200 20 hp lower unit problem

[jimepage]

Hi guys:
New to this forum and boating so bear with me...I'm a machinist, not a mechanic!!
I have a 1979 200 20hp that would not shift into reverse...had the boat out last weekend and forward is no problem (22.6kph with 2 adults) but when shifting to reverse with the mercontrol, nothing happens except when the lever is put against the stop it goes full FORWARD (??)
I had a tech with a little experience look at the cable and said there is no problem there, but said the prop should rotate freely in neutral (which is does not) and NOT go click click click (which it does).
We took the lower unit off and the main shaft turns the prop in both directions (he says it should not, but spin freely) and the small shaft (gear shift?) does not turn at all or go up and down, wheich he feels it should. He thinks it's a problem in the back section where the gears are. Stuck in forward?
Any ideas on this would be helpful, I think I will drop this off and have them restore it to normal operations. I just want to confirm what he told me is in fact accurate.
Thanks for the help!

 

[Mac uk]

Re: 200 20 hp lower unit problem

Im no expert just a boater like you. !st thing is reverse gear problems are common with the Merc 20hp.

The drive gear turns the forward & reverse gear in opposite directions constantly. Gear selection is made by the ratchet (between gears on prop shaft), which is spring loaded & is pushed up/down the prop shaft by the cam follower, which is moved by the shape of the cam. When the ratchet is in the middle between the gears it doesnt transfer the drive from a gear to the prop shaft ( The ratchet is splined on the prop shaft). As the ratchet is spring loaded it will be pushed into the forward gear unless the cam pushes it towards the middle (neutral) or further into the reverse gear. It sounds like its the cam, it could be jamed or broken. does the shift shaft turn at all,(With the lower unit off, turn the drive shaft clockwise & try to select the gears).
Give the unit a good shake is there any ratling.