Removing threaded exhaust from manifold

[mbowser]

Originally Posted by wyb2

Leave a little bit of pipe, don’t cut it totally flush with the manifold. Cut 2 slits maybe 30 deg apart, then hammer inward on the exposed lip between them. Don’t try to use the chisel as a wedge between the iron and aluminum.

Once the strip between the slots is bent in and removed, the rest will likely unthread. If not, just keep taking out strips.

This worked for me on a flange that bolts to the engine header manifold. It was steel, not aluminum though.

That makes sense, I want to avoid buggering up those soft aluminum threads and that seems like it would be the safest way to do it.

However, the more I think about it, the more I realize that it's a terrible design. Even if they insisted on using aluminum for the manifold, instead of tapping the pipe into the manifold, they could have had a 'sacrificial' end cap with a threaded male pipe joint that the exhaust pipe could screw onto, but what do I know. Maybe there is an important design consideration that I'm not seeing.

[wyb2]

Originally Posted by mbowser

That makes sense, I want to avoid buggering up those soft aluminum threads and that seems like it would be the safest way to do it.

However, the more I think about it, the more I realize that it's a terrible design. Even if they insisted on using aluminum for the manifold, instead of tapping the pipe into the manifold, they could have had a 'sacrificial' end cap with a threaded male pipe joint that the exhaust pipe could screw onto, but what do I know. Maybe there is an important design consideration that I'm not seeing.

Cost. That super important, very technical design consideration is usually just cost.

Your idea would probably work just as well and be much easier to fix. But that end cap sounds like a custom part, so only easier to fix as long as you could still buy them. And it would cost a little more.

Someone upthread mentioned aluminum pipe, also would probably work better. But I’d be curious to see the price.

I suspect if you do get it out and replace it, a healthy amount of quality anti-seize will be will be the most cost effective, and good-enoughest, solution going forward.

[pbiJim]

Aluminum expands roughly twice as much as steel does for the same change in temperature. If the steel is on the inside & the aluminum is on the outside, then heat is your friend. A few hundred degrees makes a big difference.


Slicing the inside of a pipe & hammering it out of an aluminum female thread is a good way to damage the aluminum, unless you are VERY good at doing that sort of work.

[Stu Jackson]

The blowup parts diagram seems to show the possibility of a flange that is applied to the back of the manifold into which the pipe attaches, rather than directly pipe to manifold. That's because of the three studs that appear around that circular hole. I also say this because my Universal built on a Kubota block has a flange held on by studs to the manifold to which the riser is screwed to. I did not see a specific reference to a flange in your diagram though.

Really when you think about it, how would a riser pipe be installed on a manifold when the engine was IN the boat without a separate flange?

Good luck.

[pbiJim]

Originally Posted by wyb2

...
Someone upthread mentioned aluminum pipe, also would probably work better. But I’d be curious to see the price...

https://www.fixsupply.com/tubing-pip...-pipe-nipples/

[mbowser]

Originally Posted by pbiJim

Aluminum expands roughly twice as much as steel does for the same change in temperature. If the steel is on the inside & the aluminum is on the outside, then heat is your friend. A few hundred degrees makes a big difference.

Do you think there would be any possibility of deforming the aluminum when heating with a propane torch?

Originally Posted by pbiJim

Slicing the inside of a pipe & hammering it out of an aluminum female thread is a good way to damage the aluminum, unless you are VERY good at doing that sort of work.

I am not very good at that sort of work, and that's what terrifies me.

[deblen]

Originally Posted by wyb2

Leave a little bit of pipe, don’t cut it totally flush with the manifold. Cut 2 slits maybe 30 deg apart, then hammer inward on the exposed lip between them. Don’t try to use the chisel as a wedge between the iron and aluminum.

Once the strip between the slots is bent in and removed, the rest will likely unthread. If not, just keep taking out strips.

This worked for me on a flange that bolts to the engine header manifold. It was steel, not aluminum though.

Thanks.
This is what I was suggesting-slot the pipe stub & collapse the pipe inward on itself at the manifold end plate using a cold chisel, or if you have a big vise,crush the slitted pipe stub inward on itself. This should leave the alum. threads perfect

[wyb2]

Originally Posted by pbiJim

https://www.fixsupply.com/tubing-pip...-pipe-nipples/

OK, so as an example, looks like $52 for a 2” elbow in aluminum and $25 in black iron.

Not my project, I’m not going to price it out. But 1/2 off can be alluring for both DIYers and OEMs.

I may spring for it if it were my project. Of course it likely moves the dissimilar metal interface to a different location, rather than eliminates it.

[stormalong]

Be very careful heating aluminum. Spread the heat around and do it slowly. Point heating with a butane torch could melt the aluminum. I once unintentionally melted a piece of 1/4 inch thick aluminum plate on my propane stove.

[mbowser]

Originally Posted by wyb2

OK, so as an example, looks like $52 for a 2” elbow in aluminum and $25 in black iron.

Not my project, I’m not going to price it out. But 1/2 off can be alluring for both DIYers and OEMs.

I may spring for it if it were my project. Of course it likely moves the dissimilar metal interface to a different location, rather than eliminates it.

My previous boat had a W21 in it and had same issue (that one I never even tried to get if off the manifold, but I spent a fair amount of time cleaning it up, so I think that this is a common installation material.

[deblen]

You can't be anymore crude than this guy.....
Note: the propane heat didn't help!

https://www.youtube.com/watch?v=eN49BcQ2sBo

[mbowser]

Originally Posted by deblen

You can't be anymore crude than this guy.....
Note: the propane heat didn't help!

Ha, I actually saw that one while searching online... I don't want him near my manifold.

[pbiJim]

Originally Posted by deblen

You can't be anymore crude than this guy.....
Note: the propane heat didn't help!

That guy didn't apply heat correctly. The goal is to heat the female so that it expands and creates a clearance in the threads. Heating the male is not beneficial.

[pbiJim]

Originally Posted by mbowser

Do you think there would be any possibility of deforming the aluminum when heating with a propane torch?




I am not very good at that sort of work, and that's what terrifies me.

The parts you want to be particularly careful about not overheating are heat treated parts like bearings, shafts, and gears. Heat treating of most metals is not affected by temperatures that do not exceed 300F. You can buy "temperature crayons" from welding supply shops that melt at specified temperatures. You can get one that is rated for 300F, mark a heat treated part with it, then watch the mark & stop heating if it melts.

Chances are, that although propane burns at a higher temperature (3,500F), you will likely not be able to get the part nearly that high because a little torch like that has limited heat capacity and a big part will wick away the heat faster than the torch can produce it. Aluminum melts around 1,200F, so it is technically possible to melt aluminum with a propane torch, but if the torch keeps moving that is pretty hard to do on something that is much larger & thicker than a beer can. An oxy-acetylene torch is a different story. That requires greater care, but works much better when used correctly.

For reference, Diesel exhaust gas normally runs around 900-1,300F depending on engine load & fuel mixture. Unlike gas engines, a richer fuel mixture burns hotter in a Diesel. The point is, that before the mixing elbow, exhaust parts on a diesel see an internal environment of at least 900F all day, every day when they run, & that heat source has a lot more heat capacity than a little propane torch.

Keep the torch moving. Apply heat directly to the female, not the male. Get her good & hot all the way around, then quickly try a pipe wrench on the pipe before the female cools down. You only have a few good seconds to break the seal before the female starts to cool & shrink. An additional method is to have someone run water inside the pipe just as you apply turning pressure to shrink the pipe quickly, before the female has a chance to also cool & shrink.

Some people would drill a 1/2" hole through the pipe & stick a steel shaft through it rather than use a pipe wrench. I find that to be convenient, as it lets me get equal turning pressure on both sides of the pipe & not need to worry about the jaws of the pipe wrench slipping or deforming the pipe to an oval that doesn't want to move in a round hole. It's nice to have a cool steel shaft to grab & not have to worry so much about wrench jaws slipping & causing you to bump your forearm into the hot metal.

I can't count the number of times I've welded the inside of a nut to a steel stud that broke off in an aluminum head & then turned it out with a wrench, as soon as the orange glow died down, about 3-5 seconds later. I've been doing that sort of thing for decades. There was once a bet involving a gallon of maple syrup regarding this method, but I'll leave out the sticky details of that wager.

[pbiJim]

I just noticed that you have a Niagra 35. I'm pretty fond of that boat. I've schlepped one across the Gulf Stream before. It was pretty well mannered. I find the boat to be big enough to cruise comfortably and small enough to handle easily. George Hinterhoeller was known for quality build work. Since the designer (Ellis) was an inch taller than me, it has plenty of head room for me too.