What do I torque the bolts to?

The first step is to identify which bolts you have. Eagle rods are offered with a variety of different bolts. Each of which has a different torque requirement. Proper bolt torque is paramount to rod strength and life. Eagle does not use "off the shelf" ARP bolts. Eagle has ARP custom make bolts to our specifications. DO NOT use torque specs for off-the-shelf ARP bolts. Here is a diagram of some important bolt identifying features.

The following chart shows the head of the bolt, the dimensions, and the proper torque spec. Be careful! the heads of some bolts look similar and some even have the same markings. DO NOT identify the bolt by the head alone. Verify dimensions also! If the head of your bolts do not match one of the pictures below - you do not have Eagle rods! Please consult the manufacturer of your rods for proper torque specs. Their torque spec is most likely different than ours! Always use ARP moly lube on the threads and under the head of the bolt when torquing!

material socket size under head length thread size torque 8740 7/16" 1.500" 3/8" 40 ftlbs material socket size under head length thread size torque 8740 7/16" 1.600" 7/16" 63 ftlbs material socket size under head length thread size torque 8740 7/16" 1.750" 7/16" 63 ftlbs material socket size under head length thread size torque 8740 7/16" 1.800" 7/16" 63 ftlbs material socket size under head length thread size torque 2000 3/8" 1.500" 5/16" 28 ftlbs material socket size under head length thread size torque 2000 7/16" 1.500" 3/8" 43 ftlbs material socket size under head length thread size torque 2000 7/16" 1.600" 7/16" 75 ftlbs material socket size under head length thread size torque 2000 7/16" 1.800" 7/16" 75 ftlbs material socket size under head length thread size torque L-19 1/2" 1.600" 7/16" 79 ftlbs material socket size under head length thread size torque L-19 1/2" 1.750" 7/16" 79 ftlbs material socket size under head length thread size torque CA 625+ 3/8" 1.500" 5/16" 32 ftlbs

How can I identify Eagle products?

Identifying Eagle rods is easy if you know what you are looking for.
Current production Eagle H-beam rods all have the Eagle logo on the side of the beam as shown in this picture. Older production did not have this. It was implemented around 2003-2005 in response to one of our competitors using the same part numbers that we use.
	Another design feature is the shape of the area around the bolt and the ridge in the middle of the beam. This has always been our design. If yours are rounded and/or have no ridge then you do not have Eagle rods!
Finally, our bolts are custom manufactured for us by ARP. All Eagle bolts will have "EAGLE" on the head of the bolt along with other information. Several years ago, a few bolts had "ESP" on the head instead of "EAGLE".
	Current design Eagle I-beam rods also have the Eagle logo on the beam. It is laser-etched and can be difficult to read, especially on used rods. Older designs did not have this logo. A manufacturing code is also laser etched on the opposite side of the beam. The bolts will also have "EAGLE" on the head.
Older design I-beam rods used an ARP wavelock bolt with 12 point nuts. Obviously, these did not have "EAGLE" anywhere on the bolts or nuts. Even older designs used a 6 point nut. Both of these are shown in this picture.
Around 2001, we added the Eagle logo to the face of the first counterweight on our cast crankshafts. Without the logo, there a couple of other things to look for. earlier cranks had either "ESP" or nothing on the first counterweight.
On the face of the 1st counterweight you will find two sets of numbers. One is an identifying number. The other is a manufacturing run code. For the specific meanings of these numbers, please call.
Since about 2003, all Eagle 4340 cranks have had the Eagle logo on the face of the first counterweight.
The identifying marks to look for can be in one of two different places. You will find two lines of numbers resembling the ones shown here. These will identify the material and application information. This shows an example of this information on the face of the first counterweight.
	The other common location is on the edge of the first counterweight as shown here.
The ESP Armor process will make reading the markings even more difficult, if not impossible.

"Do I need to balance this crank?" and explaining internal and external balance.

The first step in understanding balancing is to understand how a crankshaft is balanced and what the purpose of the counterweights are. The counterweights are designed to offset the weight of the rod and pistons. If the counterweights are the correct weight to offset the weight of the rods and pistons, the crankshaft is balanced. If the counterweights are too heavy, material must be removed by drilling or milling the counterweights. If the counterweights are too light, weight must be added to the counterweights. This is usually done by drilling a hole in the counterweight and filling the hole with "heavy metal" or "mallory". This filler metal is denser and heaver than steel (but not stonger) so the weight of the counterweight will increase as a result.

Internal Balance & External Balance Explained

 When the counterweights alone can be made to balance the crankshaft, the crank is said to be "internally balanced". If the counterweights are too light by themselves to balance the crankshaft and more weight is needed, an "external balance" can be used. This involves a harmonic dampener or flywheel that has a weight on it in the same position as the counterweight that effectively "adds" to the weight of the counterweight on the crankshaft.Since the harmonic dampener (front) or flywheel (rear) play a part in the balancing of the assembly, they must be installed on the crankshaft when it is balanced. This is unlike an internal balance configuration where the harmonic dampener or flywheel do not contribute to the balance of the crankshaft and are not required to be installed when the crankshaft if balanced. Both methods are used from the manufacturer. An example of some factory internally balanced engines are Chevy 305 and 350 (2 piece rear seal only!), Chevy 396/427, GM LS-series, and Ford "modular" 4.6. Some examples of factory externally balanced engines are Chevy 400 and 454, Ford 302 and 351W. Some engines are even a combination of both: being internally balanced in the front and externally balanced in the rear! The most common example of this is the Chevy 350 (1 piece rear seal) including LT1. Regardless of how an engine is balanced from the factory any balancing method is acceptable as long as the required harmonic dampener and/or flywheel is available.

 "Is my crank balanced?" and Target Bobweight Explained

Since different rods and different pistons are different weights, it is impossible to make a crankshaft that is balanced "right out of the box" for any rod and piston combination. All crankshafts must be balanced to your specific rod and piston combination. When an Eagle crankshaft is listed as "internal balance" or "external balance" this is stating how this crank is intended to be balanced. It can be balanced otherwise, but it is much more difficult to do so. Eagle crankshafts are listed with a "target bobweight". This is an approximation (+/-2%) of the bobweight the crankshaft is roughly  "out of the box". Because of the tolerance (+/-2%) the crankshaft cannot be considered balanced. For instance, for a crankshaft listed as having a 1800 target bobweight. The actual range of bobweights one of those cranks might have is from 1764 (1800-2%) to 1836 (1800 +2%). It might even be at the high end of that range on one end and the low end of that range on the other! This is not usually a problem because Eagle crankshafts are designed to have a target bobweight higher than most typical rod and piston combinations. Therefore, in most cases you will only need to remove material to balance the crankshaft instead of adding material. The main benefit of the target bobweight is to help the machine shop know what to expect before balancing so that a more accurate price estimate can be made. Eagle will balance a new crankshaft at the time of purchase. You will need to provide the bobweight you want it to be balanced to and the bobweight must be below the target bobweight listed for the crankshaft ordered. Our balancing price does not include addition of heavy metal.

Bobweight Explained

 When a crankshaft is balanced, the actual rods and pistons cannot be used in the balancing machine, so they must be simulated. This simulated weight is called the "bobweight".   Once the bobweight is calculated, weights are bolted onto the rod journals to simulate the weight of the rods and pistons during the balancing process. Due to the configuration of a "V" type engine, just adding all the weights together does not work.  There are also some dynamic considerations to be made when balancing the crankshaft. Explaining those is beyond the scope of this discussion. If you want to study those topics further, contact a crankshaft balancing machine manufacturer and they can go into greater detail. If you are a machine shop wondering if we take these things into consideration in the balanced assemblies we sell, rest assured we do. To calculate the bobweight of a particular assembly, the following formula and balance card is used:

 For example, let's say we are balancing a Chevy 383 with the following component weights:

piston:416g

pin:118g

locks:2g

rings:35g

rod big end:458g

rod small end:186g

bearings:46g

Notice the rod weight is separated into "big end" and "small end". This is necessary because the small end has a reciprocationg (back and forth) motion and the "big end" has a rotating motion. This split weight is figured on a special scale fixture that supports one end of the rod while weighing the other end. Given these component weights, the resulting bobweight would be 1770 and the calculation would look like this

  There are several things to note about this calculation. The "oil" value used on the left side of the calculation is an approximation of the weight of residual oil "hanging around" on the assembly. The number used here is a matter of preference. There is no solid "rule of thumb" for this. Eagle uses 5g for small block assemblies and 15g for big block assemblies. Since it is impossible to accurately represent this value, it is just an estimate. The actual amount of oil can change constantly and can even be different from cylinder to cylinder! We have found through experience that the numbers we use estimate this property well.

 The second thing to note is the 50% value used for the reciprocating factor. This number deals with the geometry of the engine itself. A 90 degree bank angle "V" engine will use 50% here. A V6 or a narrow or wide bank angle "V" engine will use a different value (again, consult the balancer manufacturer). Some engine builders will perform what is called "underbalancing" or "overbalancing". They will use slightly differnet values here such as 48% or 52%. This is done to help compensate for dynamic effects at extremely high or extremely low rpm operation (again, beyond the scope of this discussion). Eagle uses 50% because this value is required for almost all common street or racing engines.

Eagle Assemblies

Most Eagle rotating assemblies are sold unbalanced so that the machine shop can choose to balance it however they wish. We do offer most assemblies balanced from us. You must specify you want a balanced assembly in order to get a balanced assembly! If you do not specify, an unbalanced assembly will be shipped. All part numbers for balanced assemblies will begin with the letter B. For instance, if you want assembly part number 12006 balanced and in +.030" bore size, you would order assembly number B12006-030. The best way to tell if the assembly will be internal or external balance is to notice how the crankshaft used in that kit is intended to be balanced. All Eagle forged 4340 steel crankshafts are designed for internal balance. You can also notice the contents of the kit. An internally balanced kit will not include a harmonic dampener or flywheel because they are not required for balancing - use whatever brand you like. Externally balanced kits will include a harmonic dampener and/or flexplate as needed. If we provide a harmonic dampener and flexplate it will be a O.E. style replacement, not SFI approved. If you building a high horsepower engine, internal balance is preferred anyway. Internal balance is better for longevity of parts and fatigue life.

Stroker engines explained.

What exactly is a "Stroker engine" or a "stroker kit" , what are the advantages and disadvantages, and what is involved in building one? This is a commonly heard question. Here are the answers!

    A stroker engine is basically just an engine that has had the stroke increased to more than was originally from the factory. A stroker kit is a collection of components that make building a stroker engine possible.  Sounds easy, right? Well, there are limitations to what can be done depending on which engine you are building. More on that in a minute. Why you would want to build a stroker engine is a question that first must be answered.

    To understand the benefits is simple enough: Power and torque comes from burning fuel. While squirting more fuel into the engine is simple enough, it won't do any good if you don't provide more air also. By increasing the stroke of the engine (and also the bore, too) you can increase the size of the engine. No, I'm not talking about the physical outside dimensions of the engine, but the "breathing capacity" of the engine. For example, a 302 cubic inch engine simply means that in 2 engine revolutions, the engine will theoretically ingest and exhaust 302 cubic inches of air. More air, more fuel, more power! A 347 cubic inch engine will ingest and exhaust 347 cubic inches of air every 2 revolutions. For you mathematically challenged folks out there, that's 45 cubic inches more air every 2 revolutions! Big deal, you say. Well, that is a 14.9% bigger engine. 14.9% more air. 14.9% more fuel, and theoretically 14.9% more power! So that 350 hp 302 you built would theoretically be 402 hp as a 347!

    I know, I said "theoretically" way too much and here is why: Making more power in an engine is not only about increasing the breathing capacity. There are other things to take into account like camshaft specs, head flow, and a myriad of other things. Without getting too detailed, you need to understand that not all components that work well for a 302 cubic inch engine work best for a 331 cubic inch engine or a 347, or a 354, etc.

    It's been said before that "it's all in the combination". This is certainly true. Everything must be taken into consideration, and increasing the breathing capacity of an engine is one of them. Almost never is increasing the breathing capacity a bad thing. Yeah, I said "almost". This has to do with the limitations of the engine block and factors like that. We'll discuss that in a minute.

    Here is a handy formula for finding the engine size of a V8 engine:

    engine size = bore x bore x stroke x 6.2838

All dimensions should be in inches.

    Notice the bore is counted twice? You might think that increasing the bore would have more of an effect than increasing the stroke if you wanted to increase the engine size. You would be right except for one problem: You can't make huge increases in bore size, the block usually won't allow it. Darn those limitations. For example, most small block Ford blocks can only be bored .060" oversized (4.060" vs. a stock size of 4.000"), It is quite easy to increase the stroke by .400" (from 3.000" to 3.400"). In addition, if a block is bored to the limit, it cannot be bored again after that! Most people will want to save a little room for freshen ups or rebuilds.

    Now that we are on the subject of limitations, let's explore some of them so you'll know what you're up against. The engineers that designed each block never intended for stuff like this, but they did leave some room for improvements. Some engines more than others. Not all engines are created equal. The longer stroke crankshaft and the rods have to be able to rotate in the block without running into things like the crankcase walls, bottom of the cylinders, oil pump bosses or pickups, oil pans, windage trays, main cap girdles, or even the camshaft!

    Ouch!

    The camshaft!? Really?

    It's relatively easy to get out the grinder and grind away parts of the crankcase, notch out the bottom of the cylinder walls, buy a different oil pan or pickup, or buy a different main cap girdle. But you can't exactly clearance the camshaft now can you? Fortunately the only engine that has this problem is a Chevy small block. Unfortunately that is the most common engine people build stroker engines out of! For the Chevy small block, that is the single biggest obstacle to overcome when building a stroker. Design changes in the connecting rod and/or camshaft (smaller base circle) can help with this, but they can only go so far. You will have to consult different component manufacturers to see just how far you can go.

    OK. Block clearancing. That's one. It's also the most common.The rest are a little most obscure and might require a bit more thought to understand.

    Another limitation involves the entire crank/ rod/ piston combination. Imagine a single cylinder worth of crank, rod and piston combination all assembled at bottom dead center. Now, if you increase the stroke on the crank, it will pull the pistons down into the counterweight of the crankshaft! Not good. Remember, the original designers like to keep things tight in there. Never fear, this is remedied by increasing the rod length. Increasing the rod length moves the piston away from the counterweight and has the added effect of making the rod ratio more acceptable (more on that later). Now rotate the comination to top dead center with the increased stroke and longer rod. Now everything sticks out of the top of the block! This is solved by changing the pin location in the piston. This dimension is called the "compression height" of the piston.

    I hate that term.

    While changing the compression height by itself would alter the compression, it is not the "ideal" way to change the compression if that is what you wanted to do. The location of the pin in the piston is really dictated by the stroke and rod combination you are attempting to build instead of the compression ratio you want. Compression ratio should be changed by altering the face of the piston and/or combustion chamber of the cylinder head. If I had my way, I'd call this dimension "pin height". That way it's effect on compression ratio wouldn't be implied. Since I am writing this, and this is my world, I'm calling it "pin height".

    Imagining all of this, you should start to understand the limitations associated with moving the pin around and lengthening the rod. This is where the deck height of the block comes into play. The block's deck height is the distance from center line of the mains to the deck surface where the head gasket lives. For example, a Chevy small block has a 9.025" deck height and a Ford 302 has a 8.206" deck height. Guess which one can accept more stroke. Never fear, Ford fans. The 351W has a 9.500" deck height to out-stroke those Chevy guys. And the cam in the 351W doesn't get in the way!

    You have heard some people talk about a "zero deck engine". This refers to the deck clearance of the engine being zero (i.e. the pistons comes all the way up to the top of the deck suface with no clearance). Typically from the factory, engines will have about .020" of deck clearance. Different manufacturers and different engines will vary, of course. 

    Here is your next handy formula:

    deck height = (stroke / 2) + rod length + piston pin height + deck clearance

Some people like to think of the first part as the "assembly height", so here it is like that:

    assembly height = (stroke / 2) + rod length + piston pin height

    deck height = assembly height + deck clearance

    I guess it just makes more sense to some folks like that. Either way, that equation must balance for the engine to work on paper. I say "on paper" because you have to keep the limitations of the parts in mind. For instance, piston pin height can only be so small before it is impossible to manufacture. Usually, pin heights less than 1.000" are very difficult unless you use a really small pin. But a really small pin might not be strong enough.... You start to see the games we play. Also, cranks need to balance. If component weights go up, and strokes go up, counterweights need to be bigger to compensate. This requires longer rods, which moves the pin again.... more games.

    So, block clearancing, deck height, what else can there be?

    Not much really.

    But there are other things that occasionally come into play, so I'll mention them briefly. Since compression ratio is determined by the volume of air in the cylinder at bottom dead center (a.k.a "swept volume") divided by the volume of air at top dead center, if you increase the stroke, you increase the "swept volume" and increase the compression ratio. Increasing the bore size does the same thing although only slightly. For instance, compare a pump-gas friendly flat top 327 Chevy with 9.7:1 compression with 4.000" bore and 64cc heads. now build that block with a 4.000" stroke (yes, it will fit. It's not easy, but it will fit!) and flat top pistons. It suddenly becomes a race-gas only 11.7:1 compression! This means dished pistons or bigger chamber volume heads. Different heads might not be an option, and as the dish gets deeper on the piston, the piston face and pin might try an occupy the same space! More limitations... 

    You might have also heard people say "you can't rev a stroker motor as high as a non-stroker motor". Technically, no. Realistically, yes.

    Huh?

     OK, here's what I mean. There are two main factors at work here. One is maximum piston speed and the other is rod ratio. Maximum piston speed is the highest speed the piston (and more importantly, the rings) will see. This is directly related to the stroke of the engine and RPM (obviously the maximum piston speed will occur at maximum RPM). The limiting factor here is actually the rings. At some speed, the rings will be sliding along the bore faster than they can handle and will wear out or fail altogether. The "old school" rule of thumb is not to exceed 140 feet per second. Before this scares you, realize that a Ford 302 would have to rev to 10,700 rpm to get to 140 ft/sec. A stroker 347 would see 140 ft/sec at 9450 RPM. So technically there is a difference. Realistically, is anyone really going to be revving a 302 or 347 that high? OK, sure someone out there might be, but most of won't. For the few who will, that is the reason I brought it up at all. Modern rings and bore finishing may allow for higher maximum piston speeds. If you plan on building a high RPM engine, talk to your preferred ring manufacturer about what the rings can handle.

    Another factor is rod ratio. This is perhaps the most obscure topic of all. Rod ratio is the length of the rod divided by the stroke of the crank. Rod ratio has several effects. The most important one related to stroker motors is side loading. Yes, I know there are other factors like piston acceleration and dwell time, but neither is much of a limiting factor. They just change the engine characteristics which is a topic for a different article. Side loading is increased with lower rod ratios. Likewise, it is decreased with higher rod ratios. The best way to understand side loading is to try and imagine that the rod is trying to shove the piston through the side of the clyinder wall instead of up the cylinder where it belongs. Some people will talk about this subject and refer to "maximum rod angle". "Maximum rod angle" and "rod ratio" are directly related. They are basically two ways of saying the same thing. Higher maximum rod angle / higher side loading / lower rod ratio all describe the same problem - increased friction due to side loading. This leads to higher piston skirt wear rate, more drag and more heat. All of these things will result is some loss of power compared to the same size engine with a higher rod ratio. Higher rod ratios / lower maximum rod angles / lower side loading will have less friction, lower piston skirt wear rates, etc. So, where is the "limit" you don't want to cross? This is where it gets "fuzzy" and opinions step in. Smokey Yunick was a "put the longest rod you can find in there" kind of guy. While there is certainly a case for this argument, at some point increasing the rod ratio  more just doesn't realize any more gains. It's a diminishing return sort of thing.

    I think it's time to throw out some practical numbers to think about so here are some common rod ratios.

    Ford 302 (5.090" / 3.000") - 1.70

    Chevy 350 (5.700" / 3.48") - 1.64

    Ford 351W (5.956" / 3.500") - 1.70

    Chrysler 360 (6.123" / 3.580") - 1.71

    Chevy 400 (5.565" / 3.750") - 1.48

    Ford 460 (6.605" / 3.850") - 1.72

    Chevy 454 (6.135" / 4.000") - 1.53

    Chrysler 440 (6.760" / 3.750") - 1.81

    You can see the typical range is from about 1.50 - 1.80 with few exceptions. While there are a lot of people that believe the longer the rod the better, period. The other side of the coin is a lower rod ratio motor can have better throttle response, might be less timing-sensitive on forced induction engines, and other deeply theoretical topics. Before you worry too much about rod ratio, also understand that smaller bore engines and engines with less cylinder wall clearance tend to resist piston skirt wear better. And with better cylinder boring technology and skirt coatings, skirt wear is not as much of an issue as it used to be. Do Chevy 400s have a reputation for wearing out quickly? Do Chrysler 440s have a reputation for lasting forever? Put aside your brand bias and admit to a "no" in either case. Rod ratio, while neat to talk about and consider is not everything. There are a lot of people who will say "never give up a single cubic inch for better rod ratio". For most street engines or common racing engines, I believe in striking a happy medium. So here is your rule of thumb for rod ratio: try to stay above 1.45 or so for a street engine with modern pistons and boring technology. Racing engines that will be rebuilt often can go lower. It is generally accepted that past 1.72 you won't realize any significant gains. Diminishing returns, remember? The improvement from 1.40 to 1.50 is significant. Going from 1.75 to 1.85, not so much. Also keep in mind that this rule of thumb is just a general guide for typical V8 engines. Like I said before, you will find a lot of opinions on this subject. Part of the reason for that is that tangible results are difficult to find. Like I said, within reason, it is just not that big of a deal. Now, don't go build a 15,000 RPM bike engine with a 1.40 rod ratio and wonder why it flies apart on you. On the same note, don't hesitate to turn your Chevy 327 into a 383 with 5.7" rods because it will drop the rod ratio from 1.75 to 1.52. That is, unless you plan to rev it to 10,000 rpm. Stroker engines will usually have a lower rod ratio. How low is too low is a matter of great opinion and it also depends greatly on what the engine will be used for. Yes. There are a lot of things to consider and an engine builder's experience and 1st hand knowledge of particular applications goes a long way. If it were cut-and-dry everyone would build the same motor the same way and that would be no fun.

    I want to take an opportunity at this point to clear up a common misconception on a specific application. It is commonly thought that a Ford 347 uses oil. This comes from the unfortunate fact that early Ford 347 pistons were not made correctly. When a piston pin height gets smaller, at some point the pin will intersect the oil ring. When the piston is designed with a steel oil rail support or something similiar to support the oil ring properly this does not create a problem. Some early Ford 347 pistons were not designed this way and the oil rings "fluttered" and the engines used oil. Most every piston manufacturer now uses oil rail supports and it is not a problem. Many other engines also have pins that intersect the oil ring and do not have the same reputation. The following engines also use oil rail supports: Chevy 383 with 6.000" rods (3.750" stroke 350), Chevy 496 with 6.385" rods (4.250" stroke 454), even a Ford 331 (3.250" stroke 302), and others.

    So there you have it. Bigger is usually better. Make sure it will fit without exceeding your comfort level for clearancing. Make sure the math makes sense and parts are available. And keep your compression ratio, rev range, and rod ratio in consideration.

I spun a rod bearing. What happened?

Can a discolored rod be used?

Can I buy a single rod?

I have no side clearance. What's wrong?

What is rod ratio and is it important?

What are center counterweights and are they important?

What compression ratio should I run?