You can build surprisingly good power in a production block, but how much is left on the table and how long it will live is another story. Much of what is discussed here revolves around block selection and preparation and why a machinist performs certain procedures. Many good engine builders do not perform their own machine work and therefore depend heavily on the competency of their chosen machinist. However, you should fully understand the machining procedures they require and how to check the machinist’s work during preliminary mock-up assemblies.
You need a dial bore gauge for checking piston fitment along with main and rod journal housing bore diameters prior to checking bearing clearances. You also need a precision straightedge for checking deck surfaces and main bore alignment and a host of other measuring tools necessary to the task. You can take the machinist’s word for some things unless you have your own precision equipment. This might include lifter bore indexing, cam and crank centerline parallelism, bore finish, and so on. You can be a top-notch engine builder without being a machinist, but it definitely requires a good working relationship with a competent machinist you can trust.
Grooming the Short Block
People say there’s not much power to be gained in the short block. If that’s true, then why spend so much time massaging the block and prepping all the internals? If the engine is essentially a fuel and air processing device, it is clear that the camshaft, induction system, cylinder heads, and exhaust system pretty much dictate power levels and where torque is positioned in the engine’s effective operating range. Think of the short block as the delivery device that contains, harnesses, and transmits power to the drivetrain.
As such it is subject to all the abuse the cylinder heads and companion power producers can dish out. It has to be tough to take the punishment. When properly prepared, it can effectively enhance power production by minimizing friction and ensuring the precise operation of all the contributing components. A well-prepared short block is every bit a player as every other component in your engine’s power arsenal. The first place to start is with a well-prepared cylinder block.
Block material is limited to iron or aluminum alloy, but there are many other factors to consider. If weight is not critical, many builders still favor iron blocks for their superior dimensional stability. The gap has narrowed in recent years as OEM production science has influenced block design and aftermarket manufacturers have eliminated most of the problems previously associated with aluminum cylinder blocks. Current aluminum blocks are far more dimensionally stable than their predecessors and are no longer considered a detriment to maximum power production.
The remaining drawback is cost. Aluminum blocks are significantly more expensive and they are often passed over unless weight is critical. This applies to overall engine and vehicle weight as well as the specific placement of mass in the chassis relative to handling and vehicle dynamics. The initial criterion for cylinder block selection incorporates most of the features of dedicated race blocks. Some things to consider include the following.
Bore Size and Bore Spacing
Bore size is a primary factor for any competition engine build because it dictates valve size and ultimately the breathing capability of the engine. Recall the primary goal of maximizing VE. Builders often favor the largest available bore consistent with the target displacement and attending factors such as bore spacing (the fixed distance between cylinder centerlines) and stroke length. Along with cylinder wall thickness, bore spacing is the limiting factor in determining maximum available bore size.
Most builders feel that the breathing gains from a larger bore outweigh any friction penalties that accrue from larger pistons with more skirt surface and potentially increased ring drag. A bigger bore also provides more piston area for combustion pressure to work against, but it also creates a greater distance for the flame front to travel and more surface area to cool the flame.
Cost also becomes a factor since a change in bore spacing to increase bore size requires a dimensionally compatible crankshaft, cylinder heads with properly spaced combustion chambers, and complementary intake manifold, camshaft, and exhaust headers.
Main Cap Material
Main cap choices include iron or billet steel in either two-bolt or four-bolt versions. Two-bolt blocks are generally avoided unless class rules require them, but many sportsman classes use them successfully, particularly when the main bolts are replaced with studs. The decisive factor is the size and limited strength of the two-bolt iron caps versus the higher cylinder pressures and elevated engine speeds associated with many contemporary sportsman classes. As a rule, only use a two-bolt production block if the prevailing rules require it. Four-bolt blocks with iron main caps are preferred for general competition. Most of them handle 500 to 600 hp without distress and their durability is typically acceptable except perhaps in supercharged or nitrous applications with ultra-high cylinder pressures or extreme engine speed.
These power levels can easily be exceeded, but you run the risk of reduced durability, particularly in applications that require extended operation. With the exception of moderate performance applications, main cap studs are preferred over bolts. Studs provide superior clamping force and they help spread the load more effectively, particularly in four-bolt applications where the outer bolts are splayed outward to transmit loading across more of the main web structure. Dedicated race blocks usually employ four-bolt caps on all five main bearings as opposed to the center three found on most production blocks. If a two-bolt block is your only choice, stud kits are available, and billet steel main cap conversion kits are available to refit the block if the prevailing rules permit it.
Maximum-performance efforts anticipating high cylinder pressures, extreme engine speed, and high cyclic loading should always use fully machined 1045 billet steel, splayed main caps, and studs. Where possible they should be pinned with ring dowels to maintain accurate positioning and prevent main cap movement under high loads. This is a durability issue that can also affect power. If the main caps are moving, bearing clearances and crankshaft stability are affected. In extreme circumstances the crankshaft may deflect enough to bite a bearing with potentially disastrous results.
This can also introduce additional instability into precise crank and rod relationships, which affect piston stability and ultimately ring seal. Crankshafts are subjected to extreme forces that can easily disrupt this chain of precision relationships. For maximum efficiency the cylinder block must contain the crank in a dimensionally stable platform that maintains all critical component relationships under all operating conditions, including standing up to the hammering effects of detonation and thrust loading on gear changes.
Cylinder Wall Thickness
High RPM and extreme cylinder pressure impart staggering loads to the cylinder walls, particularly on the thrust surfaces. Uniform cylinder walls of appropriate thickness are critical to the dimensional stability of cylinder bores. Dedicated race cylinder blocks like those produced by Dart and World Products are manufactured to incorporate the necessary cylinder wall thickness and appropriate heat transfer to the cooling system. Most other blocks should be sonic tested to determine cylinder wall thickness (see “Sonic Checking” below), except perhaps for OEM race program blocks that already come with a sonic check sheet.
Production blocks must be thoroughly checked for adequate wall thickness. This is particularly important on late-model blocks that incorporate modern thin-wall castings. While a hot street/strip engine is normally okay with a minimum of .125-inch wall thickness, most sportsman racing classes should not accept anything less than .140 inch. Dedicated race blocks offer .250 inch or more and are usually accompanied by a manufacturer’s sonic check sheet so the builder gets an accurate picture of the cylinder block’s dimensional character.
Sonic checking is an ultrasonic procedure employed to verify a block’s cylinder wall thickness. While most factory and aftermarket race blocks now come with a factory sonic check sheet, many builders prefer to verify the sheet and in the case of previously bored blocks it is wise to determine the thickness of the cylinder walls. Most race blocks now provide cylinders with at least .250- to .300-inch wall thickness and it is important to maintain as much of that as possible. Sonic checking is not a lengthy process and most shops regularly have their own sheets to record the numbers. The sonic checker device comes with calibration standards that are used to calibrate the system prior to use. They have a known thickness and are made in a curved shape to simulate the cylinder bores.
Some builders break up old blocks and keep some curved sections of cylinder walls to use as real-world calibration samples that can be easily measured for comparison. Once a unit is calibrated, gel is applied to the sensor and the sensor is held firmly against the cylinder wall at specified locations depending on the type of block.
Most builders prefer to check the cylinders at four equally spaced locations starting with the primary thrust surface and working their way around the bore 90 degrees at a time about 1½ to 2 inches down from the deck surface. Once these numbers are recorded, builders repeat the process roughly halfway down the bore. Some even record numbers at the bottom of the bore. When the process is complete the builder and/or machinist has an accurate roadmap of the block’s cylinder wall thicknesses.
The primary or major thrust side is located opposite to the rotation of the engine. For clockwise rotation, stand in front of the engine and face toward it. The major thrust surface is the left side of each bank of cylinders (toward the passenger-side of the block for every cylinder). That’s where the thickest readings should be typically .300 inch or better, but no less than .250 inch. The minor thrust side is the opposite wall (the right side of all the cylinders as you face the front of the block).
If you have counter-clockwise rotation, or as in some cases are building a reverse-rotation engine, the major thrust surfaces all shift to the opposite side. Non-thrust surfaces opposite the wrist pin axis in each bore (front and back side of each bore) are typically the thinnest and some builders accept walls as thin as .100 inch in this area. Obviously, the most thickness possible on the thrust side of the bores is best, but lateral thickness is also important to maintaining the structural stiffness of the cylinder block. A sub-standard wall for any lower-level sportsman class is anything under .140 inch. For most high-end stuff a minimum of about .180 to .200 inch is desired.
You may also discover, for example, that all the bores on one bank are thinner at the front, a problem most likely attributable to core shift during manufacturing. If the shift is not too severe, builders sometimes correct it by offset-boring that bank to shift all of the cylinders toward the thicker walls. Depending on the bore size and the degree of shift this often means an offset of .0005 to .012 inch, which helps save the block and doesn’t significantly impact the cylinder bore to cylinder head/chamber relationship. Don’t forget that you need to leave some room on the thin side for honing.
Small-bore shifts like this are not uncommon in racing circles and there is little or no impact on the rod-to-pin alignment in the piston. It’s often said that the short block doesn’t contribute much to the horsepower process, but high cylinder pressure with the cam and intake system won’t do much good if the rings can’t seal the cylinder.
Ring seal, strength, and durability are primary concerns when mapping cylinder wall thickness. Good ring seal can’t be achieved if the cylinders are flexing under pressure, and at some point the cylinders will go out of round, crack, or simply collapse. Block-fill and grouting are often added to the water jackets to beef up the lower half of the cylinders, but this is a temporary fix and it doesn’t particularly apply to most engines that need full-time coolant flow through the complete water jacket. Block-fill and grouting on drag-only applications are okay for the most part.
Race blocks and some production blocks have thicker deck surfaces to help stabilize the top of the cylinder bores. If rules permit, this type of block is desirable because it optimizes and retains the benefits of precision torque plate and hot honing techniques. Thick deck surfaces also promote more consistent head gasket sealing and they typically incorporate blind head bolt holes in reinforced bosses. This eliminates corrosion and leakage by keeping the head bolts or studs securely anchored in a more stable platform separated from the cooling jacket. It also prevents localized cracking around head bolt holes that otherwise have no solid foundation.
A common practice in large-bore blocks that don’t enjoy the luxury of wider bore spacing, siamesed cylinders incorporate an area of solid material between the cylinder bores that is normally open to water circulation. Siamesed cylinder blocks are currently used in many high-performance and racing applications. The siamesed structure further stabilizes the cylinder bores while providing desirable cylinder wall thickness. With proper preparation siamesed blocks are suitable for most competition environments.
Consistent with series rules, engine builders often favor large-diameter raised camshaft bores. A typical block of this configuration has the cam raised from its production centerline and the cam bores machined to accept larger 50-mm camshaft journals. This practice permits a larger, stiffer camshaft that is resistant to distortion from high valvespring pressures. It also encourages more aggressive camshaft profiles and shorter, stiffer pushrods to combat flexing at high RPM. Race blocks are also available with standard cam centerlines, but with additional material added so larger cam bores can be used with the standard cam height.
Material and Machinability
Production blocks are cast from standard gray iron, which has long proved to be reliable for passenger car and truck blocks. It is cost efficient because it is easier to manufacture and machine. Most desirable race blocks are now cast with compacted graphite iron (CGI) offering 50 to 75 percent more tensile strength than common gray iron. It has better thermal conductivity, superior high-temperature fatigue properties, and maintains dimensional integrity better than gray iron at the expense of being more difficult to machine.
The harder material tends to wear tooling and break taps more easily. It is also more sensitive to honing technique, but overall strength, stability, and superior finished qualities generally outweigh most machining issues for most serious engine builders.
CGI also offers weight-saving properties that allow block manufacturers to add material where necessary to provide optimum strength without incurring the increased weight penalty associated with strengthening efforts applied to common iron blocks.
Heat Treating and Stress Relieving
With the new generation of race-ready blocks, heat treating and stress relieving are often performed by the block manufacturer. Racers used to prefer used cylinder blocks that had already taken a set or the storied old block out behind the shop that was slowly being seasoned for future competition use. New factory race blocks or blocks from primary aftermarket suppliers like Dart Machinery and World Products have received proper treatment. The general procedure for stress relieving an iron block is to heat it to approximately 1,000 degrees F for several hours and then slowly cool it by a couple hundred degrees every hour until it returns to room temperature.
Cryogenic Treatment: While not as widespread, cryogenic treatments have gained popularity over the past decade. A cryogenic treatment is an additional stress-relieving process also that improves a block’s wear characteristics. Because it is a follow-on treatment after traditional heat treating, it’s an additional expense that some builders feel is unnecessary and some customers aren’t willing to support. The cryogenic process is a deep cooling where the part is chilled to near absolute zero (-360 degrees F) for 24 to 36 hours using liquid nitrogen, then allowed to warm to room temperature.
Vibration Treatment: A more common method of stress relieving involves clamping the part to a vibrating steel table where it is vibrated at a lower frequency than the part’s natural harmonic frequency. The sub-harmonic vibrations are applied for 20 to 30 minutes and the part is then checked to verify that the natural frequency has changed, indicating relief of inherent stress in the part. This process is performed on a special vibratory table manufactured by Meta-Lax.
Priority Main Oiling
All serious race blocks employ priority main oiling where full oil pressure is fed to the main bearings and rods prior to lubricating the camshaft, lifters, and valvetrain. This is critical to stabilizing the crankshaft in the main bearings and cushioning it against the ravages of high cylinder pressure, elevated engine speed, and the ever lurking potential for detonation.
World Products blocks are further refined from the original small-block Chevy design with revised oiling to the lifters as well. Lifter oil is rerouted to the center of the block where it is directed to the front and the rear along the lifter galleries. This oiling strategy eliminates standard small-block oil problems caused by compromised O-rings on the distributor shaft. World Products also drills its cam journal holes at the 5 o’clock position instead of 6 o’clock to introduce cam journal oiling slightly ahead of the point of maximum loading caused by high valvespring pressures.
Main Bore Size
Selection of main bore size is limited in most production engines, but given a choice, many builders are often drawn to smaller main bores to reduce bearing speed and frictional losses. Gen 1 Chevy small-blocks, for example, have a choice between 350 mains (2.45 inch) and 400 mains (2.65 inch), referring to the production main bearing sizes for those factory engines.
Once again the choice is application specific. High cylinder pressures found in supercharged or nitrous-assisted applications typically require the more robust size of larger mains. Likewise for circle track applications, like sprint cars, that hammer the bearings relentlessly with repeated applications of maximum-throttle. Drag racing applications with shorter exposure to extreme operating conditions can use smaller mains to reduce friction.
Many drag racing and oval racing applications run even smaller bearings using main bearing spacers. In selecting a main bore size it is critical to examine how hard your application is going to lean on it in terms of cyclic loading and RPM versus time, how much cylinder pressure you intend to create, how you lubricate the mains, and how much deflection you expect to occur in the crankshaft under load. It’s very important that the cylinder bores and main bores remain dimensionally neutral except for predictable and controlled thermal expansion.
Everything builds on a dynamically stable crankshaft and a very rigid block with stable main bore housings that don’t move around under high loads. Stability is often preferred over weight savings and frictional gains, but not in every case.
Main Web Structure
Blocks equipped with billet-steel main caps generally have beefier main web structures to ensure block rigidity. This is necessary and beneficial to operational stability. A wise engine builder once noted that a block has no moving parts, but that all the parts move within the block so it had better hold its shape. Block rigidity is extremely important, but getting there invites other problems depending on the design of the block.
Deep-skirted blocks such as current GM LS series engines encounter cylinder bay-to-bay breathing problems when outfitted with large stroker cranks. When the crank is captured farther up inside the block (as it is in these newer blocks), crankcase volume beneath the pistons is limited. Windage created by the rapidly reciprocating pistons can build excessive crankcase pressure. Without relief this creates additional pumping work against the bottom of the pistons, aggravates ring seal and oil control, and encourages seal leakage. Time spent contemplating cylinder bay dimensions and how best to control and relieve crankcase pressure will prove to be beneficial at the end of the day.
Filter, Starter and Accessory Mounts
Various applications may call for a revised starter location, so many race blocks are drilled for both right-and left-hand starters. Consider this requirement during block selection. Almost all blocks have an oil filter mount, but many race blocks do not incorporate a mechanical fuel pump boss, which may be necessary in some applications. Make certain that any block you choose incorporates all the necessary auxiliary features required for your specific application.
All blocks (new and used) require meticulous examination to determine whether you should invest time and money on expensive block preparation. New race blocks usually exhibit few problems, but they still require minor dimensional adjustments to perfect their critical structure.
Thoroughly clean any block with the most current hot tank process to remove scale, corrosion, and other objectionable material that might interfere with your examination. If the block does not come with a sonic test, perform one now to verify cylinder wall thickness (see “Sonic Checking”).
Examine the block for signs of core shift around the lifter bores and main webs. Crack checking is probably unnecessary on a new block, but used blocks should be carefully checked for cracks and other distressed areas that may leak or fail under load. Pay particular attention to the main webs and housing bores, deck surfaces, head bolt holes, lifter bores, cam bores, and the lower skirt area of each cylinder. Pressure checking is mandatory prior to performing machine work and crack repair is not a viable option for a competition engine so be prepared to scrap the block if a crack is detected.
This is also a good time to visually verify that all the oil galleries and fluid passages are unobstructed and flowing free. It is pretty easy to do with a simple garden hose and a restrictor to direct water pressure through all the holes in the block. Even if everything seems in order it’s a good idea to chase all the internal passages with appropriately sized brushes to ensure that no debris contaminates the oiling passage. Some builders also polish the oil galleries using a long rod with a slot cut on the end to hold a piece of fine emery cloth. The rod is inserted into each oil gallery and spun with a drill. The best finish is obtained if you lubricate the emery cloth with WD-40.
Once you confirm the block is acceptable, it’s time to verify its critical dimensions and note necessary adjustments. Everything is measured from the crankshaft centerline. Deck surfaces have to be the same height and absolutely parallel to the crank centerline. And they have to be exactly 90 degrees apart from each other. Check the distance from the crank centerline to the cam centerline and make certain that the cam bores support the cam absolutely parallel to the main bores. It is essential that all dimensions are square and true. Check every main bore and every cam bore. Check everything twice. Align bore and/or hone the main bores to ensure perfect alignment.
BHJ’s line-boring fixture enables accurate main bearing or cam bearing boring in a common vertical mill. This ensures that the crank and cam centerlines are perfectly parallel. These are normally pretty consistent on new race blocks, but you still have to check and recheck. Check the relationship of each cylinder bore to the crankshaft centerline carefully.
Lifter bores can present a major issue. If you’re not going to bush them, make certain that each bore is perpendicular to the cam bore and perfectly aligned to the cam axis with no skew to the left or right. Lifter bores must be perfectly indexed to ensure optimum placement of flat-tappet and roller lifters on the camshaft lobes.
Although it’s suggested to purposely mismatch some engine components to achieve specific tuning goals later on, everything in the block must be perfectly square, parallel, perpendicular, and/or correctly indexed for its intended purpose. These steps are critical to properly matching and supporting all the moving parts in the engine. Perfection is imperative. Strive for it relentlessly.
Additional block preparation details also include tighter tolerances and less core shift in aftermarket race blocks and Bow Tie and Super Duty blocks from the OEMs. Four-bolt blocks with beefier main webs and additional material for added rigidity often weigh more even when manufactured from compacted graphite iron (CGI). This is unnecessary for lower classes, and the engine package benefits more from having a lighter production-style block. Be prepared to make a judgment call regarding block rigidity versus weight as it relates to your application. Some builders also stress-relieve blocks by vibrating them on a vibratory table.
Machine Shop Processes
Precision machine work is fundamental to engine building. Most race engines require some or all of the following procedures.
Squaring the Block
All cylinder block machining operations must align to a common reference point. The crank centerline is that point. Accurate machining begins with precise align honing of the main bore so that all other operations may reference from it. Most builders don’t have the luxury of high-dollar CNC machining centers to perform block preparation so they rely on the accuracy of their own particular machining equipment or BHJ’s Blok-Tru kits (the industry standard) that work in conjunction with standard machining stations such as the Storm Vulcan Blockmaster series, Winona Van Norman units, and other overhead surfacing machines. According to BHJ, one or more of the following conditions are present in almost every block:
- Production equipment typically references off the oil pan rails and often fails to machine the bores exactly 90 degrees apart from each other and 45 degrees degrees from the block’s vertical centerline. Minor variations go unnoticed on production engines, but are not tolerable on a race engine.
- Twisted blocks require the machinist to choose a reference point on the deck surface for setup, which leads to machining errors compounded by the original reference point.
- Deck clearances are often uneven between the upper and lower side of the piston tops because the deck surfaces are not 90 degrees to the cylinder bores.
- O-ring grooves are often cut unevenly on boring stands that reference off the oil pan rails.
- Poorly fitting intake manifolds caused by the deck surfaces not being machined exactly 90 degrees to each other and or parallel to the crank/centerline.
- Minor variations in cylinder head alignment causing ignition timing variations and the cylinder V not precisely 45 degrees on each side of the cam-crank centerline camshaft.
These conditions and others are corrected using BHJ’s block truing equipment. The Blok-Tru Index Plate is precision machined with 45-degree angles on either side of the centerline. Once installed on the cam/crank centerline all of the angular dimensions can be machined to within 5 minutes of 1 degree. A special deck-height micrometer attached to a heavy-duty deck bar permits exact measurements from the deck surface to the Blok-Tru plate. This is then added to the known height of the fixture plate to determine the exact deck height.
The Bore-Tru kit is a blueprinting fixture that enables the engine machinist to accurately locate cylinder bores relative to the correct crankshaft journal location. It references from the rear main surface or the rear main thrust surface to position the cylinders at factory-specified bore centers. It also permits correction of the cylinder head dowel pin holes for precise cylinder head alignment. A precision deck plate attaches to a pair of universal alignment bars front and rear to precisely locate the bores relative to the crank centerline.
The accuracy of the Bore-Tru equipment depends on perfectly square deck surfaces, which are handled by the Blok-Tru equipment. Each component of the BHJ system complements the other, allowing any competent machinist to produce a precisely machined racing engine block.
Lifter bore truing is accomplished with a BHJ Lifter-Tru kit that facilitates the process on a standard Bridgeport machining center. To use the kit, attach the precision machined aluminum end plates to each end of the cylinder block for alignment via mandrels that pass through the main bore and the cam tunnel. The plates are shaped and positioned so the lifter bore axis (relative to the cam axis) is vertical when set up in the mill. Mount the precision cutting guide across the end plates directly over the lifter bore. It functions as the upper support while the mandrel passing through the cam tunnel serves as the lower guide so the cutter is supported above and below the lifter bore for precision placement.
The BHJ kit comes with cutters for standard lifter bore sizes including .8437-, .875-, and .904-inch diameters. It is possible to overbore the smaller GM lifter bores (.8437) to accept the larger Ford lifter (.875); Ford blocks can do likewise with the larger Chrysler lifter size (.904). Check with your cam supplier for compatibility and specific recommendations if you consider this kit.
You can also oversize the lifter bores to 1.000 inch to accept sleeves or bushings that can be accurately positioned and precision bored to any desired size. Again check with your block and cam manufacturer for the appropriate length and diameter bushing; this is primarily to ensure proper clearance for different styles of roller lifter tie bars. Once the bushings are installed, use the same BHJ kit to size them correctly.
Prior to installation check the bushings for the presence of lifter gallery oiling holes. If they are not present you must drill them yourself. Most bushings are supplied with or without oiling holes so you should be able to specify the hole size to your supplier and get bushings that are properly pre-drilled. Otherwise drill each bushing by referencing the oil gallery position from the top of the existing lifter bore.
A more common practice is to drill the bushings after installation using a long drill bit. The procedure offers precision hole placement using the oil galleries as a pilot fixture and it enables you to enlarge the lifter galleries at the same time if so desired. If you go this way, drilling the bushings first and truing the lifter bores last cleans up any burrs left by the gallery drilling.
Bushing installation is straightforward, but you have to work carefully. Bushings must not extend beyond the bottom of the lifter bore opening to the cam tunnel and they have to be installed in perfect alignment, particularly those incorporating slots for guided lifters, such as Jesel units.
Final lifter bore honing is accomplished with a BHJ or Sunnen honing kit that includes the appropriate stones and guide mandrels. A U-joint and shaft assembly is provided for honing with a 1/2-inch drill, but most builders prefer to finish the procedure while the block is still on the milling machine.
Alternative Lifter Oiling
Small-block Chevy engines running flat-tappet cams have a nasty habit of flattening cam lobes and wiping out the lifter faces. The problem typically occurs during the initial break-in procedure, but it can also happen in competition with very high spring tension and insufficient lubrication. The least expensive remedy involves grooving the lifter bores with a simple tool from Comp Cams. It incorporates a lifter-shaped grooving tool with an adjustable carbide cutter and a handle for drawing the tool through the lifter bore. The cutter is set to cut a groove (almost a scratch, really) .009- to .012-inch deep from the bottom of the lifter bore up to the oil gallery feed holes. The grooves should be cut on the right side (passenger side) of the block to ensure that each lobe is pre-oiled before it is subjected to maximum valve spring pressure.
For ultra-high-spring applications special flat-tappet lifters are also available with .010- to .15-inch EDM (electrical discharge machining) oiling holes drilled directly into the face of the lifter surface. These holes are connected to a feed hole in the side of the lifter that provides full-time oil pressure directly to the lifter/lobe interface. This oiling strategy usually cures cam lobe distress under these conditions. Comp Cams offers these lifters for all popular domestic V-8s.
Now that the racing industry has largely shifted to dedicated race blocks, line boring the main cap housing bores is no longer prevalent. Align honing to ensure precision alignment is usually all that’s required with most current engine builds. If align boring is necessary, the machinist generally machines the main bores to within .005 inch of the final desired housing bore dimension. Some machinists feel comfortable align boring to the actual final dimension, but most engine builders prefer to leave the last .0015 inch for align honing to gain a better finish on the housing bore. A 150-grit aluminum-carbide stone is typically used with billet or ductile iron caps while harder stones are reserved for cast-iron blocks.
Torque Plate Honing
Honing plates are available to fit more than 400 engine applications in all sizes, from single-cylinders to V-12s. BHJ is recognized as the worldwide authority in honing plate development and production today. Since the conception of the initial honing plate designs that were introduced by BHJ Products in early 1975, continued research and development has bred numerous design improvements that bring us to the models available today.
Head-bolt torque can dramatically distort cylinders and cylinders cannot be bored or honed accurately if cylinder dimensions change so significantly after assembly. Rings won’t seal well, and scuffing is likely to occur if the engine overheats. Use of BHJ honing plates rectifies all of these problems, leading to more consistent tolerances, better sealing, and more power. They feature 1¾-inch-thick Meehanite cast-iron or cast aluminum, which gives maximum rigidity and resistance to permanent distortion and most closely simulate the stresses induced on the cylinder wall by the cylinder head when it is torqued in place.
In addition, these materials have essentially the same coefficient of expansion as cylinder heads, important to those honing at operating temperature. Cast-iron plates are Blanchard ground on both sides, flat and parallel within precision commercial tolerances. BHJ aluminum R Model plates are supplied with heat-treated steel inserts (T-washers) in all standard bolt holes. Plates are manufactured with a .090-inch to .095-inch-larger bore size than the largest standard engine bore diameter found in the applicable engine family in most applications, allowing the plate to accommodate .060- inch overbore. This maintains full gasket firing-ring compression, thus further enhancing bore stability. Special bore diameters are available upon request.
Head-bolt holes are precision machined to factory tolerances and special bolt-hole sizes are also available. Clearance holes for locating dowels are machined oversize to allow visual alignment before torquing. Indexed or “dialed-in” dowel holes are also available upon request.
The R Model Honing Plate is the established standard for duplicating cylinder bore distortion and is a must for any high-performance engine application. The R Model incorporates all of the features of the standard version, plus is specially machined, and in most cases, supplied with DOM steel spacers and washers, to duplicate cylinder head height and facilitate the use of the OEM-length head bolts or aftermarket studs during the honing operation. Optional machining is also available for hot-honing.
In order to maintain the least possible block distortion when using the R Model Honing Plate, be sure to use the same type of cylinder head gasket and bolt or stud set as during final engine assembly. Some engines require that both cylinder banks be torqued to better simulate final assembly conditions during honing. Additionally, industry tradition dictates that the honing plate should be of a similar material as the heads being used in final assembly, thus a cast-iron honing plate is preferred when using cast-iron heads in final assembly and an aluminum plate should be used when aluminum heads are installed.
Many engine builders acknowledge that hot honing cylinder blocks at a temperature closer to actual operating temperature provides superior results. Benefits include improved ring seal, reduced friction, and superior ring stability due to a more precise ring-to-cylinder-wall relationship. Most engine builders also acknowledge that hot honing is a messy, aggravating procedure that most of them avoid despite potential gains in performance.
It’s easy to suggest that this is a high-end procedure best left to professional teams with dedicated engine facilities and that it probably doesn’t make enough difference for more budget conscious sportsman efforts. But when should a known performance benefit ever be ignored? Hot honing requires a significant investment in equipment and certain modifications in honing technique, but it provides proven benefits that racers seeking maximum power and durability cannot and should not fail to consider. Even shops that do it regularly acknowledge that it is a pain in the ass, but they endure it because it is worth it.
Most builders deburr the block to eliminate the source of casting flash that might break off in the engine under severe operating conditions. Millions of engines, particularly truck engines have logged tens of millions of miles with very few if any casting flash episodes. Still, never say never. Play it safe and deburr the block. You could be the one that it happens to on the final lap of the first race that you’ve led all season.
Deburring is also a safety procedure to keep you from cutting your hands to pieces during mock-up and final assembly. Deburring should be done everywhere on the block where a sharp edge exists or where casting residue protrudes from the surface. It also includes corners, nooks, and crannies where hidden stress risers may lead to localized cracking. That means deburring inside the crankcase as well as the lifter valley, timing cover area, bellhousing area, and all exterior surfaces.
When you are finished you should be able to work on any area of the block without cutting yourself. Devotees of the deburring art often smooth and polish all inner surfaces that are exposed to oil to encourage oil drain back and minimize the amount of oil clinging to any surface. Whether or not hot oil clings to or flows from a polished surface is still a matter of debate.
Special oil-shedding coatings are available for this now, but back in the day, most builders painted these inner surfaces to seal them. The preferred product was Glyptal, but in reality, many builders simply used a spray bomb of blood-red electric motor varnish straight from a Krylon can. This provided a tough, smooth finish that sealed-in any residual dirt and promoted oil drainage.
The smoothing and polishing practice seems to have gained favor with a lot of builders who suggest that the paint might flake off. While there may be something to it, I can honestly say that in more than 40-plus years I’ve seen a lot of painted blocks and a lot of engine bearings and other components and I have never seen a failure traceable to paint chipping off an internal block surface. Not saying it couldn’t happen, but it is unlikely if the paint was applied to a clean, well-prepared surface that had been hot tanked and prepped with lacquer thinner.
Threaded Hole Preparation
One very important aspect of competition engine assembly is preparation of the threaded holes for the fasteners that hold the engine together. The widespread practice of chasing all threads with a thread tap was generally okay back in the days prior to the extraordinary power levels engine builders achieve today.
A thread-chasing tap cuts metal wherever it encounters resistance. When this happens it alters the thread dimensions slightly, and over time it can diminish the capacity of the thread to properly hold and align the fastener. Proper thread preparation for new race blocks primarily involves careful inspection and cleaning.
If you’re refurbishing a block during a rebuild it is best to thoroughly clean the block with a hot tank or other cleaning method. Next, inspect and prepare individual fastener holes as required. Clean each hole with bore- and thread-cleaning brushes and blow it out with compressed air. Finally, carefully run a thread roller tap into the hole to properly align the existing threads.
Piston Pin Oiling
Direct wristpin oiling is common enough now that engine speeds have increased and component mass has been trimmed to a minimum. Be aware that most cylinder blocks (including aftermarket race blocks) are not directly equipped to support pin oiling, but there are ways to incorporate it if desired.
Pin oiling is generally required for high RPM, severe loading, or endurance applications where pin and/or pin bore distortion may cause problems that can often be mitigated by additional pin lubrication. Pin oiling is also used to help cool the piston crown in severe-duty applications.
Cup engines run pin oilers and they’re certainly a good idea on a sprint car or a Bonneville engine, but they are not often utilized on short-duration drag racing engines except perhaps in high-boost applications with high cylinder pressures and severe pin loading. Built-in pin oilers typically incorporate squirter assemblies mounted in the crankcase where they can direct a steady stream of lubricant against the bottom of the piston deck to remove heat from the piston and then splash oil on the pin.
Some factory performance engines actually have pin oilers (Honda S2000 for example) because they rev so high, but most domestic engines require custom fabrication. Many racers drill small holes from the main bore housings through the top of the main webs with precision placement to oil the piston pins. Mike Laws Performance (MLP) makes a kit to accomplish this on Chevy and Ford V-8s.
The MLP kits feature machined mandrels equipped with drill bushings that bolt into the main bearing housing bore to accurately position the drill bit. The drilled hole is then tapped and fitted with screw-in oil jets that are then captured underneath the main bearing. A hole is drilled in the bearing to feed the pin jet, or some builders grind a small slot from the housing bore oil-feed hole over to the location of the jet so that lubricant feeds to the pin oiler underneath the bearing.
Both methods seem to work equally well. Other racers have fashioned internal oiling manifolds or tapped into pan rail oil galleries and attached their own squirters. If you feel the need for pin oilers, be aware that to some small degree they contribute to windage problems due to the extra oil falling on the crankshaft. While direct pin oiling is important for durability issues, its primary goal is usually piston cooling. In that regard it is often more effective than the normal transfer of heat to the cylinder walls via the rings.
Written by John Baechtel and Posted with Permission of CarTechBooks