1978 C3 sheared header studs

[Sparky]

Decided to change the standard single exhaust system on my C3 to a dual pipe system with 2 Magnaflow tail boxes, managed to get the old system off but sadly on the passenger side all 3 studs that connect the header to the first section of pipe sheared off, the drivers side came off easily and all look good enough to take the new pipe connector.
Any ideas on how to remove and replace the broken studs, is it easier to take the header manifold off or will that potentially cause more stud shear grief .
Any advice would be greatly appreciated...

 

[Oneball]

Is any of the thread sticking out?

Heat the studs up till they’re red hot (you can use a plumbers blow torch) and then unscrew with pliers. If there’s not thread to get hold of you’ll have to drill them out and that’s probably best done on the bench

 

[Roscobbc]

If you do need to drill the broken studs initially start with a relatively small drill bit - just that alone can heat and 'relax' the molecular structure of the broken stud sufficient enough to brake the thead loose.

 

[Sparky]

Is any of the thread sticking out?

Heat the studs up till they’re red hot (you can use a plumbers blow torch) and then unscrew with pliers. If there’s not thread to get hold of you’ll have to drill them out and that’s probably best done on the bench

Yes, all three broke with about an inch of stud sticking out, I'll give it a go with the blow torch... Thanks.

 

[Sparky]

If you do need to drill the broken studs initially start with a relatively small drill bit - just that alone can heat and 'relax' the molecular structure of the broken stud sufficient enough to brake the thead loose.

Thanks, I'll try heating them up first...

 

[Sparky]

Yes, all three broke with about an inch of stud sticking out, I'll give it a go with the blow torch... Thanks.

Looking at the parts list the nuts should be brass, mine were steel, and badly corroded.

 

[Sparky]

Does anyone know what size the studs are, I'm not very good with imperial nut and bolt sizes, 13mm socket fits perfectly on the nut but I guess they're not metric.

 

[Roscobbc]

1/4 or 5/16 UNC I think. If using headers perhaps consider using specific reduced head bolts or nuts with studs. Real Steel may carry some ARP branded carbonised or stainless steel - 12 point headed bolts make header installation easier. Be careful if using stock manifolds as flanges are thicker than headers and will need shorter/longer bolts. If replacing all studs/bolts perhaps buy a correct sized tap (or 'slot' a spare bolt) to run and 'clean' out any crud in the thread. Use a copper based grease before installing for easy removal next time.

 

[Sparky]

1/4 or 5/16 UNC I think. If using headers perhaps consider using specific reduced head bolts or nuts with studs. Real Steel may carry some ARP branded carbonised or stainless steel - 12 point headed bolts make header installation easier. Be careful if using stock manifolds as flanges are thicker than headers and will need shorter/longer bolts. If replacing all studs/bolts perhaps buy a correct sized tap (or 'slot' a spare bolt) to run and 'clean' out any crud in the thread. Use a copper based grease before installing for easy removal next time.

Yep, that makes sense, CK have a complete set for £18 with the brass nuts, might as well go for that...

 

[Sparky]

Heated up the studs until red but they still sheared off, anyway I managed to drill them out and re-tapped them 5/16 - 16 UNC.
Whilst underneath I decided to remove the heat shield and clean them up and discovered that all the screws holding the exhaust manifolds to the engine block were only finger tight, is this something that happens over time? I was very surprised... Has anyone any idea what torque they should be set to?

 

[Oneball]

Well done. The nuts usually come loose after the first heat cycle rather than over time. When you do them up. Re torque them after the first 30 mins of running.