I will be fitting a large bore exhaust system to my S4 this winter. The existing stud and nut mounting hardware is a bit tricky to get to. I have been told that some people use hex socket set screws as an alternative.
Sounds like a reasonable idea. Anyone out there using this?
What are the bolts made out of, stainless?
Where do you get UNC hex socket set screws from in the UK?
I replaced my header studs last year with socket cap screws - s/s, 5/16 UNC - length 1" (thread length, not overall). They only have to be torqued to 12-15 lb ft. Certainly have appreciated the ease of slipping off the headers if required - most recently to allow me to drop the exhaust a bit to allow more working space to overhaul the clutch slave cylinder. You will need a long 1/4" in-hex socket drive though - the standard (short) drives can’t be used in a few places where the swept back curve of the pipe obstructs access to a rear fitting and/or under thermostat housing.
Where? Sorry I don’t know for UK as am on other side of the planet but try internet or yellow pages for suppliers/retailers of “Industrial Fasteners”.
I have been using socket cap screws for many years as well - no problems. There is a variation on the hex drive socket called, I believe, a “ball driver” - the end is in the shape of a hex-sided ball rather than straight-sided. This allows a slightly angled approach to the socket if you can’t get a straight shot due to the curvature of the exhaust pipe.
Steve
I have used socket headed cap screws also for 25 years, it was one of the first things I changes on the car. Just use plain black steel and lots of copper or nickel antisieze. A ball ended hex key makes it a lot easier to get at the cap screw at an angle, expecially at the 2 studs under the thermostat housing.
Ensure the holes in the head are all deep enough and fully tapped as there is a lot of variation and occassionally I have come across a short hole that needs deepening to ensure proper clamping of the gasket.
The cap screews should be avaialble at any specialist industrial supplier or bolt and fastener shop.
regards
Rohan
I know some of the exhaust stud threads in the head are a bit tired, so I will pull the head then drill and helicoil or similar the threads.
Anyone have any preference for helicoil, taptight, recoil etc… 
Steve
I have used recoil inserts for lots of years with good results. No particular reason why I choose these except they were stcoked at my local industrail engineering supplies shop. I have had to put inserts in a couple of exhaust bolt holes over the years but never removed the head, just pulled the exhaust and done with head in situ.
regards
Rohan
The company Trident at Silverstone have a huge (!) selection of fasteners, but as Rohan says, use std. black screws. I found it helpful to drill a small hole from the “footwell” sidewall beside the very rear bolt, in order to get a good access for the key. ( right word ?) I close it with a rubber plug .
Dag
Sorry,but I don’t like the idea of screwing bolts in and out of ali,would much prefer to use studs and nuts,unless we’re talking helicoiling the ali first?
John 
Hi John
I agree that removing and replacing bolts regularly creates greater risk on stripping a thread in the head compared to leaving a stud in place with antisieze on the nut. However in practice with care and lots of anti sieze I have not found this to be a real issue. I have probably removed and replaced the exhaust on my Elan 50 times in the last 25 years and only stripped a couple of threads in the 3 heads I use on the car for racing.
Over the same period the exhaust of the plus 2 has only come off about 6 to 8 times and never stripped a thread.
Fitting the exhaust over the studs is a real pain, properly fitting the nuts especially with large diameter pipes even more of an issue, The risk is worth it in my opinion.
But its not compulsory to change !!!
Rohan
Alas one of the stripped threads is on number 4 cylinder i.e. right at the back and I can see no way of getting a drill to it with out lifting the head. I even have a 90 degree air powered drill and there is still not enough room. I would love to hear otherwise 
I have heard that with care one can helicoil it in-situ without drilling,just use the requisite tap with care?
John
Steve the alloy is soft. To drill to the right size just turn the drill a quarter turn at a time by hand with multi grips. If necessary do it in a couple of steps of drill size but if the thread is stripped then all you are doing is cleaning up the inside of the hole when you drill with the correct size drill.
Then tap and fit the insert no need for a powered drill.
Rohan
Steve
We have recently been discussing this subject:-
lotuselan.net/forums/viewtopic.php?t=13662.
In drastic times you can helicoil tap it in situ with out drilling.
You just need to take it easy and tap a bit at a time 1/8- 1/4 of a turn and wind the tap back out a bit using plenty cutting fluid a bit of paraffin or oil should do.
The tricky bit might be installing the actual helicoil with the installation tool if the access is a bit restricted.
Clive
Just been in to my garage to check. One of the threads that needs doing is the very back one and the drill bit alone is just too long to get in straight 
However if I grind off 0.75" off the end of the bit it might just fit. However the coil insertion tool is also too long Again I could cut one of those down.
I guess it is a toss up between the extra work of lifting the head plus the additional cost of gaskets vs the risk of screwing up inserting the coil and having to lift the head anyway 
