LS-based engines have proven themselves worthy time and time again as the king of the modern junkyard engines. You’ve heard the wild tales of the immense horsepower these mills can make straight out of the boneyard, but there are some steps you should take if you want one of these engines to last.
If you want to build a truly reliable LS-based engine from a junkyard, you’ll need to take the parts to a machine shop for inspection and proper prep. Sure, there are people out there who’ve done some amazing things with these engines without going to a machine shop, but that’s a big risk. These engines have been through a lifetime of use before a high-performance enthusiast harvests them for a project.
If you don't have these types of machines in your home shop, chances are you're not going to be able to truly prepare an engine properly for assembly. 
We took the 5.3 aluminum LS block, OEM 243 casting cylinder heads, and Summit Racing’s Summit Pro LS rotating assembly for Project Swedish Meatball to Craig Haslem at RPM Engine and Machine so it could be prepared for assembly. In this article, we’re going to cover why it’s a good idea to take your junkyard treasures to a machine shop before you start throwing all the boost at them.
Block Party
The engine block is the foundation of the build, so you need to make sure the foundation is solid before you begin. A junkyard engine block can hide plenty of problems under grime and rust. The first thing a shop is going to do is deep clean a block so it can properly inspect it. The shop is going to look for cracks, bad bolt holes, and threads that need help.
Our block was dirtbag dirty before Craig worked his magic to make it look better-than-new. 
Being precise prevents problems. Haslem explains why a shop is better equipped to do these tasks the right way.
“You could do the old eyeball test at home after cleaning the block up, but that doesn’t guarantee you’ll catch everything. At the shop, we are going to be able to make sure every surface is perfectly flat and all of the holes are problem-free. What happens if you do find a problem with the block at home? Most people just don’t have the right equipment to correct issues like resizing cylinder bores and so on.”
After the block has been properly cleaned, the shop can look it over for any issues. The shop will then make sure all the holes are ready for fresh hardware and also get the mains ready for machine work. 
When you instruct the shop to really go through the block and make sure it’s ready, it will actually save you time and money. This includes working on cylinder bores to ensure they are true, and line honing the block with its new main studs— a requirement when switching from bolts to studs. By having the shop go through these processes, it’s going to correct any problems that would be missed if you just slapped the engine together at home with minimal machine work.
The block needs to be squared up and smoothed over in all the right places before assembly can begin. 
“If you just put an engine together at home without having it properly machined there could be a lot of X-factors in play, like how flat a surface is, or how round a cylinder bore is. If you’re not working with a block that’s square and ready, you’ll be running a risk of there being sealing issues. You don’t want to be chasing head gasket and ring issues because you didn’t opt to have the block prepared the right way,” Haslem says.
So remember, a junkyard block isn’t going to openly confess all of its problems to you. A machine shop is going to not only catch the problems you miss upon initial inspection, but they can fix them the right way the first time. An ounce of prevention is worth the cost if its going to save you tons of headaches later during an engine build.
A good shop will make sure your parts are as clean as possible before they begin any work.
Head Games
OEM LS cylinder heads are known for providing plenty of flow for boosted applications. The 243 casting heads are highly sought after because of how much air they flow, and how well they respond to basic port work. The set we scored were minty fresh off a Z06 with low miles, but that didn’t mean we weren’t going to have Haslem inspect them.
When we dropped our heads off, they were stripped down, hot tanked, and inspected before they were media blasted. The best canvas to paint on is one that is not only blank, but clean and ready for anything.
“A shop is going to inspect the heads and check all the guides out. The clearances need to be looked at so they can be confirmed to be within factory specs. Those guides need to be straight and round, you just don’t know what a set of used heads have been through, especially if you found them in a wrecking yard. It’s better to catch a guide that’s damaged or out of spec now, rather than later when it’s already done some damage,” Haslem states.
As you can see, our heads needed plenty of work to get them ready for prime time on our engine. 
Most DIY folks can clean up a set of heads at home with a little bit of elbow grease. You might even feel comfortable enough to chase any bolt holes that need some attention too. But, a machine shop can cut valve seats, grind valves if needed, and resurface the head to make it as flat as possible. The machine shop is also going to find any issues that you’d miss at home.
This is the final product after a set of heads are gone through at a machine shop.
“The home builder is going to pull the heads apart and put some fresh valve springs on, no problem. They might even do a wiggle test on the valve to see if they feel okay, but that’s only going to take you so far. Having a shop go through a set of heads is going to increase the engine’s longevity, and prevent bad things from happening at an inopportune time,” Haslem says.
Cylinder heads are the lungs of an engine and they need to be healthy if you want it to breathe deep. Boosted applications rely on the heads to move enough air for maximum horsepower. So having your heads serviced by the machine shop will help them do their job at the highest possible level.
This new Summit Pro LS rotating assembly may look ready to install, but it still needs to be balanced before it’s added to our engine.
Rotating Assemblies Done Right
The OEM rotating assembly inside LS engines can handle a fair amount of boost. If you’re going to really push for a lot of horsepower, or want something that will last, an aftermarket forged rotating assembly Is the way to go. Chances are that if you’ve already made the choice to have your block and heads serviced at a machine shop, a new rotating assembly is going to be used.
The rotating assembly needs to be balanced, and a professional machine shop is the best place to have this done. A balancing job is pretty standard, but when you start introducing heavy-duty aftermarket parts the shop will have to apply a precise plan of attack.
There's a lot that goes into making sure a rotating assembly is balanced correctly. 
“The only thing that really starts to change thing in the balancing world is when customers are going with heavier parts. Thicker piston walls, and heavier connecting rods for large boosted applications. It’s the 15-to-30-pound boost range that adds a different factor in the balancing requirements because you have to compensate for that additional weight of rotating assembly. That means you have to add that weight to the crankshaft to get things right. I like my balance jobs to be within a couple of tenths of a gram,” Haslem explains.
Remember, there’s nothing wrong with taking the time to build an engine at home, that’s what makes the hobby of horsepower so much fun. Where you can get into trouble is if you take a junkyard engine and start really putting the boosted beans to it without the right machine work. If you spend the extra time and money to have the bones of your boosted LS build looked over and machined at a shop, you’ll be able to enjoy all the horsepower it can offer for a long time.
