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1975 Mercury 650 lower unit assembly

H

Hagopis

New member
Well this was my first encounter with this lower unit.
I changed oil seals and o rings, changed the pinion gear and the bearing carrier with installed revers gear (used identical parts for the gears and bearing carrier) and heli coiled the vent plug. No problem but putting everything back together seems to be a problem. I must be forgetting something.
I reassemble, tighten the cover nut with the spanner wrench then everythning (drive and prop shaft) is seized tight. The shifter is in forward (I did not mess with the shifter cam and is pointing toward the oil plugs)

loosen the cover nut and pull out the bearing carrier a little and it loosens up. But while turning the drive shaft sounds like pinion gear is rubbing on something.

i did did not mess with the shims. The new pinion gears looks like it aligns perfectly with the forward gear.

did I over tighten the cover nut, is that even possible? Did I forget or loose some spacer between the housing and bearing carrier?
 
I suspect you lost a spacer. They can be purchased separately (here).

Does the pinion rotate smoothly with the prop shaft assembly out or loose?

Jeff
 
Yes it does. I think I need a thrust washer housing shim. I did not remove any other shims under the bearing racers under the drive shaft nor the foreword gear racer. It original did not have the thrust washer housing shim nor the the replacement but I think I need it. Do you all agree?
Are all the shims the same? You said it can be purchased here but where is here? It's not a hyperlink if that is what you intended. Marinengine.com sells shims but seems to be for the others not the thrust-housing shim. Are they all the same?
 
Shims come in various thicknesses. What you need is merely ENOUGH shim to keep the assembly from locking up. If it's a bit loose in reverse that won't hurt a thing. So, if you can find shims, buy a few and see what happens.

Jeff
 
Jeff, when they come do I have to remove the revers gears from carrier or does it fit over the gear to fit up against the thrust washer. I would think it should.
 
The shim(s) you need are thin little things that space the entire prop shaft assembly away from the front of the housing. They go in before the assembly.

Jeff
 
Here is an update. After 7 shims still did not turn smoothly. So I did what I should have done earlier and looked closer at it. Turns out the reverse gear was just a little different then the original. The original was good so changed them out and now turn very smooth after tightening no problem, without any shims like the original.

Question I have now is the shifter does not turn by hand easily. But with wrench to fit it turns with minimal force. Is that normal? I would think it is but some feed back would be appreciated.
Thanks
 
Congrats on the gear problem. As for the binding, sounds like the black plastic cams are buggered up or need grease.

Jeff
 
Well no I put new seal on the shifter rod, new plastic cam. Greased. It's the spring in the prop shaft behind the follower. The thing nagging me is should​ I put some shims on the reverse gear? That would take some spring pressure off the shifter rod. How can you tell? I don't have tool to check backlash/gear free play but by feel it feels right. Is that enough?
 
If you put the LU in reverse (off the motor) you can feel the amount of slack in the gears by holding one shaft and turning the other.

Here's what I've found: Contrary to forward gear, you can have a ton of slop/ slack in reverse since it gets used so little (and at low throttle). So, more slop is far better than too little, which burns up bearings.

Jeff
 
Perfect that is what I wanted to hear. There is a lot of slop in reverse. I do not what to add to it with more shims. Ok I think I'm done on this one.
Thanks again.
 
Update:
finally got it in the water and worked great up until last day of use up north in Canada. Lost reverse and oil leak (this occurred after I rescued a novice who flipped his canoe in the middle of the lake).

I guessed the circular nut holding bearing carrier had slipped and when I got it off I was right.
The problem I think is that the prior owner/ repair man strip the threads on the housing itself. Also I had bought new nut but was made of a hard plastic compound.
I just ordered new Oem nut and a nut holder tab too.

Question is how to better reinforce or secure the nut to the housing after tightening it and folding down the tabs. Epoxy/job weld/lock tight?
 
Drill a series of small holes through the casing into nut,insert some counter sink s/s screws with thread lock.Should hold it
 
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