Once the decision was made that we would install a 427 engine in our CobraB. replica, and the engine was procured, the next phase was to prepare the engine for rebuilding. We began with an authentic 1966-vintage 427 engine. After disassembling the engine, we took the stripped-down block to the machine shop for preparation. This phase was performed, in part, by professionals at a machine shop. Following is a summary of the steps.
The block is first soaked overnight in an acid bath. Since it's important to start with a perfectly clean block, this step is necessary to remove any grease, dirt and debris that may be left on the block. It also facilitated closer inspection of the engine for detection of any hairline fractures or other damage to the block. After soaking overnight, the block is removed from the caustic solution and hosed off with a pressure nozzle (figure A). Following a good rinse-off, the block goes into a washer, where it is rotated and sprayed from all sides with 180-degree water for further cleaning. This will flush the engine thoroughly, both inside and out. The high temperature of the water helps facilitate rapid drying.
Once the block is clean and dry, a technician uses a dial bore-indicator to measure precisely the inner diameter of the cylinders (figure B). This step discerns the amount of wear to the cylinders and helps determine whether the block simply needs to be honed or will need to be bored further and used in conjunction with larger piston rings.
Once measured, the block is lowered into a boring machine, positioned and locked down. This is a critical, time-consuming portion of the process. Before honing begins, the block must be perfectly straight so that the cylinders are exactly parallel with the crankshaft. The center line for each cylinder must be aligned precisely. If not performed to exact specifications, this procedure can do more damage than good. Once everything is squared up and locked into position, the machinist assembles the boring tool ( figure C).
For each cylinder, the tool is raised and lowered repeatedly -- making several passes to bore out each cylinder gradually rather than trying to bore out the full diameter in a single pass. Taking this cautious, gradual approach helps ensure precision so that just the right amount of metal is removed. Trying to bore out too much at one time might overheat the cylinder and cause the engine to warp. As the tool removes metal, it also floods the inside of the cylinder with a water-based coolant to protect against overheating (figure D).
Once this process is completed, the engine's deck surface is checked for warping (figure E). If necessary, a few thousandths of an inch of metal can be removed from the deck surface to help safeguard against head-gasket failure. This step can be repeated later, during preassembly, if it's determined that more surface needs to be removed.
Next, any metal burrs, cast-flashings or pieces of loose metal are removed from the block -- both inside and out -- using a motorized die-grinder (figure F). This step is a precaution against stress cracks that might form later, as well as a prevention from impurities later breaking loose from engine surfaces and contaminating the oiling system.
The oil passages are also enlarged (figure G) so the high-volume, high-pressure oil pump can work efficiently.
Next, the block is washed thoroughly using concentrated detergents, a pressure-washer and a specialized set of brushes that can be run completely through the oil passages (figure H).
The block is then rinsed off with the pressure hose to remove any metal shavings or debris (figure I). (Note: This step is absolutely necessary at this stage to ensure a clean engine.) The engine is then brought back into the shop and dried off inside and out, using compressed air, before rust can set in.
The inside portions of the block are then painted with an epoxy sealant (figure J). This step helps further protect against contamination inside the engine, since any potential contaminants that may have been missed during cleaning are sealed off. The sealant actually fills in the microscopic pores, sealing the block with a slick finish that promotes easy, resistance-free draining of oil from the engine back into the oil pan. Once the sealant dries, all exposed surfaces are wiped down to ensure cleanliness.
Next, a thread-chaser is run through each threaded hole in the block (figure K). Unlike a thread-tap, which actually removes metal, the thread-chaser merely removes any loose dirt, rust or contaminants that might be present inside the threads, thereby "fine tuning" the threads. After the thread-chaser has been used on every threaded hole, compressed air will be used to blow out each hole for an extra measure of caution.
The engine exterior is then prepared for spray-painting by using masking tape and newspaper to block off the areas that need to be kept free of paint. It's also helpful to have an old timing cover and oil pan that can be temporarily attached, during painting, to protect those adjoining surfaces (figure L).
Once carefully blocked off, the outside of the block is spray-painted with heat-resistant paint (figure M), then allowed to dry. Black paint is used to emulate the finish that was used on original, new performance engines during the 1960s.
Once the paint has dried, the tape and other covering materials are removed (figure N). To give a good clean edge, the tape is best removed while the paint is dry but slightly tacky.
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)
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