Let’s be honest: at this point, you’re probably getting a bit tired of reading each chapter introduction. Each one contains parent-like nagging of the importance of the material therein, and threatens you with grave consequences for not paying attention to detail. However, attention to detail is what an engine rebuild is all about, and even though you’ve successfully come this far, there are still many important steps to undertake prior to final engine assembly. It is this critical time that this chapter is all about.
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This phase is best known as pre-assembly, and now is when you’ll determine once and for all whether the parts that comprise your engine will actually work together. This is also the time when you’ll be performing checks to make sure all machine work was done properly to the engine block and other components. If there is one piece of advice that you must understand right now, it is this: Do not assume that your parts will fit together, even if you have been assured they will work properly! It’s a lot easier to partially assemble your engine now and perform the required checks, rather than discover part fitment problems during final assembly. Worse yet, failure to pre-assemble could leave outstanding issues that might not even be found during final assembly; we shouldn’t have to tell you
This phase is best known as pre-assembly, and now is when you’ll determine once and for all whether the parts that comprise your engine will actually work together. This is also the time when you’ll be performing checks to make sure all machine work was done properly to the engine block and other components. If there is one piece of advice that you must understand right now, it is this: Do not assume that your parts will fit together, even if you have been assured they will work properly! It’s a lot easier to partially assemble your engine now and perform the required checks, rather than discover part fitment problems during final assembly. Worse yet, failure to pre-assemble could leave outstanding issues that might not even be found during final assembly; we shouldn’t have to tell you Do I Really Need to Pre-assemble?
Do I Really Need to Pre-assemble?
The short answer to whether every engine needs to be pre-assembled is a resounding “yes!” But this blanket statement is a little deceptive, as in reality, the fact that no two LS engines are alike means required pre-assembly is a matter of degree. All engine builds—even stock rebuilds—will require at least some amount of pre-assembly, mainly to establish basic items like proper bearing clearances and piston ring end gap (this includes verification for “drop-in” rings, mind you!). On the other hand, stock rebuilds will normally have no need to undergo more advanced checks like rotating assembly clearances or degreeing of a stock cam; pre-assembly procedures like these are far more important and involved for high-performance engines, as the likes of bigger cams and longer-throw crankshafts all mean special care and attention must be paid (and often, a few modifications made!).
Because of the discrepancies in pre-assembly necessities, we’ll mention which procedures apply to all rebuilds—and which are for high-performance engines only—as we undergo the step-by-step pre-assembly process below. We suggest that you read through all steps first to get a better idea of which will be needed for your engine. This will fill you in on exactly what tools you will need to have handy, as well as any special considerations you’ll want to know, before beginning.
Pre-assembly Supplies
While all tools required for pre-assembly were listed in Chapter 2, here are the miscellaneous supplies you’ll need during the process, along with a few final suggestions.
Clean area to work in
You just cleaned all of your parts using the procedures in Chapter 6, and know that you’ll need to go through the cleaning process one more time before final assembly. To make your life a little easier, you should do your best to keep all parts as clean as possible during the pre-assembly process, and this all starts with having clean worktables, tools, and a dust-free environment. Though components will no doubt get contaminated during pre-assembly, why not minimize this instead of setting yourself up for even more cleaning work?
Don’t contaminate your engine by using dirty tools. Just think of all of the rusty, greasy bolts you’ve worked on in the past with your socket wrenches, and you’ll understand the kinds of small particles that can reside on their surfaces and in nooks and crannies. This is important to keep in mind not only during pre-assembly, but during final assembly as well.
Clean engine oil
Pre-assembly requires tightening many fasteners to their final specifications. Though many are designed to be installed “dry,” some fasteners require lubrication to help achieve an accurate torque reading. Engine oil is the most commonly used thread lubricant, though some aftermarket fasteners require specialized moly-based thread lubricant, which is often included. Because moly lubricant is often supplied in small amounts, it should be saved for final assembly and the alternate “with oil” torque spec used during pre-assembly (unless no such specification is provided). Also, you will need to physically lubricate engine bearings to allow spinning the crankshaft during pre-assembly. A good set of small brushes and/or an oiling can is less messy and more sanitary than applying lube with your fingers.
Quality non-synthetic engine oil will aid in lubricating bearings and other surfaces during pre-assembly. Heavier-weight oils such as SAE 30 are preferred as they stick to surfaces better than lightweight oils like 5W-30. Also, if you have special assembly lubricants for bearings, now is probably not the time to use them, unless you’ll have a sufficient amount left over for final assembly.
Parts cleaning supplies
You’re already quite familiar with the cleaning supplies used for engine parts, and it’s good to have at least some of them nearby during pre-assembly. For example, mineral spirits and clean rags will allow you to quickly deal with accidental spills or contamination before it spreads (or before you slip and hurt yourself!). Also, items like main bearings will need to be installed, cleaned, and reinstalled throughout the pre-assembly process, so be prepared with what you’ll need to do this.
Step-By-Step Pre-assembly Procedures
Step 1: Ready to Begin Pre-assembly
Pre-assembly is easily the most time-consuming part of any engine build, so there is almost no way you will get it done in one sitting. It’s OK to stop and do something else for a while—just be sure that you take careful notes, and do your best to avoid immediate emergencies that might arise and prevent you from leaving your work at a natural stopping point. Have a copy of our Work-A-Long sheet (available at cartechbooks.com) ready and be sure to check off each item as you go, and have temporary means of keeping items clean (storage bags, etc.) while you are away.
Step 2: Measure Engine Block Machined Surfaces (Precision Measurement)
Chances are, your home measuring tools aren’t as accurate as those of a machine shop, but this doesn’t mean you can’t use them to double-check whether your engine block machine work was performed correctly. Utmost trust in your machine shop may tempt you to skip this step, but before doing so, keep in mind that machinists can make mistakes, too! Using the tightening specifications (sequence optional) shown in Steps 7-8 in Chapter 8, install each main cap and use a dial bore gauge to measure the diameter of each main bearing bore in a crosswise pattern (minimum two measurements per bore). All measurements should be consistent within 0.001 inch, with a maximum out-of-round of less than half a thousandth on any given bore. Remove the main caps and perform the same procedure on each cylinder bore, measuring the bore in a few different places along its height. Record these measurements, they should all be within 0.001 inch as well.
What If Anything Goes Wrong?
Much of pre-assembly is geared toward not only finding parts fitment problems, but addressing them. If as you go along you note an issue whose solution is not described in the below steps, the best thing to do is to call your machine shop. Whether it’s a potential problem with machine work or difficulty with parts fitment that you can’t quite figure out on your own, they’re an excellent resource and will often know exactly what to do without even seeing the parts themselves. Sometimes, a part problem you think is unfixable is far from it, and may only require minimal at-home work to solve (or perhaps a quick trip to the machine shop to have them take care of it for you).
That said, let’s pre-assemble!
Step 3: Measure Other Engine Parts (Precision Measurement)
It will be helpful to check the roundness of other critical surfaces, including but not limited to crank journal diameters (inspect for taper and out-of-round) and connecting rod bearing bores. This is especially true if your machine shop didn’t have much of a hand in preparing these (i.e., they are new aftermarket parts). In conjunction with the cylinder bore diameters you’ve just written down, measuring your piston diameters will allow you to verify piston-to-wall (a.k.a. piston-to-bore) clearance. Proper clearance ranges from less than a thousandth of an inch for some cast pistons and as high as 0.010-inch for forged pistons, though exact spec varies by piston alloy (aftermarket pistons normally include a spec sheet with the recommended clearance listed) as well as the type of clearances your machine shop has had success with in past engines. Error compounding for imprecise measuring tools means you may not get very accurate readings for this, but way-out-of-whack measurements should have you on the phone with your machine shop. As a side note, you may also measure specs on your cylinder heads like valve-to-guide clearance, but your tools probably lack the precision needed for these checks, too.
Step 4: Main Bearing Clearances – Install Main Bearings
With the main caps removed, install your upper main bearing shells in the block. These “upper halves” have holes in them for oil to enter from the block. Note that the center main bearing is the thrust bearing on LS engines. Also put the lower halves of the main bearings in the main caps. Use no lubricant whatsoever on any of these bearing shells—it will interfere with bearing clearance measurement. Once installed, wipe them with a clean cloth to remove any possible contamination.
Step 5: Main Bearing Clearances – Install Crankshaft and Plastigage
Now after giving the crank main journals a quick wipe, gently lay the crank in place in the block. Again, do not use oil on any surfaces—they must be clean and dry. Lay a piece of Plastigage on top of each main bearing journal once the crankshaft is in.
Step 6: Main Bearing Clearances -Install Main Caps (Torque Fasteners)
Install the main caps (again, with dry bearings) and tighten them in the sequence shown in steps 7-8 in Chapter 8. However, do not use a hammer to align the thrust bearing surfaces. Also, although their installation will likely not affect your main bearing clearance reading, you should install your main cap side bolts and tighten to spec.(If you purchased new GM side bolts, they will have sealant pre-applied, so don’t use them until final assembly. Use the old bolts for now.)
Step 7: Main Bearing Clearances – Remove Main Caps and Measure Plastigage
Loosen and remove all main cap bolts followed by the main caps themselves. Note that the tight fit between the caps and oil pan rails can make removal tricky. As during disassembly, we suggest using two long 3/8-inch extensions to gently pull them upward (rather than buying the special slide hammer tool). Underneath each cap you’ll find that the Plastigage has now been smooshed. Match its width to the nearest marking on the Plastigage sheath, and you’ve got your bearing clearance. See “Bearing Clearance Measurement” for suggestions on proper main bearing clearances and what to do if they are not satisfactory. When you’re done, clean all remnants of Plastigage from the crank journals and remove the crankshaft from the engine block.
Step 8: Check Crankshaft Runout (Precision Measurement)
Remove all upper main bearing shells from the block except the #1 and #5 (front and rear) shells. Clean these remaining shells, lubricate them with oil, then set the crank in place atop them (lube the #1 and #5 main journals on it, too). Set a dial indicator to measure along the surface of the #3 (center) main journal, being sure the indicator’s tip won’t drop into the crank oiling hole(s) as the crank is turned. Spin the crank over and note the highest and lowest readings on the dial indicator. The difference between them is what is important; anything more than a thousandth or so is cause for possible concern. Total acceptable runout varies by application, so if you see anything that perturbs you, consult your machine shop for recommendations. They may even have suggestions for straightening your crank that you may find surprising (like torquing your main caps in place and letting this straighten the crank out for you!). You should also move the dial indicator to the rear of the crank and measure runout on the rear flange, where the rear seal rides; runout here can’t exceed 0.002-inch. Please note that because there will be no thrust bearing in place during the runout checking process, you may hear the reluctor ring dragging lightly along the rear of the engine block—this is normal.
Step 9: Install Crankshaft with Lubricated Bearings
Now remove the crankshaft. Install and lubricate the remaining upper main bearing shells in the block. Set the crank atop them, lube all main journals, then install all main caps with lubricated lower main bearing shells. Use the instructions and sequences detailed in steps 6 through 8, Chapter 8, for main cap installation and tightening, being sure to use a hammer to align the thrust bearing surfaces! The crank should now move freely by hand. If it does not, repeat the thrust bearing alignment procedure. If this does not cure the problem, something may be wrong with your block’s main bearing bores and/or their alignment (possibly requiring line honing).
Step 10: Check Crankshaft Endplay (Precision Measurement)
There are a couple of ways to check that your thrust bearing (center, or #3, main bearing) is allowing the proper crankshaft endplay. The simpler way is via a feeler gauge. Insert a large flathead screwdriver between a crank counterweight and a main cap and pry rearward and forward, measuring the space between the thrust surfaces on the crank and the thrust bearing. Measure both the space in front and space behind for comparison purposes; GM recommends between 0.0015 and 0.0078 inch of clearance (always follow the recommendations of your crankshaft and/or bearing manufacturer when using aftermarket components). The more accurate way to measure this is to mount a dial indicator to read off of the crank snout (or rear crank flange) and record dial indicator movements as you pry fore and aft.
Step 11: Check Reluctor Ring Runout (Precision Measurement)
Mount a dial indicator to read off of the back of the reluctor ring, about 1mm below the teeth. While holding the crank forward or rearward with slight pressure (to eliminate thrust clearance), spin the crank and note the dial indicator reading. Lateral movement beyond 0.028 inch indicates the need to replace the reluctor ring. Some engines even require tolerances as tight as 0.010-inch. Don’t ignore a problem here, as it means your crank position sensor may not be able to deliver a proper signal!
Step 12: Install Camshaft
Lubricate the camshaft’s bearing journals (as well as the first few lobes toward the front of the cam) and slowly insert it into the block. (See step 25 in Chapter 8 for cam installation hints.) Once the cam is in, check that it spins freely. If it doesn’t (or fails to go in all the way), remove the cam and have a look inside the block for any possible problems with improperly installed, incorrect, or out-of-shape cam bearings. If the bearings are OK, the problem is likely with the cam itself. If you’re reusing a stock cam, you should have checked it for journal roundness problems in Chapter 4 (do this now if using an aftermarket cam). It is difficult, albeit possible, to get an accurate reading for cam straightness on V-blocks, so we recommend having this specification checked at your machine shop. Any more than about 0.002-inch. runout measured at the intermediate journals is generally unacceptable.
Step 13: Install Timing Set and Verify Camshaft Endplay (Precision Measurement)
After installing your crank key into the crank snout and the cam retainer plate over the cam, install your timing chain and sprockets onto the front of the engine. (See Chapter 8, steps 26-28, noting that if using a stock or stock-style chain and sprockets, you will probably have to press the crank sprocket onto the crank snout. If this is done now, you can just leave it on until final assembly.) For high-performance applications, the cam has not yet been degreed, so simply install the sprockets in their standard position at this time. After doing this, spin the crank over and watch for any physical interference between the cam sprocket and the block or retainer plate bolts. Mount a dial indicator on the back (or in the alternative, front) of the block to measure camshaft endplay. Push/pull the cam fore and aft; there should be a small amount of movement (at least 0.001 inch, though you may not see any movement at all, in this case, if the cam spins freely, you are probably OK as you know your cam retainer plate is not being smashed between the cam and sprocket). Fore/aft cam movement should not exceed 0.012 inch. If it does, there may be a problem with your cam, retainer plate, and/or cam sprocket.
Step 14: Temporarily Assemble Pistons to Connecting Rods
Even if you’re performing a stock rebuild, you will need to assemble at least two pistons to their respective connecting rods at this time. (See “Piston and Connecting Rod Orientation Rules,” on page 113 before proceeding with this step or subsequent steps that involve installation of pistons and connecting rods!) For high-performance engines using aftermarket rods and longer-throw cranks, you will now want to assemble all pistons to their respective rods. Note: for floating piston pins, lightly lubricate the friction surfaces, but do not install “spiral locks” or other pin-retaining clips at this time; just be careful the pin does not slide too far out the side of the piston at any time. As to pressed piston pins, if you haven’t had your machine shop install them already (for fear of possible additional piston machining being required) you can assemble your pistons to your rods temporarily by borrowing a “ground down” pin from your machine shop or by purchasing a special “dummy” pin of the correct diameter.
Step 15: Checking Rod Bearing Clearances – Adjust Crankshaft and Lock From Turning (Special Tool)
Measuring rod bearing clearances is a little more involved than checking those of main bearings because of the need to prevent the crank from spinning in the block (and the rod from spinning on the journal), lest the Plastigage become damaged. The only truly reliable way to do this is to install your flywheel onto the back of the crank and use a flywheel holding tool to lock the crankshaft from turning. Before doing this, though, get the crank journal you will be using to the lowest point of travel in the block (this will be as near as possible to BDC for both pistons that share that rod journal).
Step 16: Checking Rod Bearing Clearances – Install Piston/Rod Assemblies
Once the crank is locked in place, flip the engine on its stand so that it is right-side-up. Install unlubricated rod bearing shells into the rods you are using (some high-performance bearings have chamfered edges as well distinct upper and lower halves, be sure to note this). There is no need for piston rings during this process. Lightly lubricate the cylinder walls, and carefully install both the piston/rod assemblies for that crank journal into the block one at a time, tilting the engine on its stand to have the deck surface horizontal for each. Don’t nick the crank journal on the way down! Install the rod caps temporarily so that the piston/rods do not fall out when the engine is flipped over (make the bolts hand tight). (Note: we are only using the forwardmost crank journal here, which corresponds to the rod bearings for cylinders 1 and 2. Though it’s possible to check rod bearing clearances on only one crank journal as so, any doubt about your crank or rods should prompt you to verify them all.)
Step 17: Checking Rod Bearing Clearances – Install Plastigage and Tighten Rod Bolts (Important!)
Flip the engine over on its stand so that the oil pan mounting surface is horizontal. Now remove a rod cap and lay a strip of Plastigage on the upper shell of the rod bearing. (The lower shell in the rod cap, and corresponding surface of the crank journal, cannot be used—a Plastigage reading here would be adversely affected during subsequent rod cap removal.) Use extreme care to not allow the piston to fall out the top of the bore while the rod cap is off! Consider installing a TDC stop or similar device as a safety precaution. Also, it is helpful to tilt the engine in its stand slightly (making the cylinder you are working on vertical, albeit upside-down) so that the Plastigage strip rolls to the center of the rod bearing shell. With the Plastigage in, reinstall the rod cap and make the bolts hand tight. Repeat the Plastigage installation procedure for the other rod. Now, inserting two feeler gauges or similar items between the rods to prevent twisting on the journal, fully tighten the bolts to spec (see step 22 in Chapter 8 for rod bolt tightening instruction).
Step 18: Checking Rod Bearing Clearances – Separate Rod Caps and Measure Plastigage
Now, with the two feeler gauges still inserted between the rods, loosen all four rod bolts, but only a few threads. You may then remove the feeler gauges. To separate each cap from the rest of the rod, a few gentle hammer taps atop each bolt will likely be needed (as during engine disassembly). This is best done with a socket and small extension. After a cap is loose (and while holding the piston from falling), loosen its bolts the rest of the way, set the cap aside, and remove the piston/rod assembly from the engine. You may now measure your Plastigage. If clearance is acceptable for both rods, you may continue to the next step; but again, we suggest repeating steps 15-18 for the other three rod journals on the crank so as to account for any production or machining variations.
Step 19: Measure Rod Side Clearance
With all piston/rod assemblies removed from the engine, clean any and all rod bearing and crankshaft journal surfaces of Plastigage remnants. Install the #1 and #2 rods on the forwardmost crank journal, this time lubricating both the bearing surfaces and the journal. Tighten the rod bolts to spec, noting that there is no need to keep the rods from twisting on the journal this time around. Using a feeler gauge, measure the clearance between the connecting rods. Rod side clearance should be 0.0043 to 0.020 inches for stock steel or titanium rods. For aftermarket rods, follow the connecting rod manufacturer’s recommendations. For best results, you should install the remainder of your piston/rod assemblies and repeat the process on all crank journals. Stock rebuilds may now remove the pistons and rods from the engine. High-performance applications must have their rods installed during the next several pre-assembly steps.
Step 20: Check Rotating Assembly Clearances (Performance Tip)
Note: steps 20-25 apply to high-performance applications only. For stock rebuilds, skip to step 26. Remove your flywheel holding tool if you have not done so already. Spin the crankshaft over and watch for interference between any portion of the pistons and crank, rods and crank, or rods and block. Remember that because metal parts will stretch slightly under stress, many clearances will be even less when the engine is running at high RPM! Discuss problems with piston or rod-to-crank interference with your machine shop; these are not common. If you note too little clearance between the rods and block, you will need to mark the block at all such locations, remove your entire rotating assembly, and lightly grind the block with a die grinder (note that removing too much material risks damage to, and weakening of, the block). Mask carefully and clean before reinstalling the rotating assembly, checking for adequate clearance, and continuing.
Important notes:
(1) The rotating assembly clearance checking process is best performed with all rods installed in their final positions. However, when only minor clearancing will be required, you can also use only two rods and move them between crank journals.
(2) You also must verify clearance between the number 8 piston and the reluctor ring. We mentioned the possibility of contact between these parts back in Chapter 5. If you have a unique number 8 piston, it must be installed in the proper position (and orientation!) when verifying this.
Step 21: Degreeing Camshaft – Install and Roughly Position Degree Wheel (Performance Tip)
Proper cam degreeing requires, at a minimum, your #1 piston and rod to be installed in the block. Roughly get this piston to the top of the bore and ensure the cam and crank sprocket markings are in vertical alignment (the mark on the cam sprocket should be 12:00). To obtain a stationary reference point for the degree wheel, install a pointer. If one is not provided with your degree wheel kit, you can cut up a coat hanger and bolt it securely to the front of the block (sharpen the tip for best accuracy). Install your degree wheel onto the crank snout. Some specialized crank turning tools have a provision to attach the wheel built-in, but you can also use your old crank bolt to hold it. Adjust the pointer and/or degree wheel so as to indicate zero degrees.
Step 22: Degreeing Camshaft – Find True TDC (Performance Tip)
We must now determine true TDC for cylinder # 1—this is the industry standard for the crankshaft being at “zero degrees.” Install your degree wheel kit’s TDC stop. The crank will need to be turned backward slightly in order to drop the piston into the cylinder and allow the stop to be tightened in place (use a couple of old head bolts). Now turn the crank forward (i.e., clockwise when viewed from the front) until the piston hits the stop. Mark the pointer reading on the degree wheel. Then, turn the crank backward until the piston drops to BDC, comes up, and hits the piston stop again. Mark this reading on the degree wheel as well (non-permanent marker preferred!). The halfway point of the two marks you’ve just made is true TDC, so make any adjustments to the degree wheel’s position on the crank to get this halfway point to the zero mark. Verify by spinning the crank forward and then back again, making sure the pointer indicates the same number each time the piston hits the stop (albeit on either side of zero). After being sure your degree wheel is tight on the crank snout, remove your TDC stop.
Step 23: 23 Degreeing Camshaft – Install Dial Indicator on Lifter (Performance Tip)
Lubricate and install a lifter into cylinder number one’s intake position (nearest lifter bore to the front). Although having the lifter guide tray in place would prevent the lifter from rotating, this is not possible during the cam degreeing process: the tray holds the lifter so tightly, it won’t allow it to fall back onto the base circle of the cam once raised. Fortunately, thanks to the roller design of the LS lifter, it actually will self-center itself as you slowly turn the engine—but you should still watch the lifter carefully to ensure it does not rotate out of place and give a false lift reading. Now, mount your dial indicator fixture securely; using a head bolt hole as a mounting point provides excellent stability. Adjust so that the dial indicator’s stem is parallel to lifter travel. Also ensure that the dial indicator’s tip touches the center of the lifter plunger—an extension will likely be needed, as shown. Zero the dial indicator with the lifter on the cam lobe base circle (this will be the case if you are anywhere near TDC for the firing position).
Step 24: Degreeing Camshaft – Turn Crank and Verify Cam Timing (Performance Tip, Documentation Required)
Slowly turn the crankshaft clockwise until the dial indicator indicates 0.050-inch upward movement. Read the number indicated on the degree wheel; it should correspond with the intake valve opening value listed on the cam card (on our cam, -8 degrees BTDC, which is the equivalent of 8 degrees past TDC). Write the degree wheel reading down if it varies from the cam card. Turning the crank again, continue until the dial indicator cycles all the way to full upward lifter movement and then down to 0.050 again. Note the degree wheel reading at this point. In our example, this reading is 146 degrees (shown), which equals 34 degrees past BDC (“34 degrees ABDC”—the same as our cam card). Write this reading down as well if it varies from the cam card.
Step 25: Degreeing Camshaft – Calculate and Compare (Performance Tip)
Now do the math— use care in all conversions: add the intake opening and closing degree wheel values you have written down, using absolute values in comparison to TDC. In our example, the two values are 8 and 214 (180 + 34), respectively, and adding them yields 222. Dividing this number in half yields the intake centerline; in our case, 111. The number you come up with should be the same as the “installed” intake centerline position listed on your cam card, in which case your cam has been successfully installed in accordance with manufacturer recommendations.
If there are any variations between the cam card and the above measurements or calculations, repeat steps 21-24 to be sure. If the problem persists, there may be something wrong with your cam or timing set. If you are going to alter cam timing via use of an adjustable timing set, do so now by altering sprocket positioning (shown) and repeating the degreeing process to check your changes. Once you are happy with your results, write down or photograph the respective positions of the adjustable cam or crank sprocket(s) so that you can be sure to install them the exact same way during final assembly.
Step 26: Valvetrain Checks -Measure Valvespring Installed Height (Special Tool)
Note: If your machine shop has already assembled your cylinder heads, or if you are using a set of pre-assembled aftermarket heads, skip ahead to step 29. (Your valve stem seals and spring seats must be installed during the next few steps. Refer to step 2 of cylinder head assembly in Chapter 8 for how to do this.) Insert an intake valve into the cylinder head. Set your valvespring height gauge onto the valvespring seat. After installing a valvespring retainer and locks, twist the height gauge until the valve is held fully closed. Note the reading on the gauge. Valvespring manufacturers normally quote the proper installed height for their springs; stock replacement springs should use GM specifications for installed height. If the height gauge shows less than the required installed height value (or is substantially greater), you will need a different set of springs. If the height gauge reading is greater than this value (but still in the ballpark), you can purchase and add shims under the valvespring to yield the proper installed height. If any shimming is required, you will need to perform these measurements for every valve in each head and keep track of which shim(s) go where so that you can replicate your results during final cylinder head assembly.
Step 27: Valvetrain Checks – Measure Valvespring Retainer to Valvestem Seal Clearance (Precision Measurement)
With a retainer and locks installed on an intake valve, mount a dial indicator fixture on your head. The dial indicator must contact the top of the valve and be parallel to it. Note the indicator reading with the valve fully closed, then open the valve to the maximum intake valve (not lobe) lift indicated on your cam card (being sure to compensate if not using the quoted rocker ratio). In the case of stock cams, refer to the lift listed in your GM service manual. If the retainer has not yet made contact with the valve stem seal at the point of max lift, push the valve all the way down until this occurs, and note the dial indicator reading. The difference between max lift and the point of contact should be at least 0.050-inch.(Note that during this process, you will need to keep upward pressure on the retainer and locks so that they will not simply fall off of the valve. To make things a little less tricky, high-performance applications may wish to wait until after checker springs have been installed [step 29] to perform this step.)
Step 28: Valvetrain Checks – Measure Compressed Valvespring Clearance (Saftey Step)
You need to double- check that your valvesprings are capable of handling the valve lift that your cam will provide on your application. If your valvespring manufacturer didn’t supply a value for maximum spring compression, you can find it easily by placing your valvespring in a vise. Don a good pair of goggles and fully compress the spring until all coils contact each other. Measure the spring—this is the coil bind height. To figure out whether you will approach this value, subtract the intake valve lift on your cam card (again, making any compensation necessary for different rocker ratios) from the valvespring installed height you determined in step 26. This number is your compressed valvespring height, and it should be at least 0.060 inches greater than the coil bind height you’ve just measured for most springs. Repeat steps 26–28 for at least one exhaust valve.
Step 29: Valvetrain Checks – Install Checker Springs on Head (Performance Tip)
Note: This step applies to high- performance applications only. For stock rebuilds, skip to step 30. If your heads are already assembled, you’ll need to remove the valvesprings from the intake and exhaust valves of cylinder number one (follow the appropriate steps enumerated in Chapter 3 during head disassembly). Install checker springs in these locations at this time.
Important notes:
(1) The checker springs you use must be weak enough so as to not compress the plunger of hydraulic roller lifters. This will mean springs with very little tension at all! As an alternative, you may temporarily install solid lifters in lieu of your hydraulic lifters, but they must be of the exact same plunger height (or at least a known height difference) to properly perform steps 30-34 and the accompanying calculations.
(2) Be sure to also install your lash (“wear”) caps at this time if, for example, you are using titanium valves.
Step 30: Valvetrain Checks – Install Cylinder Head on Block
Note: Before performing steps 30-34, see “Determining Optimum Pushrod Length” on page 105. Make sure you have your lifters for cylinder #1 installed in the block—to avoid having to continually push the lifters back down onto the cam lobe during piston-to-valve clearance checking, high-performance rebuilds should not install the lifter guide tray. Turn the crank as needed so that both lifters are on the base circle of the cam (again, near TDC at the firing position works best). Install head locating dowel pins into the block deck surface and set a head gasket in place on the block. It is best if you have a reusable head gasket for this step (i.e., not the earlier-style graphite-layered GM head gaskets—they will stick to the deck surfaces and be destroyed, making reuse during final assembly impossible). Install your driver side cylinder head. If you will be using stock-style head bolts during final assembly, use an old set of head bolts now. Again, thanks to their torque-to-yield design, new GM bolts can only be fully tightened once. Follow the head bolt tightening specifications and sequence listed in steps 43-44 in Chapter 8.
Step 31: Valvetrain Checks – Measure Pushrod Length
Insert pushrod length checkers for the intake and exhaust valves of cylinder #1. On most LS engines the rocker pivot supports are not a machined part of the head; in these cases, lay the rocker stand in place on the head—it helps to have a couple of rocker bolts in toward the other end of the head to prevent the stand from shifting. Set the rockers loosely atop the stand and adjust the pushrod length checkers so that they are slightly too short to contact the pushrod seats on the rockers (when the rocker tips are touching the valves). Now bolt the rockers down and adjust the pushrod length checkers so that they just barely contact their pushrod seats (this will be difficult thanks to the minimal exposed area of pushrod provided by LS heads). Jiggle the checkers to ensure they are squarely positioned in both the pushrod seats and lifter plungers below. Since the lifter plungers are not visible in LS engines that have heads installed, it will be difficult to tell whether any hydraulic lifter preload is occurring (there should be none)—this is why so much care is needed when adjusting the pushrod length checkers. Also, if you’re using checker valvesprings, use extreme care not to compress them. Once you’ve achieved pushrod lengths just sufficient to remove all play from the system (and no more), remove and measure the pushrod length checkers. The proper pushrod length for your engine is this measurement plus the recommended hydraulic lifter preload provided by the lifter manufacturer (usually in the neighborhood of 0.060 inch for stock GM lifters). Pushrods are normally sold in length increments of 0.050 inch, so select the length that puts the lifter preload within its acceptable range. Please note that results may differ slightly between the intake and exhaust valves, and if the difference is significant, you may consider using a different pushrod length for each. Repeat the measurement process to ensure accuracy—it doesn’t hurt to do it on at least one other cylinder, too (especially on the other cylinder head if head resurfacing has been performed)!
Step 32: Valvetrain Checks – Install Pushrods and Rocker Arms (Performance Tip)
Note: steps 32-34 apply to high-performance applications only. For stock rebuilds, skip to step 35. Because checker springs are being used in lieu of actual valvesprings, use of your new correct-length pushrods is not possible during the next few steps. The reason for this is that correct-tension checker springs do not provide enough force to compress the hydraulic lifter plunger, so your new pushrods would actually cause the valves to hang open slightly. For this reason, use your pushrod length checkers set to the correct length minus the hydraulic lifter preload. (If you find that your checker springs are strong enough to compress the lifter plunger, consider installing a set of solid lifters, which you would leave in from now through step 34.) Before installing anything onto the head, though, spin the crankshaft over several times to allow the lifters to re-align themselves on the cam lobes (remember, you should not have lifter guide trays installed, and the lifters may have rotated during pushrod length measurement. This is OK with the lifters on the base circle of the lobes, but it will not be OK now!). Then install the pushrod length checkers and rocker arms for cylinder #1 (ensure the rocker stand does not twist on the head while doing this). If you are using aftermarket adjustable rocker arms, you will need to set the lash adjuster to a position that removes all lash but keeps the valves closed
Step 33: Valvetrain Checks – Inspect Rocker Geometry
Slowly turn the crankshaft over and watch the movement of the rocker arms. (If any resistance to movement is felt, stop: the valves may be contacting the pistons. If this is the case, you definitely do not have adequate piston-to-valve clearance. See step 34 how to address this problem.) A main area to check is interference between the underside of the rocker and the valvespring retainer (pen pointing). Fitment problems here are more likely if using valvesprings with wider-than-stock retainers (as shown), i.e., those for use with non-tapered valvesprings. One other noteworthy area of rocker geometry to look at is where the tip sits on the valve stem. It should be nearly centered when viewed from above, and beyond this, look at the rocker from the side as it traverses through low, mid, and high lift. The tip should be contacting the center of the valve stem during the midlift period. If using aftermarket rockers, some additional checks can be performed at this time (some of which will need to be done on more than one cylinder); for example, you can inspect for interference between the rockers and valve cover rail or valve cover. Minor massaging of the valve cover rail may be needed with some rocker systems (shown). You can also set your valve cover atop the head (sans bolts and gasket) and turn the engine over. If the valve cover moves or you hear any “clicks,” the rockers are contacting the underside of the valve cover and modification may be required.
Step 34: Valvetrain Checks – Check Piston-to-Valve Clearance (Performance Tip)
Rotate the crankshaft so that cylinder number one’s intake valve is closed. Mount a dial indicator so that it touches the top of the intake valvespring retainer and is parallel to the valve stem. Rotate the crankshaft until you see the intake valve just begin to open; note the indicator reading at this point. Using your hand, rotate the intake rocker until the valve contacts the piston (the valve may have to be opened very far for this, or it may never contact the piston at all, particularly toward the beginning of the opening event). Write down the dial indicator reading and release the rocker. The difference between the two indicator readings is your piston-to-valve clearance at that crank position. Now rotate the crank a few degrees and repeat, again writing down the dial indicator reading if and when the valve contacts the piston. Do this until the intake valve has completely opened and closed, then set up the dial indicator on cylinder number 1’s exhaust valve and repeat the entire process. In most cases, minimum piston to valve clearance should be 0.100 inch for the intake and 0.125 inch for the exhaust valve (bare minimums should be 0.080 and 0.100 inch, respectively). If clearance is tighter than this, you may be able to alter cam phasing slightly to accommodate, or you can swap to a different cam. If this is not an option, you may have to machine the tops of your pistons to provide deeper valve reliefs.
Step 35: Piston Ring Fitting – Setting Compression Ring End Gaps (Professional Mechanic Tip)
Remove the cylinder heads, camshaft, all parts of the rotating assembly, bearings, and all other parts you may have installed until you are left with only the bare block. Starting with cylinder number 1, slip a top compression ring in and use your ring
squaring tool to get the ring completely horizontal in the cylinder. It helps to pull up on the ring from underneath to get it flush with the bottom surface of the tool. Then, remove the squaring tool and measure the ring end gap with a feeler gauge. If you are using a drop-in ring set, the gap should match that given by the manufacturer or listed in your GM service manual. If using a file-fit set, the gap should be significantly tighter than you need it to be at the moment. To widen the gap, use your ring filer. Grind against only one side of the ring, being sure to hold it squarely against the filing wheel. Parallel ring ends are crucial to the longevity of your engine! The coarse grit of the filing wheel will remove material quickly, so take care not to go too far. Reinstall the ring in the cylinder and measure the end gap again; repeat the filing-squaring-measuring process until you’ve got the gap right. Then move to the next cylinder and continue until you have fit (or verified) top ring end gaps for them all. Repeat the entire process for the 2nd rings, performing fitting for each cylinder sequentially. (Hint: leaving each ring you’ve just done in its bore prevents you from accidentally mixing the rings up or cutting them for cylinders you have already fit rings to.)
Step 36: Piston Ring Fitting – Deburr and Label Compression Rings
After ring fitting is complete, it’s important to deburr the ends of each ring that has been file fit using a stone or similar instrument. This removes any stray pieces of metal that could score the cylinder or become lodged between the piston and the ring, thereby preventing the ring from rotating or expanding properly against the cylinder wall. (Note that it is not a bad idea to inspect the end gaps of drop-in rings to determine whether the deburring process might be needed on them, too.) Deburr one cylinder at a time so as to avoid any chance of ring mixup—each is now uniquely fit to a particular cylinder! When both the top and 2nd rings have been deburred, clean the rings and label each cylinder set (top and 2nd ring) with a magic marker and masking tape.
Pre-assembly Complete
The most tedious part of any engine build is now over! At this point, you should discuss any unresolved issues you may have encountered during pre-assembly with your machine shop. With any such problems having been taken care of, remember that you will need to clean all engine components (as detailed in Chapter 6) one more time before proceeding to Chapter 8, Final Assembly.
Written by Chris Werner and Posted with Permission of CarTechBooks
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