MerCruiser Sterndrive removal and replacement Alpha One (generation one & two) Applies to older #1 sterndrives as well.

Removal: (A helper makes a big difference)

1. Place the control box in full forward. This can be verified by rotating the prop counter-clockwise, it should lock. On generation two units, with the drive up, remove the speedometer fitting. This is located on the front of the drive unit just below the exhaust bellows. Twist or squeeze the retainer to remove. Lower the drive down.
2. Drain the gear lube. Remove the lower drain screw first, then the upper screw. On gen. two units with an internal gear lube reservoir, the lube will also drain from the reservoir. remove the fill screw gaskets and place them on the fill screws so they don't get lost.
3. Remove the aft trim cylinder anchor pins. The anchor pins have 5/8" hex nuts (older units used 9/16" nuts). It will also help to loosen the forward anchor pin nuts as well. generation two units use a solid shaft with "e" clips on the ends. Sometimes these pins and rubber bushings will be difficult to remove. If needed, gently pry between the upper housing and the trim cylinders to break them loose. In severe cases the stainless pins will be corroded in place inside the housing. The pins will have to be replaced. If the rubber bushings are worn, replace them too.
4. Remove all but one of the bell housing nuts, loosen the the last one almost all the way off. Newer units use 5 washers, they have a grounding washer attached under one nut. Older units used 6 washers. If the drive is in forward, trim cylinders are off and all nuts are removed/loose, the sterndrive should slide back with a "rocking" motion. If the sterndrive hasn't been off in a while (if ever), or if the engine alignment is off, the drive will need a bit of a "slam" to be removed. Pick up the aft end of the drive and let it come back down with a slam. This is usually enough to get it moving. in extreme cases you may have to slide a prybar between the drive and the bell housing being careful not to damage either housing.  Now, after removing the last nut the drive should come the rest of the way off. Careful! It's heavy.
5. If it STILL does not want to come off you may have a severe corrosion problem or a badly misaligned engine. There are other ways to get this drive off but some tricks can do some damage. Please call us for a helping hand!
6. Check inside the bell housing, there should not be any water or signs of water inside the bellows. The gimbal bearing at the forward end of the bellows should rotate free, not feel rough or stuck. If you have rusty parts then most likely you have a bad bellows. Rusty "U" joints must be replaced before they can fail and cause very expensive damage. A bad bellows can also sink the boat.
7. Before reinstalling the drive unit the engine alignment must be checked. You will need an alignment tool. This can be bought, borrowed, stolen, etc. This verifies proper alignment between the input shaft of the drive and the coupler. The tool should slide in to the couper with only slight resistance. If it is not correct the coupler will wear prematurely, causing loss of all propulsion. The engine must be removed to replace the coupler.  
8. If all is well it's time to reinstall your sterndrive.

Installation:

1. Clean off all old gasket material on the bell housing and outdrive. Replace all o-rings on the shaft, inside the bell housing and the water passage o-ring. The large square cut o-ring is placed inside the bell housing, it will stop against the shoulder inside near the bellows. The water passage o-ring should be glued or greased to hold it in place. Install a new gasket.
2. Using a good quality marine grease, liberally grease the U-joints, the roller on the shift lever, the shift shaft slide, and a little grease on the gasket keeps it stuck in place. Use spline grease on the input shaft splines.
3. It helps to have the drive unit close to ground when reinstalling, if you don't have to lift the drive it makes life easier.
4. You will need to shift the drive unit into forward (hopefully the boat is still in forward) This is done by turning the propshaft counter-clockwise while turning the shift shaft clockwise. generation two units use a stainless steel shift shaft. you should feel it lock solidly.
5. It helps to have the prop installed in case you need to turn the propshaft to make the input shaft splines line up.
6. With the boat and drive both in forward, everything greased, carefully slide the input shaft into the gimbal bearing. The shift lever roller should be in it's notch in the shift slide (hint: use a thick grease to help hold these parts in place).
7. If you bump the propeller, it may shift out of forward, verify it's still in forward. As you slide the drive in you should feel the the shaft go into the coupler, as it gets close you may have to turn the prop counter-clockwise to turn the input shaft slightly (don't turn it clockwise or it will come out of gear) It will be hard to turn. At the same time you will be verifying the the shift lever roller is still in place. Work the drive into the bell housing, you will feel resistance from the o-rings. You should not have to force anything!
8. Now install and tighten the 6 nuts on the studs (45 ft. lbs. or good and tight). Have a helper shift the boat into nuetral, then reverse (not running please) while spinning the prop to check shifting. If it does not shift chances are the shift lever may have moved out of place. In some case with a new or different drive unit, the shift may need adjustment. This will be discussed elsewhere.
9. Reinstall the trim cylinder anchor pins.
10. Refill the sterndrive with a good quality (we recommend synthetic) gear lube. The gear lube is filled from the bottom out to force air out, fill until lube runs out the top hole, replace the top screw, then the bottom. The gear lube level should be checked again after a day or so, then again after the boat has been run. Don't forget to fill the internal reservoir, if equipped.
11. With a garden hose flush adaptor, run the engine to verify water pump operation and good shift engagement forward and reverse (please watch for obstacles and people). Proper shifting is best determined in the water. Shifting should be postitive with no ratcheting in forward or reverse. stalling when shifting or lack of cooling water are signs of other problems. Call for help.

Recommended tools and supplies:

1. Hand tools: ratchet and/or breaker bar, sockets 5/8" (9/16" for older units), large and small screwdrivers.
2. Special tools: (optional but recommended) Alignment tool, gear lube pump, flush attachment.
3. Materials: Grease gun, quality marine grease, spline grease, gear lube, Gasket kit.
4. Quality shop manual.

Disclaimer:

***This guide is meant for basic instruction only. no guarantee is made to it's accuracy. all information here should not be construed to replace any manufacturer's procedures or instruction or the prudent advice of a professional. No liability whether personal or property will be assumed by Al's Marine Service (alsmar) and or dockpartner.com by the user of this guide.