Mercruiser Sterndrive Gear Oil Leaking by Prop

[1985 Century Mustang]

I have a gear oil leak coming from the propeller. When I removed the Leg last week, it wasn't leaking. I went to put it back on yesterday, and noticed it was pissing oil everywhere by the prop. I'm assuming it's a seal. Question: Is this a hard job to tackle by a newbie? I have some mechanical skills. My Sterndrive is a Mercruiser Alpha One Gen One. Do I need any special tools, and are they expensive? Any videos, advice etc would help. Thanks.

 

[Scott Danforth]

MUST HAVE Technical Information for DIYers.

MUST HAVE Technical Information for DIYers. (< An @ Work Safe Search Version Of ^^^) If you have NEVER posted in this forum before, please click on How to ask a question link first. 1. How to Ask a Question .... Please Read This Before Posting A Question... 2. Miscellaneous Mercruiser...

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Miscellaneous Mercruiser Information

How to ID an Alpha Style Outdrive, and History. Mercruiser Alpha ID and History.pdf - 4shared.com - document sharing - download - Don S Explainer documents. 'Pre-Alpha' drives Which 'Pre-Alpha' drive? Where to Find Mercruiser Stern Drive and Engine serial numbers. Drive units In-line Engines...

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look in these links for the special tools.

you will be pulling the bearing carrier

 

[1985 Century Mustang]

MUST HAVE Technical Information for DIYers.

MUST HAVE Technical Information for DIYers. (< An @ Work Safe Search Version Of ^^^) If you have NEVER posted in this forum before, please click on How to ask a question link first. 1. How to Ask a Question .... Please Read This Before Posting A Question... 2. Miscellaneous Mercruiser...

forums.iboats.com

Miscellaneous Mercruiser Information

How to ID an Alpha Style Outdrive, and History. Mercruiser Alpha ID and History.pdf - 4shared.com - document sharing - download - Don S Explainer documents. 'Pre-Alpha' drives Which 'Pre-Alpha' drive? Where to Find Mercruiser Stern Drive and Engine serial numbers. Drive units In-line Engines...

forums.iboats.com

look in these links for the special tools.

you will be pulling the bearing carrier

Thanks for those links. I'll check them out, and see what I can find.

 

[1985 Century Mustang]

It seems I have a leak in the upper part of the sterndrive, I noticed oil is coming down the shaft. Guess I'm going to need to do a full seal, gasket job now.

Question: Can a newbie accomplish this? I'll give it my best. I built a makeshift sterndrive stand today in my backyard, it works for me. I sure wish I had a garage.

Drained the gear oil, removed the lower sterndrive bolts, almost freed, however i need to get a 3/8 Allen Key for the zinc, I don't have a size that big. Harbor Freight will have them. I'll get there today.

 

[1985 Century Mustang]

I found this nugget of a video. This will help me out, no doubt.

 

[nola mike]

It seems I have a leak in the upper part of the sterndrive, I noticed oil is coming down the shaft. Guess I'm going to need to do a full seal, gasket job now.

Question: Can a newbie accomplish this? I'll give it my best. I built a makeshift sterndrive stand today in my backyard, it works for me. I sure wish I had a garage.

Drained the gear oil, removed the lower sterndrive bolts, almost freed, however i need to get a 3/8 Allen Key for the zinc, I don't have a size that big. Harbor Freight will have them. I'll get there todayView attachment 381072View attachment 381073.

Good news is that the seals in the upper are much easier to replace than the prop shaft. With a gen 1 you can pressure test the halves separately and see where you're leaking. I wouldn't mess with the input shaft seal, but I'm sure others would. It's not a bad job if you have an earlier style drive, otherwise it's a bit more difficult and you need a dial torque wrench ($$). Probably will need to replace the upper and lower driveshaft seals. You'll need the special wrench to remove the big castle nut on the input shaft. Cheapies on eBay.

 

[Grub54891]

With the oil drained, pressure check the drive first. spritz of soapy water will show you where it’s leaking. Shift shaft is rather common on those, easy fix if that’s all it is.

 

[1985 Century Mustang]

@Grub54891 and @nola mike . Guys can you identify this part. I'm not sure if I need to replace this also, I'm doing my water impeller. I don't want not to leave this out if it needs to be replaced. It's that metal piece with the notches around it. Does this need to be replaced too. Just checking.

 

[1985 Century Mustang]

This shaft O ring on the lower unit was really loose. Could this have been one of my issues with regards to the leak?

 

[Scott06]

This shaft O ring on the lower unit was really loose. Could this have been one of my issues with regards to the leak?

View attachment 381089View attachment 381090

You are not supposed to put that oring back on vertical drive shaft. Merc used them
Originally and found they tended to damage the drive shaft seal when putting the two haves of the drive back together


The first photo u have of the shift shaft that seal can Also leave best to pressure test the drive and see what leaks or do a complete reseal

 

[1985 Century Mustang]

I just replaced the water impeller a little while ago, for the first time. I just found a bad lower oil seal on the upper half of the drive, it's in the water pocket area. I ordered a new seal and the seal driving tool. I think I may need a bushing too, it looks like it's missing a rubber bushing as well as it looks like it's missing more than the seal. Your thoughts.

 

[1985 Century Mustang]

You are not supposed to put that oring back on vertical drive shaft. Merc used them
Originally and found they tended to damage the drive shaft seal when putting the two haves of the drive back together


The first photo u have of the shift shaft that seal can Also leave best to pressure test the drive and see what leaks or do a complete reseal

Thank you. I'll remove it.

 

[dubs283]

Lower drive shaft housing seals

To replace the upper (larger pictured) seal you need to disassemble the drive shaft housing

 

[nola mike]

So you can see that damaged o ring on the gear shaft, looks like it got caught in that lower seal (which is why Merc deleted it). That seal keeps water from the upper drive shaft. Good chance that the shaft is rusted/damaged. If so, you'll need to install a speedi sleeve on it if it's grooved. You can drive the upper seal in with a socket if you haven't already ordered the special tool. The shift shaft seal in the lower can be a pain; you can pressure test the lower separately to see if that seal is leaking

 

[1985 Century Mustang]

So you can see that damaged o ring on the gear shaft, looks like it got caught in that lower seal (which is why Merc deleted it). That seal keeps water from the upper drive shaft. Good chance that the shaft is rusted/damaged. If so, you'll need to install a speedi sleeve on it if it's grooved. You can drive the upper seal in with a socket if you haven't already ordered the special tool. The shift shaft seal in the lower can be a pain; you can pressure test the lower separately to see if that seal is leaking

Thanks for the input.

 

[dubs283]

Yeah, a lot of folks post regarding the o ring on the drive shaft needing abatement.

If mercury has disregarded the o ring I've never heard of such, it's still provided with the oem w/p kit and always gets installed on my bench. Never once had an issue regarding the o ring after hundreds of installs, ymmv

Funny question, does any long time poster on this forum know the reason why mercury uses the o ring?

 

[1985 Century Mustang]

Do I have to use that 3/8 Allen bolt on the Stern Anode, or can I use a regular stainless bolt? Mine is pretty crusty and I don't want to put it back on. They are rather pricey too, just for a dang bolt.

 

[Grub54891]

@Grub54891 and @nola mike . Guys can you identify this part. I'm not sure if I need to replace this also, I'm doing my water impeller. I don't want not to leave this out if it needs to be replaced. It's that metal piece with the notches around it. Does this need to be replaced too. Just checking. View attachment 381086

yes, that is the shift shaft seal I mentioned. They make a tool for that also, common place to have a leak. You can pressure check it by holding your finger over the quad ring hole and pressurizing it, 15 lbs is all you need for testing. good to have a helper but I do it regularly by myself. Spritz with soapy water and it'll bubble if its leaking. Jiggle it around as you do so. The o-ring is deleted on the upper shaft as explained earlier. Use a stainless bolt for the anode.

 

[Scott06]

Do I have to use that 3/8 Allen bolt on the Stern Anode, or can I use a regular stainless bolt? Mine is pretty crusty and I don't want to put it back on. They are rather pricey too, just for a dang bolt.

You wont be able to get a socket on the annode bolt if you use a hex head bolt, hole in outdrive housing is too small . Clean yours up with a wire wheel or die.

if a sockethead cap screw is too pricey boating may not be a good hobby for you

 

[Grub54891]

You wont be able to get a socket on the annode bolt if you use a hex head bolt, hole in outdrive housing is too small . Clean yours up with a wire wheel or die.

if a sockethead cap screw is too pricey boating may not be a good hobby for you

Ugh. yeah that's what I meant. Should have said allen bolt. oops...