Note: This is part 2 of the segment dealing with engine preassembly. See "Engine Prefit, Part 1," for the steps leading up to this point in the process. Preinstalling the Crankshaft
After having measured all bearing-to-crank clearances (see earlier segment), the next major step is to preinstall the crankshaft in the engine block and make certain that it will turn freely in a smooth, 360-degree rotation.
Before testing the crank, the main bearings are installed into the caps and lubricated, using a moly-based lubricant (figure A), to prevent any metal-to-metal contact. An initial application of lubricant serves to keep the crank suspended off of the bearing surfaces, and a secondary concentrated-oil lubricant is applied on top of the first one to help the crank turn very smoothly. The five main-caps are then installed into the engine block. All five are first simply put into position, and their bolts are finger-tightened (figure B). Once all have been installed, all of the bolts are tightened to specification using a torque wrench (figure C). As in earlier steps, exact adjustment of the main-cap bolts is critical. The proper technique is to step-torque each bolt, first to 50-pound, then to 100-pound torque-specifications. There is a factory-recommended sequence for tightening the bolts as well. The sequence begins with the center cap, and the bolts are tightened in an alternating pattern, moving toward the outside -- with the outermost bolts on either end being tightened last. Once all of the caps have been installed to proper specs, the crankshaft can be checked for proper rotation (figure D). The crank should turn smoothly, without much resistance. A dial indicator is then used on the end of the crankshaft to check for end-play (figure E) to allow clearance on the thrust bearing. Typically, manufacturer's recommendations call for range of about 1/1000" to 7/1000" for new bearings. In our demonstration, the measurement was 3/1000" -- an ideal setting right in the middle of the range. The next step is to assemble and prepare the rods. The parts are carefully laid out on a work table (figure F), and the moving parts are lubricated, using specialized concentrated-oil lubricant, to prevent them from scuffing each other. For each piston assembly, the wrist-pins are lubricated (figure G), then inserted to connect the piston with the rod (figure H). Each rod bearing-shield is then lubricated with moly lubricant (figure I). For each, both halves of the shield -- cap and rod -- are lubricated. Concentrated-oil lubricant is then applied over the moly lubricant. Once the rod-and-piston assemblies have all been prepared, each is then carefully installed into the proper cylinder. With the rod-caps removed, rubber boots are placed on the ends of the rod-bolts to protect against the possibility of scratching the interior surface of the cylinder as the assembly is lowered into place (figure J).
Note: For this particular phase of the preassembly, no rings are installed, since the purpose for this step in the process is simply to allow for checking of proper rod side-clearances and deck height.
With the rods and pistons positioned in the block, the rod caps are installed (figure K) and torqued to spec. With the pistons all installed, the operation of the entire assembly is checked by rotating the end of the crankshaft. All parts should operate freely and smoothly, and the pistons should all come into proper position with respect to the deck as the crank is rotated (figure L). If any problems are found at this point, with respect to the operation of the pistons, it may be necessary to take the engine back to the machine shop for further refinement. After a visual check of the operation of the pistons, the position of each piston within the cylinder is checked at top dead-center using a dial indicator (figure M). A depth micrometer is then used to measure precisely the positioning of each piston with respect to the deck. The micrometer extends down into the cylinder to measure exactly how far below the deck the surface of the piston rests (figure N). In order to achieve the proper engine compression, a deck-height of around 20/1000" is considered desirable. The block is then rotated on the engine dolly to allow access to the rod caps, and the side-clearance of each installed rod is checked using a feeler gauge (figure O). Side clearance between rods is critical so that the rods don't actually touch each other. In our demonstration, the rod clearances were measured at around 20/1000", which is considered an ideal clearance. With all checks complete, the engine is disassembled. The parts are removed from the block, broken down into their components (pistons, rods, etc.) and carefully stored in marked containers for safe transport to the machine shop for engine-balancing.
RESOURCES :
cobracountry.com
Premiere online resource for all things related to CobraB. reproductions. Established by enthusiast Curt Scott, and maintained by Crown Communications of Santa Clarita, CA, the site contains news, articles archives, a directory of Cobra-replica specialists and manufacturers, aftermarket sources, announcements of upcoming shows and rallies, listings of Cobra clubs, links to other Cobra sites, and more.
Cobra Country
Website: www.cobracountry.com
Unique Motorcars
Unique Motorcars
(Unique Cobra Specialists)
Manufacturers of high-quality Cobra® replicas since 1977, Unique Motorcars also maintains an informational and well-illustrated web site providing information about their Cobra reproductions and related products. Assembly manuals for their kits (including the one used in DIY's Build A Kit Car workshop) are available on their site.
230 E. Broad Street
Gadsden, AL 35903
Phone: 256-546-3708
Web site: www.uniquecobrareplicas.com
Information also available at:
www.cobracountry.com/unique
The Cobra Story: A Man, His Dream and His Automobile
Author: Carroll Shelby and John Bentley
1965, Trident Press
Carroll Shelby website
Shelby Cobra: The Shelby American Original Color Archives 1962-1965
Model: 0879387572
Author: Dave Friedman
(1994)
To order this title from Amazon.com, click here.
Motorbooks International (MBI Publishing)
Essential AC Cobra : The Cars and Their Story 1962-67
Model: 1870979850
Author: Rinsley Mills
(1997)
To order this title from Amazon.com, click here.
Motorbooks International (MBI Publishing)
Shelby Cobra Gold Portfolio, 1962-69
Model: 1855200236
Author: R.M. Clarke
(1990)
To order this title from Amazon.com, click here.
Motorbooks International (MBI Publishing)
Carroll Shelby's Racing Cobra
Model: 0850454573
Author: Dave Friedman and John Christy
To order this title from Amazon.com, click here.
Motorbooks International (MBI Publishing)
Shelby's Wildlife: The Cobras and Mustangs
Model: 0879380454
Author: Wallace A. Wyss
To order this title from Amazon.com, click here.
Motorbooks International (MBI Publishing)
| 
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
REAL VIDEO
