With any build, machining of the block is the foundation to engine reliability. There should be no doubts when it comes to how straight the cylinder is or how precise the bore. In this part of our series, we visit the machine shop with NPD to see what goes into machining the block and what key points to consider when machining any high-performance block. As we outlined in part one of our KA24DE series, after tear down we measured the block and pistons to figure out what bore we needed and what services we needed the machine shop to perform.
The relationship between the engine builder and machinist is key to building a reliable engine. If the machinist cannot execute the measurements that the builder specifies, then the basis of the build will be off. On the same token, builders need to know exactly what target bores and finishes they want or the machinists have to go off of their own judgment. The final product is also dependent on what measurement tools are used and how precise each side is measured. NPD's past experience has been that many run-of-the-mill machine shops use too low of a resolution (increments of measure) in measure to exactly hit his target numbers. Naoto Negishi uses a Mitutoyo Series 511 Absolute Digimatic Bore Gage and Mitutoyo Series 293 Outside Micrometers. His measurement increments are in 0.001mm, or 0.0005 inch. If he was to have a machinist measure his pistons and bore/hone his block using 0.001-inch graduations, he is working in steps of 0.025mm. If the machinist measured off by 0.001 inch on the piston and 0.001 inch on the cylinder, the total run out can be up to 0.050mm. This can mean the difference between being within or out of tolerance depending on the type of piston used.
How do I find a machine shop that I can trust? It all depends on the machine shop's track record with machining. It isn't based on what machine they use to perform the tasks, but on how much care they take in performing the tasks. Most racing teams do their machining in-house but some outsource work to smaller shops. These shops can handle the tight tolerances that race engine builders demand.
We took our block to Mike McDaniel at Ultra Performance Machining in Santa Ana, Calif. He has over 35 years of experience machining blocks and is constantly updating his skills with new technological standards. We had them machine the block to accept our new 11mm studs, deburr, bore/hone the block, and resurface the deck.
Upon receiving the block, Ultra Performance Machining sends the block to the hot tank for a thorough cleaning. We were impressed at how clean they got our donor block. When we dropped it off, it was covered in old oil and dust from sitting for so long. We also had them remove all the freeze plugs and replace them with new ones. We had them plug up our oil relief valve, as it's no longer needed for how we're planning to use the engine. The block is then deburred of any casting imperfections. This lets any oil that's against the walls of the block flow smoothly back into the pan. Since the stock head studs are a mere 10mm, NPD figured that they would not be able to handle the cylinder pressures we would be subjecting the motor to. The head stud holes are drilled and tapped for AMS 11mm head studs.
The deck of the block is then resurfaced. Just as we did with the head, we're looking for a mirror finish. Naoto communicated to Engine Supply that care should be taken on how much material is cut off in the resurfacing process. Removing too much material may affect our cam timing as we don't have the capability of fine adjustment. Instead of machining the oil cover installed on the block, Engine Supply did it on separate machine. By measuring the deck height and referencing it to the oil cover, they get better results in ensuring a level surface between the two pieces. This is critical since the head gasket lies across both surfaces.
Once the block is properly prepped, Engine Supply straps the block to the bore/hone machine. We made sure to supply them with a torque plate to use when honing the block. This keeps the amount of distortion down during machining. NPD explains that with the head torqued down, depending on what type of deck-open (i.e. Honda) or closed (i.e. Nissan)-it is, how deep the head bolt threads sit in the block, and the overall length of the cylinder, the block experiences distortion. Some may argue that under operating temperature, the block may distort differently. But machining with a torque plate reduces the amount of distortion created by the head studs pulling against the block. To truly simulate head torque distortion, we use the same type of head gasket that we'll be running during machining.
Engine Supply makes a couple passes with the bore machine to determine how much material is taken out. Remember it is easy to enlarge the bore; it's impossible to make it smaller. We're going from the stock 89mm bore to a 90mm bore. Having a general reference of how much material each pass takes off gives them a general idea of how long they need to bore the block to get to the general area they need to be in. Once the machining is done, we measure the block again. We're within our 0.01mm out of round tolerance and the final hone is within our piston-to-wall clearance. Our block is now ready to be taken back to the shop to be assembled.
Having an engine machined sounds complicated but it's really cut-and-dry. Basically, you have target numbers that you want to hit and a small window of tolerance. If your block measurements are somewhere outside of this range, then it's time to send it back to the machine shop or consider another alternative. Remember this can be applied to any engine build. Measuring in the build process lowers the risk of problems on the street or track. Check out our next installment as we start the assembly process of our KA24DE(T).
Ultra Performance Machining
NPD (Distributed by AP Boss USA)