Just wondering about this after removing semi rusty exhaust studs from the head. I need longer studs so any reason why I should not use standard bolts to secure manifold to head?

The studs just seem to be normal steel and the nuts are also steel.

Cheers

Adrian

Not so sure the stud material is the issue but what were the nuts made from for the original manifold? On other cars (mainly old MGs) they look to be made of some sort of alloy which I presume stops them from corroding onto the manifold studs.

Just a thought...

The main reason I would stick with studs is if a bolt shears close to the head face, it is more difficult to remove. A stud is more likely to shear near the nut and leave part of the stud sticking out of the head which should help with removal.
Other issues include trying to get a bolt in straight close to an exhaust bend and lining the manifold up. A nut is easier.

[Edited on 4/5/2009 by nitram38]

Just cut the head off a bolt to make a stud -- studs wil make it easier if you every have to take it off.

I have 8 mm stainless steel threaded bar I can cut that to length and use that, I guess, would that be better as less corrosive action between stainless and aluminium?

Bit more information, what made me think of it was the nuts will not come off the studs easily, but the studs have unscrewed from the head, I can soak them to separate later, and I agree that using studs as support for the manifold would make fitting easier in tight corners etc.

Adrian


[Edited on 4-5-09 by AdrianH]

There are people who swear by using stainless bolts (cap heads normally). Not convinced myself and use 10.9/12.9 grub screws; at 50mm long they do the job and have a hex head inside them to allow for easy fitment.

Proper manifold nuts are the best to use - brass or copper. Due to the softter material, they're a longer nut to compensate so you get more threads covered - and its usually the exposed bit of thread which suffers.

Saying that - we're comparing nuts from 10 year/100k engines with ones that do little annual mileage and we're constantly tinkering anyway. If they come off easy after a couple of years, they why not replace them then? A couple of quid on new nuts before they get bad is better than trying to use extractors etc..

stainless bolts - brass nuts & washers

no problem

note - same method used on gearbox belhousing but using only steel, allows parts to be supported while tightening up




[Edited on 4/5/09 by Mr Whippy]

Excellent, no problems using stainless and if my local nut and bolt place has brass nuts then that will do, time for the garage again on this wet bank holiday Monday.

There is a reason why which I will try and explain!!

If you use a bolt you tighten it up good and proper. It puts a pulling force on the thread. IE the metal is under strain. Add a few heat cycles (ie expansion and shrinking) and you can get problems.

When you use a stud you put it in place and it pulls a pulling force on the thread. However, when you then put the nut on the end and tighten it, it neutralises this pulling force. This means that the metal around the thread isn't under the same level of strain as when using the bolt.....

This is all nicked from Corky Bell supercharged btw (well the thinking behind it, not the poor explanation- that's me....)

quote:

---

Originally posted by AdrianH
I have 8 mm stainless steel threaded bar I can cut that to length and use that, I guess, would that be better as less corrosive action between stainless and aluminium?

---

Not sure i agree with the explantion of how the bolt/stuf is under less force when using a stud than a bolt.

Material type apart, the two main reasons i know of studs being used is:
- Where you are likely to be removing the item alot and the base part is expensive
- Where due to tube position etc, you can get a bolt inplace.


With a stud, stud goes into block/head and then when you remove/replace the manifold it just stay there. And should the threads get worn after a lot of times in and out, you can replace the stud and nut. Where as using a bolt, you wear the block/head threads each time, which is expensive to replace, and can be an issue. Partiularly with aluminum heads ofcause.


If you dont have studs, then wippys comment about using steel bolts, with brass nuts/washers sounds good and is something i have seen before. Although you will need room to get the bolt inplace.



Daniel

All to do with balancing the preload with the clamping force..... my explanation probably didn't explain it well!!!

used the stainless bolts and brass washers for years, never had a problem

quote:

---

Originally posted by BenB
All to do with balancing the preload with the clamping force..... my explanation probably didn't explain it well!!!

---

quote:

---

Originally posted by BenB
All to do with balancing the preload with the clamping force..... my explanation probably didn't explain it well!!!

---

I also agree with the stud protecting the internal threads of the head.

On the stainless and aluminium, I was sure it was suggested that I should use stainless rivets when fastening an aluminium floor, they being better then aluminium in steel?

Adrian

Okay well this is what Corky says!!

"A properly anchored stud, with its shank bottomed out in the block will always prove a superior fastener system to a bolt tightened onto the block. This is because the stud's chamfer presses onto the deck surface and induces compressive stress into the material surrounding the threads in the block, essentially "preloading" the block. When the head retaining nut is tightened, the tension in the stud has to pull this compressive preload out of the threads before the threads become loaded in tension. Hence, the threads can take a greater tensile load."

quote:

---

Originally posted by AdrianH

On the stainless and aluminium, I was sure it was suggested that I should use stainless rivets when fastening an aluminium floor, they being better then aluminium in steel?

---

Thanks all for the information, ideas and links.

Adrian

I took the exhaust off a Corsa the other day and only two of the studs stayed in the head anyway, all the others came out just like bolts so I can't see any problem replacing them with bolts if you can easily get at them.