1968 Merc 650 won't go into reverse

[fmfmedic]

Hello: I finally got my 650 put back together after replacing the short shaft with a long shaft housing and rebuilt lower unit. Now it won't go into reverse. Shift cam was against the follower in forward and shift guide on the power head was all the way forward when I put the lower unit back on. I can manually move it to neutral and it stays there. But to get it to reverse I have to push it all the way to the back of the slide and hold it or it slips into neutral. The shift shaft only rotates 90 degrees inside the housing, but when I took the lower unit off and checked with another shift shaft, it took well over 90 degrees to move the cam all to way to reverse. I have a bit over 1/16 of an inch end play in the propeller shaft. I think my problem is in the gear housing, but have no clue what it might be. Anybody have any suggestion? Thanks.

 

[Wingedwheel]

Re: 1968 Merc 650 won't go into reverse

When you say the LU is rebuilt do you mean the gears as well as the cam and follower?

 

[fmfmedic]

Re: 1968 Merc 650 won't go into reverse

When you say the LU is rebuilt do you mean the gears as well as the cam and follower?

What I did was take three identical 1968 lower units apart and pick out the best parts of each (carrier, bearings, gears etc.) and put them back together with new gaskets, oil seals, cam, cam follower, water pump and impeller. I used the manual religiously. One LU had a cracked casing and carrier, but good gears, another had a broken off skeg and the third wouldn't shift (bad cam and follower and worn gears). I used the LU which wouldn't shift and put all the good stuff in it. So far as I can tell, confirmed by a well-respected outboard mechanic, all the parts are supposed to be interchangeable, but you have to use the shims that came with the LU in front of the carrier. That was done. I have no clue why it takes more movement on the part of cam to go into reverse. One more clue. There was only one BB behind the cam follower on all three units, and that's all I put back in. Would that make a difference? My thought was that the reverse gear was set too far back and the clutch couldn't contact it, but when in reverse, LU off the motor, there isn't any more slack before racheting then there is in forward and not much, if any movement indicating that the gears aren't fully meshed.

 

[Wingedwheel]

Re: 1968 Merc 650 won't go into reverse

Just a question, but are you sure you put the cam on right-side up? That could make a difference.

 

[fmfmedic]

Re: 1968 Merc 650 won't go into reverse

Yeah, it's in right. Since I last wrote, I've taken the lower unit out, re-checked the shims and backlash and put it back together. The shift cam rotates about 90 degrees from forward to reverse at the lower unit. Put it back on the motor and tried again. The shift lever rotates 90 degrees but the slide goes from the very front to the very rear, with neutral in the middle. The control only goes 3/4 of the distance. I have the wrong control, or the connector from the slide to the shift rod is wrong. OR there is a LOT of flex in the shift rod. It's got me beat. I'm going to put it in the water and see if it shifts better when running. If it still doesn't work, I'll have to take some of my limited retirement money and go to a mechanic.

 

[Wingedwheel]

Re: 1968 Merc 650 won't go into reverse

It may just be an old cable that's stretched.

 

[carholme]

Re: 1968 Merc 650 won't go into reverse

It sounds more like the cam is not positioned correctly on the LU splines. Do you have a manual that shows you the picture of the cam flat side and where it should be?

When you built up the long shaft did you change the reverse lock rod to account for the increase in length?

Gerry

 

[fmfmedic]

Re: 1968 Merc 650 won't go into reverse

I used the manual to put the cam and cam shaft into place. And when putting the LU on. It does shift into all gears, but it takes a too much turn. There weren't any instructions as to where the cam should be positioned when putting the unit together except that it should be in forward. Maybe I should have ignored that advise and put it together in neutral as I started to do. If it can't get it to shift into reverse while running, that just what I'm going to do.

I used the entire long shaft without change in any parts. Just put the good power head and rebuild LU on it with a new gasket.

 

[Wingedwheel]

Re: 1968 Merc 650 won't go into reverse

It's really starting to sound like your LU and shifter are in different positions. It should go together with both in neutral.

 

[fmfmedic]

Re: 1968 Merc 650 won't go into reverse

I got it together and it shifts. Had to use neutral as suggested above. Why does the Clymer manual say to put it together in forward when that obviously doesn't work? Anyway, thanks for all the good tips!