Twin Cam engine (Harley-Davidson)
From Wikipedia, the free encyclopedia
The Harley-Davidson Twin Cam 88 engine was released for the 1999 model year in September of 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.
Contents |
[edit] 88B and 96B Engines
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 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, which is essentially the same as the original Twin Cam, but with a different engine block design and twin chain-driven counter-balancers, which 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.
[edit] 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 inch" upgrade kit a year later to increase the displacement to 1550 cc. Likewise, the Harley-Davidson Twin Cam 96 is approximately 1584 cc. The motor company has released 103"(1690 cc) and 110"(1800 cc) kits for the TC96.
| Change | Evo | Twin Cam |
|---|---|---|
| Displacement | 1340 cc (82 cu in) | 1450 cc (88 cu in) and 1584cc (96 cu in) |
| Oil pump | external. Connected through a series of gears. | internal twin-geroter. Connected directly to the drive 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 as well as higher compression. |
| spark firing | wasted spark. The ignition system uses single coil. plugs are 14 mm | no wasted spark. The ignition system employs dual coils. plugs are 12 mm. |
| 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 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[citation needed]. 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.
[edit] Recalls and other mechanical problems
[edit] 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 96ci 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.
[edit] Recall - Cam retention bolts
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.
[edit] Excessive Heat
In order to comply with the ever-stricter EPA standards, all TC96 equipped Harleys come from the factory tuned very lean, which in turn creates a great deal of heat, and loss of power. All 07 and later Big Twins are equipped with Electronic Fuel Injection (EFI) 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 in the Harley world, as many have commented that the excessive heat makes the TC96 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" mod 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.
