With the engine disassembled and the pistons and rods all balanced (see prior segment), the next step in engine-balancing is to weight and balance the crankshaft. Balancing the crankshaft requires that it be spun on a specialized machine -- much in the same way that tires are spun during a wheel-balancing. Before that can take place, however, weights need to be attached to the crankshaft to simulate the weight of the pistons and rods.
The crankshaft is first placed and set up in a balancing machine (figure A).
Once the crankshaft has been locked in place, the technician adds up the combined weights of the pistons, rods, rings bearings and wrist-pins (already established during the piston-balancing phase), and even adds in the weight of the oil that will be in the crank housing once the engine is operational. The combined weights are recorded in a log book ( figure B).
The technician then assembles bob weights -- attachable weights designed to approximate the combined weight of the components named above. The weight of each bob weight is equal to that of two piston-rod assemblies. The completed bob weights are installed onto the crank (figure C) and fastened securely so they can't release during the spinning phase.
When the crank and weights are spun, the amount of unbalance that registers on the machine's meters (figure C) gives an indication of how much adjustment will need to be made to balance the crank. A strobe light helps the technician identify in what areas weight will need to be removed from the crank.
The crank is then removed from the spinning machine, the bob weights are removed and the crank is taken to the drill press. Using the drill, tiny amounts of metal are removed from the crank to bring it closer to a proper balance (figure E). Achieving the exact balance will likely require several repetitions of the whole process -- spinning and retesting the crank, and strategically removing more metal -- until the balance readings are exact.
Special thanks for this episode of DIY's Build a Kit Car Unique Motorcars
Gadsden, AL Mid-South Gear Specialists
Knoxville, TN Curt Scott
Crown Communications, Inc.
Santa Clarita, CA Ted King
Knoxville, TN Dan and Sarah Fowler
Knoxville, TN Tony Lewis
Knoxville, TN B.J. Auto
Knoxville, TN Lynn Park Trigo, Inc.
La Crscenta, CA American Automotive and Machine
Knoxville, TN David Doll
Indianapolis, IN
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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