Cam Assembly and Crank Assembly There's a sizable difference between an ordinary auto engine, like the ones used in typical passenger vehicles, and a high-performance engine like the one installed in our CobraB. replica. This program presents many of the steps involved in the assembly of a true performance engine -- a 427-cubic-inch V8 engine modeled after the ones installed in the second generation of Carroll Shelby's original Cobras.
With the engine prefit phase complete (see episode 103 of this workshop), it's time to begin the actual assembly of the engine. As with earlier portions of this project dealing with the engine, it's best to leave engine assembly to professionals who have the specialized equipment, tools and expertise necessary to do this job correctly.
The first step in the process is the installation of the cam bearings into the engine block using a specialized driver and expanding tool (figure A). This technique is used in order to install the bearings without damaging their surfaces as they are placed in the block.
The 427 engine uses five cam-bearings to support the bearing-journals on the camshaft. Once the bearings are installed, the oil hose that supplies oil to the cam and main journals must be installed as well.
Prior to sliding the cam into place, the components are all lubricated to prevent metal-to-metal contact during assembly (i.e., in the absence of engine oil). The inner surfaces of the bearings are coated with a moly-graphite lubricant. Both the bearings and the cam are then treated with a concentrated-oil lubricant (figure B).
With the necessary parts lubricated, the cam is gently fed through the bores using caution not to nick any of the bearings in the process (figure C). Once in place, the cam should turn freely.
Moly lubricant is applied to the thrust-surface of the cam before the thrust plate is installed. Thread-lock compound is also applied to the retaining bolts that will secure the plate in place. With those preparatory steps completed, the thrust plate is installed.
The timing gear is then lubricated and preinstalled so that end-play can be checked. A dial indicator is used to measure and calibrate the amount of in-and-out play there is in the installed cam (figure D). An ideal measurement is around 3/1000" to 4/1000".
The next step is to install engine casting and oil-gallery plugs into the oil passages to seal them off. TeflonB. sealant applied to the plug-threads (figure E) acts first as a lubricant (as the plugs are installed) but then hardens to form a secure seal. The sealing compound will help ensure that the engine does not develop oil leaks at operating pressure and temperature.
Lubricant is applied to critical components such as the cam gear and the main bearings (figure F). This liberal amount of lubrication serves a dual purpose: it helps to prevent a "dry first-start" when the engine becomes functional, and in the meantime it also helps prevent damage to internal engine parts during the remainder of the assembly process.
Bearing shields are installed into the block and lubricated, and rear-main seals are installed in the cap and block. On high-performance engines such as this one, a small amount of sealer is also applied to the mating points where the caps rest on the block to prevent seepage of oil when the engine becomes hot.
Next, the crank is gently lowered back into the block (figure G), and the main caps, washers, seals, bearings and bolts are installed.
With all of the caps positioned, the bolts are first hand-tightened (figure H), then each is torqued to proper specs using the step-torque technique in three stages -- tightening each one first to 50 pounds, then 75 pounds and finally 100 pounds (figure I). The bolts are tightened in the factory-recommended sequence.
In a cross-bolted engine such as this one, bolts with machined spacers are installed through the wall of the engine and into the three center-mains to tie the lower end of the block together into one solid assembly.
With the crank and bearings installed, the timing chain, cam sprocket and crank sprocket may be installed (figure J).
The piston-and-rod assemblies are prepared and lubricated using a fine concentrated oil (figure K).
The ring packages are installed onto the pistons using a ring-expanding tool. The prenumbered rings are matched to their designated pistons as determined by earlier tolerance-testing (see Build a Kit Car, episode 103). Each piston is placed in a vice (using a rag to prevent the piston's surface from becoming marred) to hold it steady, and the expanding tool is used to ensure that the piston is not nicked and that none of the rings is broken during installation (figure L).
With all of the rings installed on the pistons, the bearing shields are installed into the rod-caps and the rods(figure M), and the shields are lubricated (figure N). The rod-bolts are also lubricated to help achieve proper torque specs.
The piston is then immersed in a bath of motor oil (figure O) to lubricate the piston and make the assembly easier to install. With protective rubber-boots installed on the rod-bolts, the assembly is removed from the oil bath and carefully slid down into the appropriate cylinder. These steps are repeated for each piston.
With the pistons installed, the rods are torque-tightened to spec (figure P). In our case, the rod-bolts were tightened first to 25 pounds, then finally to 50 pounds. (Note: Torque specifications may vary among different torque manufacturers.)
The final step in the process is to measure for top true-dead-center (TDC) for the engine. A piston-stop is first installed onto the top surface of the cylinder (figure Q). The engine is then rotated in both directions using a degree wheel and dial indicator to find true top-dead-center (figure R). This measurement is critical since the camshaft is to be "degreed in," and TDC must be established in order to follow the phasing of the cam-loads as they rotate with the crankshaft. Degree-checking the camshaft would not be considered necessary on an ordinary engine, but it is considered critical on a high-performance engine.
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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