1975 Merc 850 lower unit re-install help

[malverts]

I have 2 1975 Merc 850's, one is generally for parts. I wanted to swap lower units because the vent screw was not removeable on the active 850. I pulled both lower units and discovered that the active Merc had a pre-load pin on the top of the drive shaft and the other lower unit did not. Are these inter-changeable?

Secondly, as I attempted my reinstall I can get the lower unit to snug up within a 1/2" to 3/4" with no problems. It makes a contact noise at this point. It will snug up if I tighten the nuts (little force needed/stubby wrenches). Still, just wanted to check if this sounds normal?

Any pointers?

 

[Chris1956]

Re: 1975 Merc 850 lower unit re-install help

The LU with the preload pin do interchange with the non-preload pin ones. That is not an issue.

Have you tried a hand impact driver to loosen the vent screw? As for your reinstallation problem. You need to aline the shift shaft and drive shaft splines with the upper shift shaft and crankshaft splines, respectively. Make sure the control and the lower unit are both in neutral. Turn the flywheel until the driveshaft splines mate with the crankshaft. If the shift shaft splines don't quite lineup, you may need to rock the throttle handle a bit to line 'em up.

 

[malverts]

Re: 1975 Merc 850 lower unit re-install help

Will the last 1/2 inch fit easily or is there light pressure needed to form a complete union?

Thanks,

Mike

 

[Chris1956]

Re: 1975 Merc 850 lower unit re-install help

Mike, That is hard to say. You should be able to push or pull the LU into place with your hands. If the bolts are corroded or the bolt holes on the castings are corroded ot a tight fit, it is a bit harder to do.

Don't force it, and you should be OK.

BTW - the upper shift rod will pop up, if it is not mated properly to the lower shift rod. You will see it under the carbs. Put grease on all the splines.

 

[Moody Blue]

Re: 1975 Merc 850 lower unit re-install help

I find that the last 1/2" - 3/4" of travel is harder because the exhaust tube must seat into the rubber gasket in the LU.

Try adding a little waterproof grease to the bottom of the exhaust tube and on the inside of the rubber gasket.