The "gearhead" aftermarket gets a great deal of its business from the DIY crowd. Lots of guys (and girls) spend a lot of their hard earned money and a lot of their free time tinkering on a favorite car or truck. Many members of that same crowd entertain the thought of building their own engines at some point.
Building your own engine is a great way to learn about what's going on inside your favorite mill. Also, knowing that your mind went into the design and your hands were used for the assembly produces a great sense of accomplishment. If you happen to be a member of that crowd and want to start delving into the world of engine building, then this article (which will be continued next month) is aimed at you.
The foundation of every engine is the engine block, and a well-machined engine block isn't anything without some strength behind it. A strong engine block isn't anything without precision machine work. You have to have a block that's strong enough to hold the horsepower and rpm that you have planned, and you have to have the machine work to support the game plan. There are two choices when it comes to block options: factory and aftermarket. We don't have the time to go into each Ford engine family and discuss every single strength and weakness, but we can offer some basic rules on block strength though.
1. Don't always assume that a factory four-bolt-main block is stronger than a factory two-bolt-main block.
2. Don't always assume that a main girdle will give a block magical powers. Girdles can help with main cap walk on milder applications, but beyond that, they usually just hold the pieces together when the block explodes. We've seen 302 blocks split in half (literally) with the three middle main caps neatly tied together.
3. For factory 302s, we usually draw the horsepower line at around 450-500 hp. These blocks are really weak between the cam tunnel and main cap areas. As stated above, they will literally split right down the middle. They don't run well like that. The production 351W blocks will generally hang in there a little longer and we've seen them survive well in 550-600hp applications.
4. Watch out for cylinder wall thicknesses on the Cleveland blocks. It's not uncommon to do a sonic test and find some thrust wall thicknesses that would make you scared to bore the block 0.030-inch over. A sonic test any time you plan a Cleveland build is money well spent just to see where you stand.
5. The factory big-blocks (FEs and 385 series) will handle a decent amount of horsepower. The FEs can gain strength by adding a girdle (little more effective here since the blocks are skirted and most girdles attach to both the main caps and the oil pan rails) or by adding cross-bolted main caps. Even then, they are still susceptible to cracks in between the cam tunnel and the mains. The 385 series blocks (429s, 460s, and so on) will handle a very large amount of horsepower and it's not uncommon to see them as foundations for 700-800hp engine builds.
If you're planning a build and you're on the fence as to whether or not the block is capable of handling the stresses, it may be wise to go ahead and ante up the money for an aftermarket block. The horsepower numbers that we've quoted up above are not set in stone. We've seen 302 blocks split at 450 hp and seen others take 600 hp religiously. Your results may vary, so use your own discretion and judgment.
1. Cleaning your block is...
1. Cleaning your block is extremely important. After the block is machined, the machinist will throw the block into their “dishwasher” to clean off all honing oil, shavings, and so on. It’s also a good idea to rewash your block when you get ready to assemble. Scrub it with hot, soapy water and use bore brushes on all lifter bores, oil passages, and so on. Any stray piece of dirt/metal can find its way into the oil pump and be pumped into the bearing surfaces. You can also use an air hose to clean out the smaller areas such as the main and cam bearing oil feeds.
2. "Decking" the block is...
2. "Decking" the block is necessary for several reasons, one of which is to provide a perfectly clean, machined surface for the head gasket to seal against. Factory blocks have quite loose tolerances; and uneven deck surfaces can lead to blown head gaskets, coolant leaks, and more.
3. Some surfacing machines...
3. Some surfacing machines allow the block to be “square decked.” This ensures that both decks are perfectly parallel to the crankshaft centerline. If not, you could have one piston at 0.005-inch in the hole and the piston on the other end of the deck could be 0.015-inch in the hole.
4 The next step is preparing...
4 The next step is preparing the cylinders. With some blocks, a cylinder hone can make sure the cylinders are straight and the cylinder finish is conducive for ring seal. However, if the cylinders have a lot of taper, gouges, and so on, the block will need to be bored. this provides a rough cylinder finish (usually within 0.005- to 0.010-inch of the desired finish bore size). Before boring, it’s best to check the current bore size to make sure that the block can be reused. a thin cylinder wall can cause block integrity issues.
Fortunately, the aftermarket has provided us with a very nice selection of engine blocks for performance builds. For the Windsor crowd, there are blocks available from Ford Racing, Dart, and some others. Most of these blocks are available in either cast iron or aluminum, and offer excellent strength for big power builds, arriving with billet four-bolt-main caps and extra thick siamese cylinders. The 351W-based blocks are available with the Cleveland (2.750-inch) main bearing size. This brings the best of both worlds, the Windsor deck height (allows for big stroke) and the smaller main bearing size of the Cleveland.
The big-block guys aren't left out in the cold here either. For the 460 fans, Ford Racing has a couple of blocks available, with one being offered in a 4.600-inch bore size. With a 4.500-inch crankshaft, you can essentially squeak your way up to the 600-plus-cubic-inch- displacement range (4.625x4.500).
Genesis, Pond, and Shelby are your manufacturers for aftermarket FE blocks. Most of these are available with larger bore sizes as well, which allow displacements well into the 500ci region. Genesis and Robert Pond offer their blocks in either cast-iron or aluminum. You'll pay a higher premium for aftermarket blocks, but the up side is that you won't have to grit your teeth every time you step on the loud pedal. All of these blocks will hold a substantial amount of horsepower.
Once you've decided on the block requirements for your engine build, you will need to have it prepped and machined. If it's a factory block, then it would be beneficial to have the block checked out before you put a decent amount of money into machining it. Several key areas need to be examined first:
1. Obviously, the block needs to be inspected for apparent flaws: "windows" in the block, broken bellhousing bolt bosses, major cracks, and more.
2. The block bore needs to be measured. There's no use in taking a block to a machinist to have it bored if it's already been bored past the "comfort zone." For example, if you have a 351W block that's already at 0.060-inch overbore and it will need to be bored further to straighten the cylinders, then this would be a block that should be passed on. If you're concerned about how far you can go on a particular core, then the sonic test would be your best bet to get an accurate map.
3. Once you check those first two tasks off your list, then it's wise to have the block pressure tested and Magnafluxed. Pressure testing will ensure that there are no internal cracks or areas where the block can leak. Magnafluxing will take care of the areas that can crack but have no fluid pressure behind them (main caps, main journals, and so on).
After the block has passed all inspections, then it's time to have it machined. Let's go over what's deemed necessary for a "detailed" block machining process:
Bore & Hone: A block needs to be bored to get rid of any straightness issues in the bores, to get rid of any cylinder flaws, and to roughly prep the engine for the new pistons. I generally recommend to only bore the minimal amount needed. It's unnecessary to take 0.060-inch out of a cylinder wall, when a 0.020-inch cleanup would suffice. Adding bore doesn't add that much to the displacement of the engine. I've heard many guys boast that their engine block is "bored to capacity." This isn't really something to boast about, as they've only added 5-10 cubic inches and they've got extra thin cylinder walls now.
Following a bore, the cylinders have to be honed. Boring a block will not put the finish on a cylinder that is necessary for proper ring seal and wear. To hone a block, torque plates are bolted to the deck surface to simulate the clamping force of the cylinder heads and fasteners, and a series of honing stones are used to put a final size on the bore and to put a "cross-hatch" on the cylinders.
4a. Depending on the machine...
4a. Depending on the machine shop and its equipment, cylinders can be bored square to the deck surface, or as is the case with this small-block here, the cylinders are bored 90 degrees from each other, and 45 degrees off the cam/crank centerlines. d.s.s. racing (st. charles, illinois) machines all of its blocks in this manner as it improves cam timing accuracy, and improves the efficiency of the engine as a whole. a V-8 engine is really comprised of eight, single- cylinder engines. they must be as close to equal to each other in compression, cam timing, geometry, ignition timing, fuel curve, and more for maximum output.
5. A cylinder honing machine...
5. A cylinder honing machine is used to give the cylinder bore a final size and finish. A boring bar is used as a rough cut, but a honing machine will finish the cylinder bore the last few thousandths of an inch. Lots of honing oil is used in combination with a stroking motion to put a nice cross-hatch pattern in the cylinder, which helps with ring seal and oil control. This block is being honed with a torque plate. The plate is bolted to the block to simulate the stresses put on the block by the cylinder head. If not used, then you may have a different shaped bore when the engine is actually running, which could cause irregular wear patterns.
6. Here we see the machinist...
6. Here we see the machinist measuring the main bores before line honing. Just like cylinder honing, the main bore housings must be honed to size and made sure that they are straight. Any time a different fastener is introduced to the mains (main studs, different bolts, main girdles, and so on), it’s best to have the block at least checked, if not honed. A nice, straight main housing allows the rotating assembly to turn much easier and not irregularly wear the main bearings.
7. A fresh, correctly machined...
7. A fresh, correctly machined block should be the basis for every engine build. When choosing pistons, you’ll need to account for the piston depth in the block, as it affects compression ratio and piston-to-valve clearance, among other things.
When you use studs, the whole length of the threaded portion in the block is used. This could slightly distort the block, which in turn distorts the main journals themselves. This is also the case when main cap girdles are installed. Even when not using studs or girdles, it's a good idea to have your block's mains checked for straightness. A discrepancy here could throw out main bearing clearances or cause some unnecessary rotating drag on your crankshaft.
Square Decking: There is a difference between decking a block and square decking a block. When you deck a block, you basically remove some material to make sure the deck is flat and straight. When you square deck a block, you ensure that the deck surfaces are equally parallel to the crankshaft centerline. When this is accomplished, then each piston should nominally come up to the same deck height on each cylinder. If this is not accomplished, then you may find that your block can be up to 0.015- to 0.020-inch tall/short depending on the particular cylinder. How good would it be to have one piston at zero deck height and another piston 0.010-inch down in the hole?
As an added note here, when you square deck a block, you can specify where you want the pistons to be in relation to the deck. As my own general rule, I try to get the pistons around 0.005-inch below deck up to zero deck (where the pistons are basically flush with the deck surface). With a 0.040-inch gasket thickness, this will give a 0.040- to 0.045-inch quench distance. Any quality machine shop will have a fixture that will allow it to machine the block to this spec.
How do you determine what deck height you will need? Add your rod length, half your stroke, and your piston compression height together. Take, for example, a 347ci small-block. This is a pretty common combination and in this case we have:
5.400-inch rod length + (3.400-inch stroke/2) + 1.090-inch compression height = 8.190 inches
If we wanted the pistons to sit approximately 0.005-inch in the hole, then we would need a 8.195-inch deck height on the block.
You've probably already picked up on the fact that before you have your machine work done, you need to know (or have a really good idea on) which rotating assembly parts you're going to use.
Quality machine work is imperative for a quality engine build. Sure, you may be able to get away with running a brush hone through the cylinders, knocking some new cam bearings in, shooting some rattle-can paint at it and calling it a day. However, the more detail you place here, the more you will be rewarded; not only in assembly, but also in performance. This is the foundation and basis for the entire engine build. Money spent here is very well spent.
For the next installment of Power Principles, we'll concentrate on picking out cylinder heads, camshafts, and intake. The engine block is the foundation, but a well-designed and well-built engine relies on a clear, concise plan of attack, and a well-matched set of induction components that can move the air and fuel as efficiently as possible into and out of the cylinders.
8. A dial indicator, in combination...
8. A dial indicator, in combination with a straight edge and feeler gauge, can be used to see how far below (or above) deck the pistons are. This is an important dimension to have for your compression ratio calculations.
9. The forces that the reciprocating...
9. The forces that the reciprocating assembly can exert on the block can sometimes overwhelm the main bearing caps and the fasteners that hold them in place. Under heavy loads, the caps can shift or “walk” from side to side. This movement can then cause the threads of the fasteners to become fatigued. Eventually, the main web cracks, leading to a loss in oil pressure and possibly catastrophic damage to the block and rotating assembly. While aftermarket blocks often utilize splayed four-bolt main caps to combat this, not everyone has the budget to buy one. Main cap girdles, such as the D.S.S. Main Support System pictured here, are a cost-effective way to add strength to a production block. While some girdles are made from steel, the D.S.S. piece is made from billet 6061-T6 aluminum to effectively dampen damaging harmonics, which the company says virtually eliminates main bearing walk.
10. The aftermarket keeps...
10. The aftermarket keeps the Ford enthusiast bathed in a variety of new parts. This is one of Ford Racing’s engine blocks, the Boss 302, which offers a much higher limit for cubic inches and horsepower ratings. Combining the block’s 4.125-inch bore with a 3.400-inch stroke crankshaft can give 364 cubic inches of life back to your 302-powered vehicle.