Home › Forum › Ask A Member › 1975 Mercury 650 lower unit assembly
- This topic has 17 replies, 4 voices, and was last updated 9 years, 8 months ago by
dave-bernard.
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May 20, 2015 at 1:46 pm #1549
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 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?
🙄
May 20, 2015 at 6:29 pm #16537Just because you put the original shims back in does not mean it is properly shimmed. Every set of gears is slightly different. Also, is is possible you have the shims on the upper driveshaft mis-matched? There are sometimes shims UNDER the support bearing, as well as ABOVE the bearing. This is so the water pump base above the bearing seats against it. If you put all those shims on one side or the other, it may make a difference in pinion gear height. If the gear is too low, you may get the issue you noted.
How is the gear lash between the pinion and forward gear? I don’t have the book here, but it should be no more than a few thousandths. The gears should NOT be jammed together with no clearance.
May 20, 2015 at 9:14 pm #16544We would need an engine serial number for the exact parts breakdown. In the meantime, what did this replacement reverse gear/carrier assembly come from? Is the reverse gear pressed all the way into the bearing and the bearing, into the carrier? Is the big thrust washer in place? Shims? Chinewalker is right, too: every gear and housing is a little different. This is not OMC fantasy land. This is MERCURY, baby.
Long live American manufacturing!
May 21, 2015 at 2:15 am #16563serial number: 7059157 its a canadian motor.
i had an earlier discussion on this board taking it apart.
Chinewalker, i did not put any shims back because i did not take any out. As I remember from the manual (im at work now) the shims are under the bearing race under the drive shaft bearing and behind the forward gear bearing race. I did not need to take it out so i did not. Kinda sounds like that maybe the problem.
Billw yes it did look like the reverse gear and bearing was pressed into the carrier. I will look again. And yes the thrust washer is there also.
And yes i do like OMC much much more.
May 21, 2015 at 2:40 am #16565Ok looked at parts diagram online and looks like what i might need is a shim marked #64 on part diagram the shim for thrust washer to housing which i dod not have in my assembly. That might be it.
May 21, 2015 at 4:10 am #16572Are all the shims the same? Marine engine.com sells shims for the drive shaft and forward gear but not for the thrust washer housing shim.
May 21, 2015 at 9:19 am #16577No, they’re not all the same. Reverse is a bigger ID and OD than forward. They come as a kit with maybe five or six different sizes and you have to measure for the right size. This can be tricky if you don’t have the right tools. The good news is that the reverse shimming is far less critical than the forward and pinion shimming.
I can’t believe those have gone NLA. I even checked Mercury’s dealer site. If I had a nickle for every one of those old shims that I have tossed out…..Anyway, there are still 3 on eBay and probably hundreds more in dead dealer stock around the country. Part # 15-20927A 1.
Long live American manufacturing!
May 21, 2015 at 10:16 am #16578Thanks Bill, I’ll get order in today, do I have to take the reverse gear out to put them in ? From the diagram I think it looks like it is between the gear and thrust washer right?
May 21, 2015 at 8:57 pm #16620You pull the whole bearing carrier out, reverse gear still attached to it. The shims go between the step in the gear housing and the big beveled thrust washer. You don’t have to pull the gear out of the carrier.
Long live American manufacturing!
May 31, 2015 at 6:17 pm #17291Here 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 -
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