1978 mercury 20 hp lower unit

Queebs

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I have a 78 mercury 200 20hp outboard. I replaced the water pump impeller and housings. As I was putting the lower unit back together, I made sure the gear selector shaft was in neutral. While doing so I noticed that the shaft spun freely instead of clicking into the three different positions as it should. I wanted to ask for any advice before trying to tear into this myself. Anything would be appreciated thank you.
 

racerone

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Re: 1978 mercury 20 hp lower unit

What usually happens is that the strong spring pushes it into forward when you are not looking !!-------So use a vice-grip on the shift shaft and turn till you find nuetral again.---Then assemble to the motor.----May take some effort as it has a strong spring.
 

Queebs

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Re: 1978 mercury 20 hp lower unit

When I try turning the gear change shaft I don't feel any resistance. I can do it with my bare hands. It's like the splines aren't engaging. It caught once and I started turning it hard like you said, but it then became easy again. I pulled the shaft out and there was a gash across some if the splines as well as some metal flakes. So something isn't right here....
 

racerone

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Re: 1978 mercury 20 hp lower unit

Since you pulled the shift shaft out you now may need to dismantle the lower end for correct re-assembly.----Not that hard to do on a fresh water motor.
 

Queebs

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Re: 1978 mercury 20 hp lower unit

Well I have absolutely no fear of diving in and taking it apart! I just wasn't sure if there was an easy fix. Are there any instructions anywhere on how to take it apart and reassemble? Thanks for your help racerone.
 

jasbyo

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how did this work out for you? I purchased a 1979 20hp merc and the lower unit was taken off to change the pump. The motor is now stuck in forward. Having problems getting the shifter mechanism working. The manuals do not say to leave the shift shaft in place(as others have mentioned), and you can't b/c it is attached to the part at the head. Any suggestions?
 

racerone

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????----The shift shafts are splined !!!---They slide apart when you remove the lower unit.----When you re-assemle you need to make sure that the lower unit is in nuetral and that shift lever is in nuetral as well.----Work carefully and think this through.---It is not hard to do.
 

jasbyo

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The distal end of the shift shaft is splined(slides out of the lower unit) and the proximal end remains attached to the power head when the lower unit comes off. Some has said that the shaft should not be removed from the lower unit when removing it. This is not possible in a 1979 20 hp (likely the '78 as well). So, I am wondering is these people are incorrect, or will the cam shifter gear really come out of place and the lower unit then need to be taken apart and the cam realigned.

From the repair manual diagram, it looks like the shifter shaft has a set screw connecting it the head linkage and that it can be removed and used to shift the lower unit into neutral for reassembly. I haven't had the chance to look yet.

racerone, any thoughts? I can't imagine that that cam would pop out of place so easy, but then again, I wasn't the one who did the disassembly. The guy that I purchased it from said the gears all worked and that he was just unable to get it back together b/c the lower unit would not slide on all the way.
 
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