Show whole topic Jun 10, 2018 2:40 pm
Bill LG45 Offline
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Registered since: Sep 24, 2014
Location: -


Subject: Re: Exhaust Manifold Gasket
Agree with Colin :
1. Exhaust manifold studs need to be high tensile steel. A decent HTS should have a UTS ( ultimate tensile strength) of about 1100 MN/sq.metre and will be affected less by the heat. Stainless will be only offer about a third of the tensile strength, depending on grade.
If you use ordinary steel studs or stainless it is highly they will stretch when they get hot which will reduce the end load in the stud and of course the face stress of the gasket. If the pressure in the exhaust is more than the minimum face stress on the gasket as it heats up and cools down then it will blow.
2. Brass nuts are good as they will be much easier to get undone. Putting coppaslip or John Crane Thread Guard or similar graphite based compound, as used on steam pipework etc will also help to stop the nuts falling in love with the studs! If you come across any nuts made from Nickel aluminium Bronze or Kmonel ( Copper/ Nickel /Aluminium alloy) these are even better but expensive.
The amount of end load you put on the stud for a given torque applied to the nut also varies a lot depending on whether the thread is lubricated.
I did some tests on this once at work using strain gauges to measure the end load in the studs over various sizes...too many years ago now to remember the figures but I do remember that, in general, we found that the end load in a dry, unlubricated thread was about half that of a thread lubricated with thread guard or coppaslip and that threads lubricated by oil of normal multipurpose grease were in between. (Of course the loads also vary with thread diameter and thread form as well as the number of threads per inch and the thread angle, as well as the grade of thread... all have some impact.
As a result of these tests we amended the company's manuals and stated that all threads must be lubricated with thread guard and adjusted the torque settings specified as it was the only way to ensure a consistent result!

I would use new best quality spring washers under the nuts.

Hope the above helps
Bill Wink