all muffler and exhaust questions go here!!!!!!
CF Veteran
Joined: Sep 2010
Posts: 21,168
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From: Milwaukee, WI
Year: 1987
Engine: Check
Bam...
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.)
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.)
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.
"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.
Seasoned Member
Joined: May 2011
Posts: 358
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From: idaho falls, idaho
Year: 97
Model: Cherokee
Engine: 4.0