Gee oh Dee

I am going to replaclce my exhaust from the manifold back, but since its an87 I don't expect the two bolts holding the downpipe to the manifold to come free without breaking.

Can anyone tell me the size I should pick up from the hardware store?

I want stainless, and thread pitch doesn't matter as much as overall length of bolt.

Or are they studs that are in the manifold?

5-90

There are studs at the collector, not bolts.

The studs are threaded 3/8"-16 - use brass nuts, not CRES. CRES will gall on the steel studs, brass won't (and be much easier to remove next time. Further, they won't rust like mild steel.)

If you have to replace the studs, you'll need to press them out (can be done with a G-clamp and socket, if you're careful,) but you don't have a lot of room to work in if you don't dismount the manifold. Also, you'll have to hold the head of the bolt - which creates its own problem (they used pressed-in studs for a reason there.) I do not know if there is enough room to retain a bolt with a jam nut in that location - a jam nut is about half the thickness of a regular hex nut, but I haven't gotten an edge-on view of that junction yet.

Serious tho - use brass nuts. I've been using brass or bronze hardware on exhaust for somewhere over twenty years now - the install preload is low enough that brass is just fine, and it is invariably much easier to take the project apart again later (I use Si-bronze screws to mount the manifolds.)

Laxbro26

Try to get them out first. I got mine out(96 stock) with alot of pb blaster kroil and a 1/2 impact gun with a 3 foot extention with light taps to get them going.

djb383

Dayum! Brass nuts on the exhaust.......BRILLIANT!

schadelh

Definitely go with the brass nuts.

I work at a chemical plant with a lot of heat and a lot of corrosive gasses. Whenever we put something together that is meant to come apart often we use stainless studs/bolts and brass nuts. Other parts are silver plated (woot for swagelok).

Galling is basically when two pieces of the same material (or similar materials, as in stainless and mild steels) cold welding together. Once something galls you will have a miserable time getting it to come off, and both pieces are fscked when you do. But if you go with different materials, like brass and steel, they wont gall.

Dirk Digler

Wish I would have know this about 10 years ago. Makes perfect sense. I will deff be using brass from now on. Whats CRES though?

Gee oh Dee

I figured they were studs, most are anyway.

I don't have an impact, and I don't have anything for heat either. At least nothing that gets hot enough.

I will start by using PB blaster several times, and see what happens from there.

Brass nuts will be used, good call. Thank you sir.

sam24th

A lil trick that a friend of mines showed me when we where taking the headers off of my firebird. If you dont have a torch, you can take your jeep for a spin and get the exhaust kinda hot. It might help loosen them up a lil. Just be careful of burning your hands. It deffinately helped on my headers. We just sprayed it with PB blaster and then took it for a 15min spin then parked it and broke the (bolts in my case) loose.

5-90

Sowwies - CRES = Corrosion RESistant alloy steel

"Stainless Steel" is a very old trademark, CRES is the more proper generic term for it.

It's not just that dissimilar materials can't gall on each other - also bear in mind that copper and cuprous alloys respond to heat cycles in the opposite manner as iron & ferrous alloys. When heated and allowed to cool (as in exhaust service,) steel will get incrementally weaker over time. Copper/brass/bronze, on the other hand, will get incrementally stronger.

This is also why I suggest using SAE5 instead of SAE8 screws/nuts for the exhaust - one of my experiments in Materials & Processes a few years ago was to "heat-cycle" an assortment of hardware (I blocked out a heat-treat oven for about two weeks,) as an "accelerated aging" process for exhaust hardware.

Not only did the steel lose strength fairly quickly, but it wasn't long before the SAE5 had more remaining strength than the SAE8!

Therefore, preferred materials for exhaust hardware (in order):

Si-Bronze
Al-Bronze
Bronze
Brass (start with naval alloy, half hard, if you can find it)
SAE5
CRES
SAE8

Si- and Al-brz are generally industrial (check Fastenal,) but conventional bronze and brass can often be found in marine supply houses - also my local hardware store carries a limited selection of 60/40 half hard brass hardware, which is perfectly acceptable for exhaust use.

If it's been in service for more than a year:
- Remove hardware
- Place in oven at 500* for 30-45 minutes
- Drop immediately in clean, cold water

This will knock out some of the work hardening that may have taken place, and some of the heat-treatment that damned sure did take place, and make the brass/bronze more ductile and increase service life.

Gee oh Dee

More great info. Thanks again!

5-90

No worries. What's the point in learning and/or figuring out all I have over the years if I don't use it to try to help people?

a737mech

Try PB penitrant and these

Gee oh Dee

And that right there is a sign of true wisdom. Again, thank you for helping in my thread.

Most of the guys I learned from would rather beat you up and laugh at you while you make mistakes rather than sharing what they have learned.

Feel free to check up with any of my other threads !!

5-90

I check in around here (and a half-dozen other boards) at least a couple of times a day when I'm not on the road somewhere.

Sometimes I'll let you screw it up (ask my boys!) but only when you'll learn more from making the mistake yourself than you will from my teaching you how and why to do it that way.

Which is why my posts tend to be so long - you don't learn anything if I don't explain the decision. That, and I don't get asked a lot of simple "Yes/No" questions in the first place...

Al Schafer

Stainless has ONE benefit that is related to corrosion. It is very soft however and can easily be damaged, heads rounded off, etc in high torque situations. I'd recommend grade 8 and anti seize compound on the threads.