Can't remove lower unit - 1970s Mercury 850

[Number21]

I'm trying really really hard to remove the lower unit and extension kit from a 1970s Mercury 850. It's not in very great shape, very weathered and corroded. I already have the powerhead pulled. I got all the bolts from the lower/extension out, and it absolutely will not budge. I soaked the whole thing in PB blaster. I went at it with 2 large propane torches. I pounded wood wedges between the lower unit and the extension. I might have separated it 1/16th of an inch.

What else can I do? I'm about to slice the extension in half!

 

[buddhapi]

Re: Can't remove lower unit - 1970s Mercury 850

well, if you have the power head off, we know the drive shaft isn't stuck. remember you need to remove the trim tab, and find that there is always a bolt coming from the top down. hopefully you haven't cracked up your housing!!

 

[Number21]

Re: Can't remove lower unit - 1970s Mercury 850

Yep, I got the bolt under the trim tab.

 

[Chris1956]

Re: Can't remove lower unit - 1970s Mercury 850

You might post a picture, as I have never seen an extension on a motor that old.

 

[Chris1956]

Re: Can't remove lower unit - 1970s Mercury 850

5 nuts plus a bolt, right?

 

[Number21]

Re: Can't remove lower unit - 1970s Mercury 850

5 nuts plus a bolt, right?

Yep. I'll try to get a pic tonight, I thought the extensions were relatively common. I've been noticing a lot of them since I found this one. It's on a somewhat rare short shaft midsection so that's the part I'm trying to save.

 

[Number21]

Re: Can't remove lower unit - 1970s Mercury 850

Here's a pic:

 

[Chris1956]

Re: Can't remove lower unit - 1970s Mercury 850

OK, I have seen those on my '93 Merc. If it is the same, the studs in the midsection are real long (5" longer than regular), so that is likely where the corrosion is holding the extension to the midsection. Was the bolt you removed (under the zinc) like 6" long?

Maybe there is another bolt in the rear of the midsection, that would normally hold on the zinc? Try a 1/2" thin wall socket (3/8 drive), and see what is there.

 

[Number21]

Re: Can't remove lower unit - 1970s Mercury 850

Yeah, the bolt was about 6" long. I looked in the hole on the back above the zinc with a bore light, there's definitely not anything else in there. Also I can't get the shift shaft to pull out, it's also seized.

Do you think it would work to slice into the extension with a cutting wheel where the studs are, and hopefully miss the driveshaft? I wanted to save the extension, but I'm not sure what else I can do...

 

[carholme]

Re: Can't remove lower unit - 1970s Mercury 850

Here is link to a picture of an extension kit I have on a '68 50hp. Note the two hexagonal extension studs, 3rd and 4th from the left. I am pretty sure that they have to be removed completely to get the extension to separate, not just the nuts removed from them.

http://imageshack.us/a/img822/7956/galg.jpg

Gerry

 

[Number21]

Re: Can't remove lower unit - 1970s Mercury 850

Here is link to a picture of an extension kit I have on a '68 50hp. Note the two hexagonal extension studs, 3rd and 4th from the left. I am pretty sure that they have to be removed completely to get the extension to separate, not just the nuts removed from them.

http://imageshack.us/a/img822/7956/galg.jpg

Gerry

Interesting...how do you get them out without separating the parts?

 

[Chris1956]

Re: Can't remove lower unit - 1970s Mercury 850

If you cut into the spacer, you should be able to cut the studs, and then replace them with the shorter studs. You will need to replace the driveshaft to go to the short motor. That is not a trivial task.

 

[Number21]

Re: Can't remove lower unit - 1970s Mercury 850

Yeah...I have a few other short lower units. This one also could be short, I'm not sure, part of the normal extension "kit" is a driveshaft extension as well. I would have thought it would have fallen off by now if it was, but the way everything else is seized...

 

[Chris1956]

Re: Can't remove lower unit - 1970s Mercury 850

It that driveshaft does have an extension, I would like to see a picture of it. Just curious

 

[Chinewalker]

Re: Can't remove lower unit - 1970s Mercury 850

If you do have to cut anything, avoid cutting the short shaft bits. They're quite scarce for the big motors!