Heating the case will expand it so that IF all else is good to go the prop shaft and gear/bearing assembly can be withdrawn OR inserted back into case.
IF is of course a very big word and covers lots of contingencies....most of
which are unwelcome.
It is also possible to use a large vise to clamp prop shaft between to boards and using a rubber mallet to alternately strike top and bottom of case to ease the usually stuck assembly including water pump our of gear case that it
has resided in for lo these many years. Helps to clean things and saturate
with penetrating solvent a bit ahead of time allowing it to soak in.
Alternatively if lacking vise and/or rubber mallet a nut,pipe and a couple
of pieces of stiff metal bars across opening of gear case for pipe to bear
on...this will get things started ,but, when water pump cartridge is flush
with end of case some other technique will be needed to get everything to
clear the case.
The GOOD NEWS is the assembly should be easy to install in a warmed up gear case...assuming all parts are good and nothing untoward happened during
removal.If you have not yet removed the water pump cartridge use a fine felt
marker to indicate orientation of cartridge to gear case...so that water
intake and outlet line up when replaced.
This is procedure for NON SHIFT lower units with left hand thread water
Be sure to note position and orientation of shims and spacers as you take
components out of gear case...take notes, drawings and/or pictures.
Usual reason to delve into gear case is it makes funny noises due to chewed
up gears, bearings...often due to water entering from water pump past a
worn seal and/or worn/corroded prop shaft.
The next order of business is the drive shaft. The tab of tab washer is bent
up to keep bolt from turning...to fit a six point socket on thin head of bolt
first bend the tab flat...clamp drive shaft in vise and turn case with
socket and handle...unless bolt is stuck bolt comes out, pinion comes off
and drive shaft can be withdrawn. Again note where everything was,how
oriented and in what order.
Examine everything after cleaning. If it was bad when it came apart it will
not be any better if put back together using all the same parts.
SOMETIMES the cost of new parts far exceeds price of a good used lower unit.
Up North water remaining in lower unit will freeze, expand and leave fine
cracks...usually meaning case is distorted...welding may increase distortion
a good used case might be a better place to start rebuild from. Welding a
broken skeg is one thing...welding in area where bearing secures and aligns
drive shaft to gear set is an iffy.
Mercury and Wizard drive shafts and drive shaft housings are not all the same
length so best to get both together when looking for a good used unit.
Gear cases are not my strong point. To best of my knowledge this description
is good enough to get the idea across. Fitting gears for proper function can
be a matter of fit and try using thicker or thinner shims...not usually the
case if correct to begin with but often the case if parts that affect gear lash are changed.
The above applies ONLY to NON SHIFT lower unit. A shift type lower unit
is somewhat different but clamping prop shaft in vise between two boards
and use of rubber mallet to alternately tap skeg and tower side of gear case
is a Mercury Service Manual method to remove. Heat and solvent still apply.
Always a good practice to keep track of how things were when you found them
so they can be replaced as found UNLESS improperly assembled by a careless
Water pump moved to drive shaft to make room for shift mechanism.