Lock & Stitch Part 2

Having received all the necessary tools and supplies from Lock-N-Stitch in Turlock, California, we could begin the process of repairing our Jaguar 4.2 block. The company provides an informative DVD that explains all the steps and options which is essential. The basic idea is to replace the crack with a linear line of screws and begins with a single drill hole that will is placed well beyond the crack to ensure strength.

The above photos show the Lock-n-Stitch spacer which inserts into the first drill hole and lines up the drill bit for the next cut. The tool isn’t completely necessary, but it organizes the holes neatly and ensures proper distances between screws. For the first run, only every second screw is inserted. The holes are then countersunk with a spot face bit that will cut a controlled shoulder for the screws. The spot face distance is critical and depends on the wall thickness and thread distance.

The first set of cascading drill holes are then threaded and the pins/screws are inserted permanently into the block with thread sealant. The screw is simply wound into the block until the breakaway head shears off. The remaining stubs are then ground down so the gaps inbetween the screws can now be filled with the second series of screws. The following picture shows the second line of pins being inserted with the breakaway top of a single screw resting on the block.

After the complete line is finished a needle scaler was used to replicate the rough finish of the block. The end of the screws were left slightly protruding to retain as much strength as possible. The following picture shows the needle scaler and a finished line which was pressure tested to 10psi for leaks.

Since no bubbles were visible from the pressure test we can now begin assembly of the 4.2 engine from the bottom up. Below is Lock-N-Stitch’s own promo video for their product.


Lock & Stitch Part 1

Here’s an example of the force that frozen water can have on an otherwise robust cast-iron block. The pictures show a Jaguar 4.2-liter block from an E-Type that has been recently magnafluxed. According to Wikipedia, this process creates a magnetic field around the block which “will cause a high concentration of magnetic flux at surface cracks, which can be made visible by dusting iron powder”. In this case the problem area was painted blue and dusted with yellow iron oxide particles that easily show cracks at the surface.

The results show the weakest point of the water jacket around the block deck. The cracks are the direct result of water expanding during freezing. As this engine belongs to a matching-numbers car, the block will need to be repaired vs replaced. This will require a metal stitching process since a straight-forward weld can further crack the block as the weld cools. To successfully make an electric weld, the entire block would need to be preheated somewhere from 900º to 1500° which isn’t feasible.

The following pictures show definite cracks along the top of the water jacket. The first image shows signs of a previous metal stitching process and the circular pins that replaced the crack are only visible from the Magnaflux process. Either this fix caused crack to extend or the previous repair didn’t cover the entire crack; there is a noticeable seam beyond the pins which extends to the yellow arrows.  Some versions of the lock & stitch fix include expanded bolts which can further stress the area. To prevent this we will use the Lock-N-Stitch Inc’s C1 pins that do not expand. The opposite side of the block also has crack which is unrepaired and will require the same process. The last picture shows one of the C-Series pins next to the crack it will eventually replace.

Further posts will show the compete build of the Jaguar 4.2 including a detailed look at the Lock & Stitch process.