Build a bike

We carry the parts a custom build is made of — frames, complete engines, transmissions, primary drives and rolling chassis kits, not just service parts. This page is the front door to them, grouped the way a build actually happens.

Read this first — we group components, we do not certify combinations

Our fitment data tells you which production motorcycle a part was catalogued for. A custom build has no model and no year, so that data cannot tell you whether a given frame, engine and gearbox will go together. What decides that is interface dimensions — motor mount pattern, primary alignment, axle diameter, rotor bolt circle, master-cylinder bore ratio — and those are published by the part's own manufacturer, not by us.

So: confirm every interface against the manufacturer's own specification before you order. We would rather say that plainly than sell you a frame that will not take your motor. If you tell us what you are building we will happily check what we can — send us the build.

Rolling chassis & complete kits

45 parts · $2,882–$28,290

What decides the fit: The shortest road to a running bike. A chassis kit is sold as a matched set — frame, swingarm and usually tanks and fenders — so the hardest compatibility question has been answered by whoever assembled the kit. Check which engine family and transmission the kit is specified for before anything else.

Browse all 45 →

Frames

437 parts · $11–$10,708

What decides the fit: The frame decides the build. Its motor mounts are cut for ONE engine family — Knucklehead, Panhead, Shovelhead, Evo and Twin Cam all mount differently — and its transmission plate is cut for a particular gearbox. Neck rake and the width between the rails then set what front end and what rear tyre you can run.

Browse all 437 →

Transmissions

1,120 parts · $5–$4,124

What decides the fit: Big Twins carry the gearbox separately from the engine, joined by the primary. The gearbox must match the frame's trans plate and the engine's primary. 4-speed, 5-speed and 6-speed are not interchangeable without changing other things. The output shaft position is also what sets your rear wheel alignment.

Browse all 1,120 →

What a custom build actually asks of you

Kit or rolling chassis

Little or no fabrication

Frame, swingarm and bodywork arrive as a matched set. You still need real mechanical skill: primary alignment, wheel alignment, brake bleeding, wiring and tuning. This is assembly, not bolt-together.

Parts-bin custom

Welding and fabrication required

Mounts, brackets, tabs, fender struts and usually the exhaust get made rather than bought. This is the route that gives you your own design, and it is the one that needs a welder and somebody who can use it.

Ground-up frame

Frame jig, geometry, fabrication

At this point you are a frame builder. Rake, trail and wheelbase are yours to get right, and getting them wrong makes a bike that is unpleasant at best and unsafe at worst.

Titling is part of the build, not an afterthought

A motorcycle assembled from parts generally needs a state-assigned VIN and an inspection before it can be registered and ridden on the road. Requirements differ by state and they are not something to discover after the money is spent — check with your state motor vehicle department before you start buying.

The joints that decide whether a build works

  1. Frame ↔ engine. Motor mount pattern. Each engine family mounts differently, and aftermarket frames are sold specified for one of them.
  2. Engine ↔ transmission. The primary has to put the engine sprocket and the clutch basket in the same plane.
  3. Transmission ↔ rear wheel. The wheel centreline must line up with the gearbox output. A fat rear tyre is what forces an offset box or an offset drive.
  4. Rake, trail, fork length, tree offset. One problem with four numbers in it. This is what makes a bike steer.
  5. Brakes. Rotor to hub, caliper to bracket, and master cylinder bore against caliper piston area.
  6. Bars ↔ cables and lines. Bar height sets three cable lengths.
  7. Exhaust ↔ heads and frame. Flange and port spacing, then clearance.
  8. Oil system. Tank style follows the frame; feed and return must match the engine.

Putting a build together and not sure a part is right? Tell us what you are building. We will tell you what we know and, just as importantly, what we do not.