Modern Engine Blueprinting Techniques. Mike Mavrigian
plate, you may achieve a nice round hole, but when the heads are bolted on, some cylinder walls can distort into an out-of-round (or barrel) shape. By using a deck plate, you’re making an effort to establish consistent round holes in the assembled state. When bolting a deck plate to a block, use a crushed head gasket of the same type that you plan to use during assembly. Remember that you’re trying to simulate the condition the block faces when fully assembled.
Honing-stone pressure and feed rate is regularly monitored during hone-stroking steps. In between passes, a dial bore gauge is used to monitor current diameter and to check for out-of-round and taper. In order to maximize honing accuracy, cylinders are honed in a staggered sequence because of the heat generated by honing. For instance, after honing number-1 cylinder, honing commences at a cylinder location away from the first bore (the order might be number-1 cylinder, -3, -2, and -4). This gives each honed bore a chance to cool before honing the adjacent cylinder location.
Cylinder overboring is performed with high-speed cutters. Again, for purposes of block blueprinting, the best method is to take advantage of CNC programming to create bores that are precisely on-center per design specs.
Cylinder honing must always use deck plates. Deck plates simulate the installed cylinder heads, placing stresses in the block that it sees when assembled. This greatly improves cylinder wall geometry because the stresses imposed by clamping the cylinder head fastener slightly distort the bores slightly. When installing deck plates, precrushed head gaskets must be in place, and all cylinder head fasteners must be torqued to the same value (and in the same sequence) as the block experiences during final assembly.
Initial honing creates a microscopic series of peaks and valleys. The peaks, the high edges of the honing scratches, present a wear-in/break-in challenge for the rings.
Depending on the design of the block, also consider other highly-stressed, component-mounting locations that can affect the shape of the cylinder bores. Here’s a good example: A few seasons ago, my endurance race team ran a pair of Dodge Neons with the 2.0L Chrysler engines (4-bangers). As usual, we first honed the cylinders using a deck plate. After running the engines in track test sessions, we tore down the engines for inspection. We noticed that number-1 and -2 cylinder bores had retained their shape Number-3 was slightly out of round by about .0006 inch. Number-4 cylinder bore had been pulled out of round by about .015 inch, especially near the upper half of the bore. The reason was that the transmission bolted to the rear of the block with the upper two bolt locations very close to the rear cylinder.
After discovering this, subsequent blocks were honed with not only a deck plate, but with the addition of a thick plate bolted to the rear to simulate the installed transmission. After running a 24-hour race, teardown showed minimal out-of-round at number-3 cylinder at about .0001 inch and number-4 to the tune of about .0003 inch—a huge improvement.
You may think that an engine block is a beefy, solid chunk of material, regardless of the block (OEM, aftermarket, cast iron, cast aluminum, or billet aluminum). However, while cylinder bores may be machined perfectly round from top to bottom, cylinder shape becomes “alive” under mechanical stress and thermal changes. Bores do change their shape during engine operation, however minimal. In the attempt to obtain maximum ring performance, it’s important to understand this phenomenon and to do our best to address this and minimize these changes. (Photo Courtesy MAHLE Clevite)
Certainly, stressing the rear of the block during honing isn’t needed for every engine block, but it’s food for thought. Study the block and try to evaluate the need for stress simulation in various areas that could potentially affect cylinder bore geometry.
If you want to go a step further, consider mounting the engine mounts and the water pump as well, simulating all the mechanical stresses that a block experiences. Admittedly, for a street application, aside from a deck plate, stress simulating with other added parts is just going to be a waste of time. However, even for a race engine, where you’re trying to squeeze every bit of power and durability out of that engine as possible, going to such lengths probably doesn’t provide a real-world benefit, but in theory, it can’t hurt.
Most aluminum blocks have iron cylinder sleeves. OEM production blocks (a GM LS2 block is seen here) are notorious for featuring a rather sloppy tolerance range for cylinder-bore centerline locations. These bores were honed to size; notice the difference in liner thickness from one side to the other. This is due to small amounts of movement in the casting core. Because these liners are fairly thin to begin with, and due to the slight offset of the existing centerline, OEM blocks with integrally cast-in liners can only be slightly overbored or overhoned (usually about .005 to .010 inch oversize is all you can hope for).
Before honing, take a close look at the bottom of the cylinder bores. Depending on the specific block, it may be necessary to use a hand grinder to knock a bit of material from the webbing surfaces below the bores (for example, the center three cylinder areas where the bores Siamese and have small humps in the casting), to prevent damage to the honing stones. This takes only about 10 seconds per spot, so it’s no big deal.