Building A Harley-Davidson FXR With A Milwaukee-Eight Engine

Adding modern ingenuity into the beloved FXR

modified FXR frame

Part 1: Fitting the drivetrain into the modified FXR frame

Jeff G. Holt

What began with two guys, a 1993 H-D FXRP with a blown motor, and a bottle of Tullamore Dew has turned into a bike build that has never been attempted before. Like most monumental bike builds, this one started with a large amount of hopes and dreams. Then we added a boatload of skill and ample amount of patience to the mix. The idea was drunkenly dreamed up by me and Danny Wilson, aka Motor Witch. The mating of a 2018 Harley-Davidson Milwaukee-Eight driveline into the venerable FXR chassis was the game plan. We originally wanted to find a crashed 2018 Road King and jack it for its drivetrain and wiring harness, but we decided to just ask the fine folks at Harley-Davidson to partner with us on the build and to supply us with the parts to make this bike a reality. And they did! Speaking of partners, Danny and I both knew we fall short in the metalworking department and that this bike was going to need a lot of it. That is why we called in fabricator extraordinaire Justin Coleman, from Torch Industries. We also rang up Big Chris, from FXR Division, who knows the ins and outs of the chassis and has done many funky and fresh FXR builds with all sorts of motors and transmissions. After a meeting over some hotter-than-hell Thai food, a deal was made, the team was formed, and we were all ready to get to work on the M8FXR.

The terms next level, groundbreaking, and game changer have been thrown around so many times in the realm of custom bikes that when a build such as this comes to be there are really no adjectives left with which to describe it. This is no Twin Cam swap where you just cut out a cross-member, jam the thing in the frame, and throw a carburetor on it. This was going to be fab work done by a team of guys who, combined, have more than 100 years of real-deal motorcycle-building and metalworking skills. We knew going into it that it wasn’t going to be easy because the motor is very different from the H-D Evolution that came in the bike. Plus, we wanted to use a stock 2018 H-D wiring harness with CAN bus electronics so the bike could take advantage of a big electronically controlled throttle body and accurately be performance tuned on the Dyno when completed. And so, we started the build with much wide-eyed optimism.

Knowing that we had no guidelines to go on and that the M-8 engine and transmission were going to be in and out of the FXR frame more than a few times, Danny disassembled the brand-new factory Harley-Davidson engine and removed rolling assembly and transmission guts to make it lighter and easier to move around. The empty engine and driveline were brought from Buddy Stubbs H-D in Cave Creek, Arizona, where the bike is being put together, to FXR Division in Phoenix. Justin, Chris, and Danny then got busy figuring out what needed to be done to get the M-8 to actually fit into the FXR frame. We all agreed that we wanted the M8FXR to look as if Harley-Davidson built this bike from the factory. Danny first placed the motor into the frame without the top end on it so Justin could better assess what needed to be done on the bottom frame rails. Once that was done, a set of Chopper Hauss front motor mounts “borrowed” from Ramjet Racing was drastically modified to work with both the frame rails and the Milwaukee-Eight bottom end. After many more measurements were made to both the frame and the engine, it was decided that the bottom of the frame’s backbone needed to be seriously sectioned so the Milwaukee-Eight’s “bubble head” top end and oiling system would properly fit.

Due to the increase in horsepower with the new motor, Justin also had to make a series of braces and gussets on both front and rear for the frame, as well as turn the original lower cross-member brace into a mount for an H-D Dyna jiffy stand. Once the frame was deemed straight, Justin finish-welded it to mimic the stock welds. Justin also smoothed the hydroformed backbone so it had the same look as it did from the factory. Once all torchwork was done, the frame was sent off to be chemically stripped of all the original factory paint. Though this feature makes it look like the job of getting the Milwaukee-Eight into the FXRP frame was rather easy, we can assure you that it took almost three months of trimming, cutting, welding, and metal-finishing the frame to make it look as if it rolled off the Harley-Davidson factory floor.

Once the frame was back to Buddy Stubbs H-D and in bare metal, Danny began a mock-up of the M-8 motor to a 2018 H-D six-speed touring transmission, H-D clutch, and H-D Bagger primary drive setup.

An aluminum swingarm from C and S Custom was also mated to the frame, which will be both stiffer and lighter than the stock FXR unit. With those items mounted, we will be ready to make the M8FXR a roller with help from Race Tech Suspension, The Speed Merchant, Jade Affiliated wheels, Beringer Brakes, and Continental Tires. Check it out in Part 2, which will be in the next issue of Hot Bike.

making room for milwaukee eight

Justin Coleman, of Torch Industries, took a large amount of material out of the backbone of the FXR to make room for the Milwaukee-Eight engine.

Jeff G. Holt

Justin and Danny Wilson

Justin and Danny “Motor Witch” Wilson installed the H-D M-8 motor into the bike for what seemed like the 50th time to get all the clearances and fabrication points correct.

Jeff G. Holt

FXR frame

The FXR frame was all cleaned up and stripped of its old paint, so you can better see what was really done to it.

Jeff G. Holt

downtubes and bracing tubes

The downtubes have two bracing tubes welded onto them, as well as modified Twin Cam motor mounts from Chopper Hauss.

Jeff G. Holt

custom jiffy stand mount

The engine cross-member has been replaced with a custom jiffy stand mount, while another brace was made at the rear of the frame, where the 2018 six-speed bagger transmission will reside.

Jeff G. Holt

Milwaukee-Eight engine installation

Danny installs the Milwaukee-Eight engine for final mock-up.

Jeff G. Holt

modified stock frame

These shots show just how heavily we modified the stock frame to fit the M-8 power plant into it.

Jeff G. Holt

aluminum swingarm

A C and S Custom 6061-T6 aluminum swingarm was employed both to increase stiffness and lose weight.

Jeff G. Holt

transmission and swingarm

With the transmission and swingarm installed, it shows just how tidy of a fabrication job was done to achieve this sort of look and function.

Jeff G. Holt

removable and permanent mounts

The right-side motor mount is removable, while the left-side mount was permanently welded to the frame.

Jeff G. Holt

2018 bagger primary setup

A 2018 bagger primary setup is being used due to the fact that this is a police-model FXR and we will be running floorboards, so no mid-control provision was needed.

Jeff G. Holt

M8FXR powertrain

The M8FXR powertrain has been mocked up and ready for the next step of suspension, wheels, tires, and brakes.

Jeff G. Holt