The Harley-Davidson Twin Cam 88 engine was released for the 1999 model year in September 1998. The Harley-Davidson Twin Cam 96 was released for the 2007 model year. Although these engines were the successors to the Evolution engine ("Evo"), they share a number of characteristics with nearly all previous Harley-Davidson engines. Both engines have two cylinders in a V-twin configuration at 45 degrees, are air-cooled, and control valve timing with push-rods. The crankshafts have a single pin with a tongue and fork arrangement for the connection rods. These are sandwiched between a pair of flywheels.
88B and 96B Engines
A police issue Twin Cam 96.
The Twin Cam wasn't initially used in the Softail model family before the year 2000. This was due to the chassis' design and issues with increased vibration. The increase in vibration was a result of the direct mounting of the engine to the Softail frame. Dyna models are "rubber mounted" and therefore do not suffer the same vibration problems. Harley then solved the issue by making a redesigned version of the Twin Cam, the Twin Cam 88B. The 88B is essentially the same as the original Twin Cam, but with a different engine block design and twin chain-driven counter-balancers. This had caused some controversy among Harley veterans, claiming that the "Harley vibes" were a part of their motorcycles. The Harley-Davidson Twin Cam 96B engine was released at the same time as the Harley-Davidson Twin Cam 96A model, for the 2007 model year, and is currently used on all Softail models.
Differences to predecessor (Evolution engine)
The engine design differed considerably from its predecessor the "Evo" although shared some design elements with the Sportster line. The 88 represents the displacement of the standard engine in cubic inches. 88 cubic inches equals approximately 1450 cc. The motor company released a 95 cubic inch upgrade kit a year later to increase the displacement to 1550 cc. Likewise, the Twin Cam 96 is approximately 1584 cc. The company has released 103-cubic-inch (1,688 cc) and 110-cubic-inch (1,803 cc) kits for the TC96.
Change Evo Twin Cam Displacement 82 cu in (1340 cc) 88 cu in (1450 cc) and 96 cu in (1584 cc) Oil pump external. Connected through a series of gears. internal twin-gerotor. Connected directly to the right side pinion shaft. This pump is more efficient, maintains a higher pressure and larger volume. Cams Single, with 4 lobes One per cylinder, each with 2 lobes. The allows the push rods to be better aligned with the rocker arms. Cam drive gears silent chain. This change was reported as necessary to meet EPA noise requirements. Many users installed after market gear driven replacements to increase timing accuracy. Transmission attachment Displaced from motor Transmission casing is attached directly to the engine Oil tank Usually surrounds battery box under the seat Below and behind the transmission assembly combustion chamber "D" shape "bathtub" shape. Allowed for more efficient combustion and has higher compression. spark firing wasted spark (both plugs fire at the same time). The ignition system uses single coil. plugs are 14 mm (0.55 in) no wasted spark. The ignition system employs dual coils. plugs are 12 mm (0.47 in). cooling air cooled also air cooled. Increase cooling fin areas and an oil jet that sprays the bottom of the pistons provides additional cooling capability. When the Twin Cam engine was released, Harley-Davidson put much emphasis on the supposedly stronger case and bottom end. They claimed the older Big Twin design, with the cam bearing positioned directly above the main bearing on the right side of the engine, precluded increasing main bearing size to optimal and created structural weakness in the right side case because of the small space between the two bearings. However, after market companies have successfully used the old design in engines displacing 144 cubic inches (2360 cc) and more, producing well over 120-foot (37 m) pounds (163 Nm) of torque and 120 horsepower (89 kW) without case failure, casting doubt on Harley-Davidson's claims.
When the Evolution Big Twin engine was released, Harley-Davidson did not protect its design elements as thoroughly as they have with the Twin Cam. In fact, H-D relied on the third-party firms to add value to their products and broaden their appeal. Since the Evo's release in 1984, though, the company has moved to catalogue thousands of accessories, including engine upgrades. The company moved to the Twin Cam not because the Evo had reached its power limits as a design, but because H-D could not prevent other manufacturers from making virtual clones of the design[1]. With the Twin Cam, H-D was able to preempt cloning via the U.S. Patent Office, thereby making it a lot more difficult and expensive for the after market to compete with the Motor Co. in the development and sale of upgrades or complete motors.
Recalls and other mechanical problems
Wear of cam tensioner shoes
The Twin Cam motor has cam chain tensioners with nylon composite shoes, and these have proven to be a wear item even though they are not on the regular maintenance schedule. Some riders have seen these shoes wear down until there was metal to metal contact against the cam chain, while others have experienced no wear. Harley-Davidson changed from spring loaded to hydraulically loaded tension on the shoes in the Dyna line for the 2006 model year and for all Twin Cams with the introduction of the 96-cubic-inch Twin Cam for the 2007 model year. Some believe shoe wear and the variability of cam timing introduced by inconsistent tension on the cam chain continue to be an issue best resolved by third-party gear drive cam sets, such as those made by S&S Cycle and other aftermarket firms.
Cam retention bolt recall
In 1999 a recall was made to replace the bolts that hold the cams in place. The bolts were replaced with Grade 5 bolts to prevent a catastrophic shearing.
As Grade five is standard for most frame and general engine hardware, it's more likely that Grade five bolts were replaced with Grade eight. These have six hash marks on the bolt head. Grade five bolts have three.
Design problems
The early prototype Twin Cam engines had considerable trouble with the oiling system. These problems delayed release of the engine as scheduled for the 1997 model year. When the engines were run, oil came out any gasketed joint as well as the breather. The problem was traced to the scavenge system. After much research, the source was traced to an acoustic phenomenon that caused pressurization of the scavenge passageway when the pistons were moving down. The fix was to restrict the inlet to the scavenge line, a counter-intuitive solution.
A more serious problem was that of overheating. Piston temperatures in particular were troubling. This was solved by installing oil jets in the crankcase, aimed so that they sprayed the piston crown from underneath. While this cooled the pistons, the oil temperature then became intolerably high. The initial response from the engineers was to add an oil cooler, and this was done, with good results. However, the styling and marketing departments felt that this fix looked too much like a band-aid solution. It seemed to be an admission that Harley-Davidson had designed an engine that ran too hot. Management agreed, and the 1998 release date was also passed. Returning to the drawing board, the engineers examined the entire oil system. The excessive heat to the cylinders was not just coming from the piston crowns, but from the cylinder head and rocker boxes. In the initial design, the concept was that flowing large amounts of oil through the rocker boxes (much more than was actually needed for lubrication) would help cool the heads. In actuality, not much cooling was provided for the heads. Rather, the heads were heating the oil. The oil flow to the rocker boxes was cut down to about one-sixth of the initial design,still adequate for lubrication, and this brought the operating oil temperatures to around 220 °F (104 °C). The engines were released for the 1999 model year. High operating temperatures have continued to plague the Twin Cam engines, although the engineering refinements have resulted in a reliable and smooth-running engine.
In order to comply with the ever-stricter EPA standards, all Twin Cam 96-equipped Harleys come from the factory tuned very lean, which in turn creates a great deal of heat, and loss of power. All 2007 and later Big Twins are equipped with electronic fuel injection and 02 sensors for closed-loop operation, allowing an extremely lean tune to be safely, and consistently achieved. This has been a topic of much discussion among enthusiasts, as many have commented that the excessive heat makes the Twin Cam 96 too uncomfortable to ride in stop and go traffic, or in the heat of the summer. There are also concerns about heat's impact on the longevity of the engine. To help combat this many owners re-tune their engines, run synthetic oil or add an oil cooler; the Motor Company has also redeveloped a "Parade" mode in which one cylinder shuts down on the Twin Cam to prevent damage to the engine.
There is some debate as to whether or not the heat issue was resolved on the 2008 models.
There are also reports, across the range from the 88 cubic inch through the 110 cubic inch models, of Twin Cam flywheels falling out of alignment. These flywheels are pressed together, with no Woodruff key or splines, just a press fit to maintain alignment. It appears that the wheels may shift on the shafts, thereby throwing the timing off and introducing a wobble into the pinion shaft which then eats the bottom end catastrophically.
Source: wikipedia.org
88B and 96B Engines
A police issue Twin Cam 96.
The Twin Cam wasn't initially used in the Softail model family before the year 2000. This was due to the chassis' design and issues with increased vibration. The increase in vibration was a result of the direct mounting of the engine to the Softail frame. Dyna models are "rubber mounted" and therefore do not suffer the same vibration problems. Harley then solved the issue by making a redesigned version of the Twin Cam, the Twin Cam 88B. The 88B is essentially the same as the original Twin Cam, but with a different engine block design and twin chain-driven counter-balancers. This had caused some controversy among Harley veterans, claiming that the "Harley vibes" were a part of their motorcycles. The Harley-Davidson Twin Cam 96B engine was released at the same time as the Harley-Davidson Twin Cam 96A model, for the 2007 model year, and is currently used on all Softail models.
Differences to predecessor (Evolution engine)
The engine design differed considerably from its predecessor the "Evo" although shared some design elements with the Sportster line. The 88 represents the displacement of the standard engine in cubic inches. 88 cubic inches equals approximately 1450 cc. The motor company released a 95 cubic inch upgrade kit a year later to increase the displacement to 1550 cc. Likewise, the Twin Cam 96 is approximately 1584 cc. The company has released 103-cubic-inch (1,688 cc) and 110-cubic-inch (1,803 cc) kits for the TC96.
Change Evo Twin Cam Displacement 82 cu in (1340 cc) 88 cu in (1450 cc) and 96 cu in (1584 cc) Oil pump external. Connected through a series of gears. internal twin-gerotor. Connected directly to the right side pinion shaft. This pump is more efficient, maintains a higher pressure and larger volume. Cams Single, with 4 lobes One per cylinder, each with 2 lobes. The allows the push rods to be better aligned with the rocker arms. Cam drive gears silent chain. This change was reported as necessary to meet EPA noise requirements. Many users installed after market gear driven replacements to increase timing accuracy. Transmission attachment Displaced from motor Transmission casing is attached directly to the engine Oil tank Usually surrounds battery box under the seat Below and behind the transmission assembly combustion chamber "D" shape "bathtub" shape. Allowed for more efficient combustion and has higher compression. spark firing wasted spark (both plugs fire at the same time). The ignition system uses single coil. plugs are 14 mm (0.55 in) no wasted spark. The ignition system employs dual coils. plugs are 12 mm (0.47 in). cooling air cooled also air cooled. Increase cooling fin areas and an oil jet that sprays the bottom of the pistons provides additional cooling capability. When the Twin Cam engine was released, Harley-Davidson put much emphasis on the supposedly stronger case and bottom end. They claimed the older Big Twin design, with the cam bearing positioned directly above the main bearing on the right side of the engine, precluded increasing main bearing size to optimal and created structural weakness in the right side case because of the small space between the two bearings. However, after market companies have successfully used the old design in engines displacing 144 cubic inches (2360 cc) and more, producing well over 120-foot (37 m) pounds (163 Nm) of torque and 120 horsepower (89 kW) without case failure, casting doubt on Harley-Davidson's claims.
When the Evolution Big Twin engine was released, Harley-Davidson did not protect its design elements as thoroughly as they have with the Twin Cam. In fact, H-D relied on the third-party firms to add value to their products and broaden their appeal. Since the Evo's release in 1984, though, the company has moved to catalogue thousands of accessories, including engine upgrades. The company moved to the Twin Cam not because the Evo had reached its power limits as a design, but because H-D could not prevent other manufacturers from making virtual clones of the design[1]. With the Twin Cam, H-D was able to preempt cloning via the U.S. Patent Office, thereby making it a lot more difficult and expensive for the after market to compete with the Motor Co. in the development and sale of upgrades or complete motors.
Recalls and other mechanical problems
Wear of cam tensioner shoes
The Twin Cam motor has cam chain tensioners with nylon composite shoes, and these have proven to be a wear item even though they are not on the regular maintenance schedule. Some riders have seen these shoes wear down until there was metal to metal contact against the cam chain, while others have experienced no wear. Harley-Davidson changed from spring loaded to hydraulically loaded tension on the shoes in the Dyna line for the 2006 model year and for all Twin Cams with the introduction of the 96-cubic-inch Twin Cam for the 2007 model year. Some believe shoe wear and the variability of cam timing introduced by inconsistent tension on the cam chain continue to be an issue best resolved by third-party gear drive cam sets, such as those made by S&S Cycle and other aftermarket firms.
Cam retention bolt recall
In 1999 a recall was made to replace the bolts that hold the cams in place. The bolts were replaced with Grade 5 bolts to prevent a catastrophic shearing.
As Grade five is standard for most frame and general engine hardware, it's more likely that Grade five bolts were replaced with Grade eight. These have six hash marks on the bolt head. Grade five bolts have three.
Design problems
The early prototype Twin Cam engines had considerable trouble with the oiling system. These problems delayed release of the engine as scheduled for the 1997 model year. When the engines were run, oil came out any gasketed joint as well as the breather. The problem was traced to the scavenge system. After much research, the source was traced to an acoustic phenomenon that caused pressurization of the scavenge passageway when the pistons were moving down. The fix was to restrict the inlet to the scavenge line, a counter-intuitive solution.
A more serious problem was that of overheating. Piston temperatures in particular were troubling. This was solved by installing oil jets in the crankcase, aimed so that they sprayed the piston crown from underneath. While this cooled the pistons, the oil temperature then became intolerably high. The initial response from the engineers was to add an oil cooler, and this was done, with good results. However, the styling and marketing departments felt that this fix looked too much like a band-aid solution. It seemed to be an admission that Harley-Davidson had designed an engine that ran too hot. Management agreed, and the 1998 release date was also passed. Returning to the drawing board, the engineers examined the entire oil system. The excessive heat to the cylinders was not just coming from the piston crowns, but from the cylinder head and rocker boxes. In the initial design, the concept was that flowing large amounts of oil through the rocker boxes (much more than was actually needed for lubrication) would help cool the heads. In actuality, not much cooling was provided for the heads. Rather, the heads were heating the oil. The oil flow to the rocker boxes was cut down to about one-sixth of the initial design,still adequate for lubrication, and this brought the operating oil temperatures to around 220 °F (104 °C). The engines were released for the 1999 model year. High operating temperatures have continued to plague the Twin Cam engines, although the engineering refinements have resulted in a reliable and smooth-running engine.
In order to comply with the ever-stricter EPA standards, all Twin Cam 96-equipped Harleys come from the factory tuned very lean, which in turn creates a great deal of heat, and loss of power. All 2007 and later Big Twins are equipped with electronic fuel injection and 02 sensors for closed-loop operation, allowing an extremely lean tune to be safely, and consistently achieved. This has been a topic of much discussion among enthusiasts, as many have commented that the excessive heat makes the Twin Cam 96 too uncomfortable to ride in stop and go traffic, or in the heat of the summer. There are also concerns about heat's impact on the longevity of the engine. To help combat this many owners re-tune their engines, run synthetic oil or add an oil cooler; the Motor Company has also redeveloped a "Parade" mode in which one cylinder shuts down on the Twin Cam to prevent damage to the engine.
There is some debate as to whether or not the heat issue was resolved on the 2008 models.
There are also reports, across the range from the 88 cubic inch through the 110 cubic inch models, of Twin Cam flywheels falling out of alignment. These flywheels are pressed together, with no Woodruff key or splines, just a press fit to maintain alignment. It appears that the wheels may shift on the shafts, thereby throwing the timing off and introducing a wobble into the pinion shaft which then eats the bottom end catastrophically.
Source: wikipedia.org