Mercury Mark 20 (circa 1955) foot repair

I have inherited an old Merc Kiekhaeffer outboard engine which whose internal workings of the foot are completely shot. I have separated the bottom half of the skeg to work on the prop drive on a bench.

By virtue of its design, this unit was not intended for disassembly EVER. In order to access the inner workings of the prop output mechanism, I was required to drill two 8mm holes on either side of the flange, then with bolts and a puller, managed to get it off. There was no obvious way to hold the flange and extract it without destroying it.

I now have the bearing in sight, but again am bewildered as to how to remove it. The outer race of the bearing exposes a small shoulder of maybe 2 mm, and the inner race is running on a hollowed shaft, the prop output shaft sits in the middle of all this. I dont think there is a puller out there small enough and strong enough to grab on the inner race of the hollowed shaft (the small space between the prop shaft).

On the side of the input shaft, its as impenetrable as fort knox. Id like to get inside the foot to see what caused this catastrophic failure.

If anyone has any tips or knows where I can get a parts breakdown and a disassembly procedure Id truly be grateful.

SK.

Re: Mercury Mark 20 (circa 1955) foot repair

SK,
STOP! Okay, don't do anything else until you have a service manual in hand. Working on old Mercs is not like working on other old motors. Mercury was the first brand to really take off on the whole "special tools" thing. If you have the manual you can at least see what you would need to either acquire or fabricate. The rear gearcase cover was threaded, which is why it didn't have any obvious way of being removed.
Start at www.oldmercs.com. They have the service manual and will also have many of the other parts you'll be needing. There's lots of those gearcases out there with the rear part of the housing cracked out, so you shouldn't have trouble finding gears /shafts if you poke around for them. Try an ad at www.aomci.org (Webvertiser section).
The Mark 20 is a great old classic. Spending a bit on the manual is well worth the investment...
- Scott

Re: Mercury Mark 20 (circa 1955) foot repair

Wondering how you made out???? I just pulled mine apart and didn't need any speacial tools to do it. The only thing was a pin spanner wrench to remove the prop output shaft cover and the drive shaft cover. Each is a flat circle with 2 holes in them. You put the pins of the wrench into the holes and turn it counterclockwise to unsrew the covers. Once the prop cover is removed, Place the prop shaft in a vise with 2 pieces of wood so not to scratch the shaft, and using a raw hide mallet or a peice of wood against the case and tap the foot off the shaft. It will come right off as a complete unit. There will be one gear left in the very back of the foot. Then look into the foot and on the bottom of the drive-shaft is a 9/16" bolt with a little metal flage that must be bent to fit the wrench on. This bolt holds the gear onto the drive-shaft. After removing the bolt/gear and the water-pump cover, use the same method to remove the drive shaft you used to pull the drive shaft. It will all come-out as 1 unit, shaft, bearing,waterpump cartridge,impeller. The only thing left is the bottom needle bearing that the drive shaft used. If this is bad, you will need a tool to get that out. Like chinawalker said, you can find lower units on-line for $70.00-$150.00 depending on what shape it's in. But you can also rebuild your's with new bearings and seals, then you'll know it will last a life-time with proper care. Used ones are all over the place, but you just don't know what you're getting. You'll have to trust what the seller tells you. Either way, you can get that lower unit going again with-out much of a hassle or money. The only special tool is to remove the waterpump cartridge if still in the lower unit. And the driveshaft needle bearing. Also the shift assembly, but that rarely goes bad. It's o.k. to use some heat if things are "stuck". You'll need a press and such to change the ball bearing that are on the gears. You'll see, once you get it apart. BTW, there are sites that have an exploded view of the motor. http://www.wnyaomci.wizardoutboardforum.com/manual.html is a good one and you can get it full page. As already said, a manuel is worth it's weight in gold. Remember, there is still many,many, mark 20 floating around. They are not "collector items" and thus big money. Some people think they are. You should have no problem finding a lower unit for $85.00. Don't pay anybody more unless it's been totally rebuilt. Good luck, and don't be afraid to ask before you get the drill out again. The motors are not as bad as the reputation they have for repair. The motor is made to come-apart. It's just different than the other motors.