high tensile manifold studs

[rob07]

Hi,does any one know if exhaust manifold studs should be high tensile steel,if not what should they be ?.

[stevieturbo]

Any half decent bolt or stud will do fine. Very few steel bolts etc arent high tensile to some degree.

In fact, I dont think Ive ever seen a bolt less than 8.8

[Mr2Mike]

stevieturbo said:

In fact, I dont think Ive ever seen a bolt less than 8.8

Try the hardware isle in B&Q, they sell fasteners made from low tensile cheddar cheese.

[GavinPearson]

rob07 said:

Hi,does any one know if exhaust manifold studs should be high tensile steel,if not what should they be ?.

No, medium tensile (8.8). If they are high tensile (12.9 or 10.9) the heat just makes them lose those mechanical properties.

[Pumaracing]

rob07 said:

Hi,does any one know if exhaust manifold studs should be high tensile steel,if not what should they be ?.

If by high tensile you mean the 10.9 or 12.9 grades then no. There's no point using a fastener of a higher strength than needed to generate the required clamping loads and high tensile bolts are more brittle than lower tensile ones which gets even worse after the heat cycling at such high temperatures. In the end the heat cycling removes the extra strength of the high tensile bolt and leaves it weaker and more brittle than a lower tensile one would be. What you need is a ductile material in high temperature applications and short of using special steels a grade 8.8 stud or bolt, fitted with antiseize such as Copaslip will do the job fine.

Brass nuts used to be a favourite on old British engines because they don't corrode onto the stud.

Before removal always give old studs a good tap with a small hammer to shock them loose. It saves many a snapped stud. Fastener removal techniques are covered in a detailed article on my website.