Where is Shift shaft ? 50 Merc

[Merc805]

I have a 50 hp 1979-80 Australian S/N 8050145 Mercury 4 cyl 2 stroke.<br />I want to replace the water pump impeller, but dont know where to disconnect the shift shaft from.<br />The Clymer (which covers many models) shows a "Guide block" somewhere in the the bottom of the cowling which is only a diagram and is useless.<br />Does anyone know what I need to actually unblot prior to dropping the L/U ?I am told that the drive shaft is stainless steel and has been removed a couple of years ago, so I'm hoping it wont be stuck .

 

[emckelvy]

Re: Where is Shift shaft ? 50 Merc

The shift shaft is splined, and the upper shift rod justs slips right off when you pull the lower unit down. <br /><br />When you pull the lower unit, leave the control box in neutral and don't reposition the control lever or the shifter shaft when it's apart. If you move either one and don't reposition them properly, when you reinstall the lower unit it won't shift correctly.<br /><br />Be sure to remove all the bolts holding the lower unit on, there's ones underneath the anti-ventilation plate, and may also be one back by the Zinc. Remove the Zinc to make sure you've gotten them all.<br /><br />Check the lower pump wear plate and also the cupped insert in the pump body for wear and scoring. Renew if you find any. They are relatively inexpensive and pump action with new parts will be much improved.<br /><br />With the lower unit in neutral, you'll probably need to rotate the flywheel in a CW direction as you're inserting the lower unit, to allow enagagement of the driveshaft and crankshaft splines.<br /><br />Also, sometimes the upper shift rod needs a bit of 'finessing' to get it to re-engage the shift shaft in the lower unit. It helps to have a strong light so you can peer up into the small gap betwen lower unit and exhaust tower and see how the shaft is engaging.<br /><br />HTH...........ed

 

[Merc805]

Re: Where is Shift shaft ? 50 Merc

Thanx<br /><br />The Clymer manual says somthing like.<br />50hp models "Remove shift shaft"<br />Think your description is a little clearer.<br />Are there different types of upper/lower shaft connections for other years/Horsepowers ?<br />Or is the disconnection pretty much the same.

 

[roscoe]

Re: Where is Shift shaft ? 50 Merc

Some makes and models use a large threaded union and jam nut to hold the two together.<br />Some use a clamp type device.<br />On some you need to disconnect the shiftshaft up top, inside the cowl, near the carb.

 

[Merc805]

Re: Where is Shift shaft ? 50 Merc

So back to my question.<br />Where would it be on mine, and why does the Clymer manual show a "Guide block" lining up with the exhaust manifold when covering "Shift shaft" removal ?

 

[roscoe]

Re: Where is Shift shaft ? 50 Merc

As Ed Mc. stated, your shift shaft should have a splined union just above the lower unit. It should slide apart as you drop the lower unit, as should the driveshaft.<br /><br />A little gentle persuasion may be needed,<br />good luck.<br /><br />In the event that it does not slide apart, check to see if there is a retaining screw in the union.<br />You will be able to see the union when the lower unit drops down an inch.

 

[Merc805]

Re: Where is Shift shaft ? 50 Merc

This motor is the type that has no power tilt, and it has a cam type lock that locks onto a rod to manually adjust the trim.<br />This is activated in neutral and in reverse, but is released in forward gear.<br />Does this need to be disconnected ? or is there antything tricky about it ?<br /><br />Thanx

 

[Merc805]

Re: Where is Shift shaft ? 50 Merc

bmp

 

[Merc805]

Re: Where is Shift shaft ? 50 Merc

Looks like this.

 

[Merc805]

Re: Where is Shift shaft ? 50 Merc

bmp

 

[Ken G]

Re: Where is Shift shaft ? 50 Merc

I have a '77 50 hp Mercury which uses the exact same procedure as your '79 for lower unit removal. Shift the motor into FORWARD and support the motor in the tilted up position. Mark the position of the zinc trim tab and then remove it. There is a nut beneath the trim tab which needs to be removed. You also have a nut on either side of the lower unit. As these are loosened the lower unit should start to separate. When the nuts are removed the lower unit should slide apart. There is nothing to disconnect on the shift shaft. The shift shaft is the small splined shaft in the forward area of the LU. Mark the position of the reverse lock cam in case it is removed or accidently falls off. If the reverse lock cam is reinstalled in the wrong position the motor will not shift correctly or the reverse locks will not function.<br /><br />When reinstalling the LU I sit on the left side of the motor. Align the driveshaft and water tube as you reinstall. As the gap closes you need to wiggle the shift shaft slightly with you fingers to realign it into the female upper sleeve. I then hold the lower unit with my knee and slightly rotate the prop counter clockwise to turn the driveshaft to allow for realignment in the powerhead. As the driveshaft mates the gap in the separation will close most of the way. Then reach up with your left hand and pull the reverse locks down which raises the reverse lock shaft allowing the lower unit to mate completely. Tighten the three nuts and reinstall the trim tab and you are all set.<br /><br />It sounds like it takes 3 hands and a couple of knees to accomplish this but it isn't that bad. I can remove and reinstall my lower unit in about 10 minutes by myself. An assistant may help but may lead to mashed fingers if they push when your fingers are in the wrong place.

 

[Merc805]

Re: Where is Shift shaft ? 50 Merc

Thanks Ken<br /><br />Do you know what that reverse lock rod connects to inside the leg ? As I am struggling with the fact that it moves up and down (push and pull), but there seems like there is nothing to unbolt or disconnect. Which is different to the shift shaft that actually turns left and right.

 

[Ken G]

Re: Where is Shift shaft ? 50 Merc

The reverse lock rod is not connected to anything in the lower unit. The upper end of the rod is connected with a threaded clevis and a pin to attach it to the reverse lock hook mechanism. The threaded clevis allows for adjustment of the length of throw of the rod.<br /><br />The lower end of the rod rides on the reverse lock cam which is on the shift shaft. The reverse lock cam was originally a plastic cam, the later one's are aluminum. If I remember correctly when the LU is shifted into forward the shift shaft turns clockwise looking from the top. The slope of the cam allows the reverse lock rod to drop and the spring on the hook assembly pulls the lock hooks up. When the motor is shifted into neutral or reverse the rod rides up the cam forcing the hooks down on the tilt rod locking the motor in place.

 

[Merc805]

Re: Where is Shift shaft ? 50 Merc

Thanks Ken<br /><br />Ever thought of writing manuals ? Clymer don't seem to have the same attention to detail as iboats members...<br />It is now perfectly clear.