Exhaust Work (Muffler). Stainless Bolts Okay? Educate me on metallurgy.

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I have to replace a leaky muffler on my 1998 Toyota 4Runner so I went with the Walker Quiet-Flow which is made from grade 409 stainless. It's supposed to be a step up from the cheap-o aluminized steel that most replacement mufflers are made out of. Without paying too much attention, I ordered these stainless M10x1.25 nuts and studs off eBay (the grade is not mentioned): shorturl.at/eCGU6

However, being the OCD BITOG member that I am, I did more research into material grades and now I'm concerned that maybe I didn't get the right grade of bolts. Reason being that stainless steel may gall over time due to the high heat and dissimilar metals. Should I have gotten grade 8.8 steel flanged bolts instead? Or would simply applying copper antiseize rated for 1800 F be enough to keep the threads happy long term? The OEM bolting on the catalytic converter end appears to be steel and with some heat + lubricant I'm hoping it will come out nicely. The bolting on the tailpipe end has seized on with rust and I'll likely have to cut it off.

I am also curious why all the exhaust bolting kits (from Fel-Pro or Dorman for this vehicle) are a double ended stud style, whereas the OEM uses a steel flanged bolt on the catalytic converter end. With the doubled ended stud, you have to remove the nut, then remove the stud with vice grips if it's seized on which could be a huge pain. With a flanged bolt, you could just remove it in one go. I'm guessing with a stud you strain the threads much less during torquing such that it might be easier to remove later?
 
+1
I agree. However, if the exhaust work was closer to the engine and all of the twisting & heat that's going on up front, I'd go with the stronger bolts(grade 8).
 
High grade bolts suffer earlier corrosion and SST are not high strength … thin coat of Never Seize or Maalox (CaCO3) if you have some real reason to worry about galling and move on.
Why do they need to be high KSI to clamp thin/weak material ?
 
I've had stainless steel gall and seize the very first time you screwed them together.... some goofy thing for a steel mill filled with ceramic fiber insulation that had 18(!!!) stainless steel all thread rods poking up out of it with 18 stainless steel nuts to hold the top cover down. We made 6 of them, fought every one of them because we couldn't use anti seize on them at all. Gave me nightmares. Anti-seize and go SLOW, shouldn't have any issues.
 
Use some form of lubricant and install the stainless bolts. Anti Seize is best but anything is fine, as is any form of grease.
 
400 grades of stainless WILL corrode not rust, but almost the same. pipes wont pull apart like with 300 grades, 304 most common. 304 is non-magnetic + many stainless bolts are not very strong so check specs + as noted anti-seize on them. even 300 grade band clamps may use 400 grade bolts for strength. the plus with the wider band is better clamping + you might be able if needed remove pieces clamped together. i had a grade 304 system using borla mufflers on my 200 thou jetta over 10 yrs before trade, discolored but still pulled apart!! costly in 2001 + even more today. in most cases 400 grade is good enough for a long life, unless you need to pull it apart as i did for whatever reason.
 
I am not sure you need really strong bolts for exhaust work. The bolts you have should be OK. What about the pipes and similar, are they SS also? We have a local guy that welds up all stainless exhaust for a reasonable price. He has a supply of SS pipe and fits as needed. But pipes that will rust and a muffler that will not does not sound like a good idea.

The guy who does the SS work told me his father was one of the first shops in the Northeast to have a Midas pipe bending machine where they would bend straight pipe into an exhaust pipe. He said in the 1950s or 1960s. I heard about them but not sure I ever saw one.

Never-seize is great stuff but will wash off if exposed to road spray and salt. The area inside the nut will be fine but outside of the nut will be corroded or rusted.
 
Originally Posted by Skippy722
I've had stainless steel gall and seize the very first time you screwed them together....


This happens. Go with the stainless studs, some plain steel hardware store nuts, and anti-sieze.
 
If you are really being particular, like I am, you can order the OEM nuts and bolts from Toyota. Bolts and nuts are between $ 0.80 and $1.40 each.

I have no idea as to how to answer your question.
 
My wife's old Kia Sportage's tail pipe would rot out every 2-3 years. I got tired of fighting with the bolts, so I decided to replace them with stainless nuts bolts and lock washers. And a dab of never-seize for good luck. Never had a problem getting them off after that. I used the same one's at least 3 times before we sold the car. If standard bolts actually did come out without breaking, for some reason they would always loosen up after a while. Never happened with the stainless ones.,,,
 
I've had the hardware-store variety of stainless steel nuts and bolts seize via galling, so I would say to forget them.
I have found that drug-store antacids containing calcium carbonate work well....
 
409 is the cheapest grade of stainless. It is better than aluminized steel, but will still suffer from hot corrosion, compared with 300-series stainless, which is superior. 409 performs horribly for catalytic converter shells and shields.

Grade 8 bolts are used for strength only. They are hard. It is a terrible "upgrade" for exhaust application. Clamping strength is not a critical issue with exhaust work. You want to use soft bolts, which can be more easily cut, as is often needed to do during exhaust work.

Yes, stainless steel galls but a good slathering of neverseize should take care of that.

I made a lot of money studying metals for exhaust application in the 90s.
 
Used 5/16 grade 2 bolts etc for bolting exhaust sections together that called for 8mm.. Let 'em rust solid. Pound on a 6 point socket and a stout yank should shear the bolt.. Grade 8 with brass or copper nuts for header studs. Stainless is expensive and a PITN to drill when it breaks.
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As has been mentioned earlier. Use SS bolts in the 300 grade and silicon bronze nuts. Plenty strong , won't gall up and will last a good long time.
 
Weirdly enough, most of the stainless band style exhaust clamps I've used have had regular steel bolts. When the time comes, cut off the bolts with grinder, sawzall, etc. & put on new ones. Stainless U-bolt style clamps seem to break half the time when I install them if I crank them down, they seem weaker than the HD steel ones.
 
Originally Posted by bullwinkle
Weirdly enough, most of the stainless band style exhaust clamps I've used have had regular steel bolts. When the time comes, cut off the bolts with grinder, sawzall, etc. & put on new ones. Stainless U-bolt style clamps seem to break half the time when I install them if I crank them down, they seem weaker than the HD steel ones.


Oh yeah … cordless reciprocal saw done in a matter of minutes
Clamps are cheap … always a good chance of a twist off anyway
 
Originally Posted by bullwinkle
Weirdly enough, most of the stainless band style exhaust clamps I've used have had regular steel bolts. When the time comes, cut off the bolts with grinder, sawzall, etc. & put on new ones. Stainless U-bolt style clamps seem to break half the time when I install them if I crank them down, they seem weaker than the HD steel ones.


Cutting off U-bolts would be the easiest for exhaust work. However alot of times with OEM style flanges, one end of the flange usually has a welded nut so if you were to cut off a stuck bolt/stud, you'd have to cut it out from the welded side and replace the whole thing with two nuts + stud. Once the rust sets in, it's really hard to tell which side the welded nut is on.
 
Last time I did a stainless muffler I just got some Hillman grade 8, hex flange bolts and matching nuts from Lowe's hardware store. They were about $4 for two pairs, however I think Lowes stopped carrying those.

They were 3/8-16, don't recall if that was the original size or if original were M10. Don't care if I have to cut them off later, don't really plan on needing to, the muffler will probably outlast the rest of the vehicle and if it doesn't, I got it done the first time so it's a known job.

It's not a big deal to cut them off with an angle grinder and cutoff wheel, or a reciprocating saw but if they are hardened then get a carbide tipped blade, regular bimetal may self destruct trying to cut that.
 
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