The “W” series 45 cubic inch Harley Flathead motor has been around since 1937. It was very reliable but slow as molasses in January. Decades ago, the legendary Randy Smith came up with the idea of mating the top end of a 900cc Ironhead Sportster to the bullet proof Flatty's lower end. The result THE 45 MAGNUM.
Fresh after their six world speed records at the Maxton Mile with their 45 WLA powered Flat Out Flatty, builders Steve “Brew Dude” Garn and his son Chad were up for another challenge. They would attempt to do what Randy Smith had accomplished over a generation previous and recreate the 45 MAGNUM and race it to glory.
It may sound like an easy task. Just swap out the top end from an old sporty and bolt it up to the 45's lower end. Nothing could be further from the truth. Ask Bandit and Lee Clemens from Departure Bike Works In Richmond, as they attempt a K-Model top end to their Bonneville Belle 45 flathead lower end.
The engine building skills required to perform this transition are tremendous.
First off the 1958 H-D 45 cases had to be welded to allow opening for the larger 900cc cylinders. The cylinder base boltholes had to be plugged and welded and the holes relocated for case studs. The Sportster cylinder bases had to be turned down for removal of base and head holes drilled through for 10mm Chromoly case studs.
The Sportsters heads were then machined for dual plugs and the intake area was machined away and new intakes brazed in, then ported to allow for Dual Amal Monobloc carbs. Heavily modified early Ironhead Sportster flywheels balanced and trued by Doug Hicks at Doug's Custom Cycles in Georgia were then installed and the Ironhead's rocker boxes were split to allow access for a new dual-plug set-up in the heads. The old Ironhead rods also needed modification to work, as well as a heavily modified H-D P cams.
I could go on for days about the motor build, but you get the notion. This was no easy task.
For a lightweight, reliable transmission, Steve chose a 1950s BSA, A10 pre-unit 4-speed with a stock kicker arm and a Hippy Killer pedal. The stock BSA case was loaded with STD gears and a BSA A10 clutch unit. The Magnum's primary drive is a RK428 GBMXZ 5800lb tensile Big Twin Motor chain linking to the BSA rear sprocket.
Steve and Chad made the frame in house to assure the strength and quality. It's made up of 4130 steel tubing with a neck raked to 32-degrees and stretched 3-inches. The rear seat suspension is a BREW Prototype 1-1/2-inch travel Elastomer shock with custom Fab Kevin stainless steel seat hinge and the seat is by Duane Ballard Custom Leather.
The front forks are Betor Bultaco, from the early ‘70s with the lower legs turned to remove the fender-brake tabs, eliminating unnecessary weight. The triple trees are classic Ceriani.
The front wheel is a 19-inch Akront shoulder rim from the early ‘70s, laced to a custom flat track hub with Buchanan SS Spokes, while the rear is a 1981 Honda CR450 hub, Excell 17-inch alloy rim custom drilled by Buchanan with Buchanan SS spokes.
The Magnum's gas tank is an old 1977 Husqvarna alloy unit and the oil tank is a Sucker Punch Sally H-Bomb. The bikes 7/8ths titanium handlebars
Hold the ASV MX brake lever and the dual cable throttle. Cycle Electric Generator supplies the bikes electrics with built in regulator.
The bike’s Glitter Blue paint, graphics, black chrome, frame powder coating and the polishing, as well as the taillight, rear fender and foot controls were all made in house by Steve and his son Chad.
The total time for the entire delicate bike-build was 650 hours including 320 hours poured into the engine alone. Finally complete, the Magnum weighs in at an astonishing 311 pounds wet.
Why name it the TIME BOMB? Randy Smith, in his notes on his original build, was quoted as saying that with so much detailed and intricate welding, drilling and precise fitting, to mate up the top and bottom, from two distinctly different motors, one mistake and the motor was sure to explode.
Steve and Chad took this as a challenge, and so far it's held up to their expectations without so much as a hiccup.
We expect to hear a lot more in the future from father and son team Steve and Chad Garn. You can read more about their build on their web site: http://www.brewracingframes.com and on Bikernet.
–TB
