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Old 04-23-2011, 08:27 AM   #31
jar944 OP
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Quote:
Originally Posted by yellowbronco View Post
Great thread. I was not aware that it was possible to fit an RFS engine inside the small confines of the 250F chassis (with minor mods). This may have given my 250 a new lease on life. I've got only about 3 hours on the 300 big bore kit and now the crank bearings (or maybe it's the rod bearing) is going south.

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All of the new frames seem to have the same "main" frame. It appears they only have different cradles. Meaning you should be able to do this with any 08-10 frame.

The 450sxf + Short stroke motor is the easiest swap as only the bottom engine mount needs changed.
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Old 05-11-2011, 10:17 AM   #32
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Just ran across a 576 stroker and I'm suddenly getting a lot more serious about this. Some questions:

1. Are you using the stock 250 F radiators?

2. Did you have to machine the swingarm to fit between the engine cases and the frame?

3. Are you bothering with stress-relieving the frame after welding?

4. What exhaust components do you recommend? Looks like you're using an '08+ muffler with the stock header.

I'm on the brink and want to pull the trigger.

Tom
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Old 05-11-2011, 07:48 PM   #33
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Quote:
Originally Posted by yellowbronco View Post
Just ran across a 576 stroker and I'm suddenly getting a lot more serious about this. Some questions:

1. Are you using the stock 250 F radiators?

2. Did you have to machine the swingarm to fit between the engine cases and the frame?

3. Are you bothering with stress-relieving the frame after welding?

4. What exhaust components do you recommend? Looks like you're using an '08+ muffler with the stock header.

I'm on the brink and want to pull the trigger.

Tom
1. I have 250sxf rads on one and 450sxf rads on the other.
2. Yes (if you are using the 08+ swingarm)
3. No
4. You can run either 04-07 or 08+ cans and a stock head pipe. both will work but the early can needs a spacer on for the mount.
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Old 05-11-2011, 11:30 PM   #34
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jar944, could you tell me what the wall thicknessand dimentions of the downtubes are? i'm looking at doing a drz400(cos that's what i've got) motor swap into an 09 530exc but will need to do a few more/different modifications to the downtube area than with your swap.

Also do you think the triangular section of frame behind the steering head would be able to be sealed off and used as an oil tank for a dry-sump motor?

Keep up the great work, your bike looks mint
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Old 05-12-2011, 09:23 AM   #35
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jar944, could you tell me what the wall thicknessand dimentions of the downtubes are? i'm looking at doing a drz400(cos that's what i've got) motor swap into an 09 530exc but will need to do a few more/different modifications to the downtube area than with your swap.

Also do you think the triangular section of frame behind the steering head would be able to be sealed off and used as an oil tank for a dry-sump motor?

Keep up the great work, your bike looks mint
They are 1" dia IIRC about .065" thick, i'd have to measure when i get home to be sure.

I dont think it would be easy to seal the backbone, but i haven't studied it in detail.

The drz motor may (most likely) be significantly more work. swingrm pivot dia, counteshaft location, motor width all may cause issues.

what happened to the KTM motor in the 530?
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Old 05-12-2011, 01:45 PM   #36
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Originally Posted by jar944 View Post
They are 1" dia IIRC about .065" thick, i'd have to measure when i get home to be sure.

I dont think it would be easy to seal the backbone, but i haven't studied it in detail.

The drz motor may (most likely) be significantly more work. swingrm pivot dia, counteshaft location, motor width all may cause issues.

what happened to the KTM motor in the 530?
Cheers for that,

The 530 currently belongs to a friend but he expects the motor will require a TOTAL rebuild in the not to distant future, which will cost more than it's worth to him (plus he wants a new smaller bike for xc's). The chassis has been really well looked after so i reccon will make a great candidate for a transplant.

i've measured the drz up against a 05 525 and it'll fit inside the chassis and will actually require spacers to fit between the swingarm rather than needing any milling and the pivot is the same diameter (17mm), i'll do a good measure up against the 530 this weekend just to make sure.

The biggest issues are a/ the exhaust exits to the left on the cylinder so i'd have to do the oppisite of what you've done and extend the central downtube for clearance. b/ DRZ is a dry-sump so i really need an oil tank either in the frame or make an external tank to suit.

Cheers Topo
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Old 05-15-2011, 10:50 AM   #37
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Finally got a chance to try out my first hybrid on some hills

http://www.youtube.com/watch?v=j-HrHqS2Bi0
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Old 05-15-2011, 08:11 PM   #38
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Old 06-02-2011, 07:02 PM   #39
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Getting closer to being done with build #2 (250sxf frame)




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Old 06-03-2011, 11:32 AM   #40
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Originally Posted by jar944 View Post
1. RFS bikes handle like a truck. (Terrible)
2. SXF bikes handle very very well
3. Not even a worked 505 can match the HP and Tq of a 600-613cc rfs
4. SXF (RF4) motors dont live long
5. RFS motors do live long.
I'm all for these hybrid bikes as I really like the RFS motors but I would like to point something out because I has just become aware of this.

Your point #4 is invalid for the actual frame you are using. The engine in the 250SXF (or XCF and XCFW) is not an RF4 motor but an RC4. The RF4 (450 and 505) do have issues but for the most part the RC4 motors are some of the best, if not THE best motor KTM has ever made IMHO. Unlike most of the other 250F timebombs, the RC4 motor has an uncharacteristically lax maintenance interval and it is not unusual for racers to go beyond 100 hours on both piston and rings and over 200 hours on valves. Its only Achilles heel is the questionable OEM cam chain tensioner that usually gets replaced with a Dirt Tricks or Dave Hopkins unit. These are great little motors.

Anyway, I'm not criticizing the build or anything, just didn't want people to lump the RC4 motor in the same basket as the (more) problematic RF4 and XC4 motors.

Carry on.




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Old 06-04-2011, 06:45 AM   #41
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Originally Posted by GR0NK View Post
I'm all for these hybrid bikes as I really like the RFS motors but I would like to point something out because I has just become aware of this.

Your point #4 is invalid for the actual frame you are using. The engine in the 250SXF (or XCF and XCFW) is not an RF4 motor but an RC4. The RF4 (450 and 505) do have issues but for the most part the RC4 motors are some of the best, if not THE best motor KTM has ever made IMHO. Unlike most of the other 250F timebombs, the RC4 motor has an uncharacteristically lax maintenance interval and it is not unusual for racers to go beyond 100 hours on both piston and rings and over 200 hours on valves. Its only Achilles heel is the questionable OEM cam chain tensioner that usually gets replaced with a Dirt Tricks or Dave Hopkins unit. These are great little motors.

Anyway, I'm not criticizing the build or anything, just didn't want people to lump the RC4 motor in the same basket as the (more) problematic RF4 and XC4 motors.

Carry on.




Sean
I completely agree with you, but I don't think I said the RC4 motors were bad? The original list was specifically for the RF4.

The only reason I'm using a 250 frame (well 2 reasons) is that that are considerably cheaper and this one was (is) plated already. I have another 450sxf frame but it is titled as (off road only) and this build was specifically to be a dual sport

Any of the new style frames should work (provided you add in a new cradle.) So someone could pick up a $150 150sx frame and do the same think if they wanted

also my last post should have read 250xcf frame (you can see the spring mount for the kickstand in the pic)
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Old 06-04-2011, 07:50 AM   #42
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Old 06-06-2011, 11:46 AM   #43
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Originally Posted by jar944 View Post
I completely agree with you, but I don't think I said the RC4 motors were bad? The original list was specifically for the RF4.

The only reason I'm using a 250 frame (well 2 reasons) is that that are considerably cheaper and this one was (is) plated already. I have another 450sxf frame but it is titled as (off road only) and this build was specifically to be a dual sport

Any of the new style frames should work (provided you add in a new cradle.) So someone could pick up a $150 150sx frame and do the same think if they wanted

also my last post should have read 250xcf frame (you can see the spring mount for the kickstand in the pic)
Yeah it was just the way the info was presented made it seem like "all" those KTM SX bikes have problem engines.

I just picked up an 07 250 XCFW for my wife and she finished 2nd just yesterday in the women's class, first time on the bike!
I finished 4rth Vet Master on the very same bike in back-to-back races after switching to it because I had "issues" with my bike. Motor aside, these frames handle night and day better than the RFS bikes. Yesterday's track was half MX and half tight woods. The XCFW is about 90-95% what my 200XC can do in the woods but (for me) it was much better on the high-speed outdoor MX style track than the 200XC, and that was with my wife's suspension on the bike. Realizing that the motor plays a big part in the handling, the new generation frames can climb out of ruts much better (like a two-stroke) and somehow do not exhibit the headshaking that some RFS bikes are afflicted with. I never once though it needed a steering dampener other than when knocking trees with the bars but when you're doing that anybody on any bike could benefit from a dampener.

Like yours, our XCFW can be plated for street but short of complete catastrophic engine failure I don't think I could yank out the RC4 and replace it with an RFS. I am building a short-stroke RFS race motor so I may just need to find another frame to put it in.



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Old 06-16-2011, 06:08 PM   #44
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Frame is done and painted, 90 degree adapter has been machined and installed.





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Old 07-09-2011, 10:29 PM   #45
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dialed in the suspension and jetting on hybrid #1

took it out for a quick spin through the hillsville quarries. I haven't been there in 10 years

http://www.youtube.com/watch?v=8YjPTJjfiuk
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