May 2, 2011

BMX Cranks

Bottom Bracket Installation

Installing a Mid or Spanish BB is virtually the same. (Click on links for illustrations and complete instructions.) The optimal method of installation is to press the bearings into the frame, with the appropriate tube spacer in between the bearings, using a bearing press. The next best method is using a bench vise with some squares of plywood between the jaws of the vice and the bearings, but you will need some strength for this one.

If you don’t have a bench vice, you can get C-clamps from a hardware store for less than $20 and use them with the wood squares. You can even use your cranks, if you already have one crank arm installed on the BB spindle. The last method is to get a 2×4 and a hammer and bash the bearings into place. You can do it that way, but the bearings can get damaged, your frame can get damaged, and you really should avoid using a hammer on your bike as much as possible, it’s just not the right tool for the job in most cases. In all scenarios, you should first spread a bit of grease on the BB shell where the bearings will sit. You might need a friend to help support the frame.

  1. Using a bearing press: lay the frame flat so the BB is under the press, and place the bearing atop the shell, bring the press down, keeping the frame as square to the table as possible. Press the first bearing into place.
  2. Flip the frame over, insert the gold tube spacer, and then the other bearing.
  3. Press the second bearing into place.

If you don’t have access to a bearing press and the vice or C-clamp isn’t working for you, you can get a rubber or wooden mallet and tap the bearings in place. Do not hit the bearings as hard as you can. Do not use a regular metal hammer. Do not use a sledgehammer. Do not hit the bearings in the center race- hit the outside edges, starting at the top and working your way around the edges, with the intent of pushing the bearing in as evenly as possible.

Installing a Euro (English/ISO) BB is pretty simple.You will need a 36mm headset wrench. Ideally, you should clean the threads of the frame, and then give them a light coating of grease. If you really want to do it right, because you hate hearing your BB creaking, then you should get some teflon tape from the hardware store and wrap the threads of the cups.

The drive side cup has a line around it and is left-hand (reverse) threaded. Carefully thread this cup into place. Insert the proper tube spacer for the width of your BB shell.

The non-drive side cup is right-hand threaded, so it tightens normally. Again, wrap the threads with teflon tape if you like, and snug it up.

When the cup is almost tight, it’s not unusual for the bearings to move outwards slightly- don’t freak out here. It’s better to have a tube spacer that’s 1mm too long than it is to have one that’s too short- you might as well not have one there at all in that case, and you need a tube spacer so that the bearings don’t pinch when the cranks are tightened down.

Installing an American BB is pretty much the same as installing a Mid or a Spanish, except the fit is usually not nearly as tight, and you’re pressing aluminum cups into a usually steel frame rather than steel bearings into a steel frame so they’re going to slide easier anyway.

Before you go any further, check your tube spacer- it should be touching both bearings. If it is too short, then the bearings will pinch once you tighten the cranks and the cranks will not spin smoothly. Remove one of the bearings, add one of the thin flat washers (or a longer tube spacer) and reinstall the bearing.

Crank Installation

Before we get started, we’ll need to gather some tools. First of all, you really need the Profile Crank Install Tool. While it’s possible to just hammer the cranks on, it’s really not a good idea, and we certainly don’t recommend it. It’s a fairly quick route to voiding your warranty, actually. Save yourself the headache, get a crank tool. If you bought the cranks new, then you should have got one in the box, otherwise, borrow one from a friend, or buy one here, here, or here. You might need the hammer, so keep it handy, but don’t be eager to use it.

You will also need a wrench (or spanner for our international readers) to turn that crank tool, a medium sized crescent (adjustable) wrench will do, and the appropriate allen key or socket for the type of bolt you have, as well as for the sprocket bolt. GDH BB bolts are 8mm allen, standard flush mount bolts are 7/32″, original hollow flush mount and SS crank bolts are 1/4″, and original and Madera crank bolts require a 9/16″ socket. The CrMo and the Ti sprocket bolts both require a 7/32″ allen key. Finally, you need either the tube of Finish Line Anti-Seize that came with your cranks, or else some grease, but definitely one of the two. You’ll probably want to have a rag to clean up with as well

  1. Apply the Anti-seize
    Apply the Anti-seize

    Slide your BB spindle through the bearings of the bottom bracket and the tube spacer. Spin the spindle. If it feels rough, then the bearings aren’t perfectly parallel. Don’t panic. On Mid, Spanish, and American BB’s, slide the wider of the two cone spacers on the non-drive side of the bicycle, and the other on the drive side. or grease to the splines of the spindle. Keep that rag near to hand, just in case, a little Anti-Seize goes a long way.

  2. Take two of the flat washers
    Take two of the flat washers

    Take the drive side crank arm, and attach your sprocket to it. Tighten the sprocket bolt 85% of the way down. Take the Profile Crank tool, and slide the sleeve off of it. Take two of the flat washers that came in the box and slide them onto the crank tool. Slide the tool through the crank and thread it onto the BB spindle. Using your wrench, tighten the crank tool until it stops turning. If it’s insanely hard to turn the wrench, stop trying. Loosen the tool, remove it, and inspect the tool and the BB spindle for damage or debris that might be causing the obstruction. Remove any debris or obstructions, and attempt installation again. If you continue to have problems, please call us at (727) 391-7370.

  3. Re-tighten the tool all the way down
    Re-tighten the tool all the way down

    If you had no problems tightening the crank tool all the way down the just the washers on it, great, go ahead and remove the tool, remove the washers, slide on the sleeve, and re-tighten the tool all the way down. This will slide the crankarm far enough onto the spindle that you’ll be able to use the crank bolts to tighten it down the rest of the way.

  4. Make sure you use some anti-seize
    Make sure you use some anti-seize

    Make sure you use some anti-seize or grease on the crank bolts as well. You do not need to have the spindle 100 percent through the crank arm. I like to leave 8-10 mm of crank boss showing, it really mostly depends on how much clearance you’ll need for your crankarms to get over your chainstays, and how narrow you like to run your cranks.

  5. Has the clearance it needs
    Has the clearance it needs

    Now is a great time to check that your drive-side crank arm has the clearance it needs over the chainstay, as we just discussed. If you have 10mm or so, you’ve done well. If you have less than that, you need to decide if you want to put a spacer behind the sprocket, or take the risk of denting your chainstay if you crash on the drive side of the bike. If you choose to go the spacer route, slide the BB spindle and crank arm out of the bb, and place a thin spacer next to the sprocket washer, and slide the BB spindle back into the bb. You should now have enough clearance. If not, try a thick washer. If you need any more space than that, you’re going to need to keep a close eye on your chainline.

  6. Parallel to each other
    Parallel to each other

    To install the non-drive side arm, we’re first going to make sure we get the arms lined up straight the first time. Slide 2 or 3 of the thick spacers onto the BB spindle next to the wide cone spacer, and then take a couple more washers and slide them on the sleeveless Crank Install tool. Thread it into the BB spindle so that it’s holding the crank arm in place, but not so far that you can’t move the arm to get it parallel. Set the drive side arm so that you’re looking straight down on it, and line up the non-driveside arm to it. You can use the seat tube of the bicycle to help you judge that the cranks are parallel to each other.

  7. Tighten everything
    Tighten everything

    Tighten down the non-drive arm as we did in steps 2, 3, and 4. Tighten down your sprocket bolt. Spin the cranks, they should spin pretty smoothly. If they do not, Try hitting the crank bolt sharply with the rubber or wooden mallet several times. Take the bike for a spin around the block once or twice. If they still are very rough, then the tube spacer is likely too short for your frame, and you’ll need to take one crank arm off, remove the cranks from the bike, and go back to the BB installation instructions above. There is a difference in feel between a too short tube spacer, which is more of a pinch, and bearings being slightly out of alignment.

Crank Removal

Removing Profile cranks is easiest with a Profile Crank Install tool and a hammer, and is quite simple.

  1. Remove one of your crank bolts. Remove the aluminum washer/spacer as well. It’s not a bad idea to loosen your rear wheel so that your chain isn’t tight.
  2. Remove the sleeve from the Crank Install Tool. Tighten the sleeveless crank tool all the way into the spindle.
  3. Hit the back of the tool with the hammer. Be careful not to hit your hand, the crank arm, or anything other than the tool.
  4. Once you’ve hit the tool enough times, the crank will slide off the end of the spindle. Loosen the crank tool.

Bottom Bracket Information

Profile sells bottom brackets to fit four different types of bottom brackets, Mid, Spanish, Euro (English/ISO), and American.

Mid Bottom Bracket

The Mid BB uses the same bearings as the American BB, but they are pressed directly into the frame

Tube Spacer: 2.037″ (51.7mm)

Frames that use the Mid BB: Black Eye, BSD, Colony, Eastern (Tramp only), FBM, Federal, Fit, Haro, Hoffman, Kink, Mankind, Metal, Midnite, Mirraco, Mutiny, Premium, Quamen, S&M, SE, Standard, Subrosa, Sunday, The Take, Tree, United, Volume, We The People (as of 07/09)

Spanish Bottom Bracket

The Spanish BB uses slightly smaller bearings than the Mid, but they are also pressed directly into the frame.

Tube Spacer: 1.891″(48mm)

Frames that use the Spanish BB: Deluxe, DK, Eastern, Failure, Fly, MacNeil, Sputnik, St. Martin, Stolen, Superstar (as of 07/09)

Euro (English/ISO)

The Euro BB is the same thing as an English/ISO BB. It is mainly found on Race BMX bikes, as well as almost every Mountain and Fixed Gear Bike. The bearings are held in cups that thread into the frame. We make tube spacers for 68mm (most common), 73mm, 83mm, and 100mm wide BB shells

Tube Spacer: 68mm BB: 1.846″(46.9mm), 73mm BB:2.038″ (51.76mm)

The English/ISO BB is found on most adult bicycles, including MTB’s, road bikes, and track bikes, as well as most modern BMX race bikes. Some dirt jump style MTB frames use a BMX Mid BB, check with your frame’s manufacturer to be certain.

American Bottom Bracket

The American BB is mostly found on old school bikes these days. It uses the same bearings as the Mid BB, but they are pressed into cups that are then pressed into the frame. No two companies ever built bikes with American BB shells that were the same size, which lead Profile to invent the Evolution BB, which is an American BB with two halves that thread together, allowing for a much better fit in any frame.

Tube Spacer: 2.037″ (51.7mm) or 2.0875″ (53.03mm)

disclaimer: these instructions are provided as a service. the best way to install sealed bearings is always a bearing or arbor press. the methods discussed here are alternatives for the home bike mechanics with home bicycle tools. if you are not careful, you will damage your hubs and bearings. profile cannot be held responsible for any damage caused by attempts at repair attempted by anyone other than employees of profile racing. if you are unsure of your abilities, take your bike to a local bike shop, or contact us at profile. we are happy to overhaul your hubs for you here. contact shane at profile at 727.391.7370 for details.

May 2, 2011


We are taking precautions to protect our employees and follow CDC and state guidelines. In the meantime, our machine shop is still running, we're here to assist you and we'll be shipping product to help support bike shops during this difficult time.