for the KDX and then sell the rest of the roller. By the time you sell the KDX forks and the rest of the RMZ, I'm guessing that new front end won't cost too much.
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Re: rmz250 hybrid?

Post by cole454 »

Tedh98 wrote:
cole454 wrote:you are correct about the front down tube it does extend all the way down almost to the bottom. :sad: What issues do these frames have with the swingarm and pivot bolt that the other bikes don't have?

I think you are correct that no one has used a steel frame RMZ/KXF, so you would likely be the first. That means you've got the unknowns of how the tank will fit, how to handle the airbox and the little miscellaneous things. I would think you could count on having to do the same swingarm/engine modifications to make the 17mm swingarm bolt work.

Cutting off old motor mounts and welding on new ones isn't a big deal. Cutting downtubes and fabricating & welding on new ones seems like that takes the project to a new level. I trust my welding skills for motor mounts, but I would leave downtubes to a professional welder.

As long as the roller is in good shape, I agree that $350 is a good deal. If it were me, I'd buy the roller. I would then take measurements and do my best to mock things up to see how big of a project it will be to turn it into a hybrid.

If it looks like it will cost more than your friend is willing to risk on an unknown, then I'd take the front end from the RMZ and do a fork swap for the KDX and then sell the rest of the roller. By the time you sell the KDX forks and the rest of the RMZ, I'm guessing that new front end won't cost too much.

I was thinking exactly what you just said lol. I think that is a good way to go about this project

I haven't been able to do much research on front end swaps but will the front end of the RMZ bolt up to his KDX?
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Tedh98
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rmz250 hybrid?

Post by Tedh98 »

The forks should be the same as what came on the '04-'05 KX (and similar to '03, not sure about older than that). If the triples aren't the same, the difference is probably something like the offset.

So what I'm basically trying to say is that the swap for the RMZ forks should be the same as an '04+ KX, which is usually swapping stems. Taking a look in the fork conversion section will confirm what needs to be done.
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Re: rmz250 hybrid?

Post by cole454 »

looks as if you just have to press the KDX stem in to the lower RMZ clamp then your good to go? maybe shims? I was not quite sure on that part. We are going to look at the RMZ roller tonight so hopefully it is what all this guy says it is. If its the whole bike we still plan to get it all to see what all it would take to make a complete hybird. But I know this guy has been trying to part this bike so if everything is not there we will prob just pick up the front end and do a front end conversion. (hopefully I can make it into a hybrid)
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Re: rmz250 hybrid?

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Went and picked up the bike today. Pretty much stole it from the kid :grin: .It is going to take more work than most hybrids to get the frame to work but for what we got it for I'm not complaining. Now iv just got to find the time to work on it between collage, my local race series and GNCC my schedule is pretty packed. Its missing a few parts like the front brake system which In a front end conversion thread I read the stock kdx caliper will work :please: . Back caliper is there but its missing the master cylinder I'm going be searching ebay for one. Another thing that is missing is the RMZ airbox I would of liked to have it to work with to see whichever one would work the best KDX or RMZ but hopefully the KDX airbox will get the job done. Here is a pic of what all we got for $180 the 2006 rmz250. Also here is the 1999 KDX220 that will be the donor (BTW that like new oversize KDX tank will be for sale)

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rmz250 hybrid?

Post by rbates9 »

I might be interested in the tank and the white shrouds. :hmm:

Maybe the rear wheel too.
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Re: rmz250 hybrid?

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Yes but I don't know how quick the build is going to go since we are in the middle of race season, hes trying to race as much as possible and same with me on quads. The plan as of now it to get everything ready to go and hopefully get the entire build knocked out in a weekend or else he will probable be borrowing our spare KDX for a few races. I know the tank is in excellent condition only been raced/rode once. As the build progresses just PM me and ill give you prices, same for anybody else anything that we don't use will be for sale to help offset the cost of the build.
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rmz250 hybrid?

Post by rbates9 »

Im in no hurry but if the price is right I'll be interested.

I see the head light is off the bike. Do you still have it? Is it worth having?
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Re: rmz250 hybrid?

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I think he broke the light that's why its off.
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rmz250 hybrid?

Post by cole454 »

Got the frame cleaned up and some parts on order :grin: The plan is to start the swing arm mod next Thursday once I get back from school (hopefully the 43/64 drill bit will be here). Once I have the rear mounted I plan on starting the downtube mod. My plan as of now is the cut the downtube somewhere above where the 4 stroke engine mounts and the two bottom rails where the skid plate mounts are(yellow). Iv got to find somebody with a tubing bender that I can borrow to make the new rails :hmm: Hopefully I can find a place near me that carries steel tubing with the same OD and ID as the frame. I'm thinking that I can insert a piece of smaller tubing inside of the two so it will be a doubler, that way I can butt weld the two and use rosset welds to increase the strength. Up at the down tube I plan to just cut the new pieces at and angle and weld them on to the sides of the current square down tube much like the factory design. While inspecting the frame today the factory design at this spot (downtube meets craddle) looks very weak but I guess it works lol (Red)

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Also while disassembling the swingam and rear linkage I found these two spacers on the floor HELP!! I don't know where they go lol
First I saw the complete one then I found the two parts of the broken one.
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bufftester
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Re: rmz250 hybrid?

Post by bufftester »

The spacers look like the ones that go on the linkage (under the link arms)..p/n K9215-20108. If they are there should be 6 of them total.

You look on the right track for the frame. If you can access a KX125 you could get some measurements for the lower cradle. You'll also need to fab a front headstay bracket for the motor (as you can see in most all of the hybrid threads). as well as new front lower and rear lower engine mounts. The engine mounts are important because once the motor is bolted into place, those 4 mounts also stiffen the frame,. Should be able to pick up a KXF/RMZ airbox on ebay for cheap, likely easier than trying to fit the KDX unit.

Should be anawesome build, keep us posted. I keep saying this would be the perfect frame to drop an old air-cooled KDX motor in (it's working its way up my build list the more I think about it.)
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Re: rmz250 hybrid?

Post by cole454 »

Unfortunately I do not have a 125 available to measure from. I was planning to just use the rear headstay of the kdx head (RMZ frame has its factory mounts to the rear) I see other people are only using one. And I have not forgot about the other engine mount they shouldn't be no problem so therefor I have not been to worried about them. Thanks ill check the linkage and see which mount that the spacers came from.
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Re: rmz250 hybrid?

Post by Biggles »

bufftester wrote:The spacers look like the ones that go on the linkage (under the link arms)..p/n K9215-20108. If they are there should be 6 of them total.

You look on the right track for the frame. If you can access a KX125 you could get some measurements for the lower cradle. You'll also need to fab a front headstay bracket for the motor (as you can see in most all of the hybrid threads). as well as new front lower and rear lower engine mounts. The engine mounts are important because once the motor is bolted into place, those 4 mounts also stiffen the frame,. Should be able to pick up a KXF/RMZ airbox on ebay for cheap, likely easier than trying to fit the KDX unit.

Should be anawesome build, keep us posted. I keep saying this would be the perfect frame to drop an old air-cooled KDX motor in (it's working its way up my build list the more I think about it.)
A friend of mine here has a 500 in one of these frames and it went together easily from all accounts. As the Zook already has a rear head mount, you could make one and mill the front headstay mount off instead, may be a little easier that fabing a new front one. i know on my 03 frame (they have a rear head stay mount) this is the path I took and was easy as. :kick:
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Re: rmz250 hybrid?

Post by cole454 »

Is there a build thread of his 500 build?
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Re: rmz250 hybrid?

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cole454 wrote:Is there a build thread of his 500 build?
Sorry - the guy is flat out having email :roll: Atypical two guys in a shed with an idea type old school scenario.

I will try to get some photos of it next time I see him at a ride.
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Re: rmz250 hybrid?

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Finally got to work on the bike today. My dad helped him strip the KDX down this week while I was gone so the engine was out waiting. I did not have to cut anything off of the swingarm the engine fit exactly as it should. Image
I drilled the cases with the 43/64 drill, then when we tried to install the whole swingarm/engine assembly into the frame it was just to tight. Therefore, I filled a very small amount of metal off of each bushing on the side that is rest against the engine cases. All in Image
The plug was hitting the tank and the petcock was on the head so it was time to cut the downtube to allow the engine to rotate forward allowing for more room.
Image
Next was just to mark and cut the frame. Here the frame is cut and the engine is re installed. Then I was able to rotate it forward now there is plenty of room under the tank Image Image Image
Tomorrow Iv got to run around town and find a tubing bender and some tubing then the fun part begins :grin: . Overall today was a very productive day besides my dog eating the new airfiler :mad:
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rmz250 hybrid?

Post by rbates9 »

:hmm:

How close are the down tubes on the two frames, the KDX and the RMZ? Would it be at all possible to cut the engine cradle out of the kdx and then weld it into the RMZ frame? It might save some fabrication work around the exhaust area and you might even be able to reuse the engine mounts.
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