How to Remove and Reinstall an Outboard Gearcase (Lower Unit) Without Losing Shift

Find the gearcase removal section in your service manual and note four things: which gear position to use, where every bolt is (one is often hidden), what goes on the bolt threads and splines, and the bolt torque. Buy a new water tube grommet and, if you are doing the pump, the full water pump kit. If you have no manual, a dealer can usually tell you the gear position for your model.

Key out, kill switch clip off, battery switch off. Many owners drain the gear oil now, because they will refill it anyway and it lets you check for water or metal (see the lower unit oil change guide). Put a pan under the gearcase.

Tilt the motor fully up and lock it. Remove the propeller, thrust washer and any spacers, and lay them out in order. Without the prop the gearcase is lighter, fits in a stand and cannot cut your hands. Look for fishing line on the shaft while it is off.

Put the engine in the gear position your manual specifies. If it says neutral, check by turning the driveshaft or prop shaft: in neutral it turns freely both ways.

Now take photos and make marks. On engines with a threaded shift rod or an adjustable coupler, measure the height of the shift rod in neutral before you touch it and write it down. Boating Magazine's DIY gearcase swap made this point: you need that number when you reinstall. Do not move the shift lever or helm control again until the gearcase is back on.

Depending on your engine:

• Pin-and-clip rod: remove the clip and pin to separate the upper and lower rods.
• Splined coupler: nothing to undo; it slides apart as the gearcase drops.
• Connection under the cowl: remove the cowl and disconnect the shift linkage there, as the manual shows.

Also remove any speedometer pickup tube connection and the bonding (ground) wires between the gearcase and the midsection. Note where each one goes.

Loosen all the gearcase bolts. Check for a hidden bolt, often above or behind the trim tab or anode; on some engines you must remove the trim tab to reach it. Mark the trim tab position with a pencil before you take it off. Have your helper hold the gearcase before the last two bolts come out, then slide it straight down and away from the midsection, keeping the driveshaft vertical. Set it in a stand.

If it will not come off, you have probably missed a bolt. BoatUS says a gearcase usually needs some wiggling and pulling even with every bolt out, and a few taps on the gearcase body with a soft mallet are normal. Never strike the anti-ventilation (cavitation) plate: BoatUS warns it is sure to break. If it still won't move, corrosion may be holding it: stop prying and get a shop to help, because forcing it can crack the housing.

With the gearcase off you can see a lot:

• Driveshaft splines: they should be clean and evenly shaped. Rusty, dry or twisted splines need attention (worn splines are a pro job).
• Water tube and grommet: the tube should be straight and clear, and the grommet soft and not torn. Replace a hard or split grommet.
• Shift shaft: straight, not bent, with clean splines or a smooth rod.
• Mating surfaces: clean off old grease, sand and corrosion so the gearcase will seat flat.

Do your water pump work now if that was the goal (see the water pump impeller guide).

Coat the driveshaft splines with a thin layer of the grease your manual specifies. Do not pack grease on top of the driveshaft end: too much grease can stop it seating fully. Lightly lubricate the shift shaft splines and the water tube seal if the manual says so. Put the bolt thread compound on the bolts. Double-check the gearcase is still in the specified gear, and that the shift rod height matches what you recorded.

With your helper, raise the gearcase straight up under the midsection. Guide the water tube into its grommet first; look from the side with a flashlight to be sure it goes in and does not fold the grommet over. Then the driveshaft enters the midsection.

When the driveshaft reaches the crankshaft, it usually will not slide in by itself. Pull the gearcase back down a couple of inches and turn the driveshaft slightly (or turn the flywheel clockwise by hand, if your manual allows) until the splines line up. Only ever turn it in the engine's normal running direction: Yamaha warns never to rotate an outboard's crankshaft or driveshaft counterclockwise, because turning the pump backward can damage the impeller. At the same time, make sure the shift shaft coupler or rod lines up. Never pull the gearcase up with the bolts: it should go up by hand with no gap between the gearcase and midsection. Before the bolts go in, use a small mirror and a flashlight to confirm the shift rod or coupler actually engaged; owners often find it sitting beside its socket.

Start all the bolts by hand, then snug them evenly in a crisscross pattern. Torque them to the value in your service manual (do not guess: aluminum threads strip easily). Reconnect the shift rod pin and clip if you have one, the bonding wires, the speedometer tube and the trim tab, back in its marked position. Refill the gear oil if you drained it.

Before you start anything, check the shift, with the prop still off or with the kill switch clip out and the key removed:

1. Put the helm control in neutral: the prop shaft should turn freely both ways.
2. Shift to forward while a helper turns the prop shaft slowly by hand: it should lock in one direction.
3. Shift to reverse: it should lock in the other direction.

If forward and reverse are swapped, or one gear will not engage, the shift shaft was off position. Do not try to fix it with the cable barrel: the gearcase has to come off again and go back on in the right position.

Many owners leave the propeller off for this test so nobody can be hurt by it; follow your manual. Connect flush muffs or use a test tank, turn on the water, then start the engine in neutral. Within a few seconds you should see a steady telltale stream. If there is no stream within about 30 seconds, shut down: the water tube may have missed its grommet. Do not shift into gear on muffs or on the trailer. When the test is done, shut down, then reinstall the propeller with a new cotter pin or tab washer and torque the nut to your manual's spec. Yamaha suggests a coat of marine grease on the prop shaft splines first, which makes the prop much easier to remove next time, especially in salt water.

Check for oil at the drain and vent screws, recheck the bolts, and make sure the trim tab is straight. At the dock, with the boat tied up and the area behind clear, run the engine at idle and shift forward and reverse, pausing in neutral between them. Shifting should be crisp and the telltale strong. On your first run, watch the temperature gauge and the telltale.