Between 1936 and 2016, engine designs released by the motor company represented a constant tweaking of the same V-twin, 45-degree, air-cooled engine design. However, in 2001 Harley released its first all new design in a commercial motorcycle (the “Revolution” in the V-Rod), but it was still based on a 60-degree V-twin.
There have been only eight major engine revisions during the company’s 114-year existence. Starting with the newest engine version to the oldest, below is a brief summary of Harley-Davidson V-Twin engine history:
Milwaukee Eight
Milwaukee-Eight Engines (M-8) — The M-8 107 and 114 launched in August 2016 for the Harley-Davidson 2017 motorcycle line-up. It’s a new eight-valve Big Twin. The displacement of the standard version is 107ci (1,750cc) or in the CVO version it’s 114ci (1,870cc). The 2017 touring models received these engines first with speculation they would waterfall down to other models later in the year. The 107 leverages precision oil-cooled cylinder heads. A Twin-Cooled version with liquid-cooled cylinder heads and radiators also launched on the Ultra Limited models, the Road Glide Ultra, and Tri Glide models. The CVO Limited and CVO Street Glide models had the Twin-Cooled Milwaukee-Eight 114.
Top view of M-8 shows stiff tubular rockers, each of which operates two valves.
The 107 (3.937 x 4.375-inch bore and stroke) is cooled by pumping oil through it and then through a “chin radiator” ahead of the crankcase. In the 107 and 114 Twin-Cooled models (the 114 has 4.016 x 4.500-inch cylinder dimensions), water/antifreeze coolant is circulated through a cored heart-shaped passage that encircles the exhaust valves and then through radiators mounted forward to either side of the engine, as we’ve seen previously. The new M-8 engine uses a nearly flat chamber of minimum surface area with four valves and abandons the large surface area of the traditional deep, modified hemi two-valve combustion chamber found in the old design. The M-8 engine operates at high compression ratios (as high as 10.5:1). As a result, the 2017 Touring motorcycles will provide 10 percent more torque. Harley stated that this will translate into two to three bike lengths faster from 0–60 mph, and one to two lengths quicker in top-gear 60–80-mph roll-ons along with improved fuel economy.
A cut-away showing the oil-cooled engines flow
Overall airflow capacity of the Milwaukee-Eight is 50 percent greater versus previous Big Twin engines, and the throttle body now has a 55mm bore. Each cylinder has an acceleration-type knock sensor along with ECM control which protects the engine from detonation. The new system is an improvement over the previous ion-sensing knock detection. The exhaust components, including the catalyst, have been relocated to help move engine heat away from rider and the new engines have a single four-lobe camshaft with automatic hydraulic tensioner in place of the Twin Cam’s pair. Drive is by chain with automatic hydraulic tensioner which helped reduced the mechanical noise.
Being used for the first time in a rubber-mounted Big Twin is a single counter-rotating internal balancer. It’s meant to eliminate 75 percent of the engine’s primary shaking force. In addition, idle rpm has been cut from 1,000 to 850 rpm all in an effort to give riders improved engine smoothness. Other engine items of note is a new higher capacity alternator along with a new 1.6 kW (2.14 hp) starter that replaces the previous 1.2 kW (1.6 hp) units. There is a self-torque boosting clutch with Brembo hydraulic actuation for a lighter lever pull and the engine ECM has been changed from a mapped system to torque-based which will be interpreted as a call for a specific torque level, not a specific throttle angle.
Twin Cam 96
Twin Cam 96 Engines — The TC 96 was introduced in August 2006 for the 2007 model year, non-counterbalanced “A” and counterbalanced “B” variants arrive at the same time. Torque is up 8 percent from TC88 (displacement is up by 9 percent). The 96-cubic-inch powerplant has over 700 new parts. The only unchanged parts are some top-end components: cylinders, rocker arms, rocker boxes, and some related parts.
The TC96 dimensions are 3.750 x 4.375 inches = 96.6-cu. in. In order to comply with the increasingly-stricter EPA standards, all TC96 equipped engines come from the factory with an automotive-style closed-loop operation of EFI and tuned very lean, which in turn creates a great deal of heat. All 2007 and later Big Twins were equipped with Electronic Fuel Injection (EFI) and 02 sensors for closed-loop operation, allowing an extremely lean tune to be safely, and consistently achieved.
Many riders commented or complained about the excessive heat making the TC96 too uncomfortable to ride in stop and go traffic, or in the heat of the summer. There were also concerns about the excessive heat’s impact on the longevity of the engine. To help combat this many owners re-tune their engines, ran synthetic oil or added 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.
2007-2017 Big Twin cranks are cast, with cylindrical roller on sprocket shaft. Twin Cam 110 introduced. EFI standard all models. Pull crank position sensor and, with a penlight, look at the sensor trips (the wavy edge of the timing-side crank flywheel); if they are machined, the crank is either hot- or cold-forged. All big twins get cam plate, bearing, and chain changes described for Dyna in 2006.
2008 In July, the engine feature called “Parade Mode” becomes available as a retrofit to alleviate TC96 temperature problems.
2009 All FLs get rider-activated parade mode, called RARCO (Rider-Activated Rear Cylinder Cut-Out). Cuts fuel and spark if engine idles more than 3 seconds above 288 F. Below 275 F, normal rear cylinder operation resumes.
Twin Cam 103 (TC 103) — In May of 2009 the TC103 (1,690 cc) arrives in certain models. 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. With 3.875 x 4.375 inch bore and stroke = 103.2-cu.in. The result is a 6 percent torque increase to 96-100 lb.-ft. at 3000–3500-rpm.
Twin Cam 110 (TC 110) — Introduced mid-year 2009 the TC110, a 110-cubic-inch (1,803cc) for the 2009 CVO models (Fat Bob; Softail Springer; Road Glide; Ultra Classic Electra Glide). The TC110 also comes in an upgrade kit for the TC96.
2011 On all 2012 motorcycle models with the exception of the V-Rod, CVO and Sportster Harley started shipping with a Twin Cam 103. Previously the 2011 line up of touring models had the TC103 available only as part of a ‘Power Pak’ option. In addition, the 2012 models with the TC103 receive an automatic compression release for improved engine starting.
2012 Compression ratio 9.6:1. Torque 100 lb.-ft. at 3500-rpm. General dyno figures are 83 hp and 95 lb.-ft.
2013 In August, Project Rushmore, an upgrade program for Harley-Davidson touring bikes, was launched. Twin-Cooling circulates a 50/50 mixture of water and ethylene glycol through passages encircling the exhaust valve seats, then to heat exchangers mounted in the fairing lowers. This “Twin-Cooled” scheme allows a safe compression ratio rise from 9.7:1 to 10.0:1 and a nice 10.7 percent torque increase, but the engine’s classic look is unchanged. A similar cooling scheme, but using engine oil instead of water/glycol, was previously deployed on 1200 Sportsters.
2015 Twin Cam 110 CVO engine (Twin-Cooled Twin Cam 110) 115 lb.-ft. at 3750 rpm. Bore and stroke are 4.000 x 4.375 inches = 109.95 cu.-in. or 1801cc High Output Twin Cam 103 makes 104.7 lb.-ft. torque at 3250 rpm.
Revolution VR Engine
Revolution Engines (VR) — Harley partnered with Porsche Engineering Services and manufacturing started 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 V-Twin and represent incremental improvements, the Revolution engine is much different. This engine is water-cooled rather than air-cooled or “twin-cooled” and its V angle is 60 degrees rather than the traditional 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.
2011 – With the 10th anniversary of the V-Rod (2012 Model’s) the motorcycles received an engine upgrade to 1,250 cc. The company reported it at 125 horsepower at 8,250 RPM and 85 ft.-lbs. of torque at 7,000 RPM.
Twin Cam 88
Twin Cam 88 Engines — (aka “Fathead” or TC 88) Manufactured from 1999 – 2006. Marketing wanted a substantial power increase over the Evolution V-Twin as modifications from the aftermarket had shown what was possible.
The Twin Cam design discussions started as early as 1992, coded P-22, and was initially planned for 1997 production, however, it was delayed by high oil temperature and rejection of an oil cooler by the styling department.
The “big-fin” Twin Cam engine (Harley-Davidson promotional material stated, (“Better engine thermal management due to 50 percent more fin area and piston cooling jets”) got 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.
Speculation has been that the Motor Co. moved to the Twin Cam not so much because the Evo had reached its power limits as a design, but because Harley-Davidson could not prevent other manufacturers from making clones of the design. 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 aftermarket vendors to compete with the Motor Co. in the development and sale of upgrades or complete motors.
The Twin Cam 88 arrived in 1999 as 3.750 x 4.000-inch bore and stroke = 88.36 cu.-in. (1450cc). The spring-type cam chain tensioners were good for 30,000 miles, best case. Twin Cam engines have a crank-speed gerotor oil pump driven from the timing end of the crank. Thus excessive crank run-out, if present, can have ill effects on the oil pump. They had a 40mm Keihin CVK carb or EFI (Twin-runner 38mm throttle bore electronic sequential port fuel injection), single-fire ignition (no wasted spark), and map-controlled ignition timing. The TC88 had a compression ratio of 8.8:1 to 9.0:1. Peak torque on the FL is 86 lb.-ft. at 3500 rpm; the Dyna makes 82 lb.-ft. at 3500.
Twin Cam 88B engine – (TC88-B) Manufactured (2000-2006) it’s nearly identical as the TC88 engine only with counterbalancing shafts to reduce engine vibration.
This system added 14 pounds to engine weight and reduced primary shaking force by 90 percent. Balance shaft bearings are in forward and rearward extensions of the right and left case halves. The balancer eccentrics are approximately 3 inches long. The balancer system produced parasitic loss of approximately 2 horsepower.
The Softail’s slimmer look was incompatible with the rubber-mounted engine system and why the counter balance design was needed. A new oil pump had wave-spring to zero out end clearance in order to prevent oil drain-back. Oil passes through 10-micron spin-on filter. The TC88-B had very short three-ring hypereutectic-alloy aluminum pistons (low expansion, allowing closer clearance) and cooled by oil jets. Sparkplugs were now 12mm.
2001 DELPHI Electronic Sequential Port Fuel Injection introduced on Softail models.
2002 DELPHI Electronic Sequential Port Fuel Injection introduced on Touring models.
2005-2006 Crank halves were cast, with cylindrical roller main bearing on sprocket shaft. The price drops significantly for replacement sets.
Evolution (“Evo”) Engine
Evolution V-Twin Engines — Manufactured between 1984 and 1999. The Evolution engine (aka. “Blockhead” or “Evo”) was the result of seven years of development for Harley-Davidson, and produced more power at every speed, plus ran cooler and cleaner.
Displacement was 81.8 cubic inches (1,340 cc), and the engine produced 70 horsepower. Although the Evolution 1340cc is no longer in production, the Sportster model line of motorcycles received Evolution engines with 883 cc and 1200 cc displacements (manufactured 1986 to present).
A problem of previous Big Twins was piston fit and piston cooling. Because an aluminum piston expands more and faster than an iron cylinder, it must be given adequate clearance. But piston cooling required intimate contact between hot piston and cooler cylinder. This was a problem without a real solution. But in adopting an aluminum cylinder on the Evo engine, it became possible to run at much closer piston clearance – in tests, Harley were able to sustain full throttle operation with clearance as low as .0004 inch. How? First of all, the aluminum cylinder expanded in step with the piston, and when the piston made contact with the wall, the cooling effect of wide-area contact prevented further piston expansion. These were German-made Mahle pistons, containing 12 percent silicon to reduce expansion. Production piston clearance was set at .0014 inch. The top piston ring was a chrome-plated barrel-face type, the second ring a 2-degree taper face, and the oil scraper a three-piece type.
Combustion chambers were made shallower by a further reduction in valve included angle to 58 degrees (27 intake/31 exhaust). This, by reducing the surface area of combustion chamber and piston crown (now flat) also cut the flow of heat into those parts.
An important Evo development goal was having the ability to withstand a 100-hour full-throttle test. Evo engine testing totaled 5600 hours and road testing of 750,000 miles.
1983 To avoid betting the company on the Evo engine, the Shovelhead was kept in production for a period. Early Evolution heads were sand-cast in alloy 242 (the same used for the heads of wartime aircraft engines). This material, containing copper, nickel, and magnesium, forms hard intermetallic compounds as it cools and ages, giving it outstanding hot strength.
1984 The last solid-mounted Shovel engines leave the line June of this year. 1340cc Evolution engine is in five models and is 20 pounds lighter than previous.
1985 Final drives are all tooth belt now. At mid-year, the interim use of sand-cast cylinder heads gave way to die-casting.
1986 New intake and exhaust systems focus on reduced noise (crossover pipe in exhaust, for example). Connecting-rod big-end roller cages had been aluminum but were now switched to M-section plated steel cages.
1987 Keihin 38mm carburetor. New cams with 24 percent less intake duration, 28 percent less exhaust duration, and 14 percent less lift. The cooler-running Evo engine was thought able to tolerate more compression and was given 8.5:1 by 1987.
1988 Keihin 38mm butterfly carb continues, as does 8.5:1 compression. Oil capacity is 3 quarts. Dyno output is 55 hp, 69.4 lb.-ft. of torque at 3000 rpm, new 32 amp alternator.
1989 New 1.6-hp starter, new case, for quicker hot-starting. Electronic cruise control introduced. Carburetor is now Keihin CV (constant vacuum type), slips into rubber manifold rather than old two-bolt mounting.
1990 New clutch, 40mm Keihin.
1995 Fuel injection becomes an option. Marelli EFI available 1995-2001. Carburetor alternative was Keihin CVK40.
Shovelhead Engine
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 1/2 to 1985 they were 80 cubic inches.
First-year Shovelheads were given aluminum versions of the Sportster iron heads (long fore-and-aft fins, straighter ports giving 10 percent more power—the so-called “Power-Pac.” Also, the compression ratio rose from the 6.0:1 range of the original “E” to higher numbers such as 8.0:1.
Harley-Davidson seeked to solve its financial problems by merger with AMF in 1969.
Panhead Engine
Panhead Engines — Manufactured between 1948 and 1965. The Panhead came in 61 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.
The 61’s bore and stroke are 3.3125 x 3.5 inches = 60.3 cu.-in., and the 74’s was 3.4375 x 3.96875 in. = 73.7 cu.-in., making claimed 55 horsepower. OHV had overcome much of the 74- and 80-inch flatheads’ overheating problem. The new Panhead engine used the former bottom end.
The new engine had the ability to handle heat of higher-power operation, head cooling was greatly boosted by switching material from cast-iron to aluminum, with multiple times iron’s heat conductivity.
The large one-piece valve covers — the “pans” that gave this engine its name sought to simplify the problem of oil containment but was not completely successful. Panheads still leaked oil from the top end.
Knucklehead Engine
Knucklehead Engines — In 1936, America was digging its way out of the Great Depression and Harley-Davidson introduced an all-new engine to replace its side valve Big Twins. The new “E” model was the result.
Manufactured between 1936 and 1947. The Knucklehead (so-called because of a resemblance of its rocker-box ends to the knuckles of a clenched fist) came in 61 cubic inch (990 cc) and 74 cubic inch (1,200 cc) variations able to produce 40 and 45 horsepower respectively.
Harley engineers had previous experience with OHV engines, but this was to be the company’s first production OHV. An advancement of the new engine was it’s modern “dry sump” which pumped, recirculating oil through out the system. Previous engines had been lubricated by so-called “total-loss,” meaning that the rider or a drip-feed added oil to the crankcase as needed.
The Knucklehead in engineering terms was the engine from which all subsequent Big Twins were based-from Panhead in 1948 to Shovelhead in 1966 to Blockhead (Evolution) in 1984.
Flathead Engines — In many ways the “K” model was a consequence of WWII. At the time the British bikes were sporty-smaller and lighter, with hand clutches and foot shifting. Harley’s K engine was manufactured between 1929 and 1947.
The engine was a mix of old and new. The old part was that it was sidevalve, and an update of the W series 45. The new part was unit construction; the transmission no longer existed in a case separate from the engine.
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 spark plug.
A typical Flathead engine had a displacement of 45 cubic inches (742 cc) and produced about 22 horsepower. In 1954 displacement was increased to 55 cubic inches and the K became the KH. The racing version of the K, the KR, was competitive in flat-track and road racing into the late 1960s.
The KHK version of 1955 included the cams, valves and other tweeps developed for the racing KR.
Sources:
Northwest Harley Blog — Engine History
Northwest Harley Blog — Engine History Update
Northwest Harley Blog — Milwaukee Eight
Wikipedia — Harley-Davidson Engines
Photos courtesy of Harley-Davidson
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