Now that you’ve disassembled your engine and selected the engine components you’ll be using (or reusing) in your new engine, the next step is to select a machine shop to work with for your rebuild project.
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The type of machine shop you’ll need to find is not the one turning brake drums at the back of your local auto parts store. An automotive engine machine shop is a highly specialized kind of establishment. Such a business has the trained expertise and precision equipment needed to refurbish the engine parts you may be reusing in your project, as well as perform any work that may be necessary on new parts you have purchased. A machine shop can also be a valuable resource for information, and will be happy to guide you through any step in a rebuild that you’re not sure of—whether it be assisting you in parts selection, or giving you advice on running clearances. Consider the machine shop your partner for your rebuild project!
This chapter does not purport to describe each and every engine component machining process you may want or require for your project—the possibilities are virtually endless! It’s merely intended as a guide to help you choose a competent shop, make intelligent choices about what machine work you need, and most importantly, ensure the work is done right.
Selecting a Machine Shop
When it comes to rebuilding your LS, there is perhaps no single task more important than finding a machine shop that knows Gen III and IV engines. A shop that does “one or two of them now and then” probably won’t have the know-how to perform the machine work necessary for this particular engine family. Features like the aluminum block construction of many Gen III/IVs mean that special techniques and care are required to properly prep such an engine block. Now, don’t get us wrong—you certainly do not need to find a shop that works with LS engines exclusively. To a great degree, a machine shop that works with other engine families should be considered a plus, as it shows the depth of the machine shop personnel’s experience. An LS is, after all, an internal combustion engine, and so shares many basic traits with other engines, both GM and non-GM alike.
Expensive equipment is necessary to allow machinists to hold the tight tolerances needed for a durable engine, and a good shop will have a variety of different machinery in the facility. But at the same time, don’t be sold on a glitzy shop with nothing but shiny new equipment. Many of the finest machines have been in service for decades, and though it takes special knowledge to properly work with Gen III/IV engine components, the tools of the trade are largely the same as they have been for decades. So don’t worry if some of the machinery at the shop looks a little “experienced!”
Machine work is not free, and while it’s OK to shop around for a good price on the work you need, know that a few extra dollars spent can be well worth the investment. A capable shop may be a little more expensive than a budget one, but the added durability and performance your engine will end up with will be invaluable. On the flip side, be wary of shops that are grossly overpriced or that try and sell you much more machine work than is actually needed—use some common sense! Finding a competent, honest machine shop can be a challenge, so our best advice is to do your research and go on the advice of others.
A common misconception is that if a machine shop does not use CNC (Computerized Numerical Control) equipment, it’s behind the times. While these machines are very helpful in achieving the utmost repeatability in some processes that require it (for example, cylinder head porting), they are of little advantage to many others. In fact, some argue that high-quality, human-operated machinery can even have an accuracy advantage for many engine machining procedures. The main benefit of CNCing is reduced labor time for machinists, who can pretty much set up the machine and walk away. Since added productivity is offset by the enormous cost of a CNC machine, you’ll probably only see this type of equipment in larger machine shops.
Professional engine machinists pay the same strict attention to the finest of details on every engine component that comes through the shop. Here Lou Bengivenni of LRB Performance Machine Company (Franklin, NJ) uses a file to deburr the webbing of an LS1 block, ensuring proper seating of the main caps and upper main bearing shells. Care like this is just one indication of a machinist who knows what he’s doing!
As we go through the steps of machining, we’ll highlight many important processes that need to be done in order for LS engines to perform properly. Any deviations you see from these procedures should be discussed with your machine shop—good shop personnel will happily explain to you why things are done a certain way. Though every shop has its own set of “tricks” when it comes to getting these engines to perform best, there is a big difference between a trick and an outright gimmick! Engine machinists are experts in their trade (often having attended specialized programs like those offered at the School of Automotive Machinists) and should be treated with the utmost respect, but this doesn’t mean you shouldn’t keep an eye out for suspicious explanations of, say, why a deck plate is not used while honing cylinders (this is a huge red flag!). On a similar note, be wary of those apt to profess their abilities while making overly disparaging comments about other shops. The best shop will be more modest and have respect for its competitors, but will of course know of some bad apples as well.
Even the best intentions on a decision sometimes don’t pay off. If for some reason you get through the process of dealing with a machine shop and harbor any doubt as to the competency of the work that’s been done, don’t worry: one of the reasons for the pre-assembly process (Chapter 7) is to ensure machine work has been performed properly. But beyond this, you have other options. Armed with the information in this chapter, you can perform more extensive at-home machine work checking using the tools and techniques illustrated in Chapters 2 and 4 (though keep in mind that the accuracy of your tools will often be insufficient to properly evaluate certain issues). If nothing else, you can always take your parts to a different machine shop for post-machining analysis.
Before Heading to the Machine Shop
Once you’ve selected a machine shop to work with, there are some pre-liminary things to take care of before packing up parts and going to the shop to drop them off. The first and most obvious order of business is to discuss your rebuild project in some detail with the machine shop owner or manager. Most significantly, this will ensure that everyone is on the same page in terms of the general scope of machine work that will need to be done. While a machinist certainly cannot know the exact condition of your parts over the phone, a detailed conversation will still help give both of you a general idea of what you’re up against.
This type of talk-through will also help you understand which engine parts you’ll need to bring with you to the machine shop. For example, you might be tempted to leave your piston rings at home, thinking they won’t be needed until you’re setting end gap during pre-assembly. But you’d be wrong: piston rings must be weighed and factored into the process of balancing the rotating assembly. Inform yourself before dropping off parts so that critical items don’t get left behind, requiring multiple trips and delaying the progress of machine work.
Here’s another example of the type of neglect that can hold up the progress of parts machining. Even if you’ve purchased a pre-balanced rotating assembly and are confident you will not require any machine work on your pistons, don’t bring your block to the machine shop without them. Your machine shop will need to measure them, and after factoring in the proper piston-to-wall clearance, set the final cylinder bore diameter during honing.
It’s also an excellent idea to mark your parts—not just the boxes they are in—before dropping them off at the machine shop. Goodson sells helpful items like metal markers and parts tags that will help your machine shop identify and keep track of which parts are yours (decreasing the chance of accidental mix-up). Do not scribe, engrave, or otherwise mark your parts in any intrusive manner—this can damage them if done incorrectly, so leave it to the experts!
Finally, before even showing up at the door of the machine shop, let them give you an honest, realistic estimate for turnaround time. Machine work involves precision processes that, like the rebuilding steps you are doing at home, cannot be rushed. Most shops will do their best to accommodate the fact that you have a vehicle you need to get back on the road, or a race you’d like to complete your engine in time for. By all means, do not simply say that you need your parts “as soon as possible!” A good shop will under-promise and over-deliver, and it all starts with your having the right attitude toward the work they are doing for you.
Block Machine Work
By far, the component of your LS that needs the most machine work is the engine block. Whether you’re talking about areas that have encountered metal-to-metal wear (such as cylinder walls), or portions that have warped over time due to heat cycling (like deck surfaces), many of the block’s metal surfaces will require refinishing before it can be reused. We’ll go through the most important engine block machining procedures below.
Block cleaning and inspection
The most pertinent order of business is to determine whether the engine block can actually be reused at all, and if so, what machining procedures it will need. Although we went through some at-home block inspection procedures in Chapter 4, a machine shop has more accurate equipment and the trained eye necessary to spot potential issues that need addressing. First things first, the block will undergo a thorough cleaning, and methods of doing this vary from cabinet-type pressure washers to thermal ovens that turn contamination into a fine powder (normal washing is required after this of course). Your machine shop will then inspect critical areas of the block, and at this point a good shop should give you a written estimate of the cost of machining your block, or tell you to find another one!
Before cleaning, the machine shop will strip the block bare of the cam bearings and all engine block plugs that you may not have removed at home. This allows the cleaning solution full access within all oil and coolant galleries. As we’ve seen, most plugs in the block are of a screw-in variety, but this press-in plug located at the driver side front of the block seals the main oil gallery and needs to be tapped out with a long rod from behind. (We’ve seen machine shops that never bother removing this plug, which is a terrible idea.)
As a used block is normally caked with sludge and grime, it will need to be cleaned before a thorough inspection and evaluation can take place. One option is this so-called jet wash cabinet, which blasts the block with a non-caustic, biodegradable alkali solution for 15 minutes at temperatures between 180 and 190 degrees F. This type of machine is commonly used to clean other engine parts as well. We should note that caustic cleaning solutions will harm aluminum and may only be used on iron blocks (iron blocks can also be soaked in a so-called hot tank if particularly dirty).
Once the block is nice and clean, the machine shop can fully inspect it for any cracks as well as take measurements to see what machining processes need to be performed. For example, measuring the main bearing bores determines whether a line hone is needed.
Cylinder boring
This term refers to the process of removing a large amount of material from the block’s cylinder walls (generally, more than 0.010-inch). While “boring out” a block can be a great way to increase engine displacement (within the limits of what the block can tolerate), it’s also a common procedure used to remove worn material from the cylinder walls and get into raw material below. It is also required whenever cylinders have a heavy wear ridge at the top of the bore. As this process only gets the cylinders roughly to size, it must always be followed by cylinder honing. Boring is generally reserved for iron blocks, as most aluminum Gen III and IV blocks do not have thick enough cylinder liners to merit the removal of so much material.
Cylinder honing
Unlike boring, honing is a very precise process that removes small amounts of material from the cylinder walls and gets them into their final shape. Generally, 0.010 inches or less are removed during honing. Honing also puts the correct surface finish into the cylinder walls, giving them the ability to hold oil lubrication and allowing the piston rings to seal properly. Again, because the iron cylinder liners used in aluminum LS engine blocks are of limited thickness, material removal from these blocks generally should not exceed 0.010 inches (though the exact amount varies by the type of block you have; your machine shop can provide guidance on this). Cylinder honing is one of the few machining processes that will be required on all engine blocks, and it is crucial that it be performed correctly.
When it comes to cylinder honing, a Sunnen vertical hone is the machine of choice for top machine shops. Also notice the use of a so-called deck plate. LS blocks should always be honed with a deck plate. By duplicating the effects of a cylinder head being bolted in place (the head gasket should be in there too!), a deck plate allows the block to undergo the same slight distortions it will experience after the engine is assembled, deformations that are easily measurable, especially with aluminum blocks. For the same reason, the main caps should also be torqued in place during this process. Far from “race-only” procedures, attention to detail like this will yield an engine with better ring seal, delivering increased durability, horsepower, and fuel economy.
Cylinder shape is only half of the equation when it comes to honing. The correct combination of stones, as well as honing machine speed and feed settings, will yield the best cross-hatch pattern in the cylinder walls for optimum ring seal and component life. Honing proceeds in stages of progressively finer stones, and for standard ring sets, a 240 grit silicone carbide stone is the preferred material for the final surfacing. For high-performance moly ring sets, a 280 or finer grit stone is normally used as a somewhat smoother finish is required.
Deck resurfacing
Over time, the deck surface of an engine block can warp, which can create problems with head gasket seal. Your machine shop will measure the flatness of the block’s deck surface and determine whether removal of any deck material is necessary. Only a few thousandths of material can be safely removed from this area of the block, so severe deck warping can render a block unusable. Also, some high-performance head gaskets require a very smooth surface finish to enable a proper seal (usually 50 Roughness Aver-age (RA) or finer); if you’re using such an aftermarket head gasket, make sure your machine shop knows this and they will perform the appropriate cleanup resurfacing. Resurfacing also ensures a deck surface that’s parallel to the crank centerline.
Block deck resurfacing may or may not be needed on your engine block, depending on the surface finish of the deck and whether it’s within tolerances for flatness. Any changes in deck height (beyond a simple cleanup resurfacing) may require adjustments to pushrod length as well as changes in compression-ratio-related parameters like head gasket thickness and piston design. (See the Appendix for compression ratio calculation.)
Line honing
Roundness and concentricity of the main bearing bores is very important in any rebuild. Line honing (sometimes referred to as align honing) is a common process that, although not needed on all engine blocks, is extremely important to the ability of the crankshaft to turn freely. Your machine shop will torque your block’s main bearing caps in place and measure the main bearing bores for proper size and roundness. Any out-of-tolerance measurements indicate the need for a line hone, and there is little margin for error here—only about 0.0002 inches is considered acceptable for out-of-round! This spec can have a great impact on crankshaft and main bearing life.
Line honing addresses out-of-shape main bearing bores and removes material from the block and main bearing caps. Depending on the amount of material removed during this process—or the similar but somewhat more involved line boring—larger O.D. main bearings may be required, though this is exceedingly uncommon on LS engines. Line boring is generally reserved to engines where main caps are being substituted (whether with high-strength aftermarket main caps, or stock-type caps replacing ones that no longer fit properly between the oil pan rails) and is always followed by line honing.
Cam bearing replacement
The old cam bearings were removed before the initial wash, and new ones must be installed. This requires a special tool that you probably don’t want to buy for your home workshop. LS engines use five cam bearings that press into place in the block. Your machine shop will mea-sure the cam bearing bores to determine the bearing sizes you need. The reason for this is that while all Gen III/IV engines use a common size cam journal (and therefore common cam bearing I.D.), the sizes of the bores themselves vary between block castings, necessitating bearings of different O.D.s. Different sets are available to accommodate all blocks.
Shown here being removed, new cam bearings are normally installed using the very same hand tool, no press is needed. Cam bearing installation is normally the very last process performed on your engine block before it’s ready to go out the door, as cam bearings can be harmed by the cleaning solutions used in the final wash.
Thread cleaning and repair
We spoke a bit about thread repair in Chapter 2, and while it’s possible to per-form many such fixes on your own, you may choose to leave more involved repairs to your machine shop. Whether due to corrosion, grime buildup, thread stripping, or leftover factory sealant, many block bolt hole threads can be in need of a little TLC. Without taking care of these issues, your engine assembly may be difficult or impossible. While it’s true that jet washing helps clean out these holes, sometimes the process simply doesn’t remove all of the grime, so it’s a good idea to make sure your machine shop takes a look at all threaded holes in the block and cleans or re-taps them accordingly. Also, if you had broken off any fasteners when disassembling your engine and haven’t extracted them on your own, your machine shop can remove them for you—as well as perform any other thread repair that may be necessary.
Other processes
There are a plethora of other machine work processes your shop can perform on your engine block, and entire volumes can be written on the topic alone. These may include high-performance modifications like drilling and tapping your block for the installation of a timing chain dampener (if you didn’t have one already), machining the block for use of special head gasket sealing O-rings, or the fitting and installation of aftermarket high-strength main caps. Or they may include repair processes like installing lifter bore sleeves for worn lifter bores. Shop personnel may even suggest procedures they feel are necessary to bring an otherwise-useless engine block back from the brink of “beyond hope.” Examples of these include cylinder resleeving and engine block welding. But be wary of extensive block repairs; aside from some of these repair scenarios being question-able in mechanical integrity, their cost can often exceed that of simply buying another block.
Resleeving is a process used when a cylinder wall is too thin or too badly damaged to be cleaned up with an oversize bore or hone. The procedure is more common for aluminum blocks because (again) their iron cylinder liners dictate limited oversize allowance. However, even the most competent shop will tell you that there is a lot of margin for error in resleeving and that the time commitment will result in a rather expensive job. Also meriting brief mention is the high-performance modification of installing “big bore” cylinder sleeves (a process that has fallen out of favor as affordable large-bore engine blocks like the GMPP LSX have become available); not only can the process be cost-prohibitive, but some question the structural integrity of an engine block so modified.
Final cleaning
After all machine work has been per-formed, there will be substantial leftover metal debris throughout the block. Your machine shop will give the block a final thorough cleaning to make sure all areas—particularly the oil passages—are free of contamination. Most shops have a large tank of mineral spirits that they will submerse the block in, and will perform a thorough brushing of all passages. Your machine shop should leave out all pas-sage plugs for you to install at home during final assembly. Note that this final cleaning process does not negate your need to perform the at-home cleaning procedures detailed in Chapter 6!
After the final cleaning, your machine shop should deliver your completed block to you in a sealed bag to keep dirt, moisture, and other contaminants away. They’ll also have sprayed key areas of the block with some temporary rust protectant so that it can safely sit in storage until you’re ready to work on it.
Crankshaft Machine Work
If you’re purchasing a new crank-shaft, it should require little (if any) machine work, as they are generally shipped ready to assemble. The only exception is that, as with a used crank-shaft, a new crank must be balanced along with the rest of the rotating assembly. This process will be discussed in detail momentarily.
On the other hand, reuse of a factory crankshaft will require varying amounts of reconditioning. We discussed some examples of crankshaft journal damage in Chapter 4, and depending on its extent, a machine shop may be able to grind your crank journal(s) down past the damage. This will leave a clean surface that can be polished to like-new specs and used along with an undersized (smaller I.D.) main or rod bearing. How-ever, there is only so much material that can be taken away before the structural integrity of the crank is compromised, so some cranks may not be salvageable. Some GM literature actually recommends no grinding of LS crank journals, but skilled machine shops do it success-fully all the time!
Crank grinding can also serve purposes other than mere reconditioning. For example, one may wish to increase cubic inches via a so-called offset grind. By removing more material from one side of the rod journal than the other, crankshaft stroke is increased slightly. Although the cubic inches yielded are small compared to installing a stroker crank, it may be worth it on some applications—particularly if your crank journals need to be ground anyway. As with any “stroked” engine, keep in mind that an offset ground crank may require changes to other parts of the rotating assembly (see the Appendix). Conversely, offset grinding can be performed in order to avoid changes to other parts of the rotating assembly. For example, if you’re using a block that has had a substantial amount of material removed from its deck (uncommon for LS blocks), offset grinding can be used to decrease crank-shaft stroke slightly, thereby maintaining the proper location of the piston face at TDC. A word to the wise: if you’re going to attempt any of this, make sure the machine shop (or specialized crankshaft shop that they send work to) is a competent one; done incorrectly, crank grinding of any kind can leave you with out-of-phase piston movement, a weakened crankshaft, or other problems you don’t want to deal with!
Because crankshaft journal grinding reduces or eliminates the hardened outer layer of the journal surface of some aftermarket cranks, these cranks must be heat treated after grinding. There are a few different methods of doing this, and this is a crank fresh from being nitrided (you can tell from the dull finish of the journals; it’s not an LS crank, but you get the idea). Some more work needs to be done before it’s ready for use. Induction hardening is another popular heat treatment process, and one that generally achieves a greater depth of hardened material. We should note that factory nodular iron LS cranks are not heat treated from the factory, but can be subjected to such a process for a more durable journal surface finish.
Before polishing, it’s common practice to chamfer the openings of the oil passages in the crank journals for increased oiling efficiency to the bearings. We should note that many machine shops do not perform crankshaft machine work in-house, but rather farm it out to experts. A crankshaft is one of the most precision pieces of the entire engine, and it takes specially trained hands to prep one properly!
A typical crank journal polishing process involves spinning the crank in a special lathe while running three different polishing bands of varying coarseness over the journals. The result: super-smooth rod and main journals that will last many thousands of miles.
Crankshafts with journals in good condition represent a much simpler scenario, as they’ll simply need to be polished to achieve an acceptable surface finish. This isn’t to say such a crank won’t have other issues that must be addressed. One common crank problem is lack of straightness (or “runout”—the centerline of the crank is actually bent such that it would wobble while spinning; small amounts of this are acceptable). This may sound incurable, but believe it or not, the process of straightening a crank is often very straightforward, involving little more than clamping it into a special crankshaft straightening press and hitting key locations with a special chisel, thereby relieving the internal stresses causing it to bend.
Finally, there is one part of the LS crankshaft that was distinctly absent from past small-blocks, and that is the reluctor ring. Although sometimes this item does-n’t require addressing before the crank can be reused, on occasion the reluctor ring is out of shape and won’t allow the crankshaft position sensor to generate a usable signal. Your machine shop can remove and replace your reluctor ring for you (sometimes it’s a non-issue as it can literally fall off of the crank after heat treatment!). No matter what, don’t ignore your reluctor ring and assume that it will work, because you certainly don’t want to finish assembly of your engine only to find that it won’t fire up! (We’ll also show you how to check reluctor ring runout in Chapter 7.)
Connecting Rod Machine Work
As with new crankshafts, most new aftermarket connecting rods are shipped ready to use and require almost no machine work (other than balancing). We say “almost” because depending on whether you are using a pressed- or floating-style piston pin, your machine shop may need to install your pistons onto your rods. Regardless of whether this is necessary, you should also have your machine shop take a look at your after-market connecting rods to inspect for obvious manufacturing defects.
Happily, the case is similar with used Gen III/IV connecting rods, as they normally require surprisingly little machine work. The forged construction of these rods means they are very durable, and therefore, normally in excellent condition even after many thousands of miles of use. The first order of business for your machine shop is to scribe your rods and caps so that each pair is uniquely identified. Though the fractured design of factory steel rods means that each cap is a unique fit, some fracture patterns may be similar to the point that it’s difficult to tell which cap goes with which rod.
Goodson makes this tool to properly index and install a new reluctor ring onto the back of an LS crank. Because the process requires a press and/or heating the ring to high temperature, you should probably let your machine shop take care of this for you. If you’ll be doing it at home, be sure to pick up a set of high-heat gloves and a temperature indicating crayon from Goodson as well!(In case you’re wondering, the old ring comes off easily with a hammer.)
Reuse of factory Gen III rods (LQ9 engines excepted) will require a press-type piston pin. A hydraulic press is standard machine shop equipment to press used pistons off of connecting rods. Later, new pins are installed with a new piston, but a press is not normally used for this (the end of the rod is instead heated so that it expands and allows the pin to slide in—a procedure that requires a quick and skilled hand!). This is better considered rod machine work than piston machine work since, after all, the pin is pressing into the rod (and rotating freely in the piston).
Your connecting rods will be marked using a method that won’t create a stress riser on the surface of the rod (or ruin the roundness of the bearing bore), and scribing is perhaps the best way to go about this. This marking process is to the benefit of both you and your machine shop, preventing mix-ups on their end as well as helping you out later during assembly.
After a good cleaning, your machine shop will then perform a series of checks. Rods will be inspected thoroughly for any imperfections, including twisting, damage (such as nicks or cracks), and proper fit of the cap. At the top end, rods using a floating piston pin have a bush-ing that may need to be replaced. Earlier-style rods can also be bushed for use of a floating pin if the needs of your build dictate, though this process can be more costly than just acquiring a new set. Repair of LS connecting rods is limited, and generally rods that don’t pass muster should be thrown away. Used rods should be easy to get a hold of, and you can also buy several different brand-new Gen III/IV connecting rods from GM Performance Parts.
A few final cautionary notes are in order with regard to aftermarket rods, particularly when assembling a large-stroke engine. If you did your homework during parts selection, it’s likely that your rods will fit just fine with your rotating assembly and within your block. However, with certain high-end, high-performance applications, your machine shop may forewarn you of minor fitment issues you may be likely to encounter. You should not be overly concerned about this, as it is normally reserved to exotic applications like the use of aluminum connecting rods; but if there is any doubt as to whether your rods will need to go under the knife for a little extra machine work, your machine shop will tell you to pre-assemble first so that any issues can be identified and addressed before you spend the money to have your rotating assembly balanced.
Piston Machine Work
We stated in Chapter 4 that pistons should not be reused in a full engine rebuild. Aside from being mass-matched during the balancing process, your new pistons will require few or zero machining operations to get them ready to install.
Applications that may require some piston machining are generally reserved to higher-end custom applications. This mostly includes machining of the face of the piston (often called flycutting or milling) either for additional piston-to-valve clearance or to alter compression ratio. Although very small amounts of material removal are generally acceptable, removal of substantial quantities can weaken the piston tremendously. You are strongly cautioned against this process unless:(1) you can’t substitute different pistons with the appropriate valve reliefs or facial contours, and (2) your machinist is really sure what he or she is doing!
As with many other internal engine parts, used connecting rods will be washed in a mineral spirits solution and thoroughly scrubbed of any contaminants. Special care is taken with the bolt hole threads as any sludge here could interfere with proper bolt tightening, resulting in possible disastrous failure. Again, any physically damaged threads may render the rod unusable.
Your machine shop will tighten the rod cap in place and measure the roundness of the rod bearing bore using a precision measuring machine like the one seen here. Out-of-round beyond a few ten-thousandths indicates the need for a replacement rod—any machine work to correct the problem could be risky and expensive, and the fractured design of the cap mating surfaces typical of nearly all LS rods prohibits the practice of “cap cutting.”
Although uncommon, rods may require some machine work to properly fit with other parts of the rotating assembly, as was the case with this 427-ci, C5R-based build. Here a portion of an aftermarket aluminum rod was found to interfere with a crank counterweight during pre-assembly, requiring the rounded edge shown to be machined off. A good machine shop will advise you of the potential for any such problems so that they can be dealt with before balancing.
It’s best to select a piston with properly sized valve reliefs to allow sufficient piston-to-valve clearance before making your purchase. However, some high-performance applications using large valves and/or cam profiles may require additional machine work to make valve reliefs even larger. One important item to note is that in the case of cylinder heads with large-diameter valves, your machine shop should ensure that your piston’s valve reliefs are sufficient not only in depth, but in width and height. So-called radial piston-to-valve clearance should be at least 0.060-inch; this must be verified in addition to the “regular” piston-to-valve clearance measurements that are checked in Chapter 7.
The reluctor ring location at the rearmost crankshaft counterweight protrudes substantially into the path of the number 8 piston (top photo), and if stroke is long enough, the two can actually touch. This will not happen if the shape of the bottom of the piston has been designed with reluctor ring clearance in mind, or if one piston out of the set has the appropriate notch. Such is the case with the piston on the right (bottom photo, finger pointing).
Many LS piston sets, including some designed for strokers, feature eight identical pistons, each designed to be installed in any cylinder. But this is not always the case: on longer-stroke Gen III and IV engines, the reluctor ring can physically interfere with the design of some pistons at BDC. It is for this reason that one piston may be pre-notched to clear the reluctor ring, and this piston must be installed in the number 8 position. Ask your machine shop to look at your pistons and identify whether there is one unique piston out of the set, and if not, whether one of them will need to be machined to avoid interference with the reluctor ring (you may need to pre-assemble to verify this). It’s best to take care of any such issue before balancing the rotating assembly so that all pistons can be matched to identical weight.
Finally, your machine shop should measure your piston pin (a.k.a. wristpin) diameters, especially if you’re using floating piston pins. Since pins are almost always included with pistons, clearance between the pins and their bores in the piston should be proper on most applications (though it doesn’t hurt to verify). Therefore, this is more of an issue with rod-to-pin clearance in the bushed end of the rod. Clearance between the pin and the rod bore can be as small as only a few ten thousandths of an inch, but your machine shop may recommend honing the bushing in the end of the rod slightly for more clearance. Around 0.0007-inch is suitable for most high-performance LS engines, though more extreme applications like high-boost supercharged engines will want as much as 0.0012-inch rod-to-pin clearance.
Balancing the Rotating Assembly
Unless you’ve purchased a full rotating assembly kit that’s pre-balanced, each and every item that moves inside your engine (sans the valvetrain) must undergo the process of balancing. The exact mechanical theory behind it all is rather complex, but it helps to think about it a little in order to develop an appreciation of why balancing needs to be done, and why it is so important that it be done correctly.
Because all components moving in the crankcase are physically connected together, the motions and forces suffered by each piece are transferred to the others in some way, in turn influencing the forces they experience and motions they undergo. The list of items included in the equation is extensive: pistons, piston rings, piston pins and locks, connecting rods, connecting rod bearings, and the crankshaft all play a role. Like an improperly balanced wheel and tire, if they’re not matched properly to one another, harmful vibrations will result—only instead of being simply annoying, they’ll rob the engine of efficiency and can also quickly destroy internal engine components.
Since most will alter mass enough to affect engine balance, balancing cannot be done until all required machine work processes have been performed on all components. For this reason, you may wish to pre-assemble your engine before balancing. Discovery of a problem with piston-to-valve clearance and the need for a modified or alternative piston is some-thing you’d want to find out beforehand!
Your machine shop will precisely weigh all of your internal engine components and factor each value into the balancing equation. Though the mass of each rod bearing, piston ring, or like component can safely be assumed equivalent across the entire set, larger items (pistons and rods) must be weighed individually. Even if brand new, production variation dictates that it’s common for these parts to differ in mass. Your set of aftermarket rods may come pre-matched with a spec card to prove it, but your machine shop must still weigh each one to double-check. The machinist will then select the least massive component of the set and remove material from the others to match it.
If you’re a first-time engine builder and the thought of file-fitting piston rings scares you (see Chapter 7), you might elect to have your machine shop perform this process for you. They can do it quickly and often use an electric ring filer like the one shown here, an item which is often out of the price range of the typical garage mechanic. (Of course, if you’ve selected a “drop-in” ring set, this does not apply.)
Internal engine components are weighed on a precise scale during balancing. Connecting rods must be weighed using a special fixture that allows separate determination of their rotating and reciprocating masses. Scientific disclaimer: Note that during balancing we’re technically determining mass, not weight—though the direct correlation between them on Earth means the two terms can be used almost interchangeably!
Before being pressed onto their rods, these pistons underwent the weight-matching process. The piston on the left was too heavy and needed to have material removed (look at the area below the piston pin) to match the one on the right, which was left alone. Good piston matching can be performed to within half a gram! Similar material removal on connecting rods is normally done with a grinding wheel or like tool.
With the crankshaft set on a special balancing machine, so-called bobweights are attached to the crank to simulate both reciprocating and rotating masses. Even the oil that will cling to components is given a mass to factor in! With the crank spinning, the machine identifies exactly where material must be removed (or added) to the crank counterweights to achieve the correct balance. This particular machine was photographed at Bill Ceralli Competition Engines in Paterson, NJ.
These counterweights on an aftermarket LS crank illustrate both the material removal and addition processes that can be involved in balancing. Here we see two holes that have been drilled perpendicular to the crankshaft’s centerline, as well as one metal slug that has been inserted into one of the counterweights (top right of photo—you can even see where the machinist scribed the counterweight with its required location). This particular slug has been pressed into place, but they can also be welded in for added insurance.
Here’s an example of where the factory harmonic damper balance weights mentioned in the main text might go. Just so we’re all on the same page, balancing does not negate the need for a functional harmonic damper! Dampers absorb energy from crankshaft torsional vibrations (most significantly, from the firing of each cylinder), limiting distortion of the crank. These forces exist independently of the forces that would be created by an unbalanced rotating assembly—you still need a good damper, no matter how good your balance is!
Once all pistons and rods are matched sets, the crank can be balanced. Thanks to their vee-shaped design, all V-8 engines inherently require precisely massed crankshaft counter-weights. While drilling or other material removal from counterweights is the main order of business, sometimes additions of mass are required, a process that involves inserting heavy metal slugs into the crank. The latter is not as common and is needed where, for example, more massive internal engine components are being used than the crank counterweight was designed for (ex., larger pistons or heavier-duty rods). It can also get expensive, as these metal slugs can be pricey. This is one reason that you should pay attention to crank counterweight specs when shopping for a crank—aftermarket cranks are often sold “rough” balanced to a certain maximum bobweight value, and you should make sure you’re not going to go over this value or you risk the added expense of heavy metal insertion. The same can go for use of some GM cranks, especially when used in applications with larger displacements (i.e., bore sizes) than the crank originally was intended for.
In addition, there are a couple of items that aren’t actually inside the engine that nonetheless can affect engine balance. We’re referring to the harmonic damper and the flywheel (or flexplate). Though all good aftermarket dampers and flywheels are neutrally balanced, we mentioned in Chapter 3 that some Gen III/IV harmonic dampers had small balance weights installed into their perimeters to account for production line variation. In a way, this really did make them “balancers,” which normally would be a misnomer! Though the amount of mass used here pales in comparison to the “externally-balanced” 400-ci small-blocks of the 1970s (which had large counterweights on both the damper and flexplate), these weights are still significant enough to affect engine balance. Therefore, if you’re planning on reusing your factory harmonic damper, you’ll want to take it along with you so that the machine shop can factor it into the balance of your rotating assembly. The best thing to do is to have the machine shop add, subtract, or otherwise adjust these weights so that your damper is neutrally balanced. We also recommend checking this out for factory fly-wheels or flexplates if they are being reused. Neutrally balancing these components just makes things easier, particularly if a flywheel or damper ever needs to be replaced down the road, and also since most stock dampers have no alignment keyway!
Cylinder Head Machine Work
The amount of work you’ll need your machine shop to perform on your cylinder heads depends completely on your intended application. If you are planning on installing a set of new head castings, this represents a much easier scenario; many aftermarket and factory high-performance LS heads come fully assembled and require no machine work at all. Heads that do not come fully assembled (“bare” heads) can be sold in a variety of stages of preparation, needing as little as the installation of valve springs or as much as the installation and machining of valve seats and all other hardware.
If you plan on reusing your head castings, however, the first order of business (other than ensuring the castings are not cracked and can be reused) depends on whether you plan on having a porting job done to increase their flow potential. We talked about this in some detail in Chapter 4, so just know that if your heads are being ported, this is usually the first bit of work that gets done. Because this process is very specialized, your machine shop may send your heads out to an expert to have the porting work performed (whether it’s a traditional port and polish or a full CNC’ing).
Regardless of whether your heads are undergoing porting, they will need to have their valve seats reconditioned. Although seats can be replaced if dam-aged, this is normally not necessary, and factory LS seats are high quality since they are hardened (they’re also fine for most high-performance applications). The typical machining procedure for all seats is a 3-angle valve job, the standard being 30, 45, and 60-degree angles.
Similarly, intake and exhaust valves themselves must be reconditioned. Standard valve reconditioning involves refacing (grinding) valves on the 45-degree cut that contacts the valve seat. The width of this 45-degree cut affects valve cooling: too wide or too narrow, and the valve will overheat. The widths and angles of the cuts on a valve are all up to a given machinist, but any “tricks” to increase flow should of course only be used if they’ve stood the test of time on other engines! Some valves are not reusable because the stems themselves are worn, often the simple result of stem-to-guide friction, but traditionally also possible because of (believe it or not) valvestem seals. This is unheard of on factory Gen III and IV heads because GM uses good quality seals on all LS engines (be sure to select Viton or similar valvestem seals for your rebuild—Teflon seals cause substantial wear on the valvestem). Beyond this, there isn’t much to say about valve machining, save that worn valve tips from a faulty rocker arm, inadequate oiling, or simply an excessive number of miles of use can be ground down to a smooth finish.
While the standard 3-angle valve job is all that is needed for stock and most high-performance rebuilds, deviations in the angles of the three cuts are possible to increase flow, but often at the expense of component longevity (for example, 38-45-58 or 35-55-68, the latter being a strict race-only setup). Experienced shops like LRB know that Newen cutting equipment is top-shelf stuff and won’t use anything else for valve seat machining.
Here, a valve is refaced on a special grinding machine. Since this process spins the valve at high speed, it will also reveal any issues with valve stems that are not straight. This is not uncommon on LS engines: from this set of 16 used LS1 valves, 5 intake and 3 exhaust valves were bent! Fortunately, replacement valves are readily available from the likes of GMPP, Federal-Mogul, and other suppliers. It should also be noted that some valves are not capable of being refaced at all, so don’t be surprised if your machine shop has to acquire new ones for you.
Once the valves and their seats have been machined, valve seat quality can be verified. Layout fluid is applied, and the valve inserted and spun by hand while pressure is kept against the seat. Once removed, the valve should look shiny on the center of its 45 degree surface, with consistent lines of fluid on either side that are somewhat narrower on the outer edge all around the valve’s circumference.
Head resurfacing may be performed on the very same machine used for the block’s deck surface. In a simple cleanup resurfacing, around 0.010-inch or less is normally taken off. This is another example of where CNC equipment is not a necessity; for routine head work, tried-and-true machines like this one will do just as good of a job!
Stock Gen III/IV valve guides are of a press-in variety that drive out from the bottom and are inserted from the top (shown) using a guide driver tool. If replacing guides, they are either reamed (iron) or honed (bronze) to size after installation. As a side note, worn guides should always be replaced, never knurled. Your guides will not last long if subjected to this “stopgap” process, and if your machine shop has the audacity to suggest it, you should definitely “head” elsewhere!
When milling heads to increase compression ratio, your machine shop will use a burette to determine the combustion chamber volume. This process is sometimes known as “cc’ing the head,” since combustion chamber volume is normally measured in cubic centimeters (cc).
Regardless of whether you’ll be assembling your own cylinder heads, you might want your shop to at least measure your valvesprings and check that they deliver the proper spring rate and seat pressures. Specs can normally be verified with those listed on the instructions included with the springs (or shown on the outside of the box).
The other items that wear out in a cylinder head are the valve guides. Stock GM LS valve guides are long-lasting iron and often do not even need replacing on heads from lower-mileage engines. Your machine shop will verify valve stem-to-guide clearance—this is important not only for valve and guide longevity, but because excessive clearance will increase oil consumption. A typical specification for stem-to-guide clearance is 0.0017 to 0.0020-inch, with variation depending on whether you are talking about intake or exhaust valves and the type of guide material used. Some high-performance applications may wish to use bronze valve guides. A favorite of aftermarket cylinder head manufacturers, bronze guides are claimed to reduce friction and provide superior heat dissipation from the valvestem, but many machinists still feel that they will not last as long as iron. Unless your existing valve guides need replacement anyway, it’s probably not worth the expense of swapping over to bronze on most applications.
Cylinder head resurfacing is a very good idea for all heads, regardless of miles of prior use or intended application. A resurfacing machine is used to correct for small warpage and surface imperfections, and a machine with quality cutters will also yield a fine finish on the head deck surface (as with the block deck surface, this is a boon for high-performance MLS gaskets that often will not seal properly with anything less). Resurfacing machines are also used to mill heads to reduce combustion chamber volume and thereby increase compression ratio on high-performance applications. There are limits to how much material removal different heads will tolerate, however, and if consider-able milling is performed, the machine shop must also cut the head’s intake flange to avoid misalignment with the intake manifold.
If you’ll be assembling your own heads, the work of your machine shop pretty much ends here. However, if you don’t mind spending a few extra dollars, you can save yourself some time by having the machine shop install valve stem seals (this is strongly recommended if using early-style “2-piece” seals that are separate from the spring seat) as well as springs and related hardware, so that basically all you will need to do back at home is bolt your heads on. We’ll discuss head verification and assembly procedures in Chapter 7 and Chapter 8.
Other Machining Processes
We’ve just gone through the major types of machine work you’re likely to need on your engine parts. However, a slew of others may be recommended by your machine shop based on factors like the condition of your used engine parts and the characteristics of your particular application. It is not possible to mention them all here, but don’t be surprised if your machinist starts throwing terms like “Magnaflux,” “Meta-Lax,” and “parts demagnetization” at you. The internet and other CarTech books are great sources of information, so familiarize yourself on such items if you are not satisfied with any explanation your machanist pro-vides.
Final Machine Shop Notes
At this point, you should have a great appreciation for the wide variety of engine component machining processes your machine shop can take care of for you. Many of them are involved and complex, and the types of work needed (and extent to which each of them must be performed) all depend on the state of your parts and your desired end product.
Remember, if you come across any information that conflicts with or wasn’t mentioned in this chapter, don’t be afraid to do your research and question your machine shop about any given machining process. An educated consumer is a good consumer. But at the same time, don’t lose respect for the machinists, who have technical training and many years of specialized experience. Help them to help you by taking a positive attitude toward their work, and trust that any problems that might arise will be resolved in due course.
You may be excited once all of your freshly machined parts are in your hands, but don’t get ahead of yourself—final engine assembly is still a little ways off. With all machine work having been performed, it’s time to move on to Chapter 6, Component Cleaning and Preparation, followed by Chapter 7, Pre-Assembly Procedures.
Written by Chris Werner and Posted with Permission of CarTechBooks
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