'71 Merc 800 lower unit mating issues

[Huron Angler]

Having a tough time getting the lower to bolt up as it should.

My understanding is that everything needs to be in FWD gear to do this correctly. Is this correct? The flywheel is spun to allow the teeth to lock in I believe.

I'm also having difficulty getting it to fit around the black rectangular rubber base for the water pump as well.

I will be ordering a new impellar kit also since I managed to crack the plastic water pick-up tube during my "learning" process.:facepalm:

Any tricks I should be aware of that might help out?

 

[Laddies]

Re: '71 Merc 800 lower unit mating issues

With todays fuels the exhaust seal can expand, if yours does not set back against the casting replace it. I also prefer to assemble the units in reverse gear as the lower unit is less likely to jump gear in reverse while turning the shaft.

 

[Huron Angler]

Re: '71 Merc 800 lower unit mating issues

Thanks Laddies, we'll give it another shot this weekend and see what happens

 

[Moody Blue]

Re: '71 Merc 800 lower unit mating issues

One thing I have noticed putting mine together is that the upper and lower shift shafts tend not to line up perfectly when re-installing. The upper shaft tends to move off-center preventing the two shafts from engaging and thus preventing the LU from fully seating. I have to stick my finger in the opening at the front of the midsection just above the LU to get the upper shaft to align with the lower as I raise the LU into position.

I find that installing the LU with everything in neutral is easier for me. In neutral, the shift detent is "positive", there is no play in the shift shaft rotation at all. In FWD, there is ALOT of freeplay and in REV there is some freeplay. There have been many discussions in this forum about which method is preferred.

Another thing that may help, is apply a little vaseline on the inside of the exhaust tube seal and on the outside of the exhaust tube itself. Helps the exhaust tube slide into the seal during assy.

 

[carholme]

Re: '71 Merc 800 lower unit mating issues

Moody;

Not to open an argument but what I have found when the amount of free play exists in the detent positions, it is usually at the splined connections and coupler between the lower and upper shift rods.
With a good follower and shift cam and good spines between the top and bottom rods, the detent positions on the cam should all be positive.

Gerry

 

[Maxz695]

Re: '71 Merc 800 lower unit mating issues

Irellavent post

 

[Moody Blue]

Re: '71 Merc 800 lower unit mating issues

Moody;
With a good follower and shift cam and good spines between the top and bottom rods, the detent positions on the cam should all be positive.
Gerry

Not entirely true. The design of the shift cam is such that when in FWD gear, the cam is free to rotate about 120 degrees. The reason for this is that in FWD, the cam follower rides on the "body" of the shift cam. Not until either N or R are selected does the cam follower actually ride up onto the respective lobes and into the detents. The REV detent has a different profile than the neutral detent and thus has a little more "play" than the neutral detent which is absolute.

That all being said, I am referring to having the LU off the motor and getting it setup to re-install on the motor. Once the LU is back on the motor, then the shift positions become much more positive due to the fact that the shift cable is restricting rotation of the shift shaft thru less than 90 degrees thru F-N-R.

 

[Maxz695]

Re: '71 Merc 800 lower unit mating issues

Irellavent post

 

[carholme]

Re: '71 Merc 800 lower unit mating issues

I too give up, you cannot even have a reasonable conversation here.

Sorry Moody, wasn't in reference to you.

Gerry

 

[Maxz695]

Re: '71 Merc 800 lower unit mating issues

Irellavent post

 

[Maxz695]

Re: '71 Merc 800 lower unit mating issues

Irellavent post

 

[carholme]

Re: '71 Merc 800 lower unit mating issues

Maybe when you learn to communicate in some fashion that is understandable, I'll pay attention to you but until then, Keep on.

Gerry

 

[Maxz695]

Re: '71 Merc 800 lower unit mating issues

Irellavent post

 

[carholme]

Re: '71 Merc 800 lower unit mating issues

Last word on this matter. Maybe you cannot read either! If you notice, I was talking to Moody Blue about play in the splined connections and nothing to do with what gear the LU should be in.

End of story.

Gerry

 

[Maxz695]

Re: '71 Merc 800 lower unit mating issues

Irellavent post

 

[Moody Blue]

Re: '71 Merc 800 lower unit mating issues

Maxz695, you've managed to somehow turn a simple discussion into a heated argument. If you take a moment and go back to re-read the posts you will see that Carholme had not mentioned anything about what gear to reinstall the LU. If you read further, I was supporting the fact that I (not saying right or wrong) prefer the neutral position over FWD or REV. To each his/her own. You're getting all bent out of shape over nothing.

Huron Angler, hope you get something positive out of all this.

 

[Chris1956]

Re: '71 Merc 800 lower unit mating issues

Neutral is the only detent in the gear selector. As Moody said, forward and reverse allow the lower shift shaft to rotate a lot, which usually messes up the synch with the upper shiftshaft. Laddies has great experience, and while I respect his opinion, I have never had luck trying it his way. I also always turn the flywheel to mate splines with the driveshaft

I set the gearcase in neutral, set the control in neutral and try to install the gearcase. Turn the flywheel to mate the driveshaft splines, use the plastic casting in the midsection to line up the shift shafts and rock the shifter if necessary to mate the shift shafts.

 

[Laddies]

Re: '71 Merc 800 lower unit mating issues

Chris, I probably should not even respond to this thread as it turned into a pissing match before but I wanted to explain why, I use rev. gear for assembly. Mercury Marine says use foward in their manuals, I do not like forward as the unit will jump beyond foward because of the tension from the spring on the shift pin and the sloop on the reverse lock cam. I have never worked where there were 2 people available to install a unit, the boss said 1 man could do it and my arms where not strong enough or long enough to hold the unit and turn the flywheel, so I found that putting the unit in forward the shift detent pin was on the end or flat portion of the cam and the reverse lock cam did not turn the shaft as it was on the high point of that cam also so it did not cause a problem. The main thing is one uses what ever works for them, I will only recommend what works for me and I seldom disagree with any information inless I fell it's dangerous or will cost someone time and money.

 

[Maxz695]

Re: '71 Merc 800 lower unit mating issues

Irellavent post