Dedicated RFS build. Will be pic heavy.

[yooper01]

Spent my first year on a Timbersled with it mounted to my 530 excr. I had a blast but after swapping back i decided to look for a cheap bike to dedicate to the snow.

Enter 2003 450 sx with a 2001 520 sx motor. $1500





I know others have been here and done that already. So I'll start with this, I am not going to buy a Fi 450 or 2s 500.

I enjoy wrenching on stuff and waking this lazy beast up will be a fun summer project.

My plan is to split the cases and install ball crank bearings, add 5th and 6th gears, electric start, and a 570 kit. It will get head work, kw valves, hot cam, a 41 mm carb, carb heater, thermostat, and the likes. Should be near 60 HP. Budget : $2500.

I have a 16 Lt Timbersled with TSS. I am going to have the shocks valved, add raptor springs, and some avid extrovert drivers.

I'll be send the forks out for a snow bike setup as well.

I'll add pics here along the way.

Feel free to chime in with advice as you see fit!

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[needpowder]

Nice! Good summer project.

 

[Rush44]

There is also an CDI update that needs to be done to that motor I believe. You can also get another 700-800 revs out of that motor once you do the update.

 

[Timberview01]

I had one of those beasts as a motocross bike and loved it! So much low end torque it should do really well with a track kit - especially if you add a few more HP and two gears. I could come out of the gate in third and never shift for the whole moto. Just a little clutch at the apex of the berm and BOOM!! Such a tractor, and it didn't have the engine braking issues that the Yammi 400's and 426's had.

Keep us posted. Good luck bud!

 

[Revv Up]

Looking forward to the build. Always liked the RFS motor.

 

[barefooter]

Hmmmmm. My neighbor has one with a wrecked 3rd gear and the entire back-end wrecked (sprocket pulled off)

I would love to buy it cheap and use it as the back-up.

What kind of carb are you going to run - a Lectron?

How hard is it to add e-start?

 

[yooper01]

Hmmmmm. My neighbor has one with a wrecked 3rd gear and the entire back-end wrecked (sprocket pulled off)

I would love to buy it cheap and use it as the back-up.

What kind of carb are you going to run - a Lectron?

How hard is it to add e-start?

RFS bikes were made from 2000-2007, and all used a close ratio 4 speed, close ratio 6 speed, or wide ratio 6 speed. You can get a good used tranny from any 400, 450, 520, or 525 and any tranny should bolt into any set of cases with maybe minor bearing changes.....should (there is more to it than that but it is very very doable)

I am probably going to just buy the parts to add a wide ratio 5th and 6th to my close ratio 4 speed. Parts total is about 300 bucks and of all the ways to convert, this is likely the most inexpensive.

The stock carb is a gen 1 FCR with a 39 mm bore. I am still doing some R&D but may just run that this year and do a carb bore or different carb next year. If I stay with the 540 kit normal jetting will be pretty close. If i go 565 then I might need to lean it out a little.

All the RFS motors can accept electric start. The right side engine case has a little plug in it that just needs to be removed. I have sourced all the parts used and spent about 190 bucks on ebay. My 2001 stator produces 150 watts and can charge the battery no problem. Newer SX or MXC RFS motors may need a stator to do the electric start mod.

Countless hours of reading over on ktmtalk.com will yield magical results! That place has so much information it can make your head spin. (and your wife mad for spending too much time on it....sort of like here )

These bikes properly set up and jetted correctly can make hp in the high 60s. My buddy has an RFS based Polaris quad that is turning 67 hp at the wheels on 91 octane fuel.


Welding the crank will important as the bottom ends of the RFS motors used roller bearings instead of ball, and tend to fail in high traction applications like supermoto, and presumably snowbiking.

Right now, I am leaning towards just mailing my motor to DJH in seattle and having him do the build. He is known for making super reliable motors. Thumper Racing does great work with the RFS as well. And last but not least there is a gentleman named bob in California who I have heard excellent things about as well.

One thing is for sure, this bike right off the bat is more than 30 lbs lighter than my exc, and even with the extra gears and electric start it will still be at least 20 lbs lighter. And will probably have 15 hp more.

Can't wait!

 

[barefooter]

RFS bikes were made from 2000-2007, and all used a close ratio 4 speed, close ratio 6 speed, or wide ratio 6 speed. You can get a good used tranny from any 400, 450, 520, or 525 and any tranny should bolt into any set of cases with maybe minor bearing changes.....should (there is more to it than that but it is very very doable)

I am probably going to just buy the parts to add a wide ratio 5th and 6th to my close ratio 4 speed. Parts total is about 300 bucks and of all the ways to convert, this is likely the most inexpensive.

The stock carb is a gen 1 FCR with a 39 mm bore. I am still doing some R&D but may just run that this year and do a carb bore or different carb next year. If I stay with the 540 kit normal jetting will be pretty close. If i go 565 then I might need to lean it out a little.

All the RFS motors can accept electric start. The right side engine case has a little plug in it that just needs to be removed. I have sourced all the parts used and spent about 190 bucks on ebay. My 2001 stator produces 150 watts and can charge the battery no problem. Newer SX or MXC RFS motors may need a stator to do the electric start mod.

Countless hours of reading over on ktmtalk.com will yield magical results! That place has so much information it can make your head spin. (and your wife mad for spending too much time on it....sort of like here )

These bikes properly set up and jetted correctly can make hp in the high 60s. My buddy has an RFS based Polaris quad that is turning 67 hp at the wheels on 91 octane fuel.


Welding the crank will important as the bottom ends of the RFS motors used roller bearings instead of ball, and tend to fail in high traction applications like supermoto, and presumably snowbiking.

Right now, I am leaning towards just mailing my motor to DJH in seattle and having him do the build. He is known for making super reliable motors. Thumper Racing does great work with the RFS as well. And last but not least there is a gentleman named bob in California who I have heard excellent things about as well.

One thing is for sure, this bike right off the bat is more than 30 lbs lighter than my exc, and even with the extra gears and electric start it will still be at least 20 lbs lighter. And will probably have 15 hp more.

Can't wait!

Thank you very much. This is great.

 

[needpowder]

That tranny sounds amazing!!!

 

[sierraclimber]

Just had my tired 04 525 gone completely through by Thumper Racing. Motor is coming back next week as a 540 with bored carb. Stage 1 cam, 12.5:1 compression, new valves, high flow water pump etc. Trany fixes and a new clutch. Can't wait to see how she feels! Looks like your on the right track. Thumper Racing did a great job of looking at everything and fixing things that were on the way out. Turned it around in 2 weeks. RFS is a tough motor as long as you keep the coolant in it!

 

[yooper01]

So I got started today. I am in the process of pulling the motor which I should be done with tonight.

I bought a small 50 watt stator from regulatorrectifier.com that I plan to float the ground on, and run to a capacitor. It will be all DC to make wiring easier for everything. I will be powering a 30 watt light bar, some heated grips, and a tail light. I think it will be about maxed out but it will all be switched so I will report back on my findings this winter.

I decided that I am not going to add electric start, but will be adding 5th and 6th gears to the transmission, and likely putting a rekluse zstart in the bike.

the previous owner did a crap job painting the left and right engine covers so I pulled those off and got them seriously clean.

I am going to try a rox 3.5" riser, I will be making a custom clutch line, and plan to use the motion pro 3" extended throttle cable.

Only 4 more months till snow!

 

[yooper01]

Success!

 

[yooper01]

So tonight I finished taking the frame down and disassembled the forks. I'm going to put .54 springs in with 10 weight oil and call it good.

Plan to strip the frame and repaint this week.

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[wwillf01]

View attachment 271568View attachment 271569

So tonight I finished taking the frame down and disassembled the forks. I'm going to put .54 springs in with 10 weight oil and call it good.

Plan to strip the frame and repaint this week.

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Depending on your weight I have found without valving I would go with stiffer springs even with the weight oil you using... Especially with the LT.... On my cr500 I am going with .58 with changing the valving... I would of went into the 60's without the valving.

 

[yooper01]

Depending on your weight I have found without valving I would go with stiffer springs even with the weight oil you using... Especially with the LT.... On my cr500 I am going with .58 with changing the valving... I would of went into the 60's without the valving.

Think the gold valve kit from race tech would have parts / instructions to get me close?

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[wwillf01]

To be honest I just am having the racetech shop in my town do it... I wanted to keep some of the plushness initially but use the valving to ramp up to not bottom out in the whoops or jumps... as is with the .54 I bottom out in a heart beat ...that's with crf450 2006 forks set up for motocross

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[yooper01]

One can of paint stripper later........



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[yooper01]

So after 2 cans of striper, some sand paper, denatured alcohol, and two coats of primer, the first coat or orange is looking nice!


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[Yooperwoods]

Looking good Chris! I can see why you couldn't do your wifes brakes now lol.

 

[yooper01]

Tonight I tore the forks the rest of the way down, replaced the seals and bushings, then installed .54 springs and a whole bunch of pre load shims. I used 10w fork oil and set it to 120mm.

I started putting the bike back together so I have something fun to look at while I decide how to proceed with my engine rebuild.

The steering is going to be tall. I installed an enduro engineering riser set that I had in the garage and added a 3.5" rox riser to that. I do have an extended throttle cable, and I plan on making a clutch cable to fit.





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