A Modern Day CR250 Two-Stroke Dreamt to Life

February 27, 2018 / by John Basher

Justin Steyn is a passionate motocrosser that is no stranger to building some beautiful machines. We got the inside look at his CR250AF 2-stroke, powered by Wiseco.

Look for the full print feature on this bike in the April 2018 issue of Motocross Action.

Just as with other major things in today’s world, there are circles of interest in the world of dirt bikes. There are diehard two-stroke loyalists, and then there are the new-age four-stroke aficionados. A line has been drawn in the sand. The gradual shift in popularity to four-strokes a decade ago has slowly been met by a growing lot of two-stroke advocates. While four-strokes still rule the roost in terms of sales and volume, two-strokes are making a resurgence.

As the popular saying goes, “You can’t have your cake and eat it (too).” Don’t tell that to motocross enthusiast Justin Steyn, who has managed to do the unthinkable. The South African has blended the lines by shoehorning a 2001 Honda CR250 two-stroke engine in a 2014 Honda CRF250 four-stroke chassis. All it took was a judicious use of money, help from a stranger, a fair amount of research, and naturally a little bit of luck. Meet Justin Steyn, the man who has proven that regardless of engine tastes, all motorcycles matter.

Justin's CR250AF has a laundry list of custom features and cool touches. Read on for all the details.

Where did you come up with the idea of fabricating a 2001 CR250 engine in a 2014 CRF250?

Steyn: The Honda CR-AF idea had popped into my head when my 2011 CRF250R was ready to be upgraded. I enjoyed the four-stroke, but craved the excitement of a two-stroke again. Believe it or not, the 2014 CRF250R was my third frame acquired during the build. I first started with a generation four frame. As time passed the opportunity to acquire a clean 2014 CRF250R came up, so I grabbed a complete bike and sold the 2014 CRF250R engine for three-quarters of what the bike cost! Building from just a frame up would have been too costly to source all the parts.

Building the bike piece-by-piece from the frame up would've been too costly, so Justin sold the motor out of his 2014 CRF250R, and began fabrication to fit the CR250 engine.

Bike tests suggest that the 2001 was one of the best performing CR250 two-stroke engines, as it was the last of the cylinder reed engines before Honda went to the case reed design with an RC power valve. Is that why you chose the 2001 Honda CR250 engine? 

Steyn: Exactly! How I acquired the engine is actually a pretty funny story. I called a guy with an ad about a CR250 engine. It turned out that he had the CR250 engine and was after a first generation frame. We got to chatting. Low and behold, we had both come across a 1998 CR250 that was for sale. We met up and paid 50/50 on the ’98. I got the engine and he got the rest. I was happy as long as the engine ran. By that stage I sourced a nice 2001 CR250 head and cylinder. I also purchased all of the Wiseco internals that I could.

Justin wanted a 2001 CR250 engine, because that was the last year of the cylinder reed design.

Did you have any complaints with the second generation aluminum Honda CR250 two-stroke chassis, which led you to putting the engine in a CRF250 chassis?

Steyn: I owned a second generation CR250 years ago and loved it. Having said that, the whole project was based on building something pretty trick, for the same price (or less) than a new CRF450R. I’m an absolute Honda nut and will not ride any other brand. I had to make my own CR250, since Honda discontinued them in 2007.

How much fabricating was needed to mate the CR250 engine in the four-stroke chassis?  

Steyn: The fabrication is not too complicated, although I outsourced the welding and fabrication to a local welder–David from Dreyer Corp. I did some online research and came up with a little information on the sixth generation ‘AF’ conversions, but I learned a lot from previous generation builds. Basically, the frame ‘Y’ piece needed to be swapped out to allow the head pipe to fit through the frame. The swingarm was spaced using OEM spacers on the CR250 engine, and a new headstay had to be welded in. Fitting the carburetor and airbox together was the trickiest bit. The exhaust mounts had to be modified, as well.

Frame fabrication included modifying the 'Y' section in the front to fit the expansion chamber, adding a head stay, and modifying mounts for the carb and exhaust.

Was it difficult finding a 2001 Honda CR250 engine? 

Steyn: Luck was on my side, because I was able to find someone who was willing to share a CR250 purchase with me. We don’t have limitless choices in South Africa when it comes to parts and donor bikes. I was just lucky to come across the 1998.

How much did the total build cost?

Steyn: I’m not one to record all the costs along the way on a build, in case my wife finds the figures! In all honesty, the total price came in just below the price of a new Honda CRF450R four-stroke. A big helping factor was the exchange rate. I had ordered most of the engine bits, exhaust pipe, carburetor, Intelajet, and other parts before our currency took a dive. That happened in a span of three years.

According to Justin, the total cost came to just below the price of a new CRF450R. Kind of makes you think twice about that new bike...

What area did you focus on most?

Steyn: The engine cost the most, because I really wanted to build a strong powerplant. I ordered all new Wiseco internals–crankshaft, piston rod, bearings and piston. I also invested in a new OEM head and cylinder, Keihin carburetor, Moto Tassinari VForce reeds, Intelajet, and a full Scalvini pipe. The head, cylinder and carburetor were sent to Dick’s Racing for mods. They taper bored the carburetor from 36mm to a 39mm, as well as installed the Quad Flow Torque Wing. Most of these mods were decided on after reading about them in Motocross Action magazine. The donor bike was a steal. It was a Honda Academy demo that a Honda salesman had dropped off a trailer. The bike had some road rash on the master cylinder, front brake lever, side panel and exhaust. It was minor damage, but it caused the bike to sit on the dealer floor for ages. The dealer eventually sold it to me at cost. After I sold the engine, the rest of the bike cost me about $1000. Despite the minor damage, the bike was a low hour machine. I could tell by the brake discs and rims that it was still like new.

The CR250AF got a strong engine package, including Wiseco piston, clutch, and crankshaft, V-Force reeds, Intelajet, and a complete Scalvini exhaust, among a long list of internal engine modifications.

How challenging was it to seal the space where the fuel pump was and install a fuel line with carburetor?

Steyn: The pump was easy to remove. I had an aluminum plate fabricated to fit. It bolt right on without issue. There’s an outlet pipe to which the fuel line attaches. Truthfully that part was rather simple.

How did you configure the old-style air boot?

Steyn: DC (Duane Coatzee) did the fitment. we used a CR500 air boot and coaxed it into place with the Keihin carb and OEM CRF250R air box. The reason we used a CR500 air boot is because sourcing the older CR250 air boot is not too easy. They have become scarce.

Did you opt for a high-compression piston or go overbore?

Steyn: We went with a high-compression Wiseco piston, at the stock bore, seeing as the head and cylinder were brand new. Dicks Racing increased the compression by cutting the cylinder head. They also did a port and polish, as well as the carburetor modifications. DC (Duane Coatzee) balanced the crank and piston. The bike also has a Vortex X10 ignition. I chose to go with a Wiseco piston, because of the quality of the brand. I haven’t had any prior hassles or issues with Wiseco pistons. It was also important for me to use all the parts from one manufacturer, and Wiseco had all the parts I wanted.

The CR250 head was cut by Dicks Racing to increase compression, and was paired up with a porting and polishing on the cylinder. A forged piston is the only type that should be trusted in performance-modified two-strokes such as this.

How much does your CR250AF weigh? 

Steyn: I have not weighed the bike, but I would say that it weighs a couple of pounds less than a CRF250R four-stroke. You can feel the difference as soon as you lift the bike off the stand.

What kind of horsepower and torque numbers were you able to reach?

Steyn: We have not dyno’d the bike as of yet, but those who have ridden it all comment in a similar manner. They say things like, “What a beast!” The bike has plenty of power. Some think there is too much power! Overall, the bike is a blast to ride.

Justin rides at fairly high elevation, so choosing the proper fuel is critical. This convenient 'Lean/Rich' Intelajet adjustment makes fine tuning the 2-stroke much easier.

What kind of fuel and premix are you running, and at what ratio?

Steyn: I had some issues with knocking on 95 octane pump gas, so I switched to Avgas. I’m running it at a 40:1 ratio. We’re pretty high up from the sea here–approximately 1800 meters–in Johannesburg.

Overall, did you accomplish everything you wanted with the build?

Steyn: Yes, the bike ticks all the boxes. The CR250AF has the looks and the go to match, even if I don’t! The last item that I would like to do is get some A-kit suspension. The eBay searches are saved, and I see second-hand kits come up often. Unfortunately, our exchange rate currently makes it a little too much of a sting for now. The crazy thing is I might just sell my prized CR250AF, as the 2018 Honda CRF250R looks to be a stunner.

Follow Justin Steyn on Instagram

Photos, engine build, bike assembly by Duane Coetzee


Topics: FEATURES, featured, Powersports, BIKE FEATURES

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Written by John Basher