LS Engine Rebuilds: Final Assembly- Short Block

A dedicated bearing assembly lube (top left) will help protect your bearings and crank journals during initial startup, while a high-pressure lube (bottom right) will do the same for your pushrod seats. The Royal Purple assembly lube at top right “bridges the gap” between bearing lube and high-pressure lube, and can be used on both types of surfaces. Finally, fastener assembly lube (bottom left) assists in achieving proper torque readings, and this stuff is nearly always moly-based.

An oiling can will prove useful when applying engine oil to your parts so that they (and your hands) stay as clean as possible. A small set of brushes is another option, as we talked about in Chapter 7.

You can’t put together an LS without these: thread sealant (also known as pipe thread compound or “Teflon paste”), threadlocker (medium-strength recommended), RTV silicone, and anti-seize.

Goodson is a great source for parts organizer trays like this so-called block organizer. Piston/connecting rod assemblies are especially likely to tip over once assembled, so why not have them lying safely atop your worktable?

While you’ve hopefully been keeping your hands clean throughout all stages of your rebuild project, it’s more important than ever to do so now. The life of your LS depends on it! You may also consider wearing disposable rubber gloves during the final assembly process.

The most exciting time of the engine build is now upon you, as all of your shiny new or refurbished parts will come together to make what you’ve been dreaming of: a fresh LS engine! Don’t let the adrenaline get the better of you, though: follow the below steps carefully (and in order) to ensure you don’t make any mistakes.

Flip the engine block upside down on its stand. Install any and all block plugs of the screw-in type, including oil gallery and coolant plugs. You should have noted where they all came from during disassembly. All of these are safe to reuse if their sealing washers are in good condition, but be sure to use Teflon-based thread sealant on the threads and under the sealing washer (new plugs include sealant on them). Torque this style of plug to 44 ft-lbs, or 30 ft-lbs if one of these plugs is an engine block heater.

Install a new front oil gallery plug into the front driver side of the engine block. Apply medium-strength threadlocker to its circumference, and tap it in place using a flathead punch or similar instrument. Its outer lip should be recessed about 0.01 inch when fully installed. At this time, also install the rear oil gallery plug (a.k.a. barbell restrictor; use of a new one is strongly recommended). This item can simply push into place by hand, and will protrude just slightly when installed properly. Use no sealant on this plug, just make sure its O-ring is intact and lightly lubricated with engine oil.

Wipe each bearing shell seating surface in the block or main cap, as well as the back side of each shell, before proceeding. The upper main bearing shells (grooved) must now be installed into the engine block and the lower main bearing shells (solid) into the main caps. Be sure to install the thrust bearing shells into the center block bulkhead (bottom of first photo) and #3 cap. If you established the need to make one or more of these bearing shells undersize or oversize during pre-assembly, ensure each is being installed in its correct location. Each shell has a tab that fits into a recess in the cap or block, preventing backward installation (finger pointing in second photo). Make sure each shell is fully seated with its edges flush with those of the block or main cap—crooked bearings could spell disaster! Also ensure that your main cap locating dowels are in place in the block at this time (only certain engines have these; for example, the LS7).

Give the seating surfaces of the block and main caps, as well as the bearings themselves, a final wipe. Lubricate the upper main bearing shells. Do not forget to lubricate the thrust faces of the #3 main bearing! Spread some lube on the crank’s main journals, too. Now, grasping the crankshaft by the snout and rear flange, slowly lower the crank into the block. Use care not to nick any of the crank journals. Just as the crank is about to rest on the bearings, it may get stuck; slight adjustments in angle of the crank will likely be needed to get it to seat, as it will only go in just the right way. If gentle wiggling does not coax the crank to seat, pull the crank slowly upward and start over; excessive jostling will damage the crank journals or bearings. It may help to rotate the crank slightly as you lay it in.

Torque all M10 inner main bolts (numbered 1-10 in the accompanying diagram), in the sequence shown, to 15 ft-lbs. Before proceeding further, you must use a rubber mallet to hit the crank rearward, then forward, with a rubber mallet. This aligns the thrust bearing surfaces and it is important to note that final thrust of the crank must be in the forward direction! Then use your torque angle gauge to twist these inner main bolts in sequence an additional 80 degrees. (See “Utilizing Fastener Stretch” on page 118 for reasons why this “torque plus angle” methodology is used by GM.)

Now, torque all M10 outer main bolts (numbered 11-20 in the first picture), in sequence, to 15 ft-lbs. Once this is done, use your torque angle gauge to add an additional 51 degrees of twist to each outer main bolt, again in sequence. With all M10 main bearing bolts now tight, the main cap side bolts can be addressed. Torque each to 18 ft-lbs; there is no required sequence for these bolts save to say that you should tighten one side bolt and then the other before moving to the next cap. There is also no angle to add to the side bolts.

Unless you are using a press-fit piston pin (in which case your machine shop will already have put together your piston/rod assemblies for you), now is the time to assemble your pistons to your connecting rods. Read “Piston and Connecting Rod Orientation Rules” on page 113 before proceeding. Piston pin retaining clips vary in style; some are c-clips that install with snap ring pliers or similar tools, while others are spiral-type and must be stretched open to ease installation (shown in hand, such a spiral-type lock must then be worked into one side of the piston pin bore by simultaneously rotating and pushing it into its groove). Once you have a clip in one side, lightly lubricate the piston pin as well as the friction surfaces in the piston and rod with clean engine oil. Slide the pin through the bores in the piston and rod until it hits the clip on the far side of the piston. Then install the other clip atop the pin. Make sure these pin retaining clips are fully seated—they’ll normally click when they’re all the way in (a flathead screwdriver comes in handy for this)! Repeat for all pistons and rods, remembering to install any piston “notched” for reluctor ring clearance onto your #8 connecting rod (see Chapter 5)! At this point, we suggest marking the face of each piston with magic marker to correspond with any number previously scribed onto the rod.

Most piston or piston ring manufacturers will provide specific guidelines as to ring “clocking,” or placement of the end gaps about the piston’s perimeter. If no clocking recommendations have been specified, you should follow the ring clocking diagram shown here during the below steps of piston ring installation (compression rings can easily be repositioned once installed on the piston, while oil rings are a little more tricky to slide against one another). The most important thing to note is that the oil control rails must be placed about 1-inch to either side of the expander end gap. Most modern ring packages don’t require precise clocking other than this, but you should still space the end gaps of the top and 2nd rings approximately 180 degrees apart.

Some high-performance LS pistons with a short compression height have an oil ring groove that intersects the piston pin bore (see the Appendix). Such pistons require installation of an oil ring support, which sits beneath the oil rings and provides the necessary structure in the area of the piston pin. An oil ring support must be installed before any piston rings, and this is most easily done using ring expander pliers. Oil ring supports will often have a dimple (pointing) that must face down in the area of the piston pin bore. This dimple prevents the support from rotating out of place while the engine is running—you do not want the gap in the support entering this area!

It is easiest to install rings if your piston is standing upright (so that you have two hands to work with); your rod vise lying flat on the surface of a table works well for this purpose. Beginning with the #1 piston, lightly lubricate the surfaces of all rings with clean engine oil. Install your oil ring expander into the bottom ring groove, which is the wavy-looking ring (it may have a piece of thin wire connecting its ends, like this one). Note that some ends of expanders simply butt together, while others lock in place. Then install one oil ring control rail below the expander and another oil ring rail above the expander. Oil ring control rails are easily installed by hand using a light twist (set one end in and hold it with your thumb), and ring expander pliers are not required. Note that if your piston has a small opening beneath the oil ring groove (near left thumb in second photo), you should move the rail end gaps past this area, i.e., further apart than just the 2:30 and 3:30 positions shown in step 10.

Proceed to lightly lubricate and install your compression rings one at a time, being sure you are using the appropriate compression ring pair for the #1 piston (they should have been marked after ring fitting). Start with the 2nd ring, which sits in the lower of the two compression ring grooves and normally has a duller finish. Be sure to install the correct side facing up: this will be noted on the instructions included with your rings and is normally indicated by a small dot or a beveled/grooved inner or outer edge (which may face either up or down depending on your ring set). Use ring expander pliers to expand the ring just enough so that it slips around the piston; too much can damage the ring. If you do not have ring expander pliers, you can use your thumbs to push the end gap apart. Now install the top ring, again making sure to follow the ring manufacturer’s instructions on any bevel or dot placement. Once in their grooves, the compression rings should stick out a bit; this is normal and will help the rings put tension on the cylinder walls. Repeat steps 11-13 (as applicable) for pistons #2 through #8.

As with pre-assembly, a lot of crankshaft turning is required during final assembly. For this reason, it helps to install your crankshaft turning tool (if you have one) onto the crank snout at this point. Depending on the style of your tool, you may have to install your oil pump drive gear (which may be part of your crank sprocket) onto the crank snout before putting the crank turning tool on. Again, if you do not have a crank turning tool, we recommend simply installing your old crank bolt and using a 24mm wrench to turn it.

If your rod caps are currently installed tightly to your rods, remove them in accordance with “Proper Connecting Rod Cap Removal” on page 96. Start with the piston/rod assembly for cylinder #1 (remember, each is unique!). After ensuring the bearing shells and their seating surfaces on the rods are clean, install the lower connecting rod bearing shell into the rod cap and the upper shell into the top portion of the rod. As with main bearings, each bearing shell will have a tab that will fit into a recess in the rod or cap, and the shells must be fully seated with their edges flush with those of the rod or cap. Also note that rod bearing shells are not always the same, and your rod bearings may have a top and a bottom half. This is especially true when using chamfered rod bearings to match high-performance filleted cranks. If this is the case, check the back of the bearing shells, which are often stamped with a “U” or “L,” indicating upper and lower shells. As a double-check, watch that the chamfer in the edge of such a bearing will face the filleted edge of the crank journal (i.e., the chamfer must face the front of the engine on odd-numbered cylinders and the rear of the engine on even-numbered cylinders). Lubricate the bearing shells with assembly lube.

Turn the engine on its stand so that the cylinder deck surface is as horizontal as possible. Give the appropriate cylinder wall one final cleaning, and lightly lubricate it with clean engine oil using a lint-free towel or assembly wipe. Then turn the crankshaft so that the rod journal for the cylinder you are working on is at its furthest point below that bore (bottom dead center). This will give the most room to guide the rod onto it. Also lubricate the crank rod journal with assembly lube.

No matter what type of ring compressor you are using, lightly lubricate its inside surface with engine oil. If you have a tapered-sleeve ring compressor, set it roughly atop the bore. Adjustable sleeve-style ring compressors need to be adjusted until the cylinder liner can no longer be seen around its inner circumference. (Many machine shops make a slight chamfer in the top of the bores to ease ring installation, and you can see this in the first photo). As for band-style adjustable ring compressors, they should be wrapped snugly (not tightly) around the piston at this time, leaving the piston skirt exposed. Note: Use of band-style “oil filter wrench” compressors that do not lock to a set position is not recommended and can result in ring breakage!

After verifying ring clocking, lightly lubricate the skirt of the correct number piston/rod assembly and insert it into your sleeve-style ring compressor (or simply insert the piston skirt into the bore if using a band-style compressor). Start pushing the piston very lightly downward by hand. Further minor adjustments to adjustable-style ring compressors may be needed so that the piston can slide through it while still holding the rings firmly. When using a sleeve-style compressor, you will probably need to use your fingers and press each compression ring into its groove, to allow it to enter the tapered section of the sleeve (shown in top photo).

Once the piston skirt has entered the top of the bore and all rings are being compressed, look underneath to ensure the connecting rod is roughly centered and not about to contact any part of the crank or block (or another rod, if one has already been installed onto the journal). Shown is a rod hitting a crank counter weight, a common occurrence. Twist the piston as necessary to get the rod at a 90 degree angle to the crank centerline, and you may also need to slide the rod to center it along the piston pin. Failure to correct these problems can destroy the rod or other components!

Hold the ring compressor against the deck surface and begin tapping downward on the top of the piston with the rubber butt end of a hammer. If the piston stops at any point, do not force it! The ring compressor may be improperly adjusted and a ring may be hanging up on the bore lip. Some moderately forceful taps may be needed to get the piston to move, but anything more than this should be a red flag—in which case you’ll need to stop, pull the piston out, and make any necessary adjustments before trying again. Once you are certain the piston is going into the bore properly, reach underneath and begin guiding the end of the rod with one hand while continuing hammer taps with the other (you may remove the ring compressor at this point if you wish).

As the piston moves down, some further slight twisting of the rod may be needed to help guide it past the crankshaft counterweight (and other rod, as applicable). As the rod nears the crank journal, use extreme care, as any part of the rod touching the journal surface could cause a scratch. Hold your hand around the journal with your index finger and thumb, keeping the rod bolt holes centered on either side of the journal (shown, be prepared to get a little lube on your hand). Once the rod is seated onto the journal, install the rod cap (remember to do so in the correct orientation). On aftermarket rods that use locating dowels, it is recommended that you tap the cap in place using a rubber mallet (in lieu of drawing it down with the bolts) to seat the cap. Either way, install and tighten the bolts until snug. Repeat steps 15-21 until you have installed piston/rod assemblies into all cylinders.

Note: The procedures described in this step apply to engines using GM connecting rods and rod bolts only. If using aftermarket rods or bolts, follow the tightening procedure specified by the manufacturer, and read “Utilizing Fastener Stretch” below for more information. Flip the engine on its stand so that the oil pan rails are facing up. Starting with the #1 connecting rod, turn the crank so that both rod bolts are easy to access (the crank will be substantially more difficult to turn now that pistons and rings have been installed!). Torque each bolt initially to 15 ft-lbs. Then install your torque angle gauge and give each bolt an additional 75 degrees of twist. Mark on or near the bolt so you know you’ve tightened it, then ensure the rod can slide back and forth on the crank journal (if not, the rod bearings may be crooked). Repeat for each connecting rod until you have secured all sixteen rod bolts.

Important Note: Early-style GM rod bolts must only be twisted 60 degrees (instead of 75). The most foolproof way to determine whether your bolts are of this type is to look at the area between the bolt head and the threads: if the bolt has a thick shank with a series of shallow, vestigial threads starting just below the head, it is an early-style bolt. Later-style bolts all had a narrower shank interrupted by a larger-diameter sleeve somewhere between the bolt head and threads (exact location varied). The photo compares an earlier (left) and later-style (right) bolt removed from a rod, but you can have a look now just by loosening the bolts and pulling them out enough to look at the shank. Early- and later-style bolts should never be mixed on the same rod!!

Being sure to use some oil on its O-ring (replace if damaged), install the crank sensor into the passenger side rear of the block. Torque its retaining bolt to 18 ft-lbs. Make sure you are using the correct sensor for your engine and computer: black sensors are for 24X reluctor rings, while lighter colored sensors are for 58X rings.

The assembly of the short-block (or “bottom end”) is now complete! Take a well-deserved break, but be sure to cover up your engine while you’re gone to prevent contamination from airborne dust, bugs, and other unwelcome substances. Then, move on to the next step.