Re: 1963 Mercury 9.8 Twin Help
Leave the shift in FWD and don't touch the shift shaft once the lower unit is down. This way it'll go back together properly.
One nut at the front of the gearcase, one nut from underneath the anti-ventilation plate, right next to the water intake screen.
The lower unit should drop right down. Don't use screwdrivers to separate the gearcase from the exhaust section (aka "mid" or "tower"). A Wonder-Bar has a thin wide profile which gives a lot of surface area to pry with. Or a wooden/plastic splitting wedge if it's stubborn.
Once you have the L/U off, (2) 1/4-28 nuts hold down the pump cover. Once this is off you'll see the impeller. Likely it'll be stuck, if it isn't just pry it out with a couple of 'tweaker' screwdrivers placed opposite each other.
If stuck, split the impeller's brass insert with a thin chisel or sharpened chisel-point of an old flat-bladed screwdriver. My favorite 'special tool' for this job, the very thin blade gets right in there and splits it fast. Use care not to damage the pump insert when splitting the impeller.
Check out the stainless 'cup' insert and also the pump plate for scoring or other damage, renew as required. Also inspect the rubber grommet in the pump cover, and any other parts in the general area for wear/damage.
This style impeller uses a pin sticking out of the driveshaft and there's a groove machined into the impeller insert to fit over the drive pin. Easy to reinstall, just lube it up with vaseline, boat bearing grease, or even dishwashing soap, give it a clockwise twist as you push down, and make sure the groove in the impeller insert engages the drive pin.
Apply a very sparing coating of Permatex #3 Aviation-Type gasket dressing (or OMC Perfect Seal Compound) to the mating surfaces of the pump cover. Don't slather it on or get it on the impeller or water passages, you just want enough to help seal the joint.
There should be an O-ring groove and O-ring at the top of the driveshaft, this is an important feature which seals water out of the crankshaft splines when the L/U is assembled to the rest of the motor. Renew the O-ring and coat the sides of the driveshaft splines with waterproof boat bearing grease or equivalent. Do the same with the splines of the shift shaft, use care not to move the shaft from its current position. Wipe any excess from the top of these shafts to avoid a hydraulic-locking situation.
Also coat the (2) lower unit mounting studs with grease so they'll never get rusted stuck.
When you reassemble the lower unit, you can turn the prop CCW to move the driveshaft slightly and engage the crankshaft. Be sure the water pump tube catches into the grommet in the pump housing on the way up. Can't recall if your motor would have the plastic guide tube sticking out of the pump housing, if it does and it's fallen off the pump and stuck on the water tube, pull it down and place firmly in the pump. It's just a slip fit and is a great aid in guiding the copper water supply tube 'home' into the pump.
You may be able to find an impeller for your motor here at the iBoats store. However I don't think they have any parts diagrams so you'd have to know the number first.
You can find parts diagrams at
www.boats.net www.crowleymarine.com and
www.mercruiserparts.com to name a few places.
Anyway, that's just a rough description and I probably left something out! And as you'll see all over this site, a manual is highly recommended. Don't know if you can still get a factory manual for you old-timer, but a Seloc repair manual would have sufficient detail in the L/U servicing section, with pics, to get you thru an impeller R&R.
HTH & Have Fun!.............ed
