Engines > From Kits/Castings

Stuart No. 9

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crueby:

--- Quote from: Charles Lamont on September 28, 2025, 11:54:55 PM ---How irritating. I suggest trying a rescue first. Using a tapping guide block that can be clamped to the port face, and having a hole drilled a minimum clearance fit for the tap. Put the tap through the block and just into the hole, clamp the block, re-tap the hole and see what it is like. It will be partially cross-threaded, but it may be useable. If it is good enough to hold the stud square and allow it to be tightened without stripping, all well and good. The guide block could also be used to make sure the studs start square into the reworked holes. If not, you are no worse off, and can think about, for example, re-drilling larger and sleeving - in effect home made Helicoils. I would never try to tap those holes without some kind of mechanical guide.

--- End quote ---
One thing to beware of if trying that is the tap may catch on one of the angled bits, and if you force it it will snap the tap off. I did that on one last month where two holes had intersected and I tried tapping across the gap.

john mills:
if the location is close enough it would be worth trying the tap through the hole in valve test if it fits a sliding fit assemble the studs which will fit with that bolted up with the ones which will fit then try the tap if it will enable the stud to screw in .
the threads may not be far off and slight re cut might be enough.

internal_fire:
I believe they make special fasteners for situations like this.   :Jester:

Gene

pirmin:
I had a similiar problem with my Otto Engine Casting.
Somwhow i had not paid enough attention when i was tapping the M 2,5 holes and the exhaust casting was not able to be mounted.

The Cure was to drill a hole and tap it M 4 x 0,5

I then machined threaded plugs ,secured them with Green Loctite and then Redrilled and tapped  M2.5 .

once the exhaust casting is mounted, Nobody will know  ;D

Michael S.:
Hello everyone,

I'm currently cutting new threads into the cylinder for the valve body. I have absolutely no experience with BA threads. I also have two taps that say 4 BA on them, but they're not the same. The long 4 BA drill bit fits the nuts and bolts. What size should I drill for the core hole? 3 mm?

Best regards, Michael

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