Hi mod specialists:

I cannot seem to remove this brass nut as easy as I thought. Taking a wrench to it causes the copper tubes to bend -- I didn't realize they bended that easily! Even trying with one hand on the "dosatore volumetrico", it still won't budge, and the copper tubes get strained.

Inside the nut is the 0.8mm gigleur that I'm replacing with a 0.5mm one. Any mech tips?

What about some PB buster. Helps me break loose bolts all the time. If you go this route, let it "soak" a little while after spraying it.

You can also apply heat for a couple seconds to expand nut and try that. Heat too long though and fitting will expand too, defeating the exercise.

I do some of the maintenance on my plane. I've learned a lot about working with soft metals, like aluminum and copper.

For fittings like this, you need to use two wrenches, one on the nut to be removed and a backup wrench on the fitting it is tightened down to. You use the wrenches in opposition to each other, with no force applied to anything else. A lot of times you just position them closely together and just squeeze the them like scissor blades with one hand and break the nut loose.

Also, no adjustable crescent wrenches, they don't fit very well and cause more problems. You can also use a flare wrench, which is sort of like a box end wrench with a notch cut out of that slips over the tubing. They have more flats to engage the nuts.

AeroKroil and MouseMilk are great penetrating oils, especially on non-ferrous metals. A drop or two and 15-30 minutes time to let it creep into the threads will usually make things a lot easier.

This.

nuketopia wrote: For fittings like this, you need to use two wrenches, one on the nut to be removed and a backup wrench on the fitting it is tightened down to. You use the wrenches in opposition to each other, with no force applied to anything else. A lot of times you just position them closely together and just squeeze the them like scissor blades with one hand and break the nut loose.

This.

But that is not the immediate solution to his problem.

The problem is that the interface between the nut and the back of the mushroom fitting is slightly scaled/corroded such that they are "locked" in the vicinity of the red markers. Try letting some white vinegar seep into the space and after 30 minutes or so, try slightly tightening the fitting (using the two wrenches as suggested). Tightening may break the seal.

Agree with Eric.

If there's scale, applying a little acidic solution (vinegar/descaler) to soften it first will help a lot. Follow up with a drop or two of penetrating oil after the acid.

A very slight tightening with the two wrench method, will often break loose the corrosion/scale and allow you to remove the nut.

Yup. Use as a last resort. Only a drop or two, not a spray. And don't get in the water path. Clean thoroughly before assembly.

Oil of Wintergreen is a real good penetrant. You can mix with food-grade light mineral oil and have a pretty safe penetrant for food surfaces. Oil of wintergreen is toxic in high doses. Again, not in the water path and clean thoroughly, use sparingly.