Home fixes & guides

How to Replace a Worn Cutless Bearing on an Inboard

My shaft has play in the strut and the cutless bearing looks worn — how do I replace it?

A cutless bearing is a water-lubricated rubber-and-brass (or composite) sleeve in the strut or stern tube that centers and supports the propeller shaft. The grooved rubber lets cooling water flow through; when it wears, you get measurable shaft play, a clunk or vibration, and accelerated wear on the shaft, packing, and coupling. The fix itself is straightforward (pull the prop and shaft, press out the old bearing, press in the new one), but the boat must be hauled out, and the real cause is usually shaft misalignment or a fouled water supply that will eat the new bearing too if you do not correct it.

ℹ️ Reference only: For general reference only. This guide does not guarantee any result — every home is different. Verify against your local building codes and a licensed professional before acting, especially for electrical, gas, plumbing, structural, or roof work.

💵 Bearing itself: $30-$120. DIY total with an extractor tool: ~$80-$250 plus haul-out/blocking ($100-$400+ depending on yard). Full job at a marine yard including haul, bearing, shaft pull, and alignment: ~$400-$900, more if the shaft or strut also needs work. ⏱ 3-6 hours of hands-on work once hauled (longer if the bearing is seized in the bore or alignment fights you); a full day at a yard counting haul-out and launch. ● Use caution
Safety: This is below-the-waterline work: the shaft, stuffing box, and strut are part of what keeps the boat from sinking, so the stuffing box must be correctly repacked and leak-checked before and after launch, and the boat must be properly blocked and supported on the hard (a boat falling off jack stands is a serious crush hazard). Never work under a hull supported only by a travel-lift or a single point. Do the engine work with the battery main switch off so the engine cannot be cranked while your hands are near the coupling and shaft. After launch, watch the stuffing box and bilge closely on the first run for leaks.

Common causes

How to fix it

  1. Confirm the diagnosis first. With the boat hauled and blocked, grab the shaft just forward of the strut and push/pull vertically and side to side. More than roughly 1/16 in (0.06 in / 1.5 mm) of play, or any play you can clearly feel, means the cutless bearing is worn. Inspect the rubber through the strut: glazed, cracked, or missing flutes confirm it. Also spin the shaft and check it is straight and the prop is undamaged, so you are not just masking a bent shaft.
  2. Document alignment and the shaft before disassembly. Note coupling position and check engine alignment readings if you can; misalignment is the most common reason a new bearing wears out fast. Plan to recheck/redo alignment after reassembly.
  3. Remove the propeller. Bend back the cotter pin, remove the prop nut(s), and pull the prop with a proper prop puller (do not hammer the blades or shaft). Save the key.
  4. Disconnect the shaft coupling at the transmission and slide the shaft aft out of the strut/stern tube. You may need to loosen the stuffing box/packing gland or dripless seal and back the shaft out enough to clear, and on many boats the rudder limits how far the shaft slides aft — be ready to drop or swing the rudder if the shaft will not clear. Support the shaft so it does not drop.
  5. Identify your strut type. Most modern struts hold the cutless bearing with one or two stainless set screws (grub screws) on the side of the barrel; back these out fully before trying to move the bearing. Some stern-tube bearings are an interference (press) fit only.
  6. Remove the old bearing. The clean way is a bearing puller/extractor made for cutless bearings (a threaded rod with a backing plate and a cup that pulls the bearing out). Alternatives: a length of pipe just smaller than the bearing OD to press it through, or carefully cutting a lengthwise slot in the brass shell with a hacksaw blade so it collapses inward and taps out. Never gouge the strut bore.
  7. Clean and measure the bore. Wire-brush and inspect for scoring or out-of-round. Measure shaft OD and bore ID; order a marine cutless bearing matched to shaft size and bore. Bearings are specified as shaft OD (= bearing ID) x bearing OD x length — e.g. a 1 in shaft commonly takes a 1 in ID x 1-1/2 in OD x 4 in bearing, but OD and length vary by strut, so measure yours rather than assuming. Use a genuine marine water-lubricated cutless bearing (brass-shell or non-metallic Johnson/Duramax-type) — not a generic bushing.
  8. Press in the new bearing. Lubricate the bore lightly with soapy water (not oil/grease — petroleum swells the rubber). Press it in square with the extractor tool run in reverse, or a threaded rod with washers, keeping it dead straight. Freezing the bearing and/or gently warming the strut helps a tight fit. For non-set-screw struts, a thread-locking marine adhesive sleeve retainer can be specified by the bearing maker; for set-screw struts, seat the screws into the brass shell and stake or use thread locker so they cannot back out and score the shaft.
  9. Reinstall the shaft, prop, and packing. Slide the shaft back through, reconnect the coupling, install the prop with a new cotter pin, and reset the stuffing box (new flax packing or service the dripless seal and confirm its water-feed line is clear).
  10. Recheck engine alignment to within about 0.001 in per inch of coupling diameter (typically 0.002-0.003 in feeler-gauge gap all around). This is the step that protects the new bearing — skip it and you will be back here.
  11. After launch, verify cooling water reaches the bearing (water-lubricated bearings must never run dry), check the stuffing box drip rate, and inspect for vibration on the first run. A grooved/fluted bearing is self-flushing once water flows; a stern-tube bearing fed by a hose must have that flow confirmed.

DIY or call a pro?

DIY-friendly for a mechanically competent owner if the strut bearing comes out cleanly — the parts are cheap and the procedure is simple. The two things that push it toward a pro: the boat must be hauled and blocked (yard cost regardless), and final engine alignment plus stern-tube bearings (vs. simple bolt-on struts) take experience and sometimes a slotted extractor or hydraulic press. If you cannot get the old bearing out without damaging the bore, or alignment readings are off, hand it to a yard.

Tools & parts

Keep a record of every fix you make — what broke, what it cost, how you solved it.

Track your home's fixes in Home Story →

Based on: BoatUS / BoatUS Foundation; ABYC (American Boat & Yacht Council); NMMA (National Marine Manufacturers Association); Volvo Penta service guidance; Mercury Marine (MerCruiser) service guidance

General marine-maintenance guidance, not a substitute for a qualified marine technician or surveyor. Boats and conditions vary; for fuel, electrical, fire, or structural issues — or anything safety-critical — consult a professional. Always follow your engine and equipment manuals.