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GM’s fifth-generation small-block, the LT-series, is now 10 years old. Yep, you read that right, it has been a full 10 years since the first Corvettes, trucks, and SUVs started rolling off the assembly line and into the dealerships around the country with the most advanced small-block V8 GM has ever produced. While LT swaps started almost immediately, it was a few years before these engines could be found in salvage yards in any quantity. Today you might trip over a stack of LTs in any salvage yard you walk into. Not because there are a lot of inherent issues (there are a few), but rather because there have been millions built, sold, and wrecked.
Case in point, on one trip to Dallas last year, we picked up three LT-series engines. Two were running engines, one was “builder.” A running 5.3 L83 truck engine will set you back $1,500-$2,000, whereas the larger 6.2L L86 will run upwards of $4-6k, and an LT4 as a salvage or take-out engine will cost $10k or more. Builder engines can be had for $500-1500 depending on size, condition, and what they come with. Our 5.3 L83 builder cost us $500 and came as a long block. We didn’t know what was wrong with it but it was all there.
Gen V engines, just like their Gen III/IV counterparts, have a few issues that you need to be aware of when buying a takeout. The number one reason these engines fail are the lifters. Both standard and DOD lifters are failure prone, though the DOD lifters are the most common to fail. When you lose a lifter, you are going to get things like bent pushrods, broken rockers, and even a complete bottom-end rebuild in catastrophic scenarios. When the non-DOD lifters fail, as was the case in our 5.3 builder, the cam, cam bearings, crank, and rods are susceptible to serious damage.
Our 5.3 lost a non-DOD lifter, which smoked the cam and bearings, and then sent shrapnel through the entire oiling system. The worst of the damage outside of the cam was the crank. There were a few scratches on one crank main journal that were questionable as to whether it could be saved. After a few days at a local machine shop, the crank only needed some polishing to get the scratches out and it mic’d out within spec, so we don’t even need bigger bearings.
Another potential failure point on these engines is the intake valves. This is one of those things that is easily solved with proper maintenance, but most people who own direct-injection (DI) engines have no clue about the fact that ALL DI engines need an intake valve cleaner every other oil change. If you don’t do this, within 30k miles, the intake valves have significant carbon buildup on the stems. By 50k miles, it will not run well and can lead to total failure. Our 5.3 had this issue as well, and it had about 45-50k miles on it when it failed. It is possible the two issues were related.
When you start your teardown, don’t go into rebuilding an LT thinking it is the same as an LS, it isn’t. While the Gen V small block is a typical pushrod engine, there are several components that you may have never dealt with before, and very few parts interchange with LS engines. From the top of the engine, things are different. The fuel injection manifold is a hardline spider that lives under the intake. The high-pressure fuel pump (HPFP) is at the back of the engine on top of the valley cover. It passes through the cover and is actuated by a very large roller lifter that rides on the back of the camshaft. All Gen V engines are DOD/VVT designs, with the exception of the 6.2-liter LT5 and L8T 6.6-liter, so you won’t find a non-DOD 5.3 unless it has been modified. The front and rear covers are similar to the LS pieces, but they are different and will not interchange. The oil pan as well as the front and rear covers are bolted directly to the engine without gaskets, instead they use gray RTV. You will have to carefully pry them off.
The crank is Gen V only, but the rods are the same as the Gen IV with floating pins. Cam bearings are technically different, but when doing a rebuild, it is better to use third-design Gen IV cam bearings. The factory bearings are split-ring bearings, which can separate – buy one-piece bearings. The oil/water plugs (including the barbell) are the same as LS. The lifters are the same, as are the lifter cups (for Gen IV DOD), and the timing chain (NOT the gears).
Getting down to the block, there are a few things that you need to remove and not forget to reinstall – namely the piston squirters, which are located at the bottom of each cylinder. There is one for each piston. These need to be removed in order to properly clean the engine’s passages. It is always a good idea to deep clean any engine build, but when you know there was lots of metal moving through it, it is an absolute must.
This L83 is going into our 1962 Mercury Comet Wagon road racer, so we need it to be pretty stout. We have a pair of Precision Turbo 56mm turbos ready to go on it as well, with a plan to make 650 hp with 10 psi of boost. To get there, we could just run the stock guts, and be completely fine, but we want to build for the future. We opted for a set of Mahle’s PowerPak drop-in forged replacement pistons. These bad boys come ready to go, no balancing required, as they match the factory pistons perfectly, but are forged. They also have 1mm compression rings, which are insanely thin. This means very little cylinder wear and quick break-in on the rings.
We are also deleting the DOD and keeping the VVT. VVT can help you build big torque at the lower RPM range without doing anything but some tuning. There are many options for Gen V cams, but we opted to go the low-buck route with a stock GM LT5 camshaft. This cam has a boost-friendly design that doesn’t lose boost with overlap, and it has increased lift on the exhaust side to get the gasses out and flowing toward the turbos.
LT5 cam specs (PN 12664572, $150)
Because this is a 5.3, the valve springs are too short to handle the increased lift, so we ordered a set of L86/LT1/LT4 springs, which are single beehives and can handle the .551” of lift from the LT5 cam.
Outside of the cam, valve springs, and pistons, the rest of the internals are stock. We replaced anything that could have metal hidden away inside, including all the non-DOD lifters (the DOD units were already 86’d) and the oil pump. We used a new GM oil pump, new GM LS7 lifters, etc. GM uses a VVT-valve cam bolt, which is TTY and must be replaced, so we used a new one.
The cylinders were in excellent shape, there was no ring land wear, and the bores looked good. We used a 3-stone hone to break the glaze and put a nice crosshatch on the bores. A lot of people like dingle-berry hones, which are good, but they don’t show you if the cylinder bore is out of round or wavy because they follow the surface. A 3-stone hone will show you anywhere the stone isn’t touching, which is why we use them on basic rebuilds that are not being machined.
We stripped the engine down to the bare block, including all the galley plugs, barbell, and water jacket plugs. Then we soaked our engine brushes in diesel and got to scrubbing. You can use degreaser, hot soapy water, or have your parts hot tanked. We don’t have access to hot water in the shop, so we used diesel. Because diesel is a lightweight oil, it is very good at breaking down varnish and sludge without any harsh chemicals that can pit aluminum. Once we brushed out every single port and surface, we rolled it outside and used a pressure washer to blast it clean, blew it out with compressed air, and then sprayed the cylinders with WD-40 to protect them from flash rust. The connecting rods, bolts, and other parts being reused were cleaned in a bucket of diesel.
After cleaning, the block plugs were replaced with a Mr. Gasket block hardware set (61210G), and the oil squirters were reinstalled. This is not easily done once the crank is in, so now is the time. You do not want to forget them.
Before the rotating assembly could be started, we needed to file-fit the rings on the Mahle PowerPak Pistons. We used an old 5.3 LS piston to push each ring into the bore about 1.5”, checked the fit, then filed each one to the spec we chose. Mahle recommends a minimum of Bore X .006” on the compression rings and a minimum of .015” on the oil rings for boosted applications. We opted to go with .025” gap, which is .0066”. The 2nd compression ring was taken up to .027” so that combustion gasses can escape easily and minimize ring flutter.
Gen V pistons are much different from every other engine. The top of the piston has a large U-shaped chamber in the center. This is to help concentrate the flame kernel in the center of the chamber, keeping it away from the cylinder walls to reduce detonation. Our L83 has a static compression ratio of 11:1, detonation control is critical. This means that not only is there a front, but there is also a top to the piston, you can’t swap pistons bank to bank, there are two distinct piston layouts, four for the left bank, and four for the right. They are marked with an arrow to the front of the engine, but you need to pay attention to the orientation as they can be put in upside down. The pistons and rods use floating pins, but the rods are not chamfered as the crank does not have a radius, so direction does not matter on the rods.
Assembly of the short block is straightforward, much like any other engine. The original main cap bolts can be reused. If we switched to studs, then the block would have to be line honed, and we are not doing any machine work on a 50k-mile engine. The same goes for the rod bolts, but there is a caveat on them. The stock rod bolts are 3-times torqueable. Meaning you can re-torque them 3 times before they need to be replaced. This is the first rebuild, the original build counts as the first torqueing. Plenty of shade tree builders have reused them over and over, these are the exact same as LS rod bolts. We could swap them out for new bolts, but technically the rods should be honed if you are using new bolts. If we need to change rod bolts, you might as well just replace the rods altogether, because resizing cracked cap rods requires special bearings, and you only get one shot at it. The cost of resizing, new rods, and special bearings isn’t worth it when you can just get new rods.
The fresh short block will be topped with the original 5.3 heads for now, along with an MSD Atomic composite intake, and Hooker Mid-Mount accessory drive, and will be controlled via a Holley Terminator X ECM. The Atomic intake has the ability to add secondary fuel rails, which we will likely use once we get up past 500hp.
