replacing the exhaust/intake bolts

So im installing a new header on my 99 and i was wondering if I should replace the bolts while I have them off. Most of them look pretty good but a few of them definantly have some wear on them. I have a few that the washer wont come off the bolt from all the crud built up on them. I wired wheeled the heads and threads clean.
When I do install the new/old bolts what should I put on the threads? I know there is something I should put on them but not sure what.

copper coat its an old shadtree mac thing to do the copper melts and the bolts dont seize up that way.I have done it for yrs next time they come right off. use grade 8 bolts or stainless steel bolts .the bolts go thru alot of heating and cooling

from all my research ive read since i am doing this soon all posts say dont use grade 8 on the exhaust, they are more prone to snap when they get heated . stainless are good , grade 5 are good. you can get those washers for free at any junkyard if ya just throw a handfull in the tool box, otherwise they are like 6$ each at the dealer, i bought some then took em back and realized i had a bag of em ive collected from junkyards years ago that i forgot i had....anyway, i now have stainless. ill agree that some sort of copper on the bolts is a reasonable idea.

wildcar said:

So im installing a new header on my 99 and i was wondering if I should replace the bolts while I have them off. Most of them look pretty good but a few of them definantly have some wear on them. I have a few that the washer wont come off the bolt from all the crud built up on them. I wired wheeled the heads and threads clean.
When I do install the new/old bolts what should I put on the threads? I know there is something I should put on them but not sure what.

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PM 5-90, he has some interesting takes on manifold studs and bolts. You need to get new Belleville washers to keep things from working loose.

my uncle tought me about it he had been working on cars for 60 yrs .I was wroking on a big block Ford and the manfold bolts always brake off and you have to drill them out .he came by one day and told get the can of copper coat and put some on the new bolts next time you do that you wont break them. It was about 4 yrs later had to change the gaskets put a 9/16 scoket on them and they just poped loose and came right out no ploblem so been doing that ever sence.

blondejoncherokee said:

from all my research ive read since i am doing this soon all posts say dont use grade 8 on the exhaust, they are more prone to snap when they get heated . stainless are good , grade 5 are good. you can get those washers for free at any junkyard if ya just throw a handfull in the tool box, otherwise they are like 6$ each at the dealer, i bought some then took em back and realized i had a bag of em ive collected from junkyards years ago that i forgot i had....anyway, i now have stainless. ill agree that some sort of copper on the bolts is a reasonable idea.

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Its weird you say dont use grade 8 bolts. I thought bolts that have 6 lines on them are grade 8, thats what came off my Jeep. I dont see how grade 8 is weaker than 5.
So i definantly need copper coat, And i should get new washers. What ever the factory put on my bolts when they installed them worked, i didnt have any problems removing any of my bolts. Now the 2 exhaust bolts were another story

wildcar said:

Its weird you say dont use grade 8 bolts. I thought bolts that have 6 lines on them are grade 8, thats what came off my Jeep. I dont see how grade 8 is weaker than 5.
So i definantly need copper coat, And i should get new washers. What ever the factory put on my bolts when they installed them worked, i didnt have any problems removing any of my bolts. Now the 2 exhaust bolts were another story

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SAE8 is stronger than SAE5, but SAE8 will lose strength faster than SAE5 due to heat-cycling. That's why I say to use SAE5 in place of SAE8. I have verified this experimentally, using heat-treat ovens as a project for Materials and Processes a few years back.

The factory uses SAE8 because they use SAE8 everywhere else, and they're trying to keep logistics simple.

If you have steel screws and nuts holding your manifold in, replace them when they come out. I typically cut new studs out of brass threaded rod (3/8"-16, about 2-1/4" long) and replace them. Screws? I prefer silicon bronze screws, with SAE5 carbon steel being a second choice.

Reuse the Belleville washers, they're there for a reason! Don't bother with flat washers - they'll just magnify the problem of differential expansion (I've gone into this in some depth before, and I don't feel like doing it again. You can probably still find my discussions on it around here, if you look.)

You can use LocTite on them as well - it will help prevent seizure of carbon steel screws, but you'll want to only use LT #272. Nothing else can handle the heat, and it will break down in the first half-hour of runtime.

Replace the collector stud nuts with brass pieces - they should be threaded 3/8"-16. I use brass hardware all through my exhaust system, and it makes it so much easier to work on...

Just because the factory did it a certain way doesn't mean it's the best way to do it. Most hardware exposed to water gets replaced with brass or stainless. Exhaust hardware? Brass. You start to get the idea.

5-90 said:

SAE8 is stronger than SAE5, but SAE8 will lose strength faster than SAE5 due to heat-cycling. That's why I say to use SAE5 in place of SAE8. I have verified this experimentally, using heat-treat ovens as a project for Materials and Processes a few years back.

The factory uses SAE8 because they use SAE8 everywhere else, and they're trying to keep logistics simple.

If you have steel screws and nuts holding your manifold in, replace them when they come out. I typically cut new studs out of brass threaded rod (3/8"-16, about 2-1/4" long) and replace them. Screws? I prefer silicon bronze screws, with SAE5 carbon steel being a second choice.

Reuse the Belleville washers, they're there for a reason! Don't bother with flat washers - they'll just magnify the problem of differential expansion (I've gone into this in some depth before, and I don't feel like doing it again. You can probably still find my discussions on it around here, if you look.)

You can use LocTite on them as well - it will help prevent seizure of carbon steel screws, but you'll want to only use LT #272. Nothing else can handle the heat, and it will break down in the first half-hour of runtime.

Replace the collector stud nuts with brass pieces - they should be threaded 3/8"-16. I use brass hardware all through my exhaust system, and it makes it so much easier to work on...

Just because the factory did it a certain way doesn't mean it's the best way to do it. Most hardware exposed to water gets replaced with brass or stainless. Exhaust hardware? Brass. You start to get the idea.

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Thanks, i see you definantly did some research on the subject.

5-90 knows his metallurgy like no other by the sounds of it