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Reasons to Blueprint & Ba

Reasons to Blueprint & Balance during Rebuilds

While a rebuilt engine may be within factory tolerances and cost less, "a blueprinted engine will actually perform better and last up to twice as long".

The difference is that while the factory gave an allowable range of clearances in the factory manual, it actually manufactured all of its engines using the same clearance for each similar component with a minimal tolerance of two tenths of a thousandth of an inch. A blueprinted engine duplicates the clearances and tolerances the factory used. In other words, a blueprinted engine reduces the potential tolerance buildup of a rebuilt engine to two ten thousandths of an inch. How is this done? Read on.

1. CRANKSHAFT The reconditioning of the crankshaft is the most critical part on an engine overhaul. First, the crankshaft is inspected for wear on both the bearing journals and the thrust faces. Next, it is magnafluxed for cracks which may render it useless. .

2. CONNECTING RODS In a blueprinted engine, the rods are magnafluxed and checked for straightness. Floating wrist pin rods are then rebushed and sized to each individual wrist pin within a narrow tolerance to eliminate wrist pin knock and increase life. Ferrari V-8 engines, unlike the smaller engines are usually revved higher which produces higher stresses. As a result, the big-ends of the rods actually stretch to an out-of-round condition which must be reconditioned to prevent failure. Since bearings from different manufacturers differ in shell thickness, the bearings to be used in the engine are assembled in the rods, and the rod bolts are retorqued. The inside diameter is measured with a highly accurate micrometer and the bearing clearance to the crankshaft is determined. Next, the rods are reassembled without the bearing shells and the inside diameter is measured. Finally, the inside diameter required for the desired bearing clearance is what each rod is reconditioned to. Large clearances will result in low oil pressure and premature bearing failure while tight clearances can cause catastrophic failures. . After rechecking bearing clearances, the rod bolts are replaced during final assembly.If the rod big-ends are reconditioned in a rebuilt engine, they are usually done without regard for the reground crankshaft dimensions and have a relatively large factory tolerance. This tolerance buildup can result in grossly inaccurate bearing clearances.

3. CAMSHAFT In blueprinted engines the camshafts are reground if neccesary to either stock specifications or a grind with a slightly higher lift which improves midrange performance without sacrificing idle. Block cam journals are measured in engines without bearings .

4. ENGINE BLOCK In all blueprinted engines, the block is completely stripped and boiled out, oil gallery plugs replaced, core plugs replaced, and head gasket surface checked for flatness and milled if necessary. Since the main journals in the block stretch the same way the rods do, due to age or high stresses, the main journals are reconditioned (line honed) using the same methods used to determine the correct rod big-end diameters.

5. PISTONS AND BORES One of the most common fallacies among engine rebuilders is that pistons with 60,000 miles on them can be reused in small, highly stressed engines. As an engine wears, a taper is worn into each cylinder by the rings in addition to the skirts of the pistons being worn. This taper causes ring failure, piston wear in the ring lands (grooves), and accelerates wear on the cylinder walls. Another result is excessive piston-to-cylinder wall clearance which causes piston slap and excessive blowby. Unless the block is bored out to fit new oversize pistons, a rebuilt engine could start burning oil with 500 miles of use. In all blueprinted engines, the pistons and wrist pins are replaced with new, original equipment, "oversized" pistons. The pistons are zygloed (magnafluxing for aluminum) and the cylinders are bored and honed to provide the proper clearance for each individual piston. The new rings are then fitted to each piston and cylinder for proper gap. Thus, the block tapers are removed, and the piston-to-wall clearance is reduced to the original factory dimension allowing maximum mileage to be obtained from the blueprinted engine.

6. CYLINDER HEADS The cylinder head in each blueprinted engine is boiled out, magnafluxed, checked for flatness and milled if necessary, and has all the valve guides replaced. Valves are replaced as necessary and the guides are resized to the valves. Valve springs are checked for correct tension. If a head is cracked in a critical area then repairing by welding may be neccesary. If a head is cracked in the valve seats, sometimes the crack can be eliminated by replacing the affected valve seats. In any case, the valve seats are inspected and replaced with steel or stellite seats if necessary. . . The primary problem with unleaded gas is the lack of octane which can be compensated for retarding the ignition timing by a few degrees. Although this is rarely neccesary these days.

7. CAM FOLLOWERS All thimbles should be checked and all valve shimes replaced with new. This is important to eliminate premature wear on the cam lobes. 8. DISTRIBUTOR The distributor in a blueprinted engine is complete disassembled, cleaned, and the mechanical advance curve is checked. Points, condensors, and pickup wires are renewed if applicable.

8. FINAL ASSEMBLY Two primary rules to follow in final assembly are "Cleanliness is next to Godliness" and "Pay close attention to detail". All parts are spotlessly cleaned and all threads are "retapped or died". Timing chains/belts, tensioners, seals, and gaskets are replaced and thoroughly sealed. Marginally worn parts such as crank pulley seal surfaces and timing gears are reconditioned or replaced. New hardware is used as much as possible and the engine is painted the original color .

9. BALANCING Balancing, which can enhance performance, is neccesary on blueprinted engines . The rotating mass, including the crank pulley, timing gear, crankshaft, flywheel, and clutch pressure plate, are balanced dynamically. The piston and pin assemblies are statically balanced within a tolerance of 0.05 gram, and the connecting rods are balanced end-for-end to the same tolerance. This means that all the small ends weigh the same and all the big ends weigh the same. It is highly recommended that balancing be performed because the reconditioning process removes varied amounts of metal from each part, thus changing the balance. Also, since the factory tolerances are in the magnitude of 10 grams, your engine will run smoother, longer, and rev higher than when it was new from the factory if it is balanced to tighter tolerances. 11. OPTIONS Other options include cylinder head porting and polishing, which greatly improves midrange and top end acceleration at the expense of a higher and rougher idle. Installation of Modified carburetors or Individual Throttle Body FI set-up can also improve performance.
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