To many, it's little more...
To many, it's little more than the case that holds the important stuff. But a properly prepared block is the foundation of a durable race engine that makes good, consistent power.
Have you ever broken down the costs associated with getting a new race engine built? Or even getting an old engine rebuilt? If you have and were surprised by how much it cost just to prepare the block for the build, you certainly aren't alone. New racers especially are often surprised by how much goes into preparing a new engine block to make it race ready. "After all," they say, "it's a new block-or it was running fine before we took it out for the rebuild-is all that stuff really necessary?"
This month, we are going to take a look at all the "stuff" that goes into preparing a block before the first part gets bolted to it. From cleaning, to boring the cylinders, to freeze plugs: What's critical, what can be done without (not much, really), and what can you do yourself?
Believe it or not, the cylinder...
Believe it or not, the cylinder bores may not be correctly located from the foundry. This is because production-line tolerances aren't nearly what racers require. Using a B-H-J fixture when boring the cylinders helps center them over the crankshaft journals.
When it comes to engine block prep, most tasks can be split into two categories. Call them what you will, but they are easily summed up by calling them "The Basics" and "The Extra Mile." The Basics are those machining processes that really must be done just to have a properly operating engine. These processes include boring and honing the cylinders, align-honing the mains, and decking the block. The Extra Mile involves doing things that make sure you are squeezing every last bit of available power out of your engine. These tasks also increase durability. These include properly indexing the lifter bores, locating the height of the cam tunnel based off of the crank's centerline, and even polishing the oil galleries. Whether you spring the cash to go with The Extra Mile procedures is up to you, but if you are racing in the lower classes you can usually get by without them. If you are racing a stock block, there often isn't enough extra material to go about correcting errors with extra machining, so you simply must do the best with what you have. As we go through the procedures, we'll assume we are dealing with a new block. Whenever the criteria changes for a rebuilt block, we'll mention it specifically. Also, thanks to KT Engine Development in Concord, North Carolina, for sharing much of its price list with us for this article.
Don't let the name fool you. We call it The Basics, but that doesn't mean the procedures are necessarily simple. You may be able to assemble the engine yourself, but almost all of us must depend on a machinist to take care of the cutting on the block. Find someone you trust to hold the tightest tolerances with your block. It will pay off in the long run.
Cleaning Yes, this is a necessary step even if you are using a brand-new block. New blocks can often have casting slag hanging around in the cracks and crevices, and it becomes a big, gritty problem if not removed before assembly. This is a step you can definitely do yourself. If the block is new, all you need is a water hose and a variety of brushes to make sure you scrub everything. If you are cleaning a rebuild, however, the work gets tougher. You need to use hot water and a cleaner capable of cutting through the grease and grime that builds up just about everywhere. When you are finished, make sure to hit all the surfaces with a light coat of WD-40 or some other type of light oil as soon as the surface has been dried to prevent rust.
Line-honing the mains is the...
Line-honing the mains is the first step in the block prep process because everything else must be located off of the crankshaft's centerline.
Engine builders usually charge around $120 to clean a block, and most racers consider it money well spent to avoid the hassle. The engine builders usually use a mild acid or caustic wash, either in a hot tank or a jet sprayer. Whether you choose to do it yourself or have your engine shop handle the duties, make sure the freeze and gallery plugs are removed beforehand so that anything hidden behind them can get out. After all the machining processes are complete, the block needs to be cleaned again to get rid of any accumulated machining oils and metal slivers left over from cutting.
Sonic and Pressure Testing It doesn't make sense to do machine work on a block that may not even be usable. That's why it's wise to sonic test the block before much effort is put into it. Sonic testing can tell you the thickness of the cylinder walls quickly and easily. Even on a new block, this is important because core shift can cause one side of a cylinder wall to be too thin. Engine builder Peter Guild of PME Engines says he likes to see the cylinder wall thickness at least 0.275 inch. A sonic tester is also capable of catching a block that's just too far gone to be rebuilt again.