Written by Greg Davis

3-Piece Cranks Explained

When I first started racing BMX, way back when mullets were the rage, I desperately wanted 3-piece cranks. Everyone knew they were the best, because we all kept bending our 1-piece cranks. My trusty paper route, however, didn’t bring in enough dough to buy even a used set. Back then, there were few used sets on the market. For us poor, wannabe BMX racers, if you had a set of 3-piece on your bike, you had finally become a serious BMX racer. Fast forward over twenty years and 3-piece cranks are still one of the coolest and strongest bike parts out there, but putting them on your bike nowadays is so much easier. Most racing frames now come with “Euro” bottom brackets—no more smashing your thumbs, trying to pound your bearing cups into your frame. Euros are threaded! If you have a euro bottom bracket on your frame, you can’t even fit 1-piece cranks, anyway. 3-piece cranks are your only option. Euros use four smaller sets of sealed bearings rather than the larger non-threaded old-style that has only two larger sets of bearings.

Step-By-Step:

1. This seems fairly obvious, but loosen your back wheel, slide your wheel forward, and pop your chain off the sprocket, and remove your old cranks.

2. With Profile-style 3-piece, spacing is critical. You need to have the right spacer inside the bottom bracket, or the cranks will either be too loose or too tight to spin correctly. If they are too loose, you’ll likely damage your bearings. If they are too tight, you’ll likely damage your finishes in the race—as well as your bearings. Profiles generally come with a couple of different spacers, since many frames are slightly different in size. So in order to gauge the spacer correctly, assemble the cranks, spacer (the one that looks the correct size), and spindle while it’s off the bike. Now flip your bike upside down and hold the assembly up against the bottom bracket housing on your bike. See if it looks like a good fit before you assemble it all inside.

3. Begin by screwing in the bearing housing that will be on the left side (non-sprocket side) of the cranks. Dab a bit of grease on the double bearings inside the bottom bracket and slide the spindle into the housing, before sliding the spacer onto the spindle, and screwing in the freshly-greased crank-side bearing housing. Now you should have the bearings, spindle, and spacer inside the bottom bracket assembly.

4. Spacing is also critical on the outside of the bottom bracket. Slide your sprocket onto the right side and see if it lines up with your rear sprocket. You may need an extra little washer-style spacer (other than the one that sits inside your sprocket), or you may not. It depends on your bike frame. On the other side (the non-sprocket side), you’ll need to add spacers. NOTE: Also make sure your crank arms are far enough away from your chainstays after you add your spacers. If not, you’ll need to add more.

5. Now, if everything is lined up properly, attach the sprocket to the crank arm, and use the spindle bolts to tighten the crank arms to the spindle. After you put your pedals on, check to make sure the cranks spin properly. If not, you may not have the correct spacer inside (also check again that your crank arms aren’t hitting your frame). If everything is spaced correctly and spins good, put your chain back on and adjust your rear wheel. Check your brakes, and you’re ready to go.

The contents of this article are informational only, and are to be used by the reader at their sole discretion.  The user assumes any and all liability with regard to utilization of the information.  The National Bicycle League, its employees, administrators, directors, officers and volunteers will be held harmless for misuse of this information.