KTM RFS/SXF Hybrid

[jar944]

Originally Posted by KTMandu

Lukas
Thanks for the reply. There's a lot to read in that link.
I don't know if doing this is worthwhile. I do not have the time, expertise or the machinery to tackle a project of this nature. Bums me out.

The "easy" way is to cut the cradle out of the 400 and weld it into the sxf frame. Same as I did with my 250sxf chassis in this thread. After that everything is a bolt on deal.

Any competent welder should be able to do it in a couple hours

Originally Posted by LukasM

Or maybe Jar wants to do it for a fee, he is the de-facto expert on the hybrid builds now.

Unfortunately I have to many projects of my own. Not sure how I became the expert, I just like building things

[dieselcruiserhead]

thank you for this thread, really captivating and definitely has me thinking.

I found a second completely built '02 RFS that is bored out to 540 for very cheap. I like the earlier pipes because I like the additional torque as well. And then some cheaper '08 250 SX-F.

I like the idea of being into less than a '08+ EXC would cost as well...

[LukasM]

If you can do the fabrication and you enjoy projects like this, go for it man. You will be able to make most (all?) of your money back if you take your time selling the rest of the parts.

Whoever is thinking about a hybrid, Navin is offering a smoking deal in the Flea Market, $99 for a SX-F frame.

[Navin]

Originally Posted by LukasM

If you can do the fabrication and you enjoy projects like this, go for it man. You will be able to make most (all?) of your money back if you take your time selling the rest of the parts.

Whoever is thinking about a hybrid, Navin is offering a smoking deal in the Flea Market, $99 for a SX-F frame.

Thanks for the mention Lukas! I've got a subframe, a couple tanks too. Man, the used market is tough these days!

[dieselcruiserhead]

Definitely can do the fabrication and definitely enjoy stuff like this.

The issue is I'd want to just get the $$ out of my dialed '02 that I want some components off of, so I'd have to buy a second RFS bike to make it work. I found some cheap ones locally that will do great but they're also older style '02ish.

I might consider sending the engine over to DJH to get checked over and possible a 540 kit and the stainless valves. Not sure if the '02 means much in terms of weaknesses. The only one I see if that the '02s don't have a Rekluse that can be used. Which I may or may not ever use, my frineds on the Rekluse love them and say I should get one but I've never really used one.

I have a 41mm carb already so I'd also get the head bored out I figure as well.

So I'm definitely definitely intrigued. I'd be about $4G into a 250 SX-F and a '02 520 EXC before selling anything...

[cross-country]

If you used a 450sx(RFS 04-07) motor, you would not need to chop the frame. You would only need to move (cut off and reweld) the rear motor mounts and find a yz400/426 carb bell. If you find an SMR it would already have a 6 speed in it. There is one on KTMtalk for sale.

[LukasM]

Originally Posted by cross-country

If you used a 450sx(RFS 04-07) motor, you would not need to chop the frame. You would only need to move (cut off and reweld) the rear motor mounts and find a yz400/426 carb bell. If you find an SMR it would already have a 6 speed in it. There is one on KTMtalk for sale.

It's actually the bottom mounts that you need to move/reweld, and you also have to modify the front mounts, either by milling down the cases on each side or by bending the mounts out, IIRC it's 1mm per side.

But you probably knew this seeing how you built one.

[cross-country]

Originally Posted by LukasM

It's actually the bottom mounts that you need to move/reweld, and you also have to modify the front mounts, either by milling down the cases on each side or by bending the mounts out, IIRC it's 1mm per side.

But you probably knew this seeing how you built one.

Haha, yeah but I built a 540. Dirttricks did the fab. I think the short stroke is the way to go to fully take advantage of the improved handling, but that is just a theory since I never tried it. I really wanted a 450sx with and exc tranny and flywheel. I think that would have been a great bike, at least where I live/ride.

[Rot Box]

Awesome!

[jar944]

Originally Posted by cross-country

Haha, yeah but I built a 540. Dirttricks did the fab. I think the short stroke is the way to go to fully take advantage of the improved handling, but that is just a theory since I never tried it. I really wanted a 450sx with and exc tranny and flywheel. I think that would have been a great bike, at least where I live/ride.

I was close to doing a 450/488, but decided my 505/477 was too close to the same thing. The fact that I don't have any short stroke parts didn't help.

My 555 is getting a piston/cam/trans swap, and the other is growing to a 637 to try and out power my cr5 conversion.

[cross-country]

Originally Posted by jar944

I was close to doing a 450/488, but decided my 505/477 was too close to the same thing. The fact that I don't have any short stroke parts didn't help.

My 555 is getting a piston/cam/trans swap, and the other is growing to a 637 to try and out power my cr5 conversion.

I was thinking that the short crank was the key to the handling. Again, that is just a thought, I never tried it.

What tranny combo's are you using?

This thread needs more pics! The CR is very cool!

Add a hydro clutch and leaky CS and no one would ever know it's Japanese heritage.

[dieselcruiserhead]

How is the '08ish 250 SX-F suspension? I know it's pretty good compared to older models. I'd be looking for more of a trail friendly push ride for a heavy guy/gear (I weight 230 before gear). I think the 250 suspension is the same as a 450, and with the SX it just has more adjustment controls over the EXCs, right?

[jar944]

Originally Posted by cross-country

I was thinking that the short crank was the key to the handling. Again, that is just a thought, I never tried it.

What tranny combo's are you using?

This thread needs more pics! The CR is very cool!

Add a hydro clutch and leaky CS and no one would ever know it's Japanese heritage.

As for the cr5 It has a magura clutch already. No leaky cs though. looks more euro with a RFS kicker on it:


Not sure if you saw my thread on the cr5 conversion:http://advrider.com/forums/showthread.php?t=757835

as for the RFS hybrids, The transmissions are still up in the air. I have a few exc trans and one mxc sitting in boxes. I'll likely go with close 1-4 and wide 5-6 on the 555 and all close on the 637. I agree on the handling being related to the stroke. The 72mm's don't feel the same as the 60mm

[jar944]

Originally Posted by dieselcruiserhead

How is the '08ish 250 SX-F suspension? I know it's pretty good compared to older models. I'd be looking for more of a trail friendly push ride for a heavy guy/gear (I weight 230 before gear). I think the 250 suspension is the same as a 450, and with the SX it just has more adjustment controls over the EXCs, right?

The 250sxf forks are closed chamber like the 450 but the 250 has softer springs and softer valving. Neither the 450 or 250sxf has good trail suspension. To not beat yourself up you would need to revalve front and rear.

The exc has open chamber forks.

[dentvet]

Hey Jar, Is it feasible to do a reversible hybrid? I have an 08 christini 300 and would love to put my 520 into it for a trip out west.