Re: 1979 MERCURY 140HP
The fore and aft gears turn all the time the drive shaft is turning. The clutch dog slides back and forth on the propshaft (moved by the shifting fork) and either slides forward and engages the forward gear, or aft to engage reverse. With the lower unit removed the splined shift shaft moves rotationally (around in a semicircle) through the three positions...about 30 degrees apart as I recall.<br /><br />If you can control it ok like that (make it shift thru F N R) your lower unit is ok. If not, something is binding in the lower unit....possibly the dog is not free to slide up the shaft to engage the forward gear. Have you checked your oil for water? Did you find any if you did?<br /><br />Otherwise it's a matter of marrying your shift shaft spline to the engines when you insert the lower unit. You can play with both the lower unit and the engine's remote control levers and get both centered (neutral) then stab it. Should work.<br /><br />If you can't get the splines to line up so that the lower unit will go in that last couple of inches, you may have to go to forward gear on both so that you can rotate the prop to stab it. I like neutral better because you have a better chance of getting both centered. Can wrap a piece of rope around the shift shaft (in N) and slowly rotate it while attempting to marry the two sections. It'll work.<br /><br />Mark
<br /><br />Google Mercury Parts Express. Click on the Outboard Parts tab on the left. You'll need the serial number and they'll want a zip code. If entering your zip is uncomfortable, make one up. Then you can see a breakdown there. I believe you can also print.
