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.

Chevrolet Sprint Cup R07 block. (Courtesy General Motors)

Iron blocks, particularly those manufactured with harder CGI remain the primary choice for many high-end competition engine builds.

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.

[pro_ad_display_adzone id="16495"]

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 Type

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.

Aluminum blocks have enjoyed con¬siderable favor in the recent decade thanks in part to the influence of high-performance and race-prepped factory-style blocks based on contemporary production engines.

Most dedicated race blocks are equipped with splayed four-bolt caps made from billet material such as 1020 or 1045 steel alloy. The splayed bolt arrangement anchors the outer bolts into the beefiest part of the main webs. Lower-tier four-bolt blocks typically have main caps manufactured from ductile iron.

Dart Big M Chevy blocks come with either ductile iron four-bolt caps (Sportsman version) or billet steel four-bolt main caps. Main cap bolts are suitable for most applications but are often replaced with optional studs.

This Dart block’s thicker cylinder walls stabilize the cylinders and promote superior ring seal under high cylinder pressures and elevated engine speed.

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

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).

Aftermarket Sportsman cylinder blocks like this Dart SHP block incorporate many of the most desir¬able features of more expensive full-race blocks. These blocks are an excellent choice for many budget-conscious racers seeking affordable alternatives for their racing efforts.

Modern race blocks are prepped on CNC machining centers like this at Dart Machinery. Modern casting techniques and CNC precision have made high-quality race blocks easily available to all racers.

NDT Systems is a major provider of sonic-checking equipment for auto¬motive cylinder blocks. The units are easy to use and they provide very accurate results. (Courtesy NDT Systems, Inc.)

Sonic testing a race block’s cylinder wall thickness at multiple points within each cylinder bore is the only accurate way to verify adequate cylin¬der wall thickness for any competition engine build. Here the engine builder is holding the sensor firmly against the cylinder wall to ensure an accurate reading. (Courtesy NDT Systems, Inc.)

This NDT Systems cylinder data report for a 1958 283-ci Chevy V-8 illustrates the measured cylinder wall thickness data for the front, back, and major and minor thrust sides of all the cylinder walls. For this particular engine the major thrust surfaces are on the exhaust side for cylinders 5-6-7-8 and the intake side for cylinders 1-2-3-4. (Courtesy NDT Systems, Inc.)

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.

Deck Thickness

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.

Thicker deck surfaces add consider¬able support to the top of the block, contributing stability to the cylinders while minimizing bore distortion and providing a superior gasket sealing surface. (Courtesy Dart)

Siamesed Cylinders

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.

This view through the open core plug on the side of this Dart SHP block reveals the solid structure between the siamesed cylinders. The siamesed structure stabilizes adjacent cylinders and provides superior rigidity.

Camshaft Position

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.

BHJ’s Cam-Crank Center Distance Gauge uses a large micrometer and precision machined cam and crank bore mandrels to verify the camshaft height dimension in relation to the crankshaft.

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.

Top engine shops like Automotive Specialists leave no stone unturned to ensure maximum power and durability for engine customers. Here a MetaLax vibratory table from Bonal Industries is used to vibrate engine components outside their natural frequency to remove stress. (Courtesy Auto¬motive Specialists)

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.

Priority main oiling routes oil from the main oil gallery straight to the main bearings and then the camshaft as shown on this Dart small-block. The camshaft and valve train are fed by the secondary vertical passage from the upper main bearing.

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.

Main bearing size is sometimes application specific. Durability engine builds typically call for larger stock-size mains while many naturally aspirated high-RPM, high-horsepower applications take advantage of smaller main bearings with bearing spacer inserts to reduce friction.

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.

Cutaway view of a Dart high-performance race block shows the penetration of the main cap studs or bolts into the strongest part of the main webs.

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.

Block Inspection

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.

Precise cylinder bore alignment in relation to the crankshaft centerline is a fundamental step in basic cylinder block preparation. BHJ’s block truing alignment fixture helps machinists position each deck exactly 90 degrees from the other and perfectly perpendicular to the crankshaft. (Courtesy BHJ Products)

BHJ’s line boring fixture facilitates main bearing and cam bearing align¬ment using a standard vertical mill. This procedure corrects misalignment and makes the main bores and cam bores parallel while properly sizing the main housing bores. (Courtesy BHJ Products)

Shops already equipped with a line boring machine can use BHJ’s cam tunnel alignment fixture to index the cam tunnel parallel to the crank centerline. (Courtesy BHJ Products)

BHJ’s Blok-Tru kit aligns deck surfaces to the crankshaft centerline. The precision index plate is machined with 45-degree angles for both deck surfaces. The basic kit is the necessary starting point for tailoring the Blok- Tru system to fit resurfacing machines supplied with a 2-inch-diameter support bar from the manufacturer. It consists of a precision-machined index plate, cam tunnel alignment cones, and cam tunnel clamping hardware. (Courtesy BHJ Products)

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 system also incorporates a deck height micrometer with an oversize, heavy-duty base, allowing the attached measuring spindle to easily reach from the edge of the deck surface out and down to the Blok-Tru Index Plate. Actual deck height is determined by adding the measured distance to the Blok-Tru cen¬ter machined on the face of the plate.

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 Bores

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.

BHJ’s Lifter-Tru fixture kit allows machinists to properly index lifter bore position front-to-rear and up-and-down, as well as restore the correct lifter bore angle as referenced from the cam/crank centerline. Blocks without finished lifter bosses may also be machined with new lifter bores using optional cutters. The cylinder block is set up in the fixture at the prescribed angle while a piloted cutter is precisely guided from both above and below the lifter bore. This operation is typically performed in a vertical milling machine, but a valve seat and guide machine, or even a large drill press can be used effectively.

 

Bushed lifter bores are perfectly aligned to minimize friction and pro¬vide optimum cam-to-lifter alignment. They also permit the use of larger-diameter lifters for more aggressive camshafts.

Torque plate honing is mandatory practice for all race blocks. It minimizes bore distortion when cylinder head clamping loads are applied and is particularly effective when combined with hot-honing techniques.

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.

The BHJ Blok-Tru setup corrects mis¬aligned deck surfaces by registering off the crank centerline, establishing parallel decks and a true 45-degree angle to the cam/crank centerline.

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.

Align Honing

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.

BHJ honing plates are the standard of the industry. The company offers a broad line of plates specifically designed for racing applications.

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.

New race blocks are high-quality castings, but still require careful deburring and basic preparation prior to final assembly. This Dart Big M block illustrates the excellent casting quality available in modern aftermarket race blocks.

Carefully inspecting and deburring the cylinder block is the first step in any com¬petition engine build. The deburring process removes all sharp edges and casting flash. It also includes chamfering the freeze plug holes and break¬ing the leading edge of each cam bearing bore to facilitate the easy installation of the cam bearings.

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.

Hot Honing

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.

Deburring Procedures

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.

Special thread-chasing taps from ARP clean the threads in the block and other parts without cutting away more metal. This promotes proper thread engagement to ensure opti¬mum fastener performance.

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.

This Tech Tip is From the Full Book, COMPETITION ENGINE BUILDING. For a comprehensive guide on this entire subject you can visit this link:

LEARN MORE ABOUT THIS BOOK HERE