Block Talk: Having An Engine Block Machined For A Build

There are countless engine combinations that an enthusiast can build. But every one of them has the same thing in common, they require an engine block. It doesn’t matter if you’re using an engine block that came out of a vehicle, a fresh OEM block, or an aftermarket block, they all need prep work. We talk with Jack McInnis from World Products to learn the advantages of aftermarket blocks, and what goes into preparing an engine block for a build.

Advantages Of Aftermarket Blocks

OEM blocks have come a long way and modern blocks can hold a lot of horsepower. That said, these blocks are still mass-produced, and are limited to how much horsepower they can deal with before they fail. An OEM block is manufactured in the most efficient and cost-effective way possible, so there are rarely any running changes made to increase their strength or the amount of horsepower they can handle.

Aftermarket blocks are highly refined compared to the OEM blocks they're based on.

Now, aftermarket blocks are a whole different story. These blocks are designed to deal with more horsepower than their OEM cousins.

“Years of racing and hot-rodding experience have done a good job of demonstrating where the weak points are in OEM blocks when used for high-performance applications. Proper high-performance aftermarket blocks are engineered and built to eliminate those weak points. These blocks also add new features which are beneficial to racers and engine builders,” McInnis says.

There’s significantly less machine work required to get an aftermarket block ready. – Jack McInnis

If you’re thinking about investing in an aftermarket block instead of using an OEM block but are questioning the cost, you need to look at the value an aftermarket block provides. There are a lot of OEM blocks still available for you to use, but it’s getting harder to find blocks that are in usable condition. There’s no telling how many times a block has been worked over unless you have the right tools to check it before you purchase it.

“You can buy a used engine, spend the time and money to tear it down, have it cleaned and machined, only to find that it has cracks or the cylinders have already been bored beyond their safe capacity. If it’s determined to be sound, it will require quite a bit of machine work before it’s ready for use. Investing in a new aftermarket block assures you that there is no hidden damage from previous abuse, most of the machine work is already done for you, and there is plenty of material available for future rebuilds,” McInnis explains.

The aftermarket block is going to provide you with an increased amount of strength and durability. Racers are really good at tearing stuff up, and the engineers at each company that make aftermarket blocks have used the results to build better blocks. Aftermarket blocks will have more material in high-stress areas, an improved main cap retention design, a better oiling system, and numerous other upgrades. These blocks will also be cast from a higher grade material for greater tensile strength and improved fatigue-fighting characteristics.

Aftermarket block companies put a huge amount of thought into the designs of these blocks to maximize their strength.

Aftermarket blocks are created from a blank slate, therefore, a lot of enhanced features can be added before production begins.

“These blocks will have thick cylinder walls, which means they can be bored and stroked to large cubic inch displacements far greater than their OEM counterparts are capable of. Thick decks and the capacity for extra head bolts provide security for the high cylinder pressures associated with superchargers, turbos, or nitrous. Provisions for larger camshafts, lifters, dry-sump oiling, and other features give engine builders the opportunity to explore new ideas, and create extremely powerful engines that are reliable,” McInnis says.

OEM Block Prep  

There are still plenty of people making lots of horsepower with OEM blocks. Many modern OEM units can hold well over 1,000 horsepower when the right parts are used. This can be achieved with a block that came out of a junkyard, or with a fresh OEM block that can be purchased from a retailer.

An OEM block is going to require more prep work than an aftermarket block. The first thing you need to do is talk with your engine builder about what your goals and expectations are, that way they can let you know what will need to be done to the block. Both a used OEM block and a new one will need similar work done before the engine build can begin.

OEM engine blocks need a good bath before the machining process can begin.

If you’re going to use a block that came out of a vehicle, the first thing a machine shop will do to prepare it for a build is strip it down and give it a good cleaning. That means every fastener, freeze plug, and dowel is going to come out so all contaminants can be removed. When the block is cleaned, it needs to be examined for any damage and should be magnafluxed to make sure it’s structurally sound.

Lance Stillwell at Motorsports Unlimited has built plenty of high-horsepower engines that were based on OEM and aftermarket blocks. Stillwell provides some insight into how OEM blocks are prepared at Motorsports Unlimited.

“First, we chase all the threaded holes with a tap to clean up the threads. Then, the block goes on the mill to cut clearance for the crank and rods if it’s a stroker application. The main caps are then re-fitted using new studs or bolts. After that, the block goes to the line hone to true up the mains. The cam journals will also be line honed. This is important in stock blocks because in manufacturing, it’s common for the cam tunnel to be out of true with the mains, known as cam sway. This can cause issues including premature camshaft wear, especially with flat tappet cams,” Stillwell explains.

The machine work required to get an OEM block ready for a high-performance build can be intense. The machine shop has to really massage the block to ensure that everything is squared up and ready for assembly.

These are just the first steps that need to be completed when an OEM block is being prepared for a build. The lifter bores will also need to be examined and honed to make sure they’re true. Each deck of the block will need to be milled to ensure that it’s square with the cam and crankshaft. This will usually require a .010-inch cut, or possibly more, depending on the required deck height.

“After the block has been decked, we’ll turn our attention to the cylinders. They will be bored to achieve the desired size for the combination and to square them up to the decks. Often, a previous re-bore has left them out of square. The cylinders are then honed with a torque plate to suit the pistons and rings that are going to be used. Finally, we deburr the block to remove sharp edges, which can damage parts during assembly. After that’s done, the block is ready for a final wash and work can begin,” Stillwell says.

Aftermarket Block Prep 

One of the nice things about an aftermarket block is the amount of time and money that will be saved on preparing the block for machining. The machine shop will need to thoroughly clean the block after it arrives to remove all the rust inhibitors. After that’s done, along with a quick visual inspection, the block is ready for machine work to start.

Aftermarket blocks arrive at the machine shop in much better shape than an OEM block. Everything is much closer to being ready for assembly and the block will only require finishing machine work.

The quality control on an aftermarket block is going to be significantly higher than an OEM block. The elevated level of quality means the machine shop won’t have to go through the same machine processes it does with an OEM block to make sure it’s squared up. An aftermarket block can be ordered with a specific bore size, thus removing the need for the machine shop to bore the block. This again saves time and money since the machine shop will only need to finish hone the block to work with your ring and piston package. The lifter bores will also need some attention from the hone since they’ll need to be machined to fit the lifters you’re going to use.

“Depending on the specification of the build, and the individual components used, the builder may choose to do various machining processes to get the block ready. The decks come finished and ready for assembly but may require milling to achieve the desired dimension for the rotating assembly. Many builders like to mill the decks as a matter of routine in their process. You’ll also see builders prefer to line-hone the mains as part of their process. This helps to improve heat transfer from the bearings,” McInnis states.

Years of racing and hot-rodding experience have done a good job of demonstrating where the weak points are in OEM blocks when used for high-performance applications. – Jack McInnis, PBM/World Products

As we mentioned earlier, an OEM block will need to be clearanced if you’re building a stroker engine. World Products offers its blocks with those clearances cast into them. This added feature of an aftermarket block will save you time and money at the machine shop.

The aftermarket blocks need to be machined for the specific build they're going to be used for. That usually only requires cylinders to be cleaned up for rings, light honing, and adjustments for deck height.

“There’s significantly less machine work required to get an aftermarket block ready. You still need to deburr everything to prevent damage to the engine’s internal components during assembly. When that’s done, the machine shop will clean the block so they can start the mock-up process to check all the clearances for the moving components of the engine,” McInnis explains.

So, is it worth the extra money to buy an aftermarket block for a build? According to Stillwell, the cost of the additional machine work an OEM block needs can add up quickly when compared to an aftermarket block.

“The cost to prep an aftermarket block like you can get from World will usually run around $500-$700 depending on which shop you go to. That’s roughly about eight hours of machine time. For our shop, the base cost to machine an OEM block will be around $1,000. That includes a thermal clean, magnaflux, chasing of the threads, an align hone, squaring the deck, bore and torque plate hone, installing the cam bearings, and freeze plugs. You’d then have additional costs for the plug kit, main studs, and main caps. If you want clearance work for a stroker motor, lifter bore correction, or installation of billet main caps that will cost you more, too.” 

As you can see, there’s a lot of work that needs to go into any engine block to prepare it for a build. An OEM block is still a great choice for those who are on a budget but want to make good power. The aftermarket block will certainly provide more strength and save money on machine work, but it comes at a higher initial cost. Either way, it’s important to make sure your engine block is properly prepared by the machine shop before assembly can begin.

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About the author

Brian Wagner

Spending his childhood at different race tracks around Ohio with his family’s 1967 Nova, Brian developed a true love for drag racing. When Brian is not writing, you can find him at the track as a crew chief, doing freelance photography, or beating on his nitrous-fed 2000 Trans Am.
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