When assembling any engine, its intended output and operating range must be within the realistic realm of possibility. While any Pontiac can perform suitably in stock form, modifying the original pieces or purchasing aftermarket components is often required to achieve significant performance increases. Each new component must be carefully selected to ensure that its operating characteristics complement the others. Haphazardly combining parts could otherwise produce an engine that only runs well in a limited RPM range or one that could self-destruct at high RPM.
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The owner of our project 1967 400 being rebuilt wanted his engine to produce at least 360 hp. He based that number on the original rating of the 400 H.O. offered that year. Before spending dollar one on the project, I clarified several factors with him. This 400 in his 1967 GTO was original, and he didn’t want to compromise originality in any way. That meant reusing the original block, cylinder heads, intake manifold, and carburetor if possible. And we depended upon the machine shop to determine whether any of it was reusable or we had to begin searching for replacements.
At this point, you have completely disassembled the engine and selected a reputable machine shop, so the rebuild portion of the project is ready to begin. I feel that it’s best to take the entire engine to the machinist for complete inspection, even those parts that he might not otherwise touch. His experienced and discerning eye may notice something that you overlooked or didn’t have proper equipment to detect.
I make it a habit to tag or mark any component I take with me to the machine shop so each can be quickly identified. I also suggest making a detailed list of the components that are being left behind so you can be sure each component is accounted for when that portion of project is complete.
The owner and I agreed to have Willard Auto Machine (WAM) in Omaha, Nebraska, perform the 400 rebuild. Many consider WAM one of the area’s top engine building shops. WAM not only has the capability to fully machine any engine component in-house, its Land & Sea Dynomite engine dyno has been used to measure the output of the many Pontiac engines that owner Chuck Willard has rebuilt over the years. I was completely confident in Chuck’s ability to properly rebuild the 400. I asked that I be regularly updated of its progress and immediately notified of any irregularities, and he obliged.
A complete engine rebuild begins with a deep cleaning of each component. That can include a thorough washing, acid bath, non-abrasive media blasting, or a relatively new process known as ultrasonic cleaning, which uses high-frequency sounds waves and a soapy mixture to clean components. The goal is to remove all traces of grease and grime from all of the engine components, which makes performing the visual inspection and any machining much easier. Under no circumstances should abrasive media, such as steel, sand, or glass, be used to clean any component. Minute particles can imbed into the component pores and/or cracks and crevices, making it impossible to completely remove. The media can dislodge during normal engine operation much later, causing serious internal damage.
Once each piece is completely clean, a quality machine shop inspects each component for any crank that could affect integrity. That process generally includes a magnetic particle inspection or pressure testing. When searching for external cracks, a component is dusted with small metallic particles, which tend to gather in cracks and become visible when the component is magnetized. Pressurized air can reveal any internal oil or coolant leaks. Your machinist can advise whether a component is salvageable if any cracks are detected.
The block is the foundation of any engine. Its internal and external tolerances must be exact or any component bolted to it may not function properly. In addition to thoroughly cleaning every coolant and oil passage to remove all traces or sludge or trapped grit, complete block machining should include boring and honing the cylinders, machining the cylinder head deck surface, and boring or honing the main journals. The cam tunnel can also be checked if any usual bearing wear was found during disassembly. In our instance, the cam tunnel was straight. WAM determined that the abnormal wear was likely due to improperly installed cam bearings.
If the cylinders show little taper, it’s possible that honing can restore the cylinder wall finish and promote maximum seal by using the existing pistons with new rings or replacement pistons of the same dimension. Most often, however, the cylinders need to be enlarged to repair worn or damaged walls. An overbore of .030 to .060 inch is common during Pontiac V-8 rebuilds, but it’s recommended that wall thickness be sonically checked to ensure it’s not less than about .125 inch after machining for a street-driven Pontiac. New pistons and corresponding rings are required any time the bore is enlarged. Final honing to achieve the recommended amount of piston-to-cylinder-wall clearance should only be performed after the new pistons arrive. Pontiac engines generally have good main cap alignment and rarely require any additional machining beyond a basic line hone. Anytime new main caps are installed, the block should be line bored or honed, which ensures that the main journals are absolutely straight. Absolute precision is required during the process. The machinist should also use a small stone or file to deburr the main saddle and cap parting lines to remove any sharp edges that could prevent the bearings from being installed properly, or insert material behind it during bearing installation.
Step 1: Wash Components
Before any machining is performed, Willard Auto Machine (WAM) thoroughly cleaned each component of the engine to remove any sludge and contaminants that might inhibit proper inspection and machining. The process can be performed in a number of ways. This includes solvent washing, non-abrasive media blasting, and ultrasonic cleaning. Any of these methods work quite well. What’s available to you may depend upon the area in which you live. Local laws in some portions of the country may restrict the types of chemicals or methods that can be used.
Step 2: Bore Block
After carefully inspecting the block for cracks and measuring cylinder wall thickness to verify that no less than .125 inch remains after machining, the block is sonic tested. Sound waves are blasted into the material and the reflectivity is calculated into thickness. The cylinders are then bored to a dimension that provides optimal cylinder ring seal. For Pontiacs, this usually starts at .030 inch and can increase to as much as .060 inch, if thickness testing allows. This 400 had already been bored .030 inch. WAM removes only .010 more, taking the bore diameter to a total of 4.16 inches. A steel torque plate should be used during boring and honing. It replicates the effects that the cylinder heads have on the cylinders when bolted to the block.
Step 3: Purchase New Pistons
After determining how much material must be removed from the block’s cylinder walls, WAM sourced the correct size pistons and corresponding rings. The bore of this 400 was increased by .040 inch. Sealed Power is one company that offers a high-quality forged-aluminum piston that’s ready-made for .040+ 400 applications (number L2262F040). The company’s recommended moly-coated piston ring set was used to complement the pistons.
Step 4: Measure Piston Diameter
When purchasing pistons and rings, the set often includes the exact piston dimensions and suggested piston-to-cylinderwall clearance and ring end gap. Even so, WAM still physically measured each piston diameter with an outside micrometer positioned about 2.5 inches downward from the head to ensure complete accuracy. In this instance, Sealed Power recommends .002 to .003 inch of clearance for its forged pistons.
Step 5: Hone Block
When boring a block, the machinist usually stops .005 to .010 inch short of the final bore dimension. That’s then followed by the honing process, which removes small amounts of material and allows the machinist to finely tailor the bore diameter to the precise amount of piston-to-cylinderwall clearance. The process also leaves behind a distinct crosshatch appearance that’s required for maximum ring seal and lubrication.
Step 6: Machine Block Deck
A block’s deck surfaces are often distorted from years of use, especially if the engine was subject to significant overheating. A precision straightedge and feeler gauge is used to determine any areas that may not be straight. Optimal straightness can be achieved by lightly milling the deck surface on a horizontal mill. Compression height, as measured from the centerline of the crankshaft to the deck surface, should measure around 10.22 to 10.24 inches, depending upon the pistons and connecting rods being used.
Many modern machine shops do not have the proper equipment to machine crankshafts simply because of its rather high cost and limited usage. You shouldn’t immediately assume that your chosen shop is inferior if it doesn’t have such equipment, however. A quality machine shop can arrange to have your crankshaft sent to a reputable shop that specializes in servicing crankshafts.
If your rebuild includes an aftermarket crankshaft, it shouldn’t require any additional machining, but your machinist should still verify that its rod and main journals measure correctly, and that it’s balanced properly. Your machinist can determine if your original Pontiac crankshaft is reusable and the condition of its journals if you plan to reuse it. If they are in relatively good shape, micro polishing may be all that’s needed to renew the surfaces.
Journal machining is typically required and that generally consists of undersizing the journals, which is usually in .010-inch increments. The main journals of a Pontiac crankshaft can be undersized as much as .030 inch without compromising integrity. The rod journals can be undersized as much as .15 inch to big-block Chevy journal diameter of 2.1 inches without issue. No additional surface hardening treatments such as nitride or chroming are required when building a street engine.
Occasionally, an original crankshaft can be bent. Straightening it is a delicate process that involves setting the crankshaft in a jig and carefully driving the counterweights in the required direction to ensure the main journals are straight. But it doesn’t guarantee any result. A replacement crankshaft may be required if the original cannot be sufficiently adjusted.
Step 7: Line Hone Main Journals
To ensure that the main journals are perfectly straight and that the crankshaft isn’t subjected to any undue stress, the main caps are installed and the block is line honed on a Sunnen Line Hone machine. This procedure removes a slight amount of material from the cap and block, and can move the crankshaft centerline a bit closer to the camshaft. If the main journals require a considerable amount of machining, a slight amount of material can be removed from the mounting flange of the main caps and the assembly is line bored, which can be performed without moving the crankshaft centerline any closer to the camshaft. Ask your machinist if the parting lines were deburred and how much material was removed during the line-hone process. A shorter timing chain may be required in certain circumstances.
Step 8: Grind Crankshaft Journals
The stock Pontiac crankshaft is quite durable. It did not need its journals hardened from the factory to improve strength as did some other makes, so no additional hardening is required for a rebuild. A significant amount of material can be removed from its rod and main journals without greatly affecting durability. The most apparent limiting factor is the immediate availability of undersized bearings for Pontiac journals, which is as much as .030 inch in most instances. If either journal surface requires excessive undersizing, it may be best to find a replacement crankshaft.
Connecting Rod Preparation
Pontiac’s cast ArmaSteel connecting rod has gained a negative reputation over the years. Many hobbyists believe that it immediately selfdestructs much above 5,000 rpm. In reality, Pontiac’s cast rod is quite durable and has been used successfully in engines that turn 6,000 rpm or slightly more. I don’t suggest reusing original cast rods for a highperformance rebuild, mostly because affordable forged-steel options are readily available. But I am not suggesting that the original rods cannot be used once prepared properly.
If original cast rods are part of any rebuild, the machinist should carefully magnetic-particle inspect the rod body and cap for cracks. Any rod that even looks as if it has any area that could evolve into a crack should be replaced with another, without exception. The rods should be checked for straightness, and modern high-quality 3/8-inch fasteners, such as PN 190-6001 from ARP, are highly recommended. These require 50 ft-lbs of torque using ARP’s moly-based thread lubricant. The ARP fasteners replace the originals, which require 43 ft-lbs using 30-weight oil. The crankshaft end of the rod should be resized. That includes removing a bit of material from the cap and body parting lines and machining the bore to return it to proper dimension. The parting lines should be deburred for optimal bearing installation.
There are two main types of aftermarket forged rods available for Pontiac V-8 engines: I-beam and H-beam. The debate over which type is better largely depends upon the intended application, but it’s generally stated that an H-beam rod is more resistant to bending when compared to an I-beam rod. In reality, either should be quite sufficient for most streetdriven Pontiac V-8s.
Even though it may seem that aftermarket connecting rods should arrive in ready-to-run condition, it’s highly advisable that the machinist measure the entire set to verify that each is within the stated tolerances. It’s not uncommon to find one or several needing its crankshaft bore honed slightly. Whether running original cast rods or aftermarket forged units, the piston wrist pin bores usually have to be honed to achieve proper clearance for the wrist pin that’s included with the new piston.
I routinely consider all connecting rod options when choosing a connecting rod for an engine. Because most street-driven Pontiac engines, like this 400, do not usually turn more than 5,500 rpm or generate much more than 400 hp, a set of stocklength 5140-steel forgings from RPM International were more than sufficient for a build of this level, and the cost is quite reasonable. These are the rods I chose for this particular rebuild.
Step 9: Measure Connecting Rod Crankshaft Bore
After placing each RPM rod into a soft-jaw vice and tightening the nuts of the ARP fasteners to 75 ft-lbs, WAM checks the crankshaft bore (or large end) of each new forgedsteel connecting rod to ensure that the opening is perfectly round. A slight amount of variance is corrected by removing material from the parting line of the rod cap, reinstalling the cap, and honing the bore to the proper specification. The parting line should be deburred after machining to prevent bearing damage during installation.
Step 10: Hone Connecting Rod and Piston for Wrist Pin
The wrist pin bore (or small end) of each connecting rod and corresponding hole on the piston is honed to .001 inch to accommodate the press-fit wrist pin. The honing process ensures a precise amount of clearance between the connecting rod and wrist pin. The piston wrist pin bore is about .0005 inch larger than the pin, which allows the piston to pivot freely on the wrist pin once the engine comes up to normal operating temperature.
Component balancing should be part of any rebuild, no matter how basic. The process consists of weight matching the entire reciprocating assembly. This includes the pistons, connecting rods, and crankshaft. The harmonic balancer and flywheel or flexplate are also included in certain applications. Balancing minimizes engine vibrations through a certain RPM and serves to maximize performance while increasing engine life, particularly of the main bearings.
Step 11: Balance Connecting Rods and Pistons
Balancing the reciprocating assembly ensures smooth, consistent engine operation and should be part of any rebuild. A precision scale is used to measure the weight of each piston, pin, and connecting rod individually. Material is then removed from designated areas of the pistons and rods until the heaviest pieces weigh nearly the same as the lightest. When weighing connecting rods, better shops use a specific hanger like this, which allows the operator to accurately measure both ends of the rod for exact balance.
The crankshaft machining process generally leaves behind a rough journal surface that can quickly destroy a new bearing. After all machining and balancing is complete, the crankshaft is installed onto a special lathe, where it is rotated at relatively low speed while the operator uses a belt polisher to polish the freshly machined journals, removing all minute rough edges and burrs. The result is a super-smooth journal surface, which should provide optimal lubrication and long bearing life.
Step 12: Balance Crankshaft
A series of bobweights are fastened to the crankshaft rod journals, which replicates the effects of the rotating and reciprocating masses. The crankshaft is spun at low speed and a strobe light tells the operator exactly where weight should be added or removed from the factory counterweights. WAM generally gets the crankshaft very close before adding the timing chain gear, harmonic balancer, and flywheel or flexplate, and then finishes the process. The flywheel or flexplate the engine is balanced with should be the one that’s used in the vehicle. So if a replacement is required, it should be purchased by this portion of the rebuild. It ensures that the entire reciprocating assembly is fully balanced. You should have your machine shop perform this function, so your engine operates at maximum efficiency.
Step 13: Chamfer Oil Holes
The technician waits to polish the crankshaft journals until the unit is fully balanced, which is intended to avoid any marring that could occur when the bobweights are installed to the rod journals during the balancing process. Before beginning, he or she chamfers the oil holes to improve bearing lubrication on a round grinding stone—a step many machine shops do not perform.
Intake Manifold Selection
An intake manifold is designed to operate within a specific RPM range on a given engine combination. Plenum volume, cross-sectional runner area, and overall runner length are factors that help a manifold achieve optimal performance for the intended application. Though any manifold operates on any engine at any practical engine speed, performance ultimately suffers as engine speed varies outside the manifold’s intended operating range. There are two major groups of 4-barrel intake manifolds: single-plane and dualplane, and the operational characteristic of either is somewhat specific.
Single-plane castings generally favor higher-horsepower combinations that operate at high engine speed. These have an open plenum design, in which each of the eight runners pulls from the entire carburetor to improve high-speed cylinder fill. A direct trade-off, however, is less carburetor signal at idle and lowengine speed, which tends to negatively affect throttle response, low-speed performance, and overall economy.
Dual-plane manifolds are designed to develop maximum average power over a broad RPM range. They consist of a split plenum in which four cylinders pull from one half of the carburetor and the remaining four pull from the other half. The design increases the speed of the air passing through the carburetor, which tends to improve fuel atomization, making dual-plane manifolds very efficient at low- and mid-RPM ranges. However, this design can adversely affect high-speed operation because only half of the carburetor is available to supply air to each cylinder.
The best intake manifold for any application depends upon engine displacement, cylinder-head flow, camshaft duration, and the intended purpose and operating range of the engine. The stock Pontiac intake manifold was developed to produce maximum usable torque, and this design remains an excellent choice for most street-driven applications. It should sustain 5,500 rpm (or slightly more) on any 350 or 400, while that may be a few hundred RPM less on larger engines. I felt that the 400’s original cast-iron intake manifold was the best choice for its intended operating parameters.
Step 14: Crankshaft Polishing
The crankshaft polishing process is rather straightforward. The crankshaft is mounted into a special lathe, and it’s spun at low speed while the journals are polished with specific polishing bands of varied coarseness. The end result is super-smooth main and rod journals that should provide thousands of miles of reliable operation.
Step 15: Valveguides
As a valve guide wears over the course of many thousands of miles or normal operation, it tends to lose its ability to properly locate the valve and prevent oil from passing by. A common repair is to hone the castiron guides and install thin-wall bronze liners (left). Another common repair that seems to be much more permanent includes machining the existing cast-iron guide and installing an entirely new guide constructed of cast iron or bronze (right). When using cast-iron cylinder heads, 0.0015-inch intake and 0.0020-inch exhaust of valvestem clearance should be sufficient.
Step 16: Hardened Exhaust Seats
When lead was removed from gasoline in the early 1970s, premature exhaust seat failure was fairly common. Consequently, Pontiac began hardening its cylinder head’s exhaust valve seats in 1972, but the process only hardened the material at the surface and immediately beneath it. It was generally removed after two valve jobs. Hardened exhaust valve seats are required on engines that are driven daily or run hard. The process of adding hardened seats is relatively simple. The seat is cut to a specific dimension and a hardened seat is coated with liquid sealer and driven into place. After allowing sufficient time to cure, the new valve seat is permanently located and ready to have the valve seat cut in.
Step 17: Determine the Correct Size Bearings
While it may seem that all engine bearings are created equal, the thickness of various bearings can differ among manufacturers and types offered. Unless you provide your machinist with a specific brand or set of connecting rod and main journal bearings, he or she undoubtedly has a brand and type in mind while machining your components. The specific thickness is calculated into the clearance measurements and using other bearings can affect the result. It may be best to let your machinist supply you with his or her preferred brand of bearings for your rebuild. Just the same, a different brand of bearing can sometimes be used if slightly more or less clearance is required.
Cylinder Head Preparation
An engine inhales and exhales through the cylinder head intake and exhaust ports. The overall condition of the valves and seats can have a dramatic effect on total airflow. Worn or leaky valveguides or seals can allow the engine to pull oil into its cylinders. Weak valvesprings can cause the valves to bounce, which can cause any number of operating issues. Excessive bolt torque, running excessively hot, and heating and cooling cycles in general can distort any of the cylinder head surfaces.
Proper machining of original Pontiac heads should include a quality valve job and quite possibly new valve seats, if the existing units have been cut too many times or damage is detected. The valveguides found on original Pontiac cylinder heads were constructed of cast iron and are essentially an integral part of the casting. When repair is required, knurling was popular in the past, but it’s not recommended in any instance today. A thin-wall bronze liner is a popular method of repairing worn guides, but machining the cylinder head to accept a new guide is generally the best solution.
Some companies offer new valveguides constructed of cast iron, but manganese-bronze is a more popular alloy. According to SI Valves, an industry leader, bronze generally wears less under load when compared to iron, and its porous nature allows it to retain oil, which tends to better lubricate the valvestem. Bronze requires slightly more valvestem clearance when compared to cast iron, however, since it expands quicker than iron when exposed to the heat generated during normal operation. Using the valvestem clearance specifications found in the Pontiac Service Manual along with bronze guides can significantly limit valve travel, causing it to “stick” in the guide.
Exhaust valve seat wear became a concern in the early 1970s when most tetraethyl lead was removed from gasoline. The lead acted as a high-temperature lubricant that protected the valve seat against significant wear caused by the exhaust valve during normal operation. Internal testing at Pontiac showed that significant valve seat wear was common, especially in engines that regularly operated under heavy loads, such as high-performance race applications or those vehicles equipped with trailer packages.
Machining the cylinder head to accept a hardened-steel exhaust valve seat, which is far less susceptible to wear, is considered a permanent solution. But it wasn’t cost effective for manufacturers from a production standpoint. Pontiac developed a process known as “induction hardening,” which consists of electronically heating an exhaust seat and then immediately quenching it. It artificially hardens the iron to a depth of .050 to .100 inch, which combats seat wear. Pontiac began using the process on all its cylinder heads from 1972 forward, but the inductionhardened material was generally cut away after two valve jobs.
Using hardened exhaust seats should be a consideration when performing a valve job on any Pontiac cylinder head. Installation is relatively easy, and the process is one that any quality machine shop should be equipped to perform. Hardened exhaust seats can increase service life and extend the effects that a multiple-angle valve job offers. Because fuel lubricates the intake valve seat, it is not subjected to such wear. Intake valve seats may be required to restore valvetrain geometry if a cylinder head has had several valve jobs over the years.
Pontiac revised most of its cylinder heads for the 1967 model year. The number-670 casting found on the 400 being rebuilt is among the best D-port Pontiac ever produced. Using my Superflow SF-110 flow bench, I found that the intake ports of these particular castings peak at 212 cfm at 28 inches of pressure at just under .500-inch valve lift. I’ve learned over the years that most D-port castings with 2.11-inch valves flow similarly and that the available amount of airflow is more than enough to support 400 hp with the right combination of components.
During the compression stroke, the tighter the fuel/air mixture is compressed within a cylinder, the more intense the combustion. Each point of compression added to a street-driven Pontiac V-8 can result in an increase of some 8 to 12 hp and ft-lbs of torque at every RPM point. In fact, a compression ratio increase does not produce any negative attributes so long as sufficient octane fuel is available. But insufficient octane for a given compression ratio can lead to an engine that self-destructs from detonation.
The fuel octane ratings most commonly available at service station pumps are now 89 and 91. The maximum compression ratio I recommend for safe operation of a Pontiac V-8 with cast-iron cylinder heads on 91-octane fuel is 9.5:1. Some hobbyists are willing to push that to 10:1 or slightly more, which can result in an additional 5 to 10 hp and ft-lbs of torque, but it can require closely monitoring an engine’s fuel and timing curves and always listening intently for detonation. If you plan to use 89 octane, I recommend limiting compression to 9:1. While a machine shop may use more precise equipment, a simple graduated syringe can be used to determine approximate chamber volume and resultant compression ratio, using the calculator found on the Performance Trends Engine Analyzer program.
Engines that use aftermarket aluminum cylinder heads can tolerate an additional .500 to .750 point of compression for typical operation on a given fuel octane. The ability to run a higher compression ratio with aluminum castings doesn’t directly equate to a power increase. Aluminum dissipates heat quicker than cast iron, so slightly more compression is required to overcome the thermal loss, allowing an engine to produce the same amount of power as a similar engine fitted with similarflowing cast-iron cylinder heads. I recommend limiting compression to 10.25:1 when using aluminum castings and 91-octane fuel.
When originality is less of a concern, simply selecting a similar D-port cylinder head with the desired amount of chamber volume may be the easiest way to set compression ratio. A common modification to decrease combustion chamber volume is to mill the cylinder head deck flange, which effectively reduces volume and raises compression. If more combustion chamber volume is required, a popular method is to remove material in areas of the combustion chamber that do not affect quench. Pistons with a significant dish can also be used to reduce compression ratio.
After consulting with a number of reputable Pontiac engine builders, I planned for a compression ratio of 10:1 to maintain peak performance from this 400. The closed-combustion-chamber 670 casting measured at 72 cc and would produce slightly more compression than I wanted. Kauffman Racing Equipment (KRE) is one company that has developed a method of modifying 670 combustion chambers to increase volume and improve flame propagation. The owner sent these castings to KRE where chamber volume was increased to 75 cc.
Choosing a camshaft may seem as easy as opening a manufacturer’s catalog and selecting a grind that contains the same approximate operating range as the engine you’re building. However, you can’t always rely on the catalog suggestions to be accurate. While the information may be usable as a guideline to loosely interpret the operating differences between two or more grinds, the actual power band is often less relevant when considering a camshaft for a Pontiac.
Any camshaft can be physically installed into any Pontiac V-8 from 287 to 455, but there are consequences. For instance, the operating range of a 287 using a specific camshaft may be several hundred RPM different if it were used in a 455. Also the cylinder head airflow, exhaust system efficiency, transmission type and rear axle gearing, and the way the car is to be used, are all factors that must be considered when selecting a camshaft for any engine.
When comparing camshafts, duration at .050-inch lifter rise may be the most accurate way to predict how similar units might affect performance. Generally, a camshaft with more duration tends to favor higher-RPM operation than one with less duration. A camshaft with a wider lobe separation angle (LSA) tends to provide better idle quality while spreading the power over a wider range when compared to a similar grind with less LSA. A moderate amount of valve lift is desirable for performance, but the valve lift should not exceed the airflow capacity of the cylinder heads or lift range of the valvesprings.
Flat-tappet camshafts are cheap, readily available, and generally install into a Pontiac V-8 without any modifications. While flattappet cams perform well and remain an excellent value, the hobby has seen a distinct trend toward hydraulic roller camshafts for street-driven applications.
Not only does the roller action reduce friction and allow for a more aggressive lobe profile, initial breakin isn’t required and there’s no real chance of lobe and/or lifter failure that’s so commonly associated with modern-spec oil. Converting an existing engine from a flat-tappet to a hydraulic roller cam can cost several hundred dollars, but the cost is much more affordable if a new cam is needed during a rebuild.
When considering a camshaft for this 400, I wanted a grind that provided strong full-throttle response. It also had to idle well to accommodate the additional load from the air conditioning compressor and produce plenty of low-speed torque because the relatively high rear-axle gearing meant the 400 would be around 2,000 rpm while cruising on the highway. From past experience with similar combinations, I knew the chosen hydraulic flat-tappet or roller cam needed no more than about 220 degrees of intake duration at .050 inch and an LSA of 112 to 114 degrees to produce a smoother idle.
I consulted with many top-name Pontiac builders to find a cam that best suited this 400’s needs. Each stated that, if the budget allowed, a hydraulic roller was a wise choice. All agreed that, because of our limitations, .050-inch intake duration of 220 degrees (or less) and a wider LSA best suited the 400’s intended operating parameters. We couldn’t locate a hydraulic roller camshaft containing the exact specifications we wanted, however, so Comp Cams produced for us a custom-spec hydraulic roller camshaft with 218/224 degrees of .050-inch duration, an LSA of 112 degrees, and an intake centerline of 108 degrees. Valve lift was limited to .500 inch to complement the airflow capacity of the cylinder heads.
With machining complete, engine assembly is nearly ready to begin. You have to decide whether you want to handle the task yourself or let the machine shop assemble all or a portion of the engine for you. I have had WAM completely assemble engines for me as well as simply machine the components while I handle the complete assembly myself. Each time, I’ve found their measurements to be exact, which makes home assembly much less stressful, but that doesn’t mean that I don’t check their work by using a thorough pre-assembly process.
Once machining is complete, you must claim all of an engine’s components and each returned component should be checked against the list you made during drop-off to ensure that everything is accounted for. Plan to intently discuss the entire machining process with your machinist and specifically ask if any irregularities were found. He or she should also provide a detailed list of the critical clearance specifications that were recorded during machining and the appropriate piston rings and bearing sets suggested for use. You may be able to use other bearings, but thickness can vary slightly among the types and available brands.
The amount of component clearance you record during the preassembly process should mirror that supplied by the machinist for every component involved. I highly recommend measuring two and sometimes three times to ensure repeatable accuracy. Any significant variance should immediately be brought to your machinist’s attention. It may involve returning certain components to the shop for verification, and he or she should be willing to assist.
My pre-assembly process consists of many steps. It’s performed in a clean and dry environment and each component is handled carefully. The machined surfaces and bearing coatings are delicate and can scratch easily, and any error can require additional machining or purchasing new pieces. I’m confident that if you find clearance specifications similar to those supplied by the machinist, you have an engine that’s machined properly and should provide you with many miles of issue-free operation after proper final assembly.
Step 1: Wash the Block
Though the machine shop should have cleaned all of the components after the machining process, pre-assembly begins by thoroughly washing the block and crankshaft with hot, soapy water to remove any trace debris that could dislodge and damage the engine bearings. Scrub every passage with an appropriately sized wire brush and force pressurized water into every opening or crevice. I prefer to let the components air-dry and then blow compressed air throughout the entire piece to remove any trapped water. Each bolt hole is chased with a lubricated tap to clean the threads. Use lint-free towels and a high-power cleaner that leaves behind no residue to clean all the contact surfaces. If the components have to be stored any length of time, the freshly machined surfaces must be sprayed down with a water-displacing lubricant for protection.
Step 2: Measure Piston-to-Cylinder-Wall Clearance (Special Tool, Precision Measurement)
A specific amount of piston-to-cylinder-wall clearance is required during assembly to maintain consistent operation once the different metals expand as the engine reaches normal operating temperature. Too little clearance can score the piston skirt and cylinder wall; too much clearance can cause excessive noise known as “piston slap,” and oil consumption or blow-by is often the result. Piston-to-cylinder-wall clearance is determined by subtracting the piston diameter from the bore diameter. The exact amount of clearance varies with the type of piston being used—cast-alloy pistons differ from forgings. Each piston manufacturer provides a suggested clearance tolerance for its pistons, and the manufacturer or machinist can provide you with that. Using a dial bore gauge to measure all eight cylinders and an outside micrometer to measure each piston, speak directly to your machinist if any of your measurements fall outside of the suggested clearance tolerance.
Step 3: Measure Piston Ring Gap (Special Tool, Precision Measurement)
The piston ring pack being used in the 400 is a moly-coated set designed specifically for the Sealed Power pistons and a bore diameter of 4.16 inches. These rings come pre-gapped, and the top and second rings have different gaps. Each ring must be checked to be sure its gap measures within the manufacturer’s suggested tolerance. To measure the gap, a ring is installed into a cylinder and a squaring tool is used to properly locate the piston ring down into the cylinder. A piston can also be used. Gap is measured by placing a feeler gauge between the ring ends. If the gap measures within the manufacturer’s suggested tolerances, then the ring’s position is noted, so it can be reunited with that cylinder during assembly. That process continues until each cylinder and piston ring is accounted for. The ring ends can be carefully filed if slightly more clearance is needed, but it’s best to simply replace any ring that requires more than a reasonable amount of filing. Cast-alloy pistons may require a different gap than forged-aluminum pistons. If you’re using pistons and rings from different suppliers, then contact the piston and ring manufacturers to verify the piston ring gap spec is compatible with that particular combination.
Step 4: Orient Pistons and Rods (Important!)
The connecting rod must be properly oriented with the piston before the piston wrist pins are installed. Connecting rods are chamfered on one side and flat on the other. The chamfered side corresponds with the rod journal fillet on the crankshaft. Stock-type pistons with an offset wrist pin are marked with a notch or symbol indicating which end should face toward the front of the engine. Some aftermarket pistons have specific valve clearance notches that must correspond with the intake and exhaust valve positions. Your machinist can assist if you have any question. When assembling the piston and connecting rod assembly, the piston arrow should face forward while the chamfers should face the counterweight. The chamfer on connecting rods designated for cylinder numbers-2, -4, -6, and -8 faces toward the front of the engine, while the chamfer on numbers-1, -3, -5, and -7 faces the flywheel. An easy way to differentiate proper rod orientation is to use the bearing notches. They should always face toward the camshaft during proper installation.
Step 5: Measure Connecting Rod Side Clearance (Special Tool, Precision Measurement)
Your machinist may have noted the intended cylinder position for each respective connecting rod during the machining process. If reusing connecting rods, you must verify the method the machinist used, so you do not confuse any indicators he or she may have added with any you might have made during disassembly. Measure the diameter of each pair of connecting rods to verify the amount of side clearance once installed. Using a dial caliper, the rods are held tightly together with the chamfered side of each rod facing outward. They should be rotated slightly so the wrist pin bores are not touching and then the measurement is recorded. The caliper is also used to measure the diameter of the intended connecting rod journal on the crankshaft. The difference equates to the amount of connecting rod side clearance. It should be very close to the number specified by the connecting rod manufacturer and that noted by your machinist.
Step 6: Install Wrist Pins (Special Tool)
On pressed-wrist-pin applications, the wrist pin needs to be pressed through the wrist pin bore of the connecting rod. Most shops have a specific heater that’s capable of heating the small end of the rod to roughly 400 degrees F. It should have a fixture that holds the piston and prevents the wrist pin from being driven in too far. The task can also be performed by using a large press or a handheld propane torch. However, improper technique can gall the surfaces. And a connecting rod’s integrity can be severely compromised if the rod is excessively or improperly overheated. If the machinist hasn’t denoted a connecting rod’s cylinder orientation during machining, the respective position of the piston and connecting rod assembly can be written on each piston head.
Step 7: Measure Main Bearing Clearance (Special Tool, Precision Measurement, Torque Fasteners)
An outside micrometer can be used to measure each crankshaft main-journal diameter and determine main bearing clearance. A dial bore gauge is used to measure the diameter of each main journal with the bearings and main cap installed. Subtracting the values determines the amount of bearing clearance at each respective main journal. It can also be determined with Plastigage. That process consists of wiping clean the bearing surface of each main journal saddle and main cap, installing the bearings into the block and main caps, and setting the crankshaft into place. A length of Plastigage is set onto the crankshaft journal and the main caps are installed. Gentle tapping with a hammer may be required to get the main caps to fully seat on the alignment dowels, but any twisting or turning of the crankshaft ruins the effort. It’s unlikely that your machinist removed the main cap alignment dowels during machining. If any are missing, you should contact the shop and ask for replacements. Otherwise, Pioneer replacement dowels (number PG-225) can be sourced from a local parts store. The bolt threads are coated with 30-weight oil, and the front four are tightened from front to rear with a 3/4- inch socket to a maximum of 100 ft-lbs in 20 ft-lb increments. The bolts for the rear main caps are torqued to a maximum of 120 ft-lbs with a 15/16-inch socket and a similar sequence. The strip of Plastigage crushes as the bolts are tightened. After the bolts and main caps are removed, comparing the Plastigage width against the wrapper reveals the amount of bearing clearance at each main journal. The same procedure is repeated for the remaining four main journals. The numbers should all be very close and around .002 to .0035 inch, depending upon the engine. If any variance is detected from the machinist’s recommended specs for the main bearing clearance, you need to start the Plastigage process over and verify the measurements. Consult your machinist if the variance persists.
Step 8: Rotate Crankshaft and Inspect for Block Clearance (Torque Fasteners)
After very carefully removing the Plastigage residue from the crankshaft journal surface and bearings, using extreme caution to not damage the machined surfaces or bearing coatings, remove the crankshaft and carefully set it aside. Make sure the crank and bearings are free from any debris and apply a liberal coating of assembly lube on the main saddle bearings. Reinstall the crankshaft, apply assembly lube onto the main journal surfaces, and reinstall the main bearings caps. The main cap bolts should again be torqued to the amounts and procedure outlined in Step 7. The crankshaft should rotate very easily, using your fingertips and light pressure. Rotate it several times, closely inspecting for any area where its counterweights could contact the block. It should be no less than .250 inch in any direction. Consult with your machinist if the crankshaft exhibits any rotational difficulty or detectable block contact.
Step 9: Measure Thrust Clearance (Special Tool, Precision Measurement)
Also commonly referred to as “crankshaft endplay,” a slight amount of front-to-rear crankshaft movement is required for normal operation. It is easiest to measure this with a dial-indicator that is perfectly aligned with the crankshaft centerline. Using a large screwdriver, the crankshaft is pried rearward and the dial indicator is reset to zero. The crankshaft is then pried forward and the amount of forward thrust is displayed on the dial indicator. Factory specs call for .003 to .009 inch. This 400 crankshaft measures .007 inch.
Step 10: Measure Connecting Rod Bearing Clearance (Special Tool, Precision Measurement, Torque Fasteners)
Connecting rod bearing clearance can be more difficult to measure than main bearing clearance. An outside micrometer can also be used to measure crankshaft journal dimension, and a dial bore gauge is used to measure the crankshaft bore of each connecting rod with the bearings installed and the fasteners tightened to the manufacturer’s recommended torque spec. The connecting rods can be locked in a soft-jawed vice to properly torque the cap nuts. It is sometimes more convenient to use Plastigage to determine the approximate amount of bearing clearance, but any crankshaft movement or rotating can severely skew the result. By installing an opposing pair of connecting rods intended for the crankshaft rod journal, bearing clearance is checked one journal at a time. Using a soft-jaw vice, the connecting rod cap nuts are removed, the bearing surface is wiped clean, a bearing is carefully installed, and the piston-and-connecting rod assembly is inserted into its designated cylinder. Extreme caution is used to prevent marring any of the machined surfaces. The bearing surface of the cap is wiped clean, a bearing is carefully installed, and a length of Plastigage is laid onto the crankshaft journal surface. The rod cap is installed, and the nuts are tightened finger-tight. The corresponding connecting rod assembly is inserted into the opposing cylinder in a similar manner. Stock cast connecting rod bolts are torqued to a total of 43 ft-lbs in about 15-ft-lb increments using 30-weight oil to lubricate the threads. ARP’s 3/8-inch replacements require 50 ft-lbs with moly-based lube. If using aftermarket connecting rods as we are in this 400, refer to the manufacturer’s recommended torque specification and lubricant. The Plastigage crushes evenly as the bolts are tightened. When applying torque, the nuts must be tightened and loosened in a manner that absolutely prevents the crankshaft from rotating. I have found wrenching to or from the front or rear of the engine provides the best results. After removing the nuts and connecting rod caps, connecting rod bearing clearance is determined by comparing the width of the Plastigage to the measurements on its wrapper. The amount of clearance should be somewhere between .0015 and .0025 depending upon the application. The process is repeated until bearing clearance is measured for all eight connecting rods. The Plastigage process must be repeated if much variance is found. Immediately consult your machinist if your rod bearing clearances vary from his or her suggestions.
Step 11: Verify Connecting Rod Side Clearance (Precision Measurement)
After the rod bearing clearance has been recorded for an opposing pair of connecting rods on a crankshaft rod journal, and the Plastigage residue has been removed from the journal and bearings, the bearing is lubricated, the connecting rod caps can be reinstalled, and the nuts are again tightened to the proper torque specification for the fastener and/or connecting rod being used. The connecting rods can be spread apart and a feeler gauge inserted between them to verify that the amount of connecting-rod side clearance calculated earlier is accurate. Your machinist can advise if any variance is found. Also rotate the engine several times with each pair of opposing connecting rods installed to closely check for any area where the connecting rod body or cap may contact the block or opposing piston. It’s generally not an issue when using original or stock-replacement components, but clearance should be verified anytime aftermarket rotating assembly pieces are used.
Step 12: Measure Deck Height (Precision Measurement)
When speaking of deck height for an engine rebuild, it refers to the amount of clearance between the block deck surface and the piston head. Ideally the piston head and block deck are on the same plane, which is generally referred to as “zero deck,” but usually the piston sits a few thousandths below the deck surface. To determine deck height, while measuring side clearance and the number-1 piston is installed, rotate the block so it is top-side up, and rotate the crankshaft so the number-1 piston is at TDC. Using a precision straight edge and a feeler gauge, place the straightedge across the deck surface and measure the clearance between it and the straightedge.
Cylinder Heads Pre-Assembly
Step 1: Install Piston Rings (Special Tool)
When installing piston rings, some hobbyists choose to install them by walking a ring around the piston and into the groove. That can sometimes permanently distort the ring or cause it to lose tension. I much prefer to use this special tool, which evenly spreads the ring at the gap and makes installation much less risky. It’s available from a number of sources. Some piston rings are beveled or tapered and require specific installation. Follow the manufacturer’s suggestions for proper orientation during install.
Step 2: Verify Valveguide Clearance
Measuring valvestem clearance requires a valveguide dial-bore indicator, and it’s a task-specific tool that’s impractical for hobbyists to purchase. An easier method is to liberally coat a valvestem with 30-weight oil and slowly insert it into its respective valveguide. The valve is rotated while using an in-and-out motion to fully lubricate the new guide. After several seconds of this action to allow for sufficient lubrication, the valve should move in and out with relative ease. It is then held slightly open and shifted in every direction to verify that the guide is completely tight and that no unwanted movement is present.
Step 3: Measure Valvespring Install Height (Special Tool, Precision Measurement)
Manufacturers rate valvesprings at specific amounts of pressure at certain coil heights. A camshaft manufacturer recommends the amount of open and closed spring pressure that’s required for a specific cam, and that can depend upon the type. The cam company, your favorite Pontiac vendor, or your machinist can provide you with a set of valvesprings that best fits your needs, and your machinist can verify valvespring pressure and coil bind point by using a specific compressor. Your machinist should prepare your cylinder heads for a specific valvespring “install height,” which is required to maintain the recommended amount of closed pressure and coil clearance at peak valve lift. Installation height is checked by using a valve, a valve retainer, the locks you plan to use, and a valvespring micrometer. Your machinist can machine the spring pocket if slightly more height is required or supply you with valvespring shims if less height is required.
Step 4: Install Valve Seals
Pontiac originally used rubber O-rings and metal spring shields for oil control, but modern positive valve seals are a much better option. Your machinist can machine the top of your valveguides to accept the type of valve seal you chose to run. In this instance, the valve seal simply presses onto the top of the valveguide. Once a valve is inserted into the guide and through the seal, however, the valve should not be removed without a special sleeve that covers the valvestem tip. The tip can contain sharp edges that can tear the seal, compromising its oil control ability. Your machinist can supply you with this small sleeve.
Step 5: Measure Retainer-to-Seal Clearance (Special Tool, Precision Measurement)
Using a camshaft with relatively high valve lift can cause the retainer to contact the valve seal during operation, and that can create any number of operating issues. The amount of clearance can be determined by using a valve, a valve retainer, and locks you plan to use, and combining them with a test spring. Insert the valve into the guide and assemble the test spring, retainer, and locks. Manually forcing the retainer into the seal, while recording the travel with a dial indicator, reveals the amount of available clearance. It should be no less than .075 inch after subtracting peak valve lift.
Step 6: Install Valvesprings (Special Tool)
Your cylinder heads should still be clean from the thorough washing the machine shop performed after the machining process. If not, they can be thoroughly washed with soap and water, and the excess water blown away with compressed air. If all your measurements check out satisfactorily, you can install the new valvesprings and valvetrain hardware with a valvespring compressor.
Step 7: Install Freeze Plugs
After designating a driver- and passenger-side head, the coolant jacket plugs can be installed. If your machinist didn’t supply you with a set, a Dorman or Melling set can be sourced from a local parts store. The opening in the cylinder head is coated with high-temperature liquid sealer, which flows out once the engine reaches normal operating temperature. Drive the plug into the opening with an appropriately sized socket. Install a plug into the rear opening on the intake manifold flange on the driver-side head. A heater core nipple is installed into the rear opening of the intake flange on the passenger side. A new heater core nipple is available from most Pontiac vendors at a reasonable cost. The completed cylinder heads can be set aside until needed during engine assembly.
Written by Rocky Rotella and Posted with Permission of CarTechBooks