Best method to undo/fasten 6mm nuts at exhaust pipe joints

[deltarider]

Some years ago, I have had some trouble with the 6mm nuts and studs at the exhaust pipe joints. A friend, who runs a yacht service and has lots of experience, offered to help with time sert, an American invention, in his opinion superior to the helicoil. I owed him many thanks and offered him and his sons my 4 gauge vacuum set which I didn't and do not really need.
At the occasion I have asked him, if there is a preferable method to undo and to fasten these nuts, so that the studs and/or the bores in the head run the least risk of getting damaged. Warm or cold? In his opinion it didn't matter.
Before the start of the riding season, I want to tighten some of these nuts just a tad further, because at least one pipe is not 100% tight. Now some of the studs were helped with time sert and some are still as they were. I can't remember which and for me it's not possible to see.
Before I undertake this, I'd like to hear what you think. My goal is to lower the risk the studs start turning. Is undoing and fastening best done with the engine cold of hot? Or is my friend right and does it not really matter. Please motivate your answer.

[Bryanj]

Rusty ones tend to undo better hot but all of them can and do sometimes bring the stud with them

[K2-K6]

I'd go with hot too.

Also, I use a drill with screwdriver function (definitely NOT the impact driver type) that you can move the torque setting up and down. These usually provide just rotory torque control with no impact vertically into the bolt.
Wind the torque setting down, put a piece of coloured tape onto the socket so you can see if it moves, then try tightening slightly first to see if it will actually turn, before trying to undo if that's what you want.

The aim is to put vibrations into it with as low torque as possible to get any corrosion to release and free the threads so you can then work on it normally.

[deltarider]

Thanks Bryan, it is the latter I try to avoid. Do UBS nuts, like the later models had, offer an advantage in this, or is it a matter of cosmetics only?
Thanks K2-K6. I have not been lucky in using a torque tool here. I have torqued the nuts only once to Honda spec, which in itself has been succesful. On the next removal, years later, the trouble began. Personally I'd advise it to do it by feel. These nuts need just a little and the copper gaskets are cooperative in this.
Whatever you do, make sure the fastening nuts at the rear footpegs are loosened first, so the exhausts can move that fraction of a millimeter.

[Johnwebley]

Before touching the nuts,

Copious applications of penetrating fluid,

Several cycles of heating,

Use a blowtorch on each one

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[McCabe-Thiele (Ted)]

My approach would be overnight soak with penetrating oil - then use a cordless impact driver.

[deltarider]

Maybe there's some misunderstanding. Rust is not in play. Not at all. The studs are 46 years old and my only concern is that when I turn the nuts - BTW, I see no need for another tool than just a socketwrench by hand - the studs will not also move. This because on reinstalling them, there's a risk the threads will damage. This is what happened the last time with some of them. So it's just whether it should be done cold or hot and if it is any use to replace the nuts by flange nuts.

[Johnwebley]

Basically your hoping the friction between the nut and the stud is less than the stud and the head?

My original suggestion of penetrating oil, and time to let it work is  my best plan,

If any of the studs do come out,

Remove the nut, using the method you prefer,

Then using 2 nuts locked together screw back in the head,

Not sure if I would use threadlock,

What do others think?


Then assemble as normal, using coppaslip on the thread, hopefully to cure future problems.

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[deltarider]

Thanks, John. I have done all that in the past. I guess the threads eventually become too old. When the worst comes to the worst, it's good to to know Honda4.nl has this on offer: https://honda4parts.nl/product_info.php?products_id=2378&language=en&ceid=4c92518617e2495bc6f4ea7dcaddf20e

[McCabe-Thiele (Ted)]

My 400 came with SS studs already fitted - when I removed the steel nuts they all stayed in place - might be that the previous owner put some locktite on the threads when he fitted the studs.