09/02/2026
Major surgery today for Trinity Restorations. This is a little citroen head as far as I know. Someone had done a spark plug thread repair, and then that worked its way out too. We tried running the tap for the larger "thread repair" tool down through, but the major diameter on the upper half of the hole was already too large.
To the welding bench. We welded it from both the chamber and plug side and worked outwards to fill the entire plug hole in with fresh aluminum. The hammer marks are from trying to peen the aluminum and reduce the stress of shrinkage from filling such a large hole.
Next, the 1/8 drill went in by eye to try and make a new centerline for the plug. Straight, but slightly leaned towards the exhaust valve. Then a 1/4 drill following the same path.
Now that a 1/4 drill was through, it was clamped in the mill, and the mill head was aligned with the drill to locate the chuck for the milling operations.
First a 1 inch endmill to spot face the weld repair. Then the 1/2 hole for the 14mm spark plug thread. After that, a 3/4 endmill was used to counter bore and create the surface for the plug gasket, and set the depth of the plug in the chamber.
Great Success!
#802
