BROKEN HEAD STUDS

If you have broken off a head stud in the block, to make sure you drill and tap out the remaining stub centrally to the head, turn up some sleeves to guide the drill down the holes in the cylinder head to the broken stud centrally and vertically.

If you haven’t got access to a lathe, have a rummage around the old bitsa-box for a suitable bit of tube.  Put a small pilot drill down first and then open it out to the correct tapping size. I did use an old head to do the job.

The heads were originally drilled 11/32" (8.7mm) but there will be a bit of crud down the holes after 80 years, so they will need cleaning out and then a tube made a few thou narrower with a 7mm inner diameter since the tapping drill for the 5/16" BSF stud is 6.75mm, or alternatively, 17/64" (1/10 thou difference). Draper sell imperial sets with a 17/64” included and it is possible to purchase 6.6 & 6.8 mm drills.

You will have to make two of these tubes—the main one as above and one with a smaller inner diameter for the pilot drill. The pilot drill can be anything suitable but one that is long enough to reach through the head and into the block a decent way. A standard 3/16" diam drill should be long enough but there isn’t any standard regarding the length of drills.

Roger Ballard