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1978 Mercury 200 20hp help

scoomas

New member
I picked up a 78 Mercury 200 20hp and have been reviving it and have hit a speedbump. I had good compression, rebuilt the carb, changed the plugs and the motor started pretty easily.

I moved on to servicing the water pump and must've bumped the shift shaft somehow and read somewhere that the gear housing had to be disassembled to install the shift shaft.

So I ordered a lower unit seal kit and figured I'd replace everything I could while in there. The problem I'm having is the gear case cover retaining ring seems seized and I can't find a replacement or I'd just drill this one and break it apart and just replace it. I'm trying to figure out how different these retaining rings are throughout the years bc mines not making sense.

The serial number of my motor is 4955786 and all the diagrams I've looked at suggest my replacement ring is PN-72710. The one installed in my lower unit is marked "72695" and the only other numbers I was able to find in my LU were "16276006"

The only thing that *looks* identical that I can find online is PN-33410 which I believe is for the 77 model with serial number below 4351589.

I have the seal soaking in PB Blaster and I laser cut my own tool to try to turn the seal so I'm going to try tomorrow to see if the penetrant has worked at all. Has anyone else dealt with this? Am I screwed? Do I need a new lower unit that uses the 33410 cover ring that's available? Is the shift shaft able to be installed without pulling apart the gear case?

Thank you for any help. I hope I haven't rambled too much
 
I've tried turning in both directions even tho the ring on mine has "OFF" and am arrow pointing left and "ON" with an arrow pointing right.

I've let it sit overnight in penetrating oil and I'm going to leave it while at work today to soak as well. I'll see what happens when I get home.
 
The one installed in my LU is stamped with ON/OFF in the same direction as the 33410 in this listing. Im really curious as to how different the 33410 and the 72710 are

33410
 
Yeah I ordered a 33410 just to put my hands on it. If I had a line on the actual 72710 I would just drill this one out and be done with it
 
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