Unsticking a stuck lower unit

[panasonic]

Unfortunately, to get a torch in there, it's a pretty small area and I don't want to risk damaging other things.

Mini Mapp torch is your friend.

https://www.amazon.ca/RTMMFG-Oxygen-...34058813&psc=1

[zenoahphobic]

Heat without flame is best.
But it is the expansion that heat produces we want. It works both ways If you could freeze the shaft with liquid nitrogen may help (doesn’t burn paint that way).

[panasonic]

I use liquid nitrogen a lot, and it is funny stuff to work with. You have to put what you are trying to shrink into the container filled with it and wait until the boiling stops...then it is at the smallest it will be.
If you pour it on something that can't contain it then it will just boil away almost immediately.

You can stick your fingers in and out of a cup full quickly and it feels basically like cool air! Of course you can't leave them in there for more than a few seconds...less it will start to freeze your skin. There is a scientific term for this effect that I cant remember right now...lol

[DennisG01]

Mini Mapp torch is your friend.

https://www.amazon.ca/RTMMFG-Oxygen-...34058813&psc=1

Because of the location, though, the heat is going to transfer to other places. It's just too close to other things to risk it.

[DennisG01]

I use liquid nitrogen a lot, and it is funny stuff to work with. You have to put what you are trying to shrink into the container filled with it and wait until the boiling stops...then it is at the smallest it will be.
If you pour it on something that can't contain it then it will just boil away almost immediately.

You can stick your fingers in and out of a cup full quickly and it feels basically like cool air! Of course you can't leave them in there for more than a few seconds...less it will start to freeze your skin. There is a scientific term for this effect that I cant remember right now...lol

Ha! Mythbusters did an episode on something like that. They did it with, I think, molten metal - but I suspect the same principle would hold true with liquid N. Something about a temporary thermal barrier created around your hand. It was "something"-frost effect, I believe?

[panasonic]

Yes the Liedenfrost effect! On Mythbusters they used molten lead.

[DennisG01]

Yes the Liedenfrost effect! On Mythbusters they used molten lead.

That's one of those things were you can see someone do it... and you know if your "brain" that it will work... but your "gut" still won't let you try it!

[DennisG01]

Well... no luck. I tried everything. The comment about the shaft/crank currently being "welded" where when pulling them apart would cause the splines to disintegrate stuck with me all this time so I decided against cutting the shaft as there would be a good chance it would end up rendering the engine useless. I do have another crank sitting in another engine with a bad cylinder... but quite honestly, I don't feel like spending the time swapping the cranks.

Yesterday... I put the engine back on and will run it till the impeller gives up. In the meantime, I'll keep my eye out for a good deal on a sub-$10K F250.

Thanks for all the suggestions along the way!

[zenoahphobic]

Rusting is not welding. The problem is the metal that rusts expands from the added oxygen atoms.
So the problem here is that the bonding is going to get stronger and those forces will exert more and more onto the crankshaft until it fails. When that might occur? Atleast then they will probably separate. (Into a pile of rust)

[DennisG01]

UPDATE:

As a last ditch effort, I was at a local Yamaha shop for something else and got talking with their lead tech about my lower unit. I explained everything I did but he said he felt confident that he could get it apart. I figured, what the heck - give it a shot! A week later he called me and said "OK, I see what you were talking about, now!" He said he never came across one this hard. But we agreed to go ahead and keep going - he called a day later and said he had it about 1" apart - which is more than I ever got.

He said the upper splines of the driveshaft/crank seemed solid - which, in my mind, made continuing with this effort worthwhile. With that in mind, I said go ahead and keep going. I also dropped off my spare lower unit and our thought was that if it didn't all of sudden start to come off, then go ahead and destroy the existing lower and put a slide hammer on the remaining driveshaft stub. That's what he did. The spare lower is rebuilt and on the engine and he said the test ride went well... other than dropping RPM at high RPM's... but I already knew that

Anyways, just wanted to follow up that it's off. Although considering most people don't have a spare lower unit laying around, it's probably not a technique that most would use to get it off!

[DennisG01]

Rusting is not welding. The problem is the metal that rusts expands from the added oxygen atoms.
So the problem here is that the bonding is going to get stronger and those forces will exert more and more onto the crankshaft until it fails. When that might occur? Atleast then they will probably separate. (Into a pile of rust)

I understand the difference between rusting and welding. You read things too literally - hence the reason I used the quotation marks around the term welded.

[99yam40]

UPDATE:

As a last ditch effort, I was at a local Yamaha shop for something else and got talking with their lead tech about my lower unit. I explained everything I did but he said he felt confident that he could get it apart. I figured, what the heck - give it a shot! A week later he called me and said "OK, I see what you were talking about, now!" He said he never came across one this hard. But we agreed to go ahead and keep going - he called a day later and said he had it about 1" apart - which is more than I ever got.

He said the upper splines of the driveshaft/crank seemed solid - which, in my mind, made continuing with this effort worthwhile. With that in mind, I said go ahead and keep going. I also dropped off my spare lower unit and our thought was that if it didn't all of sudden start to come off, then go ahead and destroy the existing lower and put a slide hammer on the remaining driveshaft stub. That's what he did. The spare lower is rebuilt and on the engine and he said the test ride went well... other than dropping RPM at high RPM's... but I already knew that

Anyways, just wanted to follow up that it's off. Although considering most people don't have a spare lower unit laying around, it's probably not a technique that most would use to get it off!

well did he cut the shaft to get the lower off?
where did he cut it?
It would be nice if you had some pics to share ,even if it was after it was all done.
the shaft stub he pulled out ( see what condition it was in) and maybe the crank shaft hole after it came out to see how bad the rust was on the crank

[DennisG01]

I was out of town when he worked on this, but since the objective was to destroy the lower unit to access the shaft to cut it, I would assume it got cut at about the impeller level as that would probably be the easiest way to slip a zip saw in.

[99yam40]

so, I guess he did not show you the shaft he pulled out for you to see what condition the splines were in?

[ausnoelm]

A slide hammer is not going to be real good for the bearings……..best guess, seeing as he had it moved about an inch, is, he cut it through the lower unit join, done that a couple of times.