What does this plug cover?

[Uraijit]

So a few days ago, when I was pulling my outdrive, to get ready for my big engine replacement project, I was trying to drain the oil from the unit, and I mistook a plug for an oil drain plug. It was pretty badly stripped, and my attempts at removing it only further damaged it.

Once I'd determined that it was a lost cause removing by conventional means (heat, Impact driver, etc), I determined that I would have to drill it out before removal would be possible. Since my main priority was removing the drive, I decided to drill it, let it drain, and mess with fighting the bastard later, once the drive was off. Well I drilled it, and lo and behold, NOTHING came out. Well, at this point, I quickly realize that this is NOT a drain plug, and refer back to my manual. I then realize that the drain/fill plug is at the BOTTOM of the drive. *Doh!*

Anyway the drive is off now, and I'm waiting 'till Saturday to pull the engine, because I'll be able to use a forklift. Meanwhile, it's been in the back of my mind that I still need to finish removing that plug and replace it. According to this drawing, http://sterndrive.info.hosting.domaindirect.com/sterndriveparts/upper_gearcase_parts_drawing.html , part number 41, is simply called a "pipe plug". It looks to be about where the water tube would sit... What's it's purpose? I didn't feel like I hit anything when I drilled through the plug (I was careful), it just seemed like an empty void behind it.

I'm going to go ahead and replace the water pump while I'm in there, since I don't really know the history of the unit, and I'd rather just replace it now, rather than have to pull it all apart again in a couple of months, so while I'm in there, anything I should look for that, by some slim chance, may have been damaged?

 

[TilliamWe]

Re: What does this plug cover?

That's the vent/overflow plug for the gear oil. When you fill that drive, you fill it from the bottom. You pump the gear oil in until it starts to run out that hole. You then plug that hole and the bottom one.
Not uncommon for nothing to run out, as you always lose a little oil when you remove the fill fitting from the bottom. Just try to make sure that there was actually gear oil in the drive, though, okay?

 

[Uraijit]

Re: What does this plug cover?

No, the vent plug for the oil is on the left side of the drive.

This is on the right side of the drive, under a snap-in plug. You can see the end of the shift cable through there when the boat is put into gear...

If you click the link I posted, you can see a picture of the part I'm talking about. It's an MC1 drive. The Alpha drives don't have this plug...

 

[ziggy]

Re: What does this plug cover?

i don't know the purpose of the plug. but it needs to be there. i'm thinking it's now open to seawater. i think the plug leads to the shift slide area. so if it ain't there, ya can get water into yer shift cable area. ya didn't hit anything with the drill, replace it and move on.
while yer doing the impeller. if it's the first time yer doing it. ya might consider doing the waterpump houseing too. at the top of the drive shaft. look for an oil seal wear groove. there's also a seal on the bottom of the waterpump. i've never looked at mine. but it could groove the shaft too i'd think. ya could do a pressure test on the lower while it's off too. and then after reassembly, another pressure test of the drive when upper and lower are together to confirm that it's sealed.....
use a oem service manual when doing yer repairs.

 

[Uraijit]

Re: What does this plug cover?

Yeah, there's a button-type cover that is supposed to be there that covers the cable area. It wasn't there. What I'm talking about is the threaded plug beneath that.

I'm planning on redoing the whole impeller set (housing and all). The previous owner told me that the entire drive was rebuilt only about 2-3 hours before the 'incident' that took out the engine. Being that the guy had to be a total idiot for the 'incident' to have taken place though, I don't put much stock in what he has to say. I'm going to pull the drive apart this week and have a look. If drive has indeed been rebuilt, I'll throw it back together, and call it a day. But that gear oil was looking a bit dark when it came out, to have only had 2-3 hours put on it after a rebuild. I didn't see any silver in it either, like I would expect to see in a rebuilt gearbox... I'm a car guy though, not a boat guy, so I could be way off my mark here...

Anyway, anybody have any idea what this plug is for? I'm going to replace it anyway, but I'm just mighty curious what it is, and why it's there...

I'd like to get my hands on a #4 manual, but I can't, for the life of me, seem to locate one. I think the Alpha 1 manual will be close enough for me to be able to replace the impeller for now though... If I ever have to do anything more involved, I'll have to consider paying $100+ for a new one...

 

[TilliamWe]

Re: What does this plug cover?

If it's not a vent plug for the lube, then it's an access hole for something.

 

[JCF350]

Re: What does this plug cover?

If I ever have to do anything more involved, I'll have to consider paying $100+ for a new one...

Little over $70.00 listed from Merc on line.

 

[Uraijit]

Re: What does this plug cover?

If it's not a vent plug for the lube, then it's an access hole for something.

Sweet, it's confirmed then! We now know that the plug is there for SOME reason!

 

[whywhyzed]

Re: What does this plug cover?

......

 

[Fishermark]

Re: What does this plug cover?

Anyway, anybody have any idea what this plug is for? I'm going to replace it anyway, but I'm just mighty curious what it is, and why it's there...

Actually I believe it is simply a casting plug esentially. It simply covers a hole made during the casting / assembly process. It serves no purpose.... BUT - does need to be there.

 

[ziggy]

Re: What does this plug cover?

Actually I believe it is simply a casting plug esentially. It simply covers a hole made during the casting / assembly process.

i think that's a reasonable idea too. i don't have a alpha1, but when i was working on my 1 drive, which don't have the plug. i noticed while cleaning out the shift slide area. at the very back of the area where the shift slide, slides in. there was what appeared to be a hole going into the drive. where it leads i don't know or if it really was even a hole. but it woulda been about right inline with yer plug though i'd guess. if it really was a hole leading to somewhere, it might be easier to put there with a hole from the outside. plug required to seal it back up...... pure speculation on my part........

 

[JustJason]

Re: What does this plug cover?

It is a casting plug...
Instead of just putting a welsh plug over the hole Merc taps it... puts a screw in it, then puts a welsh over the whole thing...
The plug has probably never been out since the drive was made... no wonder you couldn't get it out.
The best thing to do obviously would be to get a new plug and loctite the thing in there. and get a new welsh. But if worse comes to worse you can probably epoxy the welsh plug back on as long as you don't use to much epoxy as to interfere with the shift slide....
If you don't get it right... your gonna get water in your bellows and probably in your boat.