LS1 Engine Build - My First Stroker

As GM's Gen III and newer V-8s use 6-bolt main bearing caps, each cap has two side bolts in addition to the four that have already been tightened. These side bolts thread from the exterior of the engine block, so a touch of silicone must be used under the head of each bolt or else they can leak oil to the outside of the engine. Torque to ARP's 19 lb-ft spec.

It's time to reinstall the stock GM crank position sensor. This sensor works off of the LS1 crank's built-in reluctor wheel and gives the engine computer a signal indicating the rotational position of the crank. Just clean the sensor's o-ring and wipe it with some oil; torque the retainer bolt to 18 lb-

Before moving on, we need to check that our crank thrust bearing is allowing the correct crankshaft endplay. To do this, the crank is pried forward and rearward using a screwdriver and the clearance between the thrust bearing surface and the crank measured using a feeler gauge: there should be between 0.0015 and 0.0078 inches of clearance. The thrust bearing could theoretically be ground to give more clearance if needed, but fortunately we're within spec.

The Lunati Pro Billet Super Light connecting rods (Lunati's finest), like all performance rods, come shipped with the rod caps secured to the rods--and they are tight! To get them apart, do not use an impact wrench, as it will damage the rod. Instead, a vise needs to be used to hold the rod in place while the bolts are loosened using a hand-operated wrench. But not just any vise will do: a rod vise, like this one from Powerhouse, is made from soft aluminum and won't damage the steel surface of the rod. Any nick in the surface could mean a stress riser and rod failure. After clamping the rod vise into a standard bench vise, tighten the rod into the vise firmly and loosen the bolts.

With the bolts loose, flip the rod around and clamp onto the cap only. Rock up and down on the rod to loosen and get it apart. Note that we labeled both the rod and cap before disassembly so nothing would get mixed up; the rods are a high-strength "cracked" design so the caps uniquely match each rod. It's impossible, however, to install a cap backward as the rods are chamfered on one side only to match the aforementioned fillets at the edge of each crank journal. At around 630 grams apiece, these rods feature an exclusive barrel-shaped beam and rounded end, reducing stress risers and complementing the natural grain flow of the billet. Lunati prides itself on holding the tightest machining tolerances in the industry, and these rods are a testament to that commitment to quality.

While stock GM pistons have their pins press-fit into the rods (thereby limiting how far the pin can travel out of the piston's pin bore), performance pistons use so-called "spirallocks" to hold the piston pin in place. This makes for a "full-floating" piston pin, which gives more bearing surface for the piston pin (in the rod and in the piston as opposed to just in the piston), reducing friction and thereby increasing component life. The spirallocks come as shown on the right, but must be stretched open like a slinky in order to get them ready for installation (left).

Spirallocks can normally be installed almost completely by hand. Simultaneously rotate and push the spirallock into the groove in the piston pin bore. These pistons only use one spirallock on each side of the piston pin; some other pistons use two per side, allegedly for added insurance. But these suckers aren't going anywhere, so don't fret it. A small flathead screwdriver will come in handy to get the spirallock completely into its groove; it will make an audible click when seated correctly.

Now, orient the piston so the larger valve relief (for the intake valve) is on the left, and both reliefs are more toward the top of the piston. In this orientation, the connecting rod will be assembled to the piston with the chamfered side facing left (toward the intake valve). Fortunately, each piston/rod is of identical design, so we'll be installing them all the same way. Simply lube the bushed end of the rod with oil, lube the Lunati chromemoly piston pin, and carefully slip the pin through the side of the piston and through the bushed end of the rod until it butts against the already-installed spirralock on the other side. Secure the free end of the pin with a spirrallock.

With a light coat of oil on each, the piston rings can be installed. First comes the oil ring support, an item that isn't used on all pistons, but necessary on ours thanks to the piston pin bore protruding partially into the oil ring area. The piston pin must be located high up in these pistons because of the long stroke and long connecting rods being used in a stock-deck-height LS1 block.

The support holds the oil rings in place where there is no piston material beneath the rings (in the vicinity of the pin), but in order to function properly the gap in the support can't be anywhere near the piston pin area. Therefore, the support has a built-in dimple to prevent it from rotating around the piston, keeping the gap 90 degrees from the pin area at all times. This dimple must face away from the oil rings (i.e. downward, away from the face of the piston) or it will not be able to serve its purpose.

Piston rings differ greatly not only in material, but how the manufacturer wants them installed. For us, Lunati wanted the oil control expander (the wavy ring seen here) installed so its gap lined up with the centerline of the piston pin.

An oil rail then installs above the oil control expander and another installs below it (between the expander and the support). The gaps in these two oil rails need to be about an inch away from, and on opposite sides of, the piston pin. While every effort should be made not to scratch the piston during ring assembly, don't lose your lunch if you mark the upper part of the piston a bit; this area never really touches the cylinder walls (thanks to the rings). Rather, it's the skirt of the piston that takes the load.

Finally, the compression rings can be put on; these rings are the most stiff and will require the most effort to install. Orient these rings so that any dots or bevels face toward the top of the piston. Once in their grooves, the top and second rings will stick out a bit when done, this is normal; after all, you want them putting tension against the cylinder walls. The piston ring compressor will help get them into the bore. The part of the piston above the top compression ring is the "ring land" we mentioned earlier, and again, its thickness is important to piston strength and in shielding the top ring from heat.

After clocking the gaps in the top and second rings so they are about 180 degrees apart, the complete ring set is fully installed. You can see here the compression height (distance between the centerline of the pin and the face of the piston) that we discussed earlier in the story. Again, a decent size stroke has been coupled with a fairly long rod here, so these pistons have a 1.123-inch compression height. Consequently, the pin protrudes slightly into the oil ring area. The top compression ring (bottom of photo) is still kept a reasonably safe distance from the piston face, leaving adequate ring land for when things get hot in the combustion chamber during our moderate nitrous usage. And we'll still be able to enjoy the dividends of a good rod-to-stroke ratio.

We'll need to be turning the crank quite a bit in order to line up each rod journal with the particular cylinder we are working on at the moment. Not doing this would make it much more difficult to install the rod/piston assembly and would risk possibly scratching the crank. In addition, it will require more and more force to turn the crank as more and more pistons are installed, so we'll need some help. To get it, we first need to hammer the Lunati-provided crank keyway into the crank snout.