If you are starting with a used block, the very first step is to qualify your candidate and make sure it’s sound for the build-up process. Each step in this process is intended to eliminate any problems before they are found—before wasting money on an unusable block.
Do a rough bore measurement. With very rare exception the FE family is noted for fairly thin cylinderwall thicknesses, so it is best to keep the overboring at a minimum. On any 390 or 428 block, I prefer to stay at .030- or .040-inch over when feasible, and to avoid going much larger unless it’s required.
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Since 390 blocks are relatively inexpensive, it’s usually easy to find a standard bore of .030-inch over (4.080) one to start from. Unless you are in a “numbers matching” situation, a rough or larger overbored 390 block should be simply replaced. Some online marketers make a business of boring 390 blocks .080-inch over and calling them standardbore 428s. This should be avoided in the vast majority of cases (more on this later).
On 428 blocks, the game is a bit different because they are much harder to come by. I have been able to use a program from Diamond pistonsto go larger in very small increments, .025-, .035-, or .045-inch over. Couple this with the readily available .030- and .040-inch-over pistons and you have lot of options. Again, the best strategy by far is to keep bore diameter to a minimum. You lose a lot more power due to poor cylinder sealing than you can possibly gain in cubic inches.
On the most valuable 427s, it’s best to stay as close to the original bore as possible. These are the thinnest-wall FE blocks, and yet they see the hardest use. It is very common for the first oversize to be 4.250—.017-inch over. After that, builders often use a custom piston to keep material removal to the bare minimum. In the context of a 427 build, the added expense of the custom piston is modest.
Now do a quick physical inspection. Look for the obvious. FE engines are noted for cracks in the deck running into the head bolt holes, and they sometimes crack in the main oiling galleys running up to the cam. I’ve seen some that had cracks at the root of the main bolts, and plenty with freeze damage in the lifter valley area. Stripped-out head bolt holes are not unusual. Weldedshut “windows” from thrown rods in the pan rail area are common in old race 427s. Any of these probably relegates a 390 to the scrap pile, but even a badly broken 427 gets fixed almost without exception.
If you have found a block with a decently modest bore size and no visible major flaws, it’s time to get started. My shop preference is a bake/media blast/wash cleaning process that leaves an old block looking like a new casting. Other shops use other methods. No matter how, you must get the block as clean as possible. Run a cleaning tap into all of the threaded holes (this is not the same as a threading tap, which removes more material). Once 40 years of grime and scale are removed you might see flaws that were previously invisible. You need the water jackets really clean in order to perform the next step—a sonic test.
A sonic test is not mandatory, but is a very good investment (around $100) that can help define your build strategy for a marginal block. An inexpensive 390 block that is at standard bore or .030-inch over won’t likely get a sonic test, but it should be budgeted as part of every expensive build or for an older 427.
Done properly, a sonic test delivers a map of each cylinder at several spots around the bore and in multiple positions up and down the cylinder. A dozen measurements per cylinder are common. The sonic tester uses sound waves to get a thickness reading and requires the user to properly calibrate the device and to use the right contact probe. It reads rust and scale as well as iron; that’s why things have to be cleaned first.
If you have done a drill-bit test earlier in your qualification process, you have the data to cross check the sonic measurements for accuracy. The FE engine has 4.630-inch bore centers. If the cylinder bores are at 4.250 inches, and there is .140 inch (9/64 inch) measured between the cylinder cores, it would be physically impossible for the added wall thicknesses of the two adjoining cylinders to exceed .240 inch. If the readings show otherwise—like .135 inch and .130 inch—you know they are wrong and need to be redone.
A sonic reading that shows a wall thickness below .100 inch is cause for some concern. Any reading below .090 inch is getting to the low safe limits. The location of the thin spots should determine whether or not to use the block. A thin wall low on the cylinder is not going to see as much cylinder pressure or heat. However, a thin section in the middle of the cylinder is an opportunity for failure because the heat levels are the highest, flex is the greatest, and support the lowest. And likewise, those online auction blocks with “standard-bore 428s” created from .080-inch over 390 blocks are going to fail in this same area. On the highdollar 427 blocks that come in thin at the bottom of the bore, I often use a short pour of block filler in the water jackets (an inch or so) before machining commences, to provide some extra support to the bores.
This is something that needs to be checked before engine machining, but almost never is. You won’t have a problem with most FE combinations, but a couple can “catch you.” The exhaust valve on an FE is closer to the cylinder bore than the intake, so a larger exhaust—like 1.710 inch or bigger—hits the bore on a 390-based engine. Some of the more uncommon 427 heads (tunnel ports and high-risers) had 2.250- inch intakes and 1.750 inches installed; these sometimes hit on a 428 or a standard-bore 427. In any case, the bores can be notched for clearance as long as you keep the notch above the “ring belt” where the piston rings travel.
Machining the Block
After cleaning, checking, and qualifying the chosen block, the machining process can finally begin. Because it is 30 to 40 years old, it’s best to assume that your block is going to need the full treatment, which includes boring, honing, decking, and line honing. A superbudget 390 build might get away with just a hone job, but this book is about “Max Performance.”
Every shop is going to have its own sequence of doing things, and it can change based on the type of build being performed. One example is the decking operation. While a street engine gets a straightforward parallel deck job based on getting both sides even and square, a race block gets decked after test installing the rotating components and measuring actual deck clearance against the desired value. What matters is being certain that each operation is done properly and is not adversely affected by subsequent work.
Bore and Hone—Cylinder Prep
For this project, cylinder prep is oriented around the use of the exceedingly popular plasma-moly facing on a ductile-iron top-ring combination. These parameters have been repeatedly proven in countless street, track, and production applications. While it’s entirely possible for a certain unique finish to have a benefit in a certain unique application, the honing techniques, measurements, and processes described will get you very close every time.
Boring and honing is best done with a torque plate. While plenty of engines are assembled and run fine without one, this is one area where added effort and expense show real benefits. Piston-ring seal is a critical factor for effectively building horsepower, and the FE engine with its thin-wall casting, shows significant bore distortion from the head fasteners. When installing the torque plate, be certain to use the same torque values, type of fastener, and head gasket that will be installed in the engine because each type loads and distorts the cylinders a bit differently. Head bolts tend to pull “up” on the block’s upper threads while studs more evenly distribute tightening stress. Wire ring reinforced-style head gaskets try to bend the head and block around the sealing element, while multi-layersteel (MLS) gaskets do not have such highly concentrated local loads. Therefore, the MLS gaskets are a better option. Therefore, the MLS gaskets are a better option. Since the whole idea of a torque plate is to get a round cylinder under installed conditions, you should use one to eliminate as many variables as possible.
Rough boring should take you within .010 inch of the desired finished cylinder diameter, and not any closer than .003 inch. This leaves enough material for the honing operation to develop a good surface finish. The OEM vehicle and pistonring manufacturers have literally written books about cylinder-wallpreparation techniques and topography. With piston-ring seal being critical to performance, I cover it in a general “industry standard” fashion here—with a strong recommendation to consult your ring supplier’s documentation for added detail.
The desired cylinder finish has thousands of minute cross-hatched scratches surrounding diamondshaped plateaus of smooth metal. The concept is that the scratches actas reservoirs for oil—needed for lubrication and sealing—while the smooth plateaus act as the loadbearing and sealing surfaces.
I specify a power hone, such as the Sunnen CV-616, and like to use a traditional vitreous stone for honing, rather than diamond stones. The diamonds are faster and cost less in production use. With the correct control and processes, they can work very well. But diamond stones tend to tear and fracture the metal on a microscopic level; they do not provide as controlled a surface finish in a performance-shop environment. The vitreous stones down during use and constantly present new sharp cutting edges, delivering a clean and repeatable cylinder finish as a result.
The first sizing pass on my cylinders is done with a fairly coarse (around 280) grit. Within .0005 inch of the desired diameter, severa strokes with a 400-grit hone follow so that the highest spots from the first stones are leveled out and plateaus are developed. I finish with a few strokes of a hone-mounted brush, which serves as a cleaner and removes any torn or folded metal. On occasion I may tweak this process by changing grit, speed, or load, or by polishing the finished bore with some 600 wet/dry paper wrapped around the hone, but this basic procedure gets 90+ percent of the engines to where they need to be.
I don’t advocate a completely polished or mirror-like cylinder-wall finish. Inadequate scratch depth or area does not give the oil scraped off by the rings any place to go, and the rings can then hydroplane on the resultant thicker oil film. Oil control issues can result, that in turn permit contamination of the combustion area.
Profilometers and fax film are a couple more sophisticated measurement tools used in the high-end racing and developmental environments, and are rarely seen in the average or even above-average shop. However, knowing that they are available can be helpful when confronted with a ring sealing problem or the need to try something new.
A profilometer can be used to generate a series of measurements that quantify the cylinder’s surface by defining the average roughness of the surface (rk), the depth of the scratches (rpk), and the volume of the scratches as a percentage of the overall surface area (rvk). The basic roughness number is referenced most often yet is the least informative because it is a simple average— you can get the same number from a very deeply scratched surface as from a shallow scratched surface if the high and low portions are of the same percentage. The volume number is most useful because it quantifies the plateau area against the scratches/voids, which are necessary parts of the cylinder-finish equation.
Fax film is dissolved acetate, applied to the finished cylinder bore. Once dried, the acetate can be carefully peeled off to provide a direct imprint of the finish, which is then examined under a microscope. This non-destructive test can quickly pinpoint torn metal, one-way hone scratches, and other issues that may be otherwise invisible. The fax film shows the difference between a diamond hone and a vitreous hone finish in an instant. At the proverbial “end of the day,” a lot of research and experimentation has proven that the long-accepted honing techniques are actually pretty darn good. Sometimes old ideas and methods were the right ones.
Line Honing or Boring
With a 30- to 40-year-old block, it’s best to assume that everything needs service. Line honing—the establishment of straight, round main-bearing bores that have the correct diametrical is one of those service items. The main bores have a tendency to distort after use, and the proper alignment and diameter are critical factors in bearing durability.
In a similar manner, most new blocks are machined in fixtures that do not permit sizing the main tunnel in a single pass. This means that the machine has to come first from one end of the block for three of the main saddles, and then from the other end for the final pair. Some degree of misalignment is an inherent risk.
The method for checking main bearing tunnel geometry is twofold. First is a check for alignment using a precise dowel rod and feeler gauges to check for variations in the main saddle’s position relative to each other. Once this has been determined, I then use a dial bore gauge to measure for the roundness and sizing of each saddle. These dimensions are critical in that they provide for adequate crush and the underlying geometry for the bearings.
“Crush” is a bearing engineering term that best translates to: press fit in a split-bearing installation. This press fit is what actually keeps the bearings in position and prevents “spinning.” Those small tangs are only locating devices and are often not present on newer engines. It has become common practice to target the tighter end of the specified range for main saddle diameter with the intention of obtaining the most crush without deforming the bearing itself. Race bearings have stronger steel-backing alloys, which permit installation with greater amounts of crush, and are better suited to this strategy.
The normal method of correcting for improper main saddle dimensions is to mill or grind a small amount of material from the main caps and then use a long mandrel hone to resize the tunnel in a single operation. As with cylinder honing, you should use the same fasteners that will be installed during final assembly.
There are definite limits to the amount of material that can be or should be removed in a honing operation. Large misalignments or working with dissimilar material, such as steel caps on an aluminum block, require line boring. Boring is a more complex operation in terms of setup, and requires less-common equipment, but it is sometimes the only appropriate option.
Whether from repeated line honing or boring, it is possible to remove enough material to impact the center-to-center distances between the cam and crankshaft tunnels. Cloyes offers special “-.005” and “-.010” timing sets for FE engines to address this issue should it arise. Making significant changes in main cap vertical orientation can also become problematic in 427 FE engines due to the main cap cross bolts. These fasteners need to be test fit and the block’s cross-bolt holes and spot faces may need added clearance if the caps have been cut by a large amount.
Check for adequate clearance in the rear cap for the oil slinger machined into the crankshaft. If you’ve cut a lot off the cap it can get “tight.”
One other thing to check for is a large enough chamfer on the thrust bearing saddle. OEM blocks have a very large 45-degree chamfer where the thrust bends going from the straight shell to the thrust face. Some Genesis blocks have a smaller chamfer, which interferes with some brands of thrust bearing. It’s best to check and enlarge that chamfer now.
Machining the Decks
Similar to the other operations, deck machining should be considered a “given” during budgeting. The nominal deck height for all FE Ford blocks is 10.170 inches. Given the age and unknown history of older blocks, it is safe to assume that they have seen service in the past. At the very least, a clean, flat deck surface goes a long way toward ensuring a good head-gasket seal.
With the main saddle line hone finished, it is pretty easy to get an initial reading on deck height using nothing more than a 12-inch dial caliper. Measure from the main bore to the center of the deck at all four corners—front left and right, and rear left and right. Choosing the lowest corner and using the appropriate fixture to mill both decks to that level gets you close enough for the majority of street and bracket racing builds. For these types of engine builds, cylinder-to-cylinder equality is more important than the actual value you arrive at. And it’s a good spot to start on a race engine as well, since you are targeting a specific deck clearance, and that lowest point is certainly not going to get any higher. On a serious race engine, you will likely revisit this operation after trial assembly if you need to achieve a particular dimension because there is enough potential for dimensional variation in crankshaft stroke, rod length, piston pin position, or bearing variation to warrant the effort.
When milling the deck, it is important to determine the head gasket you will be using. The popular wire ring gaskets, such as the Fel- Pro 1020, are quite forgiving on surface finish. But the multi-layersteel (MLS) type of gasket requires a much smoother deck surface to perform properly.
After the milling, it is important to chamfer the head bolt holes, especially if you are using bolts. You should also chamfer the dowel pin positions, as they will be much easier to tap into place without distorting them. I prefer to very lightly break the upper edge on cylinder bores as well. You only need a smooth edge break on these and not a big chamfer— just enough so that rings and fingers don’t get caught on an overhanging or sharp edge.
Here is where you get into some controversial territory. Some folks feel that the FE engines have a marginal oiling system that requires a great deal of modification. Others believe that the system is okay with only modest attention to detail required. I tend to fall in with the latter group, making few significant changes on my own engines, but I try to cover some of the alternate approaches because the arguments in favor of the former do have some merit.
There seems to be no rhyme or reason for factory use of threaded versus non-threaded plugs. In fact, I’ve seen both used on the same block. I actually attempt to replace all of the oil galley pressed-in plugs with 1/4-inch NPT plugs. Sometimes you cannot get them all due to core shift and drilling variances. Thin cast iron can be very fragile and some risks are not worth taking, but try to get as many as possible. The pipe tap tells you to use a 7/16- inch drill. I’ve found that an additional short-entry drilling with a 1/2-inch bit helps get enough threads started for a clean tapping with less side loading and stress to the casting. You need the plugs to go in deep enough, especially the ones in the rear, which can interfere with the flywheel cover plate or in front by the distributor hole.
Be sure to install the hidden plug behind the distributor hole. That one trips up novice and professional alike. It’s a safe one to leave as a press-in plug because it cannot go anywhere once the distributor is installed. If you choose to thread it, be certain to check for adequate distributor clearance after the threaded plug is installed. I’ve seen many engines where this plug interfered with distributor installation or locked up the distributor once installed.
Oil Pump Mounting Area—Pump Outlet
Many of the factory FE blocks have a very small opening passage into the block from the pump. This passage is far smaller than the outlet on the commonly used Melling oil pumps, and has a nearly immediate 90-degree turn leading into the oil filter mounting pad. Mark the opening to match the pump outlet and then use a combination of carbide burrs and cartridge rolls on a die grinder to open up, smooth, and blend this passage. Some builders use a three-fluted drill and open up the galley to 7/16 inch, but I remain more concerned with the shape than the diameter, feeling that a 3/8-inch hole can flow plenty of oil.
Oil Filter Pad—Leading Back into the Block
This is an area where I do not go as far as some other builders. Most blocks have something of a “step” in this passage where the drill size changes. I remove and blend that step, but others drill the entire passage out to a larger size. Similar to the pump outlet, I feel that the galley is adequate once the bumps and burrs are removed.
Oil Passage Alignment
The main bearing oil-feed passages on many FE engines are offcenter and significantly out of line with the holes in the bearings. While the reasons may be “lost to the sands of time,” it appears to be more a result of manufacturing convenience than any particular design element. The feed holes are drilled straight through the center of the cam bearing journal, and since the cam journals are not in line with the mains, you end up with a variance. The degree of feed-hole impedance varies with brand and type of main bearing. Some have a large feed hole and others a narrow feed slot. The factory 427 engines had the holes chamfered over to line up with the bearing, and this has become common practice with most performance-oriented FE builds. Under extreme race duress, the 390 and 428 engines split through this hole, so it is a good idea to remove as little material as possible in this area. I use the desired bearing as a reference and just blend the edge with a die grinder and a carbide bit.
Restrictions—Lifters and Valvetrain
There was no oiling at all to the lifters in the original 427 Ford engines. This fact led builders converting other FE engines to solid lifters into completely blocking off oil on those too. You never see that done on any other engine, and there is no reason to do so on an FE. You can restrict the lifter oiling on solid or solid-roller engines by using .060-inch drilled set screws, installed into the lifter galley feeds that “V” off from the center of the intake valley. Most blocks can be simply tapped to 3/8 inch in those locations. On the occasional block where this cannot be done, I go without restricting and do so with no regrets whatsoever.
Restricting the oil feeds to the rocker assembly is a good idea on most FE engine builds. These engines seem to put a great deal of oil up to the top end and have lesser drainback provisions. The restrictions are most often installed in the cylinder heads, but the feed holes can also be drilled and tapped for 5/16-inch setscrew restrictions in the cylinder decks if desired. Restriction to .060 inch is common; the Fel-Pro 1020 already has a feed hole with a reduced diameter of .093 inch. On certain Genesis aftermarket blocks, it’s important to check oil-feed hole alignment with the Fel-Pro head gasket. They have been known to be off location, and this is by far the best time to identify and correct any such issue. Either drill an extra feed hole in the gasket or use a die grinder to put a shallow transfer groove into the block’s deck surface.
Use a small flashlight and guncleaning brushes to ensure that all the galleys are clear, clean, and free of burrs and misalignment. I do not advocate drilling out the entire center feed passage to a larger size. It’s a big risk with no real benefit, but others disagree.
The front and rear cam bearings have oil holes that need to be in the proper orientation. On side-oiler engines, it’s important that the cam bearing side holes line up with the valvetrain feeds to the decks. Using an LED flashlight and looking through the deck feeds, you can see the center of the cam bearing. The hole’s position is not as critical in center-oiler engines because they have an annular groove surrounding the three center cam bearings. It’s “nice” to have the cam feed hole at around 4 o’clock as viewed from the front, but I’ve seen them installed every which way without apparent ill effect. You can add grooves connecting the oil passages in the cam bearing tunnels of a side-oiler to permit the use of common FE cam bearings.
I do not like to paint the insides of my blocks. Some folks use Glyptal or similar products, but in my opinion, paint inside an engine is a risk with no real reward. Paint is not going to significantly affect oil drainback. For proof, pour some oil on a rough casting and see how fast it runs off. It’ll hit the floor before you can catch it. Paint inside the engine isn’t effective for capturing dirt, either, because significant dirt or debris under that coating causes the paint to come off.
I spend time smoothing rough edges and removing casting flash. But I do not polish the inside of a block. I have never seen a block crack initiated from a rough spot in a casting, but have seen plenty of damage from grinding dust and dirt. Why add more of that?
Be sure to chase all the threads, both internal and external, before putting the block into the assembly room. Few things are more frustrating than finding a broken bolt or a stripped hole in a minor accessory position after much of the assembly work is done.
Many early blocks have an intake alignment dowel pin installed on the front intake rail. Most aftermarket intakes do not accommodate the pin, and I remove them as a part of normal prep.
I do paint the outside of blocks before assembly. Right after washing them for the last time, I mask them off and spray the color. I seem to get a nicer finish and better adhesion before putting assembly lube and such on the casting.
And then it’s time for the other parts.
Written by Barry Robotnik and Republished with Permission of CarTech Inc
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