Broken exhaust stud

[dlgis]

Hi All, one of the first jobs I’d like to get done on my recent acquisition is to get a broken exhaust manifold stud replaced so I don’t get gassed by the fumes It won’t be a job I’ll be trying to do myself, I’ll leave it to someone who knows what they’re doing. But it would be good it you could give me your thoughts on how much of a problem this is likely to be, and what the likely solution is.

Darryl

Here’s a couple of pics:

[mgcjag]

Hi Darryl........you definatly needs someone who knows what they are doing......its a steel stud into an aluminium head.....it could be a job that snowballs quickley.......i would be looking at ideas like welding a nut onto the short piece of stud if there is still a bit protruding. ...the heat would hopefully enable the stud to be undone.....but in removeing the manifolds you may find others that are corroded in place.....Steve

[Gfhug]

If there’s not enough stud to weld a nut to as Steve suggests then there are “easy out stud extractors” but they will need to be properly used for the reasons Steve says. Lots of care not to damage the head and lots of plus-gas or similar (no not WD40!) often left for days to gradually penetrate. Do make sure they know what they are doing and don’t try to bamboozle you.

Geoff

[dlgis]

Thanks chaps, It looks to me like there is no remaining stud protruding sadly, so I’ll have a word with a mate who runs a garage and often does this kind of awkward stuff. He’ll be honest with me if thinks it’s too risky for him, and in the meantime I’ll get some penetrating fluid in there.

[Fuel.inj]

I totally agree with what Geoff states and make sure you know what you are doing or it could prove costly in the end. Using easy out stud extractors can be fraught with problems as drilling the old stud must be central which is not the easiest with the head in situ.

[Gfhug]

Removing the head isn’t difficult which I would do to get that stud drilled accurately to use a stud extractor.

Geoff

[angelw]

Darryl Wrote:

But it would be good it you could give me your thoughts on how much of a problem this is likely to be, and what the likely solution is.

Hello Darryl,
I get a few of these to do every year. When a nut can't be welded onto the broken stud, I have a plate we made with the hole pattern of the stud arrangement of one header (they are both the same), with the hole size minimal clearance on the 5/16" studs. The plate is located on the remaining studs and held secure with nuts. A cylindrical insert, with a bore the drill size of the correct stud remover for 5/16", is placed in the hole of the plate where the offending stud is. This arrangement provides a drill bush guide to ensure accurate drilling of the hole in the stud for the Stud Remover.

The hole in the stud is drilled right through (by measurement and feel, this is not hard to do), after which, a copper rod is placed in the hole and heat applied to the length that protrudes from the hole, followed by penetrating oil down the hole and left for a few hours. This process is repeated a few times over a couple of days before attempting to use the Stud Extractor. Just before using the Stud Extractor, we get the area around the stud quite warm and then squirt a freezing compound down the centre hole of the stud and move quickly to use the Stud Extractor. This method has never failed to safely and without any damage to the head, to remove a broken stud.

Regards,

Bill

[dlgis]

Thanks Bill that sounds like a great technique. I’ll talk it through with my garage mate tomorrow

[mgcjag]

Hi Darryl.......I know that this is a new car to you....first is the manifold actually leaking exhaust gasses.....It would be good to use the car for a while to get used to it and evaluate any work that may be required....even if it is leaking you could remove the manifold put on a new gasket with high temp silicone sealer and use it for a while....Steve

[christopher storey]

So far, I am not entirely convinced from the pics that there is any stud broken off and left in the hole . The studs are rather unusual , with a 5/16" UNF outer thread, and a 5/16" UNC inner thread, i.e. the end that goes into the cylinder head . I do not know the exact length of the complete stud, but it is not all that long i.e. the bit that goes into the head is probably no more than 3/8"-1/2", so that the first thing I would do is to measure the depth of the hole in the head. This will give you some definitive idea of what you are dealing with

PS I would also say as a general rule that it is very unusual for these studs to break off in the head, for the simple reason that the tensile strength of the stud is far greater than the rotational force necessary to break the UNC thread in the alloy of the head i.e the thread goes before the stud breaks

[Series1 Stu]

PS I would also say as a general rule that it is very unusual for these studs to break off in the head, for the simple reason that the tensile strength of the stud is far greater than the rotational force necessary to break the UNC thread in the alloy of the head i.e the thread goes before the stud breaks

Well, not entirely correct, Christopher. A threaded joint should be designed such that the male stud will fracture before the thread strips. That is why nuts are the thickness they are. Generally speaking, a snapped stud is easier to replace than a stripped female thread. When it comes to steel studs in aluminium female threads, there is usually an increased depth of thread engagement to compensate for the lower strength of the aluminium. However, there is a law of diminishing returns as the stress loading on the threads is roughly parabolic, with the first 2 threads carrying around 50% of the load. That's when things like Helicoils come into play.

That stud appears to have sheared against the manifold face, which is classic stud failure. It might be possible to get a hold of the remainder of the stud if the manifold is removed and penetrating oil etc used, as previously described.

Exhaust manifold studs have a tough life with heat exacerbated and dissimilar metal corrosion to contend with.

Regards

[dlgis]

I’ve managed to get a stud in there and found a spare nut, all torqued up to 12ft lbs. Some of the other manifold nuts were a bit loose too. Haven’t had time to find the key and start her up so I’ll get her going tomorrow and see if the leak is cured. Thanks for all the help and advice so far. More questions coming soon

[Gfhug]

So was the stud totally missing rather than broken?

Geoff

[mgcjag]

Looks like Christopher was right...............good news......Steve

[Series1 Stu]

Good news Darryl.

It looks like you may have fitted a steel nut. I would replace that with a brass item as soon as possible.

Regards

[dlgis]

Yep turned out to be just missing. Phew! Will be ordering up a proper brass nut, i just fitted what i could find for now

[Robsan]

Just a thought,,,,,,,,,,,,,,,,,,,,,,, the new stud protrudes more than others. Is it not fully screwed in ? and if not could any blockage in the head thread have contributed to the soriginal tud loosening itself ?

If you have a UNC thread tap then try to check for clearance ? just an idea :-)

[dlgis]

Yes i noticed it sticks out more so a bit more work will be needed to check why. It may just be that I was using 2 nuts locked together to tighten the stud and did have enough space on the outer end to get it in further. I was just trying to stop gassing myself til i could do a better job, although that plan may have failed because there’s a (more minor) leak between the manifold and downpipe!