One-person Method for Re-installation of Lower Unit

Repair or modification of Boston Whaler boats, their engines, trailers, and gear
tomolalla
Posts: 33
Joined: Sat Feb 12, 2022 9:52 am
Location: Tampa FL and Gig Harbor WA

One-person Method for Re-installation of Lower Unit

Postby tomolalla » Sat Jul 02, 2022 11:30 am

One-Person Lower Unit Reassembly for 2014 Mercury 90 HP FOURSTROKE Engine

Refer to Figure 1 below to see how the ratchet strap is positioned to lift the lower unit upward and into the midsection.

  1. shift engine into forward gear using remote control
  2. drain the engine crankcase oil to prevent oil loss when gear case is removed
  3. remove lower unit
  4. replace impeller; some movement of the drive shaft when replacing water pump impeller will be unavoidable; the shift shaft might also get turned; these splined shafts will later have to be turned to align with the mating shafts from the power head; the method is explained below;
  5. make sure the lower unit gear case is in Forward gear before attempting to reassemble; this is a must for the shift shaft position to be back to original;
  6. use a bungee cord wrapped around the propeller counterclockwise to maintain the the gear case firmly in forward gear during reassembly;
  7. attach a ratchet strap to the lower area of the cowling using rubberized hooks, creating a loop that will hold and lift the lower unit.
  8. slide the lower unit carefully into place under the engine;
  9. put the ratchet loop under the anti-ventilation plate immediately above the propeller
  10. slowly ratchet upward the lower unit while, making sure the various drive shaft and shift shaft are aligning. When the gear case drive shaft meets the engine drive shaft they are unlikely to have splines aligned perfectly. At this point raise the lower unit slightly so there is compression at the drive shaft mating point;
  11. tilt down the engine so the skep of the gear case skeg is only one inch above ground (or a temporary support) so that in the strap loosens the gear case cannot fall far;
  12. at the engine power head rotate the flywheel [in the normal direction] until you feel or hear the splines of the drive shaft connector engage; the flywheel rotation will only beed to be a fraction of an inch to align the splines.
  13. tilt up the engine;
  14. continue to slowly raise the lower unit with the ratchet strap as the drive shaft joint is fully engages; this will need about an inch or two of raising;
  15. as raising continues, eventually the shift shaft splined joint to come into contact, and again put some compression force at the mating point using the ratchet strap;
  16. using the remote shift control, move or jiggle the shift lever, until you feel or hear the mating shift lever splines engaging.
  17. continue to slowly raise the gear case with the ratchet strap to fully engage the splines of the shift shaft joint;
  18. replace all nuts onto the studs from the mid-section; tightening the nuts in an alternating sequence aas use on the a wheel to hub nuts; until the nuts are tightened to the specified torque;
  19. test the shift positioning by shifting into neutral and checking the propeller for free turn in either direction without clicking;
  20. refill engine crankcase oil with new oil;
  21. using hose adaptor for engine cooling, start engine;
  22. verify proper cooling water flow at overboard confidence stream nozzle;
  23. shift to Forward from Neutral; shift should be smooth; repeat for shift to Reverse from Neutral; shift should be smooth.

NOTE: to find forward on Mercury 90 I gently used a pliers on the protected shift shaft, and turned in clockwise while at the same time rotating the propeller counter clockwise. Other brands or models may differ. I felt [the dog clutch] go into forward gear; the drive shaft would rotate clockwise if I continued to rotate the propeller. After this there is virtually no chance that the shift rod or drive shaft splines are in the correct position to match with their corresponding parts in the power head portion of the outboard.

one person lower unit reassembly.jpg
Fig. 1. View of lower unit supported by ratchet straps for easier one-person reassembly.
one person lower unit reassembly.jpg (53.09 KiB) Viewed 1129 times


BACKGROUND
Over the years I’ve changed several water pump impellers on different outboards. I’ve always been able to easily take them apart and always had trouble putting the shafts back together. After hours of frustration I would eventually figure out a way to reassemble the outboard, and usually by finding a helper and an extra set of eyes. The main problem when working along is the alignment of the spline shaft joints for the drive shaft and the shift shaft.

jimh
Posts: 11673
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
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Re: One-person Method for Re-installation of Lower Unit

Postby jimh » Sat Jul 02, 2022 2:24 pm

I like your clever use of a bungie cord to maintain the dog clutch shifted into Forward gear by holding the propeller in position.

I like your use of the ratchet strap. I don't understand how the ratchet strap is attached to the lower cowling pan as shown in Figure 1. Please elaborate on that attachment. Are the hooks of strap attached to the steering mechanism?

tomolalla
Posts: 33
Joined: Sat Feb 12, 2022 9:52 am
Location: Tampa FL and Gig Harbor WA

Re: One-person Method for Re-installation of Lower Unit

Postby tomolalla » Sun Jul 03, 2022 9:19 am

The rubberized hooks of the ratchet straps are simply laid over the area where the cowling attaches. Just place them in a logical area where the straps have a straight line to the cavitation plate. Foam contacts the hooks at this location and helps to keep them from slipping. If I haven't already put my boat away I'd just send more photos.

I take no credit for those two methods except that I found them on the internet (two different sources). They seem to work quite well on the Merc 90hp and I'll give it a shot on some of my other outboards when the time comes. I hope this methods it is useful to others.