How to Replace a Worn Outboard Bottom Bearing Without a New Crank

Most riders assume a knocking crankset means a new chainset is on the cards, yet the actual culprit is often a pair of tired bearings pressed into the bottom bracket shell. Outboard bearing systems — the type used by Shimano Hollowtech II, SRAM GXP, Race Face and many modern cranks — use two sealed cartridge bearings that can be replaced independently of the crank arms. Saving the arms keeps quality aluminium or carbon intact and saves riders a couple of hundred dollars at the workshop. This walk-through covers the whole job at home with basic tools.

A Melbourne rider tackling a worn Trek or a Brisbane commuter noticing a gritty feel on a city bike will face the same task: extract, press, refit. Australian conditions — salt air along the Mornington Peninsula, red dust out near Alice Springs, humid summers in Cairns — all accelerate bearing wear, so knowing this repair pays for itself quickly.

Spotting the Signs of a Tired Outboard Bearing

A bearing on its way out rarely fails suddenly. The first clue is usually a faint gritty sensation under pedalling load, often mistaken for a stiff new chain. Spinning the crank with the chain off should feel completely silent and smooth; any ticking, rumbling or uneven resistance points to the bearings. Worn units also develop lateral play — push the crank side-to-side and watch for any rocking at the pedal end.

Water ingress is a major contributor in Australia. Riding through wet grass in the Adelaide Hills, blasting across creek crossings during a Darwin commute or hosing the bike down at the car wash in Perth all push moisture past worn seals. Once corrosion begins, pitting spreads fast and the bearing loses its smooth rotation within a few hundred kilometres. Catching the issue early keeps the axle and the cups in good shape, which is what makes the swap worthwhile.

Other secondary symptoms include crank flex under hard standing starts, a slight creak that survives lubrication of the pedal threads, and dark paste around the seals rather than clean grease. Any of these on their own justify pulling the crank for a closer inspection.

Tools, Bearings and Parts to Lay Out

Before pulling anything apart, gather everything so the bike isn't off the road longer than necessary. The list is short, which is why this is one of the most satisfying home jobs on a modern bike.

For Australian riders sourcing parts, 99 Bikes and Reid Cycles stock common sizes in-store across Sydney and Melbourne, while Enduro Bearings and Token are easily ordered through local distributors for performance applications. Match the bearing inner diameter to the crank axle — 24 mm for Shimano, 22 mm for some SRAM GXP units, 24/22 mm stepped for GXP — before ordering. Buying the wrong size is the single most common mistake and it ruins an otherwise good afternoon.

Bearing brand Common size Seal type Typical service life Best application
Shimano OEM 6805 / 6806 Contact 8,000–12,000 km Direct replacement on stock cranks
Enduro 6805 / 6806 LLU / LLB 15,000–25,000 km All-round upgrade for any rider
Token 6805 / 6806 Premium rubber 12,000–18,000 km Performance road and gravel builds
FSA 6805 / 6806 Standard 8,000–10,000 km Budget repair on older commuter bikes
SKF 6805 / 6806 2RS 14,000–20,000 km Wet climates and coastal Australian riding

Any of these will restore the original feel of the crank, although riders in coastal cities such as Sydney or Hobart benefit most from a fully sealed LLU-grade bearing that keeps salt spray out for longer.

Pulling the Crank and Extracting the Old Bearings

Start by removing the pedals with the right size allen key — usually 6 mm or 8 mm — then loosen the two pinch bolts holding the drive-side crank arm onto the spindle. A plastic mallet tap on the back of the non-drive crank usually pops the arms apart cleanly. Slide the drive-side arm and preload collar off the axle, then withdraw the axle itself from the non-drive cup.

With the crank off, the outboard bearing sits exposed in its cup. Pressing it out from the opposite side with a socket of the correct outer diameter pops the old bearing free. Take note of which way the bearing is orientated — most have a shielded side facing outward — so the new one goes in the same direction. Drop the second bearing out the same way, keeping the cups in place; the cups themselves only need replacement if the seal surfaces are scored or the threads are damaged. Inspect the axle under a good light for scoring, which would mean a new spindle is needed instead.

Pressing the New Bearings Home

Clean every surface before pressing anything in. Wipe the cups out with degreaser, blow them dry and apply a thin smear of marine-grade grease to the inside of the cup. This is where the bearing will sit for the next few thousand kilometres, so don't skimp on the prep. Press each new bearing in square and true using a socket that contacts the outer race only — never press through the inner race, which damages the bearing before it has turned a stroke.

A common workshop trick is to use a dedicated bearing press, but a pair of appropriately sized sockets and a vice or G-clamp works fine at home. Press until the bearing sits flush with the cup face, then fit the rubber seal if the bearing didn't come pre-sealed. Repeat on the non-drive side, then refit the dust covers and any wave washers or spacers that came out. A dab of thread-locker on the cup threads is worthwhile if the bike sees a lot of rain — a habit worth picking up for any rider commuting through a Sydney winter.

Reassembly, Torque Checks and a Test Ride

Reassembly is the reverse of removal, with attention to torque. Slide the spindle back through the non-drive bearing, fit the drive-side bearing, then the preload collar. Snug the crank arms onto the spindle, tighten the pinch bolts to the manufacturer figure — usually 12–14 Nm for Hollowtech II — and check for smooth rotation. The crank should spin freely with no lateral wobble and no binding when the axle is fully clamped.

A proper test ride is the final check. Ride the bike around the block a few times, then check for any creak that wasn't there before. Many Australian cyclists log their test rides to compare feel before and after a service, and the change in smoothness is usually obvious from the first kilometre. If something still doesn't feel right, the cups may be worn and need replacement — or a spacer may have been left out during reassembly.

When a Bearing Swap Won't Solve It

The job described here assumes the crank arms, spindle and cups are all in good condition. If the spindle shows scoring where the bearings sit, or if the cup threads are stripped from a previous cross-threaded install, the repair expands considerably. Cups can usually be replaced separately, but a damaged spindle often means a new crankset is the only sensible option. Similarly, if the frame's bottom bracket shell is faced poorly — common on cheaper frames — the new bearings will bind no matter how carefully they're pressed in.

A pre-ride check after the swap keeps small issues from becoming big ones:

For riders tackling the job at home for the first time, budget an unhurried afternoon with the bike in a stand or hanging from a hook off the garage ceiling. Take photos at every stage so reassembly is straightforward, and label each washer and spacer as it comes out. Once done, the crankset should feel factory-fresh for tens of thousands of kilometres, and the wallet will thank you for avoiding a chainset that was otherwise perfectly fine. Tools in the shed, a few hours of patience, and the next gravel adventure up the Old Great North Road or a loop around Geelong is back on without spending a cent on a new chainset.