As expert level off-road racers and longtime KTM loyalists, the techies here at Dirt Tricks have become disenchanted with the new generation engines. We love the 08 and newer KTM handling. They are the best that money can buy. We love the power delivery and reliability of the older RFS motors. So the best of both worlds was to marry the two - an RFS motor in a new frame!

In our opinion, these are the serious issues with the XC4 and RC4 engines:

We have found that the new engine top ends (pistons) cannot go much beyond 150 hours for avid riders, and when used for off-road racing only can be as little as 50 hours.
Significant oil consumption is common starting at 50 hours. We regularly see 200cc of use with each tank of fuel. That represents 1/5 of the oil capacity.
These engines have significantly less low end power than the RFS engines. This requires running them "on the pipe" at higher revs and more shifting. This undoubtedly contributes to the reduced top end life.
KTM seems to be incapable of correcting an engineering flaw in something as simple as a timing chain tensioner. Bikes out of the box frequently rattle at idle. We at Dirt Tricks are astounded that the problem has persisted now through four model years. We appreciate the business the problem has created with the introduction of the Dirt Tricks Tensioner which easily and permanently solves the problem.

In our opinion, these are the great handling features of the 08 and newer KTMs:

KTM got it right with these bikes when it comes to overall handling on the 08 and newer off-road bikes.
These are the best cornering machines that KTM has ever made. They will carve a berm with any Jap machine.
The straight line stability is unbeatable.
The smoothness over rocks is better than any other machine out of the box.
The suspension is competitive at the pro levels right out of the box. We have raced with pros who fly in from across the country to ride a brand new machine - off the showroom and they are on the podium ( Jordan Brandt. Sept 08)
In our opinion, all of these great handling bonuses are why KTMs are now dominating the off-road race scene. But the resurgence of the two-stroke 250 and 300 market is a result of the unreliable four-stroke platform. Racers are disenchanted with the four-stroke reliability issues, but love the KTM handling. That creates a real dilemma when pondering a $9000 investment.

These are the key points we feel make the RFS motors so good:

Top of the list - They run a long time and die slowly and predictably! Our project bike had 1500 hours of racing and hard riding without ever having split the cases. In five years and all those hours, it had only seen two pistons (changed out of guilt) and one valve job. (finishing 60 out of 60 races).
It's a "one gear" machine. From zero to forty, these engines have enough "grunt" to use only third gear (with 14/48 gearing). That means faster corner to corner speeds with little shifting.
These engines make their power from 3000-7000 RPM. The dynamic loads on engine components spinning at 9000 RPM verses 6000 RPM are 2.2 times greater. That's why low RPM engines stay together (airplanes, diesels, generators), aside from making fewer trips up and down. Check out the expected piston life of a 250F super-crosser that spins at 14,000 RPM. I think they're measured in minutes.

Getting the Job Done:

(See pictures below of two separate conversions.)

Parts needed:

"Wishbone" tubular frame section in the exhaust area.
Center bottom engine mounts.
Carburetor to boot adapter. The carburetor assembled to the RFS motor is 19mm to short to reach the newer air filter boot.

Machining required:

On the 03 and older engine, the rear engine mount/swing-arm pivot must be drilled and reamed from 15mm to 17mm to accept the new larger swing-arm pivot bolt. This is tricky to do by hand. The hole must be straight with no elongation and on the exact same center as the original. The 04 and newer RFS engines already have a 17mm pivot hole and do not require modification.
If you are using an SX or XC frame, the swing arm must be machined narrower at the pivot to match the XCRW/EXC swing arm. This requires machining the inner faces (which contact the engine) back by 9mm and machining the inside seal counter bores. This is tricky machining and requires constructing a special reverse counter bore cutting tool. After machining, the XCRW/EXC narrower bearing/seal kit is installed.

(Contact Dirt Tricks if you require any of this machining .)

Fabrication/welding tasks:

Remove the center bottom original engine mounts. A Sawzall followed with a disk sander works well for all of the described removal operations. Use a two-speed saw at the slow setting and a bi-metal fine blade.
Remove the OE "wishbone" section using a cutting template provided by Dirt Tricks.
Cut off and save the exhaust pipe bracket near the kick starter.
On SX and XC frames, grind the underside of the heavy mounting lugs on the backbone underside (near the carburetor) that attaches the frame-to-head brace. The brace will not be used, but the carburetor comes very close to the frame lugs.
Mount the engine at the front and rear with the swing arm in place using the 17mm swing arm bolt.
Bolt in the new center engine mounts and tack weld firmly to the frame. All tack welds need to be adequate to allow engine removal without disturbing the component positions.
Locate and tack weld the new machined wishbone frame section making sure that the exhaust header and mounting springs have clearance.
Using the exhaust pipe/silencer as a guide, locate and tack weld the previously removed exhaust bracket near the kick starter. Confirm clearance around the shock spring. On our prototype we used an FMF Ti exhaust system and we removed about 16mm from the entrance end of the silencer section (shortened) to get a nice fit. This is near the kick starter.
Remove the engine and strip the frame, and finish all TIG welds using AWS ER70S-2 rod.
Post heat with acetylene all weld areas at 800 degrees F using a "temp stick" to confirm temperature. This tempers the welded areas that become brittle from the quick cooling that occurs during welding. Alternately, the entire stripped and sandblasted frame can be oven heated at 800 degrees F for one hour.
Finish paint or powder the frame.

Notes:

Without modifications, only the SX tank will fit the Hybrid. We have found that by carefully using a heat gun and reshaping a small area near the water pump, the EXC/XC tanks can be used. See the tank picture below.
Tools/skills needed: Sawzall, wire feed welder and/or TIG welder, acetylene torch for post heat.
Time required: Cutting, fitting and re-welding the frame will require 6-10 hours. Most of that time will be spent assembling and disassembling components to check fitment. Tearing down a a running bike to a bare frame can be done in two hours. Reassembling the finished machine will take 3-6 hours.

How Dirt Tricks can help you:

Option One - You do the work with our help and parts: If you have the welding skills, we can provide you with all of the machined parts and the instructions necessary to do the job: (a) CNC machined tubular wishbone replacement section with cutting template - $180 , (b) CNC machined center engine mount set - $60, (c) RFS carburetor to new boot adapter - $75, Total - $315 (available after 1-25-10)

Option Two - We perform the fabrication, you do the rest. Send us your bare frame, and we will use our engine fixture to reassemble, TIG weld, and stress relieve your frame. The following three areas are modified: a) front "wishbone" header area, b) bottom center engine mounts, c) exhaust bracket. The cost is $475 (Add $185 if SX/XC swing arm requires modification). Lead time: 3 business days in house.

Option Three - We do the fabrication, powder coating, and engine/swing arm mounting: Send us your bare frame, a swing arm, and an RFS engine, and we will do all the work described above including powder coating the frame (orange or black). The engine will be mounted to the frame and swing arm. The cost is $875 (Add $185 if SX/XC swing arm requires modification). Lead time: 5 business days in house.

Option Four - We do everything: Ship us a rolling 08 or newer 450, 505, 530 SX, XC or EXC (less engine) and a running RFS 400, 450 or 525 engine. We will send you back a complete ready to race or ride Hybrid with custom graphics. The cost FOB Minden, Nevada is $1890. Lead time: 10 business days in house.

Machining Services: Modify SX/XC swing arm - $95 ($185 with new bearings and seals installed.) Machine 03 and older engine rear mount from 15mm to 17mm - $60.

Shop Services: Reshape the 08 and newer 2.4 gallon (9.1L) tank to clear the RFS motor - $40

Dirt Tricks
2559 Precision Drive Unit 4
Minden, NV 89423

Phone: (775) 267-6361
Fax: (775) 267-2585

Questions: sales@dirttricks.com

Production Unit #2:

525 RFS in a 2008 XC frame.

This project bike is also one of our own. Our goal was to keep all of the stock 08 XC radiators and plastic and do as few frame modifications as necessary. In order to make the frame change near the header and still keep the stocks radiator location, we needed to reshape our prototype "wishbone". In re-designing this frame section, we again used a CNC machined "half-tube" profile, which is then TIG-welded together. The wall thickness actually varies so that the heavier wall is in the area of greatest bending maximizing the section modulus.

What did we start with?

An 04 525 EXC with a motor that had been recently and completely gone through.
An 08 450 XC with a blown motor. Paid $2500. (Thanks Chip at Munn racing.)

Engine.

All stock 04 EXC

Frame/Engine Modifications.

On the engine: None. Stock.
Cut and removed the wishbone frame section in the header area. TIG weld CNC machined tapered tubular section.
Cut and remove the bottom-mid engine mount. TIG weld in place with CNC machined new mount.
Cut and move one of the CDI standoffs.
The SX and XC have a mount above the carburetor that attaches a brace from the backbone to the head. That is not used on the enduro bikes. It gets very close and touches the RFS carburetor, so we grind off the portion that interferes. It appears as though part of it could be cleared and one could fashion a frame to engine brace for additional frame rigidity. We did not.
Replace plastic carburetor throat with machined unit to connect to smaller 08 SX boot. It appears as though the XC and XCRW 08 and newer boot will fit the RFS carburetor, but we are confirming that the length is correct.
Cut and re-position pipe hanger near the kick start.
Sand blast and powder coat modified frame.
Transfer all of the 03 wiring, CDI, battery. It all fits right in.

Project pictures:

Wishbone frame half machined from Chrome-moly heat treated stock.
Replacement wishbone frame section installed.
New bottom engine mounts welded in position.
Finished powder-coated frame: A blue KTM? You can be the judge when the graphics are complete. Dirt Tricks Nate and his pimped-out KTM.
Engine and stock XC radiators mounted. We even have a way of using the way-clean, in-frame 08 coolant plumbing.

Carburetor to boot adapter. This has to be 3/4" (19mm) longer than the stock plastic unit in order for the filter boot and carburetor to mate.
The 08 and newer EXC/XC tank needs to be reshaped in one small area where it interferes with the RFS water pump. We used a heat gun and some welding clamps and carefully heated up the plastic, reshaping it then cooling it with a water spray bottle. This inner surface needs to move about 12mm in the area shown.
Finished Bike

The Prototype Project:

December, 2009

What did we start with?

An 03 525 EXC with 1500 hours of very hard riding and racing. Probably worth $2200
An 08 450 SX without motor. Paid $1600. (Thanks Chip at Munn racing.)

Engine Modifications.

Complete rebuild by Travis at Thumper Racing: bottom end, rod kit, 540 barrel, 12.5:1 piston, valve job, SX cam. ($2000)

Frame/Engine Modifications.

On the engine: (1) The rear swing arm pivot needs to be drilled and reamed from 15mm to 17mm. (2) The front engine mount (under the header) needs 1.5mm of material milled from each side. This makes the old engine the same width as the new on the front. This operation could be avoided if you cut and spread the front engine mount.
Cut and remove the wishbone frame section in the header area. TIG weld CNC machined tapered tubular section.
Cut and remove the bottom-mid engine mount. TIG weld in place with CNC machined new mount.
Cut and move one of the CDI standoffs.
The SX and XC have a mount above the carburetor that attaches a brace from the backbone to the head. That is not used on the enduro bikes. It gets very close and touches the RFS carburetor, so we cut off. It appears as though part of it could be cleared and one could fashion a frame to engine brace for additional frame rigidity. We did not.
Replace plastic carburetor throat with machined unit to connect to smaller 08 SX boot. It appears as though the XC and EXC 08 and newer boot fit the RFS carburetor, but we are confirming that the length is correct.
Cut and re-position pipe hanger near the kick start.
Sand blast and powder coat modified frame.
Transfer all of the 03 wiring, CDI, battery. It all fits right in.
Build small brackets to attach the radiator plastic if using the RFS radiators. (Our latest project bike uses the original SX radiators and inside frame plumbing and does not require radiator mount changes.)

Issues:

So far, the only component interchangeability issue has been in fitting various fuel tanks. The 08 2.4 gallon EXC tank touches the water pump. The stock SX tank fits with plenty of room. We have successfully modified the 2.4 gallon tank using a heat gun to reshape the small interference area near the water pump. Not more than a few ounces are lost.
Swing-arms: The newer SX RC4 machines have a narrower rear swing-arm/engine mount. We used an 08 EXC swing arm with no issues. If you use the SX or XC swing-arm, it will need to be machined to fit the RFS motor and have the narrower pivot bearings installed.

Summary (as of 12-30-09).

The power is off the charts for low end. Top end is as fast as any four-stroke going. We are at 5000' and usually a 15% power deprivation compared to sea level, and the front end comes up (smoothly) through forth gear on pavement.
Handling: We can only play on the paved parking lot this week because of snow, but we fully expect the great cornering and handling like the stock 08. The engine weight and C.G. is indistinguishable from the 08 motor.
We are driving to dirt this weekend to break in the engine and compare three machines: the Hybrid, an 04 525 EXC, and an 080 530 EXC. We should have some good reporting on Monday the 4th.
Our plan is complete some solid testing using two local desert pro racers. We will then produce the conversion parts in production to be sold as a kit for those able to do the fabrication. We also plan to do the conversion for you provided an engine and a bare frame.

After Ride Review (1-4-10).

Power Delivery: This bike is very comparable to the 505 KTM. One of our test riders came off of a 505. In his words, "This is a 505 on steroids." We rode wet sand hillsides and sand washes for three hours. Even on the tightest turns, lugging down in third gear with a little clutch just decimated berms (and the poor soul following.). The engine is about on par with the 505 on top end. It still has the EXC CDI. I'm told the SX ignition will wake it up on top. These are the engine modifications from a stock 03 525 EXC: 540 kit, high compression piston, SX cam, FMF power-bomb Ti exhaust. Like RFS 525 engines, the bike likes to be short-shifted. If you are not over the bars through fourth gear, the front end will ease itself up. Keep in mind, we are at a 15% power deficit riding and racing at 6000' (1850m) above sea level. This machine would be a real handful anywhere near sea level.
Handling: Right now with the SX suspension, things are on the stiff side which was great in the whoops but harsh in the rocks. We will be softening it up a bit. The engine swap has had no impact at all on the cornering. These 08 an newer frames are the best cornering of any KTM and that's what makes this machine so sweet.
Summary: We have the great handling we wanted. We have the best power that can be bought without being scary, and we have an engine that will stay running for years. We are satisfied to the extent that we know the frame and engine are solid. So we are tearing it back down to clean, sandblast and powder coat the frame. So in a week we'll have some new pictures of this bike decked out. Stay posted.