Lotus Elan

Alfa exhaust manifold stud

PostPost by: martinbrowning » Mon Jul 27, 2015 9:25 am

Hi folks!
My "other car" is an Alfa Spider, for which the cast exhaust manifold is currently on my bench. Problem is that one of the four manifold to down pipe flange studs has sheared off.The smooth section between the two threaded ends of the stud is proud of the flange, but threaded section has broken off. I seem to have three options:

- tried heat but my blowlamp just isn't up to the job so will ask a local garage today to give it a go with hotter flame.
-If that fails then drill out the stud and re-tap. The stud is M8 and tables say that the pilot drill should be 6.8mm (17/64 inch in old money). Question is - could I get away with a 1/4 inch pilot drill - only 1/64 in it.

Final option, buy a new manifold - available but at a price.

Cheers

Martin B
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PostPost by: rgh0 » Mon Jul 27, 2015 9:41 am

If you cant remove it with heat alone. Try to drill a hole in it for a stud extractor, Heat the manifold and then spray chill spray into the hole to chill the stud then quickly try to remove with screw extractor.

If this does not work then slowly increase the size of the drill hole until you break through into the base of the studs threads the broken stud section collapses and can be removed.

You should not have to damage the threads in the manifold but you can always use a thread insert if its damaged beyond repair.

cheers
Rohan
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PostPost by: Chancer » Mon Jul 27, 2015 10:43 am

Try and find a 1/4" left hand flute drill, the remaining part of the stud, the threads will back out when the drill bottoms out.

Maybe even a 6mm left hand flute drill.

If not just go up in drill sizes, you probably wont need the 17/64" and often the threads will come out even with a RH flute drill, the important thing is to be dead centre and concentric.

If the first pilot hole is off centre it can be corrected by using a centre punch before the second one if you have not drilled to depth, always check as soon as the drill has centred, once you drill any deeper you are stuck with it.

I have sucessfully drilled out studs even when off centre.
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PostPost by: normand » Mon Jul 27, 2015 6:40 pm

If there is some stud protruding then fit a nut over the stud and weld the nut to the stud, the heat from welding will help loosen stud and then just undo nut with spanner, If only small amount of stud protruding then weld large washer to stud and weld nut to washer.
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PostPost by: martinbrowning » Wed Jul 29, 2015 12:45 pm

Hi there, Just a note of thanks to those who offered advice with this manifold problem. Had another look under the car and found that the front pipe/cat section looked to have been cobbled together by PO so have decided to replace manifold and front section with European, non cat version.

Martin B
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