Dart Big-M Block Machined Upgrade - Scratching The Surface

CNC Machining
No doubt, having access to a CNC machine is a great resource for engine machine work. Is it worth it? Yes, the advantages outweigh the cost. Not only do you have the ability to run specific programs, but they can be tailored to your specific race applications. The CNC is more precise than a human, and the machine work gets done faster and more accurately--so you get to the track sooner. Typically, machine work on a CNC program might cost around $750.

After the measuring and recording were complete, our Big-M was ready to begin the machining on the CNC. Initial measurements showed that our lifter bores measured 0.842 inch, but we needed 0.904 inch for our lifter bushings. A lifter bore cutting tool was added, and the CNC began to hog out each lifter bore in order to gain the clearance for our CHE lifter bushings.

Here the lifter bores are enlarged for the CHE bushings. The walls of the lifter valley were also cut, otherwise the lifters will not fit properly.

The initial deck height measured between 9.803 and 9.804 inches. However, we wanted to clean things up a bit, and give the deck a mirror finish. A cutting-tool specifically designed to deck the surface was added to the CNC, cutting exactly 0.004 inch off the deck on both banks to square off the surface.

You can see the difference before and after the deck was cut. Notice the slight imperfections in the deck surface before...

...and the mirror finish achieved after. Not only will this make the deck surface true throughout, but it'll improve gasket seal under extreme cylinder pressures.

The bore sizes of our Dart Big-M measured in at 4.500 inches, but we needed it bored 0.030 over to fit our pistons. Lagman was at the controls of the giant, and before we could begin boring the block, he started measuring the bore depth. With the boring-tool added to the CNC, it began the automated process of removing unnecessary material from the walls of each cylinder.

CHE Lifter Bushings
There is no sense completely machining an engine block for a race application and not machining for lifter bushings too. Machining for lifter bushings will add some cost to the bill, but it's well worth it. The Lifter Tru process corrects for angles and positions the lifter exactly where it's supposed to be and even corrects for any casting flaws. Also, the lifters will endure less friction and, as a result, have an extended life; the lifter bushing is smoother over the cast iron walls.

With the final cuts complete, each cylinder measured exactly 4.525 inches. While this wasn't the final measurement, it got us close enough to begin honing out the rest.