Merc 800 Reverse Problem

AugustMoose87

Seaman Apprentice
Joined
Mar 21, 2010
Messages
36
Really hoping I can get some help figuring this one out... I've been chasing this problem for a while now. See http://forums.iboats.com/forum/engi...iner-outboards/549720-1978-merc-800-shift-cam and http://forums.iboats.com/forum/engi...boards/500139-shifting-problems-in-lower-unit


The motor is a 1978 800 (80 Hp, 4 cylinder) serial 4832396. I have been having trouble shifting in to reverse. I have replaced all three of the cams/cogs in the control box, as well as the shifting cam and follower in the lower unit. Yet I STILL can't shift in to reverse... The center "cog" (not sure what it really should be called) in the control box just slips past the shifting cam - the motor stays in neutral, and the control box is stuck in reverse. I can tear the control box apart, realign things, and I'm good to go, as long as I don't try to shift in to reverse...

Twice now this has caused a test drive for a possible sale of my boat to go south... Any thoughts before I take it to the middle of the lake and turn this motor in to fish habitat?? :frusty:
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Have you tried a different control box? How easily does it shift with just the cable? (You should be able to select and deselect Reverse (and forward ) with very little effort on you hand.)
 
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GA_Boater

Honorary Moderator Emeritus
Joined
May 24, 2011
Messages
49,038
Why don't you re-cap from when the problem began. Doing a quick look back, it started when you removed the LU to fix a "small hole". Can I assume it was fine before this "small hole" appeared?
 

AugustMoose87

Seaman Apprentice
Joined
Mar 21, 2010
Messages
36
Have you tried a different control box? How easily does it shift with just the cable?

No, mainly because when the lower unit is off, everything is like butter - virtually zero resistance. I took the box apart, and using my hands to push the shift cable, it was all over - some times it took a pretty good amount of force to get it to reverse, and other times it took very little.

Why don't you re-cap from when the problem began. Doing a quick look back, it started when you removed the LU to fix a "small hole". Can I assume it was fine before this "small hole" appeared?

To be honest, I don't know... I have always hand launched (no power) and only remember using the 800 in forward. It is entirely possible that this has always been an issue, and I just never realized it. And the hole was from corrosion and was above the gear housing - it was just an ascetic repair.


I THINK that I remember correctly that once I replaced the clutch cam and follower, it worked ok. But it has sat unused for over a year now. I originally thought it was the cables binding up, so I started treating them with WD-40 - but once I disconnected them at the motor, I realized there was zero resistance in them... My next thought was to check the LU oil - it wasn't great, but it wasn't terrible either (not dirty at all, and a little bit of water). My current thought/hope is that the water allowed a bit of corrosion on things, and now that I have clean oil in there, if I continue to work things back and forth, the lube will free things up and the corrosion will get knocked loose... But I'm also wise enough to realize that's a pretty long shot...
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
38,111
Propeller must be turning when shifting from nuetral to reverse.-----There are supposed to be small holes in the lower unit for freeze protection in cold climates.
 

AugustMoose87

Seaman Apprentice
Joined
Mar 21, 2010
Messages
36
Prop is turned by hand when the motor isn't running. And the hole repaired wasn't one from the manufacturer - it corroded from the previous owner taking poor care of it, and leaked exhaust when the motor was running.

I'm cautiously optimistic that I was on the right track thinking things in the lower unit may have seized up from sitting over a year. I pulled the lower unit and started messin'. When I took it off, my ghetto method of measurement (a fish scale at the end of a box wrench) said it took 0# to go from R-->N and from N-->F, 3.5# to go from N-->F and over 20# to go from N-->R. After working things back and forth repeatedly, I let it sit for an hour or so, and when I came back to it, it took 0# R-->N and N-->F, and 3-4# F-->N and N-->R. I'm going to work things back and forth a little more, then reinstall the LU and see what my control box does... Wish me luck
 
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