UPDATED: April 24, 2017 — Added a tab “Engine History” on the blog home page with updated V-Twin engine history including the Milwaukee Eight.
Have you ever wondered about the history of Harley-Davidson engines?
Compared to other motorcycle manufactures or custom shops, Harley works on a complete different time clock with new engine designs.
They seem to launch every 15 years or so. Between 1936 and 2003, engine designs released by Harley represented a constant tweaking of the same V-twin, 45-degree, air-cooled engine design. In 2001, Harley released its first new design in a commercial motorcycle, but it was still based on a V-twin. There have been only seven major engine revisions during the company’s 105 year existence:
Revolution engines – Manufactured starting in 2001. The Revolution engine is currently used on only one Harley model — the “V-Rod” or VSRC. While all of the engines mentioned are largely the same and represent incremental improvements, the Revolution engine is different. This engine is water-cooled rather than air-cooled and its V angle is 60 degrees rather than 45. It has four overhead cams rather than two cams in the crankcase and is fuel injected. This engine is smaller — only 69 cubic inches (1,130 cc). It has a much shorter stroke, allowing it to rev to 9,000 RPM and it produces 115 horsepower.
UPDATED: August 11, 2011 – With the 10th anniversary of the V-Rod (2012 Model’s) the motorcycles receive an engine upgrade to 1,250 cc. H-D reports it at 125 horsepower at 8,250 RPM and 85 ft.-lbs. of torque at 7,000 RPM.
Twin Cam 96 engines – The Twin Cam 96 launched in August 2006 and was manufactured from 2007 through the current model year. At 96 cubic inches (1584 cc) it claims an 8% increase in torque from the TC88 now at 93 ft.lbs. All Twin Cam 96 engines are fuel injected. The bore is 3.75in (95.25mm) x storke is 4.38in (111.25mm). Harley left the bore the same, but lengthened the stroke from 101.6 mm on the TC 88. The TC 96/96B motor also adopted a pair of computer-controlled valves, one each in the exhaust and intake systems to help meet the EU noise and emission standards. The TC 96/96B crankcases have a new crankshaft assembly versus the TC 88, with lighter, shorter connecting rods and redesigned, less heavy pistons delivering a raised 9.2:1 compression. New camshafts deliver revised valve timing in the re-ported cylinder heads, with an up-rated oil pump to enhance lubrication by 8% for the dry-sump motor. Harley also completely remapped the Delphi ECU controlling the sequential port fuel-injection (ESPFI). The TC has cam chain tensioners with nylon composite shoes. Harley 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 TC 96. The variability of cam timing introduced by inconsistent tension on the cam chain continue to be an issue best resolved by after market gear drive cam sets (S&S and others). The 96B version contains gear-driven counterbalancer to reduce engine vibration.
UPDATED: May 8, 2009 – The motor company released Screamin’ Eagle models named TC103, a 103-cubic-inch (1,690cc) which is used in the 2009 Tri-Glide Ultra Classic (Trike) and the TC110, a 110-cubic-inch (1,803cc) in the 2009 CVO models (Fat Bob; Softail Springer; Road Glide; Ultra Classic Electra Glide). The TC110 comes in an upgrade kit for the TC96.
Speculation is the Motor Co. moved to the Twin Cam not because the Evo had reached its power limits as a design, but because HD could not prevent other manufacturers from making clones of the design. With the Twin Cam, HD was able to preempt cloning via the U.S. Patent Office, thereby making it a lot more difficult and expensive for the aftermarket vendors to compete with the Motor Co. in the development and sale of upgrades or complete motors.
In order to comply with the increasingly-stricter EPA standards, all TC96 equipped Harleys come from the factory tuned very lean, which in turn creates a great deal of heat. 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; and HD developed a “Parade” mode in which one cylinder shuts down on the Twin Cam to prevent damage to the engine.
UPDATE: August 11, 2011 – Bigger is better. On all 2012 H-D motorcycle models with the exception of the V-Rod, CVO and Sportster models they now come with a Twin Cam 103. H-D reports it’s about a 6% increase in torque. Previously the 2011 line up of touring models had the TC103 available as part of a ‘Power Pak’ option. The increased displacement from the standard TC96’s (1584 cc) to the TC103 (1690 cc) is the result of an increase in cylinder bore from 3.750-inches to 3.875 inches. The stroke is unchanged at 4.375 inches. In addition, the 2012 models with the TC103 receive an automatic compression release for improved engine starting. Depending on 2012 model the increase in peak torque ranges from 92 to 94 ft.-lbs. at 3000 to 3500 RPM on the TC96 to a 97 to 100 ft.-lbs. at the same RPM on the TC103.
Twin Cam 88 engines – (aka “Fathead) was manufactured from 1999 – 2006. The Twin Cam gets its name from the fact that it has two cams in the crankcase to activate the valves. At 88 cubic inches (1,450 cc) of displacement, it was the largest Harley motorcycle engine at the time, and it produced 80 horsepower. The engine was air-cooled, and used overhead valves activated by pushrods. The 88B version (2000-2006) of the engine, which came out in 2000, contains counterbalancing shafts to reduce engine vibration.
Evolution engines – Manufactured between 1984 and 1999. Displacement is 81.8 cubic inches (1,340 cc), and the engine produces 70 horsepower. Although the Evolution 1340cc is no longer in production, the Sportster model line of motorcycles receives Evolution engines with 883 cc and 1200 cc displacements (manufactured 1986 to present).
Shovelhead engines – Manufactured between 1966 and 1985. Shovelheads displaced 74 cubic inches (1,200 cc) and produced 60 horsepower from years 1966 to 1977. From 1978 to 1985 they were 80 cubic inches.
Panhead engines – Manufactured between 1948 and 1965. The panhead also came in 60 cubic inch (990 cc) and 74 cubic inch (1,200 cc) variations and produced 50 and 55 horsepower respectively. Big differences between the knucklehead and the panhead included aluminum heads on the panhead and internal oil lines, as opposed to external lines on the knucklehead.
Knucklehead engines – Manufactured between 1936 and 1947. The knucklehead came in 60 cubic inch (990 cc) and 74 cubic inch (1,200 cc) variations able to produce 40 and 45 horsepower respectively.
Flathead engines – Manufactured between 1929 and 1974. Flatheads did not have overhead valves. Instead, the valves ran alongside the engine and opened upwards into a chamber beside the combustion chamber. The advantage of a flathead was simplicity — no pushrods or rocker arms, and the head was a simple casting with a hole in it for the sparkplug. A typical Flathead engine had a displacement of 45 cubic inches (742 cc) and produced about 22 horsepower.
Sources: Various shop manuals, Chopper and Hotrods, American-V, Wikipedia, MSL Magazine, Jay Leno Garage, HOG Magazine (#011, 2011)
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