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Is there and engineering reason...?


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Why on a 200TDI the connection between the exhaust manifold and the turbo is made using studs rather than bolts?

I have a broken stud and at the moment it is resisting all attempts to remove it.

Easi outs will be tried tomorrow but if that fails I will have to drill it out.

I can't see a reason why the stud is an better than a bolt unless it has mass production benefits?

So can I use an M8 bolt in its place?

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Studs are often used where locating the part is difficult and particularly when cross threading a bolt is easy (going in to aluminium) or problematic if it needs to be fixed.

Exhaust manifolds are much easier to put on when you can hang the gasket on the studs, locate the manifold then tighten the nuts as access is often tricky.


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Studs are nicer than bolts in some applications, especially when attaching things to aluminium - you can wind the stud in under almost zero torque, then pop a nut on the end and torque it. Less likely to strip the threads out of the ali than winding a bolt in under torque. This is much of the reasoning behind having ARP head studs on the V8.

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Another reason for studs is where the material being screwed into is prone to wear from repeated application (ie screwing in and out into an aluminium casting). Using a stud means that it stays in place and the nut and stud take the wear rather than the ally.



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In a high temp application like this there will be a tenancy for the fixing to become seized.

By designing it to use a nut as the moving part it is possible to cut or split the nut off rather than break the fixing.

At one time brass nuts were used and VW beetle exhausts were held with nuts incorporating a wire thread insert (Helicoil) both designed to minimise seizure.


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Thanks for the input folks.

It would appear then that as long as locking tabs / spring washers etc are use then drilling out the manifold and using a bolt shouldn't be a problem? The other three will still be studs.

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I would not bother with the grief of trying to create a lock tab arrangement I would just use an 'Aero' style lock nut. This is like a Nyloc nut but is all metal so will work in your high temp situation.


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The nuts we use at work are a philidas application.


These are used in my industry to prevent nuts coming off rail points applications. They have been good in service.

we have changed some safety critical ones to hardlock

There are excellent reports on nordlock too

Personally I would use a Philidas nut with a locking tab made from a penny washer and an angle grinder if a standard lock washer wouldn't fit, and I would only use the lock washer if I was TERRIFIED of it falling off. The Philidas nuts are pretty reliable.

My 2p!

Ps forgot to add that kwik fit repaired my 216 coupe downpipe with a bolt and nut after having to drill it out. Not moved in 2 years and that's not even a lock nut.

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I have tried:

Mole grips

Socket type stud extractors

Heat plus mole grips

Welding on a bar to the protruding stud

Easi outs

All failed to shift it so I moved on to drilling it out. I worked my way up the bit sizes in the vain hope of being able to remove what's left of the stud without compromising the threads in the casting. No dice.

So now a nice M8 bolt is in there with the standard flanged nut as used with the studs. I think it will be fine as the engine did at least 5 k with only three studs holding the turbo on.

Interestingly, looking at the shape of the casting, I think that this particular location is the only one where there is space for the head of the bolt!! Lets hope none of the others shear!

Thanks for all the advice and guidance, most appreciated. :i-m_so_happy:

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