A Half-century, Half-liter, Hot rod Horex
It was 1968. We were just on our way to the moon. The Beatles sang about going Back to the USSR. I was still in college. And had a wicked crush on a titian blonde coed. Meanwhile, an actual letter was slowly wending its way to me from then West Germany. It was from one Wolfgang Kayser -- and so began an 50 year odyssey.
That's because Herr Kayser had a serious motorcycle engine workshop halfway around the planet. And once I laboriously translated the technical German, I discovered he offered a raft of hot rod parts for a bike virtually unknown in the States. Then or now. Known variously as the Horex Imperator or the Zundapp Citation, it had a parallel vertical twin-cylinder engine with chain driven overhead cam.
I had one of these rare birds, a 1959 model. Good raw material for a café racer, I audaciously thought at the time. The Kayser speed parts would be icing on the coffee cake.
So I got out my handy German phrase book and basically answered, I will take one of everything, kind sir. I robbed some money earmarked for college expenses. And sent him a bunch of German marks. Plus, some of my old parts for modification.
What I got back in return a few months later was a treasure trove of clever engineering, beautiful machining, and careful design.
The crankshaft sported full circle flywheels and five main bearings instead of the standard three.
A little speed reduction unit on one end now allowed twin ignition points with a cable operated advance.
A brand new transmission gearset had much closer ratios. Gone was the original cast iron cylinder block. A new lightweight aluminum replacement with big bore, high dome pistons now yielded 500cc.
Numerous mods in the crankcase improved lubrication, especially the all-important camshaft oil delivery. Also lurking in the crate were a pair of hungry looking 32mm Dellorto carburetors. The cylinder head had been ported out to match them perfectly. The cam had much bigger lobes, more lift and more duration. My young head spun over all the goodies. What I now had was basically a pure racing engine. A real half liter horror for its track competition. Could I adapt it for the street?
A little speed reduction unit on one end now allowed twin ignition points with a cable operated advance.
A brand new transmission gearset had much closer ratios. Gone was the original cast iron cylinder block. A new lightweight aluminum replacement with big bore, high dome pistons now yielded 500cc.
Suitably inspired, I took a figurative -- but not literal -- axe to the rest of the machine and began jettisoning weighty unwanted parts. Heavy gauge steel fenders, battery box, standard mufflers and full rear chain enclosure got carefully put aside. (With a bike this rare nothing was scrap yard bound, of course.) I made a notebook of reminders, things to do and mods to be made.
I found a rare set of tele forks for the bike and had the tubes ground and hard chromed to mimic a Ceriani front end. I sent the frame out for stove enamel . (Powder coat was decades off in the future.) I adapted Girling shocks in the rear and a Honda CB750 front hub and disk brake, thanks to excellent work machining work by Barry Little of Specialty Automotive Engineering (now in Santa Ana, CA).
And then, as is often in life, stuff happened. There were jobs to do, girls to chase, money to make, trips and pictures to take. There was California, motorcycle magazines, the computer biz, the stock market, the internet, a house on a hill. Among another zillion distractions.
Years, years, and still more years more passed. There was always that thing called Tomorrow, right? The Kayser parts stayed box-bound, waiting patiently.
But then for a variety of reasons (spelled, getting old and sick), and a half century later, Tomorrow finally arrived. It was time. Build it now or take the parts to your grave. The engine goodies once again saw the light of day. The frame got pulled from its mothballed cocoon. Kayser's now yellowing assembly instructions (and their translation) were retrieved from a dusty ancient file folder. Not a thumb drive.
And, I got a lot of recent help for this interrupted 50-year trip down memory lane. Aaron Richard of Revive Custom Motorcycles (Coventry, RI) hand fabricated a beautiful aluminum gas tank that weighs half the original. Harry's Machined Parts (Westboro, MA) blue printed and clearanced the engine and adapted Harley Evo valve stem seals.
A special oil pan has a forward projection between the downtubes for an extra quart capacity. It came from German Horex genius Michael Stück. The high capacity dry clutch conversion? Same amazing source. Ammon Technik (www.horex-ammon.de) provided heavy duty clutch springs and numerous other parts. The seat base was fabbed by Pete Sykes, Vintage Sykles LLC, Worcester, PA. (www.vintagesykles.com).
The nice rolled naugahyde cover came from New England Trim (Shrewsbury, MA). And Stone's Motorcycle Company (Northborough, Mass.) handled a raft of fabrication and assembly.
Somehow over the years the top motor mount got lost. Not exactly a hardware store trip to replace it. In its place Stone adapted an industrial shaft collar. You'll see its brethren sprinkled around the chassis. Adel clamps and t-bolt clamps convert to good mounting tabs, as well.
What's the payoff? The old Kayser literature estimates horsepower of this half liter horror at something around 55. And thanks to all the aluminum parts, weight has shrunk from the original 432 pounds to 356.
And those open megaphone exhausts? Serious neighbor-unfriendly ear abuse. It all adds up to a 50 year old bike that acts like a rowdy muscular teenager.
Wish I could say the same for the owner!
--Sandy Roca
Spec Sheet
General
Owner- Jake
Shop- Stones Motorcycle Co.
Shop Phone- 1-508-393-6816
Year/Make/Model- 1959 Horex Imperator
Fabrication- Stone's MC
Build Time- 50 years
Engine- Horex / Wolfgang Kayser
Year/Type/Size. 1959 / parallel twin / 493cc
Builder- Kayser/ Harry's Machined Parts
Cases- Horex / Kayser mods
Cylinders- Kayser aluminum big bore
Heads- Horex / Kayser porting
Cam- Kayser high lift RSP
Carb- Pair, 32mm Dellorto SS1
Air Cleaner- Dellorto velocity stacks
Exhaust- Kayser megaphones
Transmission-
Year / type- 1968 / close ratio by Kayser
Gears- 4 speed
Clutch- Kayser / Ammon Technik
Primary Drive- Horex, gear
Frame
Year/Type- 1959 / dual cradle
Suspension
Front end- 34 mm Horex / Ammon Technik
Triple Trees- Horex, alloy
Swingarm- Horex / Silentbloc
Rear Shocks- Girling
Wheels, Tires, and Brakes
Front
Builder/Size- Stone's MC/ 18inch
Rim: Anodized, Akront
Rim: Anodized, Akront
Tire/Size- Pirelli 100/90 x 18 inch
Calipers- Honda CB750, SAE adapter
Rotors- Honda, drilled
Hub- Honda CB750
Rear
Builder/Size- Stone's MC / 18 inch /
Rim: Anodized, Akront
Rim: Anodized, Akront
Tire/Size- Pirelli 110/90 x18
Drum- Horex Imperator 150mm
Hub- Horex Imperator
Sprocket- 7075 Aluminum, Tabloc. ......................hard anodized
Finish/Paint
Manufacturer- Stove enamel
Colors- Grey metallic
Painter- Industrial Metal Finishing
Graphics- Stone’s MC
Plating- Hard chromed fork tubes
Polishing- Jim Papeia
Accessories
Front Fender- Wassell on Webco brace
Rear Fender- Wassel / Stone’s MC Co.
Gas Tank- Aaron Richards
Gauges Kayser 10k tach, CHT
Handlebars- Tomasselli clip ons
Grips- GT Grips, Low Brow Customs
Mirrors- Oberon
Hand Controls- Tomasselli
Foot Controls- Horex, Triumph rubbers
Pegs- Denfeld
Headlight- Steadfast Cycles
Taillight Lucas Cats eye, blue dot
Turn Signals- Anemic arm
License Mount- Lucas repop
Seat- Pete at VintageSykles.com
Special features
Weight: 356 pounds
Extra capacity oil pan by Michael Stück
HD Evo valve seal conversion by Harry's Machined Parts
Anti Gravity lithium 12V battery
Safety features: Fresno bell, 4 tone bulb horn
Earls braided stainless oil and gas lines
Yamaha G16 golf cart starter/generator
Seat cover by NewEngland Trim.com
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