Pressing Issues: How To Install A Press-Fit BB

I really gotta stop posting these ‘red-herrings’. I just like fucking with you people though. For the record; not a press-fit BB…

You kick your front foot back hard, scooping the pedal back and flicking the cranks around underneath you with your battered Vans.  Something is wrong.  Your cranks squeak to a halt a mere 180 degrees from their original position.  Your feet slap down anti-climatically upon the asphalt.  Your heel-bruise worsens.  The attractive woman who was showing mild interest as she walked past looks away in embarrassment and quickens her pace.  Your peers nonchalantly look back down to their smartphones in silence; Courage Adams just posted on Insta and he actually lands his tricks… You try again- you kick back harder, grunt a little, people can smell your desperation now.  This time you get a better grip of the remaining three pins left in your pedal.  ‘This is the one…’ you think, ‘the fist bumps are coming my way.’
As you lay there, tangled among steel tubes, bleeding from a chunk missing from your Achilles tendon (probably caused by a Schrödinger’s pedal; a pedal that paradoxically seems unable to grip the bottom of your shoes yet will savagely butcher any part of your body it may end up touching) with your pride in tatters, thinking ‘Maybe I should make crankflips easy for myself and just ride a cassette…. like Courage.’  you might be better off by simply lubing your chain and changing your bottom bracket.

There are plenty of crank installation videos out there, this Merritt one being the latest example.  While it gives you some good pointers on crank installation, it completely skips the BB installation stage so today I’m going to take you through what it takes to properly measure and install your new bottom bracket like a goddamn… god!  We’ve all seen a number of wrong ways to fit a BB; some accidental, some on purpose, and with the evolution of the BB slowed down to a halt on the extremely efficient press-fit Mid sized BB shell, I’d say it’s high time to explain how to install the sucker correctly.

Firstly, you’ll need the following:
1. A BB.  Seeing as it’s 2017, it’s almost definitely going to be Mid sized unless it’s an older frame, even Fly Bikes have seemingly abandoned the Spanish BB shell from their frames in favour of Mid.  This will (or at least should) include; 2x cartridge bearings, a SPACER TUBE (no, they’re not guitar slides that come free…) and some crank spacers of various thicknesses.
2.  A tape measure/ ruler/ calipers.  Digital calipers are preferable as you will get an accurate reading to within 2 decimal places.
3. Lithium (white) or Teflon grease will do as an anti-seize…
4. A plastic mallet/ hammer and a small block of scrap wood/ prehistoric wooden club and your sister’s Barbie…
5. A G-cramp for spindle installation (if the bearings are a looser fit in the frame)  Far from essential but it will save time and headaches if you have one kicking about in the garage.
6. About 10 minutes.

With wider tyres becoming the norm, there needs to be more clearance for said tyres in between the frame’s stays, therefore the chainstays have to be welded further apart on the BB shell.  If there is no room left to weld the stays further apart on a ‘normal’ sized BB shell, then a wider one will be needed.  Being that there’s no real standard BB shell width to speak of, this makes getting a correctly sized spacer tube a little more work than simply slapping three components together in the right order.  The spacer tube is the small, often forgotten tube that fits over your crank spindle and in between the two inner bearing contacts to stop side loads (caused by dropping your bike onto your pedals, quick rotations, etc) from prematurely destroying your BB bearings.  Without it, the bearings themselves take the entire load instead of dissipating it along the whole crank via the spacer tube.

The caliper reads 74.06mm- the bearings and spacer tubes will need to be slightly ABOVE this number when measured.

1. Take your digital caliper and measure your (empty) BB shell width from end-to-end.  Jot this measurement down as you will need it later.

2. Pop some grease on your finger and run it around the inner rim of both ends of the BB shell ready for installing the cartridge bearings later.

In this picture; alone, the bearings and spacer tube combined are not as wide as the frame’s BB shell. If installed as such, the BB will fail.

3. Using your crank spindle as a ‘kebab skewer’ to keep everything in-line, slide the two cartridge bearings with the spacer tube in between them, onto the spindle and push together until flush.  Measure the width between the two cartridge bearings on the spindle with the caliper.  Again, jot this measurement down as it’s important for the next step.

4. Take the first measurement (the BB shell) and compare it to the second measurement (the bearings and spacer tube)  If the first measurement is greater that the second then simply calculate the difference between the two (BB shell – minus bearings and spacer tube = ….) The difference will probably only be a few millimeters or so, but enough to render the spacer tube a useless piece of pipe rattling around in the middle of your bike.  If the BB is smaller than the BB cluster, then you’ll need to either source a shorter spacer tube from your local BMX shop or make one yourself using the technique described in the step below.

The added 2mm of crank spacer (seen next to the right hand cartridge bearing) fills the void between the spacer tube and bearing inside the BB shell with an extra 0.16mm to spare. If you only have a ruler, a couple of millimeters or so extra is acceptable.

5. The way to fill the up gap between the spacer and the inner contacts of the bearings is with the crank spacers.  Choose the spacer or spacers that come closest to the difference between the two written down measurements, rounding up to the nearest millimeter. Eg. if the gap is 3.6 mm, choose a 4 or a 5mm crank spacer.  If the difference is 6.4mm, choose a 2 and a 5mm crank spacer etc, etc…  The idea is that the bearing and spacer tube ‘cluster’ should be ever so slightly wider than the shell itself, even if it means one bearing is visible from the outside of the BB shell and not quite seated completely in the frame.  If this is the case, don’t panic, this is fine as long as both bearings are touching the spacer tube and the crank spacer with no gaps- always better to have too much spacer tube than too little.

Installing is only to be done once you are doubly sure that your spacer tube is long enough.   You’ll curse yourself if you have to take it apart again (and then praise the heavens above that you’re not doing it on a US bottom bracket…)

6. Tap the first bearing into either side of your frame, making sure it’s greased and that you ALWAYS use the outer contact edge of the cartridge to push it in.  Never hit the inner contact ring with anything while installing the bearing, that is the kind of side load we’re trying to prevent…

7. Grab the crank spindle and push it though the bearing about halfway so one end stays inside the BB shell.  Using the spindle as a guide, pop the spacer tube and any required crank spacers onto the spindle inside the BB shell crank spacers first so there’s no danger of them dropping and rattling around the shell if the spindle has to be moved back or forth while installing the last bearing.

8. Next, tap the second bearing into the frame.  You may have to pull the spindle back through the spacer tube for clearance which is why I said put the smaller crank spacers on first, if you didn’t, they’re probably rolling around inside your frame about now giving you high blood pressure.

9. Being press-fit not only makes Mid BB’s easier to install but also easier to uninstall, sometimes to your frustration.  Machining tolerances can vary from frame to frame, company to company so sometimes your new bearings will glide in with a tap from a teaspoon, sometimes you’ll be reaching for a club hammer…  It can be more of a hassle if your bearings go in easily as they can be dislodged when installing the spindle and send the spacer tube to the bottom of the BB shell.  If this is the case, once both bearings are in as far as they will go, use the aforementioned G cramp to hold the bearings at the outer contact ring while tapping out the spindle without moving the bearings or spacer tube.

10. The very last step is to check that both the bearings and spacer tube line up flush and spin simultaneously when turning the inner contact of one of the bearings.  If anything is out of line, try and manipulate it into place at first with your fingers and then use the spindle to line it up into it’s final position.  If everything is still not spinning at the same time then you may need an extra crank spacer in between the bearings.

Once everything is solid and flush, pop the spindle back through the BB and take off the G cramp (if you needed it- you probably didn’t…)  Your cranks are now ready to install, your BB will last a lot longer and crankflips wont plague you quite as badly as before.  Maybe.

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