2008 Honda CR500

Wow! Thanks for all the "thumbs up" guys - I really appreciate it.

I'll try to answer some of the questions posted.

Vibration - Yes big bore two strokes can vibrate pretty good. To minimize that, I sent the crankshaft, rod and piston
assembly to Crankworks to get balanced as a unit. This brought the vibration down to the same level as my CR250s.

Handling - The handling is amazing! The CRF 250R frame has a fairly steep steering angle to start with. Now add the
the CR500 engine with the bulk of it's weight concentrated further forward and lower than the CRF 250 engine and the
result is a nice stable, precise package that will carve under a lot of bikes just by thinking about it. It also doesn't hurt
to have more than 60 hp on tap to encourage rear wheel steering.

Powerband - The port and head work that Eric Gorr did on this bike was designed to up the power a little, but more
importantly, to smooth the hit. I added the CR250 ignition and Vortex ignition controller to lessen the flywheel effect
(due to the smaller, lighter rotor), and allow me to program the advance curve which also changes the way the power
is delivered. As a result, the power band is "healthy" but relatively smooth. It's still a big bore two stroke, but the power
delivery doesn't beat you up and spit you out like the early CR500s.

Packaging - I guess what I like about this hybrid the most, is the size. When you sit on the bike, you have no idea
you are sitting on anything other than a CRF 250 until you go to kick it over. The four stroke tiddler chassis gives
this bike a compact, buttoned down feeling. For all the steel framed 500 veterans, this would be the most noticeable
difference and improvement.

I'm so stoked about the way it turned out, I've already started on a matching CR250 using a 2000 CR250 engine
and a 2010-12 CRF250R frame. If anyone is interested I'll post updates on that build as it progresses.

dogger

Thanks a bunch!

The 500 is still going strong. I did a couple of rebuilds on the engine. Last time I replaced the steel sleeve with an
Aluminum one. That eliminates the cold seizure problems and I can run tighter tolerances on the piston and rings.
I also installed a compression release to help save my Right side case cover from cracking. Pro Circuit rebuilt the
suspension and added all the latest internals. I installed a longer swingarm from a CRF450R to lengthen the wheel
base a bit and help me keep the front end on the ground more often. The bike liked to stall at the worst time (face
of a jump, etc.), so I poked around and found the carb vents were being flattened by the swingarm. I re-routed the
vent lines to a carb vent cannister located between the head stays. New plastic and graphics every year along with
anything else that's worn. Still a great ride.

I'm still working on the CR250. Since the original post in 2012, I decided to abandon the 2010-12 CRF frame idea
for a 2009. Honda never got the geometry right on the gen 5 frames (or anything newer), so I stuck with the great
handling gen 4. The bike has taken a long time for several reasons. First, I'm swamped with other projects and
personal projects always take a back seat. Second, There is virtually no information floating around on a gen 4
CR250 conversion, so everything I do is new. This leads to a lot of "one step forward, two steps back". Finally,
the frame conversion was very difficult because I wanted to use the OE alloy tubing for the replacement cradle,
and I wanted to use the OE "Y" instead of an aftermarket billet piece - all to keep as much of the original frame
dynamics as possible.

With that said, the bike is nearly done. I've been posting updates on another forum here, but here are some pictures
of the highlights so far:


Finished 2000 engine. Crankworks balanced crank, HRC single ring piston, TMR cylinder and head work, REM bottom end,
Hinson clutch, HRC stator, Vortex X10 IC, VForce 3, and a Dick's racing PWK (not in the picture)


Pro Circuit "works" SFF Air


DID Dirstar LTX rims, Excel spline drives and TCR hubs


Converted airbox. 2005 CRF250R airbox, 1997 CR250 intake hose, 2002 Twin Air Power flow ring, billet Aluminum face plate




Dick's racing carburetor. taper bore 36-39mm, Intelajet, air straightener




Finished frame with hybrid 2005 CR250 cradle


Roller


Latest picture

I'm hoping to wrap this up soon. I'll post pictures when finished.

dogger

Thanks!

It is pretty sad, Falcon. But if you think about it, it's been 20 years since the AMA dumped the 500 class.
A whole generation of racers have grown up never seeing the spectacle.

Joko, AJ Wagner did the sweet job on my CR500 frame, but I do my own frames now. Here is a series of pictures
detailing the evolution from stock '09 CRF250R frame to what I have now:


New (takeoff) 2009 CRF250R frame


Cradle removed, dummy engine installed revealing all the problems with the fit.


After many hours with an angle grinder and a flap wheel


OE "Y". I have over 20 hours of work with a vertical mill to get to this point


Same process to clean out the lower cradle pockets, except this time I had to do it free hand


Test fitting new cradle rails. These rails are made of the same alloy and wall thickness as the originals. The bend is patterned
after the 2002-07 CR250 cradle. This opens up the engine area enough to allow the engine to rotate down into the correct
position to maintain the same CS sprocket to swingarm pivot bolt angle and distance as the CRF engine. I lost one inch of
ground clearance, now it's the same as a 2002-07 CR250.


Clearance with engine installed




I TIG welded the new cradle and "Y" into place


Engine mounts mocked up


Engine mounts welded in. Frame finished

As you can see from the pictures, this conversion is a PITB, easily the most difficult of any. The CR250 engine is shorter and
wider than the CR500 engine. This causes all kinds of havoc with the clearance between the pivot bolt and the lower frame
cast sections and cradle as shown in the first picture with the dummy engine.

Most that have done these either cut a divot out of the bottom rail or tilt the engine up for clearance. Neither is what you would
see from Honda, so I did it the hard way. What all this work gets me is the best handling CRF250 frame with as much of the
original chassis dynamics (flex vs stiffness), as possible, powered by the best CR250 engine Honda ever produced - all in my
opinion of course.

Once this bike is done and sorted out, i plan to hand it over to some "talent" that can still wring 100% out of a stout 250 two
stroke to see if I'm right about this combination.

dogger

Thanks for the very kind words, CR250Rider. By the way, very cool avatar.

I'm sure it's pretty obvious, these bikes aren't low cost. I built a 1993 CR250 from scratch using all new parts, a few
years ago. The total cost was staggering when compared to the cost to buy that same bike new.

I do build "budget" versions of these bikes for others that just want an up-to-date frame with a 250 or 500 two stroke
engine. Those can be pretty inexpensive if I'm using used parts.

The conversions I do for myself are built with all new parts and quite a few expensive aftermarket goodies as well.
These are NOT budget bikes - just the opposite, they are pretty much cost no object to the extent my income can
support.

As far as an investment, I'm not sure they can be looked at that way. I consider bikes like my 1973 CR250M and
1979 CR250R good investments because I have already been offered considerably more money for both than
what I have tied up in them. I look at these two conversions more as "protest" bikes. This is me telling Honda
this is what I'd rather ride/race than the new junk you're selling. I'm also sure Honda couldn't care less.

While it can be a real challenge, it's also a lot of fun building these conversions. I especially like being able to pick
all the best parts from various years to try and come up with the ultimate combination. It's also pretty cool knowing
you won't see another bike like yours when you pull into the pits.

Joko, Service replaces a good portion of the OE cradle with a solid billet piece. It starts just below the radiators and
extends to just forward of the foot pegs. The billet piece has the new engine mounts machined in place. They also
provided the necessary radiator mods, special PC pipe and silencer, airbox mods, one piece billet head stay and
some other pieces. Unfortunately, business is so good that AJ doesn't have time to do just frame mods anymore.

dogger