Harley-Davidson Twin Cam engine
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The Harley-Davidson Twin Cam engines are motorcycle engines made by Harley-Davidson since 1998. Although these engines differed significantly from the Evolution engine, which in turn was derived from the series of single camshaft, overhead valve motors that were first released in 1936, 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°, are air-cooled, and activate valves with push-rods. The crankshafts have a single pin with a knife and fork arrangement for the connecting rods. These are sandwiched between a pair of flywheels.
The Twin Cam 88 was released for the 1999 model year in September 1998. The Twin Cam 96 was released for the 2007 model year.
88B and 96B Engines
The Twin Cam initially was not used in the Softail model family before the year 2000. This was due to the chassis design and vibration transfer to the Softail frame as a result of the direct (hard) mounting of the engine. Dyna models are "rubber mounted", damping the majority of vibration transfer to the frame and rider. Harley solved the issue for the Softail family by designing an engine variant known as Twin Cam 88B. It is basically the same engine as the original (now called "Twin Cam 88A"), but with a modified engine block design that incorporates twin chain-driven balance shafts. The Twin Cam 96B engine was released at the same time as the Twin Cam 96A model, for the 2007 model year, and is currently used on all Softail models.
Differences from predecessor (Evolution engine)
The engine design differed considerably from its predecessor the "Evo" although it shared some design elements with the Sportster line. The 88 represents the displacement in cubic inches of the standard engine in cubic inches. The bore is 95.3 mm (3.75 in) and the stroke is 101.6 mm (4.00 in), meaning the displacement is 88 cu in (1,449 cc). The Twin Cam 96 displaces 96.7 cu in (1,584 cc). The company released 103 cu in (1,690 cc) for 2012 Softail models and 110 cu in (1,802 cc) for Screamin' Eagle/CVO Models.
|Displacement||82 cu in (1,340 cc)||88 cu in (1,449 cc), 96 cu in (1,584 cc), 103 cu in (1,690 cc), 110 cu. in. (1,803 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. This 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 (except Softails, which are same as noted for the Evo)|
|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. Increased cooling fin areas and an oil jet that sprays the bottom of the pistons provide additional cooling capability.|
Design and development problems
In the book The Harley Davidson Century (edited by Darwin Holstrom, Barnes and Noble Press, 2005) Steven Anderson, detailing the Twin Cam story in the chapter "The Twin Cam Era," explains the huge development problems Harley-Davidson had while trying to bring this engine to market. 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. Harley sought the help of Paul Troxler, a young engineer from Southwest Research Institute and eventually the problem was traced to a design which drained the cam case into the crankcase, and used a single scavenge pump. Due to airflow through ports in the crankcase wall, the cam case was not draining properly. After much testing, the solution was to seal the cam case from the crankcase and use a dual scavenge system. However, oil was still not scavenging properly from the crankcase, and this was traced to an acoustic phenomenon due to the caliber of the scavenge inlet. Restricting the diameter of the inlet, a counter-intuitive solution, solved that problem.
Notes and references
- Petersen, Donny (2011-01-19). "VII". Donny's Unauthorized Technical Guide to Harley-davidson, 1936 to Present: The Twin Cam. iUniverse. pp. 307–. ISBN 9781450267724. Retrieved 6 March 2013.
- "The Big V-Twins Test". Motorcyclist Online. Source Interlink Media. Retrieved 12 August 2013.
- "MD First Test: Harley-Davidson’s New Twin-Cam 96 Engine and Cruise Drive Six-Speed Transmission « MotorcycleDaily.com – Motorcycle News, Editorials, Product Reviews and Bike Reviews". Motorcycle Daily. Retrieved 12 August 2013.
- "2006+ Twin Cam 96" Motor to EVO Frame Adapter Plate :: Twin Cam Engine Parts :: Motorway Engineering Co.". Vulcan Engineering. Retrieved 6 March 2013.