WR Chrome Moly Frame

Lighter than steel.  Extra support bars on rear section.  Extra holes in the neck casting.  These frames broke kinda easy I've been told . . . not many left intact anymore. 

Real Expensive.

I guess the "black colored" front hubs are probably aluminum too, just painted black?  Harley-Davidson Racing had a rear drum kinda like this too?  However,  I think the rear drum on Leo Payne's Bonneville Race bike is this front drum, adapted for a rear drive sprocket?  Correct me if I'm wrong. (Look how teeny tiny that sprocket is ! )
"What do you run for a front sprocket?"  Answer: " A 21 Tooth"
"What do you run for a rear sprocket?"  Answer: A 21 Tooth"

They'll Pay . . . on Ebay

Veteran, experienced racers don't like to pay much for racing parts.  They'll make due with a chipped gear, 'cause the parts will eventually get all blown to bits, wrecked, destroyed and thoroughly abused.  Pistons with small scuffs get sanded and reused.  Small cracks get JB Weld.  Cams with welded up lobes, frames with extra gussets, funky brackets, duct tape, wire, welded nuts.  Real racing motorcycles have all-of-the-above.  Buckets and boxes of wrecked, unusable parts serve as filing cabinets, only to be gone through and inspected, fixed, rigged, and reused again.  In a pinch.  Anything to get back on the track.  To compete no matter what it takes to get points.  New, original builds always look so perfect, but after extended track time, the end of the season - all the racing motorcycles start to look the same.  More cracked fiberglass.  Skid marked.  Chips in the paint.  Pop Rivets.  More duct tape.  More beads of weld.

I love old racing parts and how they work (over a stock part) in a engine rebuild.  NOS parts are the supreme find.  When I see the vintage parts and accessories I've read about my entire life (in person) and hold these parts in my hand - it's like . . . wow !  XLR aluminum fork caps !  Iron XR pipes (new - in-the-box) !

These parts(new and used) show up on Ebay at insanely high prices - only to be purchased by the rich collector - and never (I suspect) by a real racer or current competitor. 
$900.00 for these PB cams ? 
$ 1,900.00 for these C-Grind KR cams ? 
$350.00 + for this KR head ?  That is cracked.
I can't afford this stuff.  I suspect all were purchased to go on a museum bike? or to hang on the wall of a collection?  The real racers know how to modify their engines, and they don't really need these parts.  They've got the know-how.  The $75.00 P cams work better anyway . . . Leineweber or Enfield has $500.00 lobes to cut your old cams, and degree and weld (J- Grind better than C anyway) With a modern flow bench, and some fixtures, modify your $100.00 K head to out flow the KR head.  The rich guy takes the bolt-ons . . . the poor man takes the scrubs and makes his due.  Knowledge is power . . . is money still in your pockets . . . for gas - or Sambos !

The WR is different . . .

These motors are much different from the 45" engines in army bikes and servi-cars.  Not many parts will interchange.  The WR was built for low-drag (meaning low resistance) and less friction for increased power.  If you can't get the power from cubic inches, look elsewhere. 
This cover blocks off the original timer(or magneto) position.  Some racers install a specially manufactured tach-drive here - for a gear driven, cable driven rev counter.
The Wico single fire magneto runs a rotor (just like your car) and fires each cylinder separately.  It's mounted horizontally to reduce drag between gears.  Whenever you have a bevel gear(vertical) driving a bevel gear(horizontal) you have increased friction, and drag (robbing power). 
The MR-3 is a short-barrel Linkert racing version.  It has no choke.  The choke would block the way for air, restricting flow.  It utilizes an adjustable high-speed main jet circuit with a needle.  The slotted set screws in the carburetor body(inside the float bowl) are removed to facilitate higher fuel flow. 
These carburetors run best at wide open throttle.  It's common for the engine to run a bit rough, babble and snort . . . until it cleans out - then it's HOLD ON !
The bombsite is designed to assist in mixing and directing fuel and air vapor.  Oxygen and flammable liquid to create the largest, controlled explosion possible.  Cylinder fins are larger for improved and consistent cooling - for long races on hot summer nights !
The tiny engine sprocket keeps the rpms in the power band, gets your ass pullin' out of corners . . . and gets you up and over the steep hills.  In 1952 when the H-D factory came out with the more powerful KR racer . . . the WRs still took fast times, and feature wins.  It took a few years for the WR to lose it's competitive status.  To hear a WR wound out tight is music to my ears.  Nothing is sweeter.  Classic side valve performance never goes out-of-style. 

Ice Wars - North Iowa

35F and wind made the track nice & loose. 
Above: Crooks pulls a pass on the rear wheel as Burton charges....
Above: Jeff Hawbaker takes a "loaner for a couple laps . . .