Читать книгу Modern Engine Blueprinting Techniques - Mike Mavrigian - Страница 7
ОглавлениеThe term “engine blueprinting” means different things to different people, so it’s important to clarify it because it is often misused.
Many seasoned engine builders have an accurate and complete understanding of the procedures involved in blueprinting. But in many cases, enthusiasts and customers don’t have the same understanding. Some believe that balancing and blueprinting are interchangeable terms, and that both procedures are performed when the term blueprinting is discussed. Some assume that if a component has been balanced, it has also been blueprinted, and vice versa. As an astute engine builder, you cannot make that assumption. If you review Craigslist or other online ads, you’re bound to see multiple ads listing engines that have been “balanced and blueprinted,” when in most cases the crankshaft has simply been balanced.
In most cases, owners and/or sellers of these engines are not intentionally trying to deceive. Rather, they simply have a misunderstanding of the blueprinting process. Blueprinting an entire engine assembly involves a high degree of skilled labor that goes far beyond a routine rebuild or a bolt-together assembly or reassembly. As a result, a blueprinting procedure adds substantial cost to an engine build. Balancing (which involves weight-matching pistons and rods and correcting the balance of the crankshaft to accommodate the weight of the pistons, rods, piston pins, rod bearings, and rings) is simply one aspect of a blueprinting procedure. An engine build can feature a balanced crankshaft without a blueprinting procedure, or an engine assembly may be blueprinted, which also involves crank balancing. Simply because a crankshaft has been balanced, it does not mean that the engine has been blueprinted.
Are OEM production engines blueprinted? No, they are not. Although a production engine may be based on specific design parameters, the reality of mass production results in deviations due to core shifts in castings and allowable tolerance ranges for parts, dimensions, and machining. Although a production engine may be perfectly suitable for use, it may not have been produced precisely to the design specifications. This isn’t because car manufacturers don’t take this seriously or are trying to short-change anyone, and this certainly doesn’t infer that production engines are faulty. It’s simply the reality of producing engines on a large scale.
The processes of blueprinting are performed when the performance and/or racing application calls for optimizing the engine’s performance and durability.
In a nutshell, the basic goal of blueprinting is to gain a high degree of precision in order to achieve, as closely as possible, a “zero-resistance” engine assembly. This means all parts are properly aligned and clearances are achieved for optimum efficiency. In essence, you’re trying to create the perfect engine by eliminating any variances that affect power and engine durability.
Of course, blueprinting can be utilized to achieve the OEM design specification, but the process is not limited to this. In most cases, a blueprinting approach is used to carefully accurize the block in order to locate all bore centerlines, bore diameters, and bore angles to eliminate deviation, even though you may be altering certain bore diameters. With the main bore corrected to a perfectly straight alignment, cylinder bore centerlines are corrected, lifter bores are corrected for centerline and angle, and decks are machined to be perfectly parallel to and equidistant in height from the main bore centerline. Regardless of the cylinder-bore diameter (whether at OEM diameter or overbored for increased displacement), blueprinting involves accurizing the block as the basis of the foundation.
Beyond block accurizing, blueprinting involves optimizing all clearances in the pursuit of performance and longevity. OEM production may allow a certain tolerance range for areas such as piston-to-wall clearance, bearing clearance, deck height, etc. But when blueprinting, you decrease the tolerance range significantly. For example, if an OEM specification allows a clearance of .020 inch, +/– .005 inch, you try to achieve exactly the optimal .020-inch clearance when blueprinting. You’re refining all clearances while greatly minimizing allowable ranges.
Let’s look at a specific example. Say that an engine manufacturer lists piston ring end gap at .003 to .005 inch for a specific engine application. Rather than varying end gap while staying within that tolerance range, you can tailor the gap to the application at hand. An ideal end gap for a road-racing endurance application might be .0045 to .005 inch. For a drag racing application this might be better suited to .0035 to .0040 inch. This is just one example.
By initially considering the published clearances, you can then fine-tune the gaps in order to obtain the best dimension for an application. Much of this depends on the engine builder’s personal experience with various ring end gaps for specific racing applications. In blueprinting you narrow down various clearances in order to achieve the ideal clearance, instead of simply falling into the wider range acceptable for the average street engine.
Areas to Consider during Blueprinting
• Flaw inspection of all components (checking for cracks/flaws)
• Main bore position and alignment, which includes line boring the main bore
• Position (relative to the main bore) and alignment of the cam tunnel
• Block deck accurizing, including height (distance from the main bore centerline and correction of deck angle)
• Cylinder bore indexing (establishing accurate centerline)
• Lifter bore accurizing (establishing lifter bore centerline and angle)
• Bellhousing dowel location accurizing
• Correction of the crankshaft’s main journal alignment and spacing, endplay, rod journal alignment and spacing, stroke throw length, and clock-position of each throw (angularity of the rod throws)
• Indexing cylinder heads (correcting intake port centerline; scribing cylinder bores on the deck surface of the heads for consistent chamber layout
• Static weight matching of all pistons, rods, rod pins, and rod bearings
• Crankshaft dynamic balancing using bobweights to simulate static reciprocating weight packages
• Inspecting and correcting (if needed) crankshaft main and rod journal diameters
• Connecting rod dimensions and checks (big-end bore diameter, pin-end bore diameter, center-to-center length, checking for bend and twist)
• Checking piston pin bore centerline-to-dome distance (and verifying that this is equal on all pistons)
• Measuring the camshaft for journal diameter, straightness, lobe spacing, lobe lift, and ramp angles
• Measuring all pushrods for length and straightness
• Inspecting all lifters for length and diameter
• Measuring cylinder head combustion chambers for volume and (if needed) machining to equalize all chamber volumes
• Measuring all intake valves for height, stem diameter, and head diameter
• Measuring and equalizing all valve seating depths
• Valveguide sizing for desired valvestem oil clearance
• Measuring all valvesprings for open and closed seat pressure and height, and checking for coil bind at the fully closed position
• Checking rocker arms for proper geometry and contact at the valve tips through the rocker arm’s arc
• Inspecting and verifying crankshaft counterweight to block clearance, connecting rod big end to block clearance, connecting rod big end to camshaft clearance, etc.
• Intake port matching (of intake manifold-to-cylinder head)
Part and parcel of blueprinting involves inspecting everything. Never assume that any new or used component is dimensionally correct. Don’t just take it out of the box and bolt it on. Blueprinting involves close examination of absolutely everything. Where variances exist, depending on the specific component, the part must be machined for correction or replaced with another that matches the desired dimensions. The golden rule is to assume nothing and measure everything.
Parts Selection
A true blueprinting job is very time consuming and labor intensive. So it doesn’t make sense to start the job with inferior or questionable parts. Buy the highest-quality components that you can afford, and don’t try to skimp.
Regardless of your component selection, if you’re going to invest in a blueprinting approach, it’s highly advisable to perform a flaw detection on components such as the block, cylinder heads, crankshaft, and connecting rods and check for cracks and porosity. For the block, this also means checking for cylinder wall thickness at each bore location. If you start the job with questionable or unknown parts, you’re just defeating the purpose.
The quality issue aside, also consider the type of material and construction (for instance, when choosing between a casting, forging, or a machined-from-billet piece). As an example, depending on the manufacturer, a cast-iron crankshaft might be dependable up to, say, 400 hp. If you plan to produce more power, moving up to a forged crank is recommended. Select the parts based on the application. By choosing a component that is stronger and more resistant to failure, you increase your chances of avoiding a failure when producing increased power and/or increasing engine speed.
Can’t Blueprint?
Certain race sanctioning body rules may not allow blueprinting (old SCCA showroom stock road racing as an example). However, there are ways around such nonsense. Even a stock engine can be improved, and mildly blueprinted by mixing and matching engine components in order to improve the engine’s dynamic operation. Instead of machining various parts in order to optimize, an alternative may be to spend the time to locate stock parts that provide the improvement.
For example, an engine’s original set of connecting rods may be specified as having a 6.000-inch center-to-center length. But, as a result of mass production and a factory tolerance range, your engine may actually have rods that vary in length from 5.996 to 6.002 inches. Instead of “illegally” machining to correct, you can take the time to create a matching set of rods that actually measure 6.000 inches. This may be aggravating and tedious, but it’s a way around a silly ruling. The same holds true for OEM camshafts; if yours doesn’t measure at the published specs, you can hunt through several others of the same part number until you find one that’s on the money.
Remember: Blueprinting involves much more than simply balancing the crankshaft. This is serious business that goes far beyond the simple re-assembly of an engine with new parts. It’s an investment in time, skill, labor, and money.
