S&S Cycle X-Wedge Engine - First Look

Shown is the complete X-Wedge engine. It is an air-cooled, pushrod, 56-degree V-Twin. Built with commonized engine parts and fasteners, it utilizes a simplified design, providing 30% fewer parts than earlier V-Twins. The X-Wedge is '08 emissions compliant, thanks to an efficient combustion chamber and proprietary engine-management control system.

A one-piece forged crank is used in the X-Wedge. The Nitrated pork chop-style crank uses two-piece side-by-side rods running on plain bearings. An assembled crank weighs about six pounds more than an S&S; Evo-style crank.

Here's the X-Wedge crankshaft and I-beam rods installed in the left-side crankcase. The series of elongated holes is for the electronic timing. A horizontal oil scraper chamber is built into the rear of the case. During the pistons' downward stroke, oil is forced from the case's crankshaft cavity, into the scraper chamber, through a one-way reed valve and eventually into the cam case for scavenging by the oil pump.

Shown is the side-by-side connecting rod setup. The cylinders and crankcase spigot holes are offset side-to-side to match the rod offset.

Here are the three cams (two exhaust, one common intake) attached to the cam plate. The cams are lubricated by oil while the belt runs dry. Also seen is the gerotor oil pump surrounding the right-side pinion shaft. Top-end oil is returned via pushrod tubes to the cam case. There are no oil return galleys in the cylinders and no external oil lines. A crankcase-mounted reed valve eliminates the need for a rotary breather valve. The gerotor pump picks up oil at the base of the cam case for increased efficiency and better flow. All bolts used on the cam cover, cam plate, and rocker covers are the same size and length to simplify assembly.

The heart of the X-Wedge is the three-cam layout driven by a dry carbon-fiber cord belt kept in adjustment by an automatic tensioner. A three-cam design offers straighter pushrod angles and shorter pushrods for improved valve timing and higher rpm. Visible in this cutaway is the gerotor oil pump at the bottom of the cam case.

Lifters and pushrods are shorter and weigh less than with earlier V-Twins. Lifter blocks are integrated into the right-side crankcase while lifter covers are interchangeable front to rear. With a large and small hole in the case, there is sufficient space for top-end oil to drain into the cam case and for internal engine air to move freely.

Common front and rear flattop pistons are forged for strength and designed with anti-friction coated slipper skirts. Slipper-style pistons provide minimum skirt area for reduced friction, narrow pin towers for a short and lightweight pin, and judicious lightening where possible. One benefit of the X-Wedge's 56-degree design is that there is no need for piston-skirt reliefs to accommodate large bores, resulting in improved piston stabilization, reduced wear and increased cylinder sealing.

X-Wedge cylinders are short and use a five-stud cylinder bolt pattern, providing higher and more even clamping forces for improved base and head gasket sealing. Identical front and rear cylinders, lifter covers, and other components increase simplicity while reducing costs.

The automotive-style combustion chambers are compact, efficient and designed for a flattop piston using pump-gas compression ratios. Design features include a generous squish area, centrally located spark plug, and a straight line from intake to exhaust, allowing optimized performance from the wedge-style chamber.

The cylinder head's rocker box area houses roller rockers set parallel to the valves and attached to head studs instead of the rocker cover. A single beehive valve spring per valve allows for reduced spring pressure. Since the rocker cover is not structural, there is only one gasket surface to maintain, which has a wide clamping area for solid gasket sealing.

With the Teardrop air cleaner removed, the S&S; 52.3mm single-bore throttle body is seen. The X-Wedge uses a closed-loop fuel-injection system with fuel injectors installed into the intake ports for improved fuel atomization in the cylinder.

Here at HOT BIKE, we strive to stay on top of the most innovative parts to hit the American V-Twin industry, so we're bringing you a new tech piece entitled "First Look." With this series, we will search out the newest parts and get you the inside scoop on what they are and how they work. Then we will follow up in a future issue by actually installing the part(s), explaining the install process, and giving an evaluation.

S&S; Cycle, of Viola, WI, formally unveiled its all-new X-Wedge engine earlier this year at the Cincinnati V-Twin trade show. S&S; President Brett Smith said, "We wanted to do something completely different and off the map." And something completely different they surely did. The new engine, dubbed the "X-Wedge," is a 117ci air-cooled pushrod V-Twin with an emissions-legal fuel-injection management system. Smith went on to say, "The 45-degree V-Twin is rather old technology and creates limitations."

Code-named "Fred" by S&S; engineers, the X-Wedge program began in 2002. Design goals for the X-Wedge engine were to solve problems that have plagued earlier V-Twins while adding innovative functionality, simplicity, and ease of production. Moreover, S&S; wanted to ensure compliance with future worldwide emissions regulations. If you are the owner, rider, or builder of an earlier V-Twin, you probably are aware of traditional problems such as wobbly and out-of-true cranks, undue camtrain wear and noise, oil puking, overheating, and excessive vibration. S&S; addressed these and other issues with their new, fully EPA-compliant X-Wedge engine.

The new X-Wedge engine is a 117 cubic inch displacement (4-1/8-inch bore x 4-3/8-inch stroke), 56 degree (actually 56.25 degrees), air-cooled, pushrod-valvetrain V-Twin. It has a belt-driven 3-cam layout, one-piece forged crankshaft, automotive-style two-piece rods, and closed-loop fuel injection. The new engine accepts the standard V-Twin charging system and common primary drive components, but has unique engine-to-chassis mounts for additional strength. Since X-Wedge cylinders are designed to accommodate bore sizes from 4.125 inch to 4.375 inch, S&S; will be offering additional engine combinations and Hot Set Up Kits.

The foundation of any quality engine is a stout bottom end. As such, S&S; departed from the traditional three- and five-piece V-Twin crank and designed a forged, one-piece crankshaft. Connected to single 2.2-inch crankpin are automotive-style two-piece connecting rods arranged side-by-side. Instead of riding on needle bearings, the I-beam rods run on plain bearings lubricated by oil fed at up to 80 psi. The pork chop-styled Nitrated crank includes a series of elongated holes on the right-side half that a crank position sensor reads for the engine's electronic management control. At 43 pounds, the new crank is roughly six pounds heavier than an S&S; Evo-style crank. The extra weight is intended to help reduce vibration.

Supporting the pork chop-style crank is a robust crankcase with offset cylinder spigot holes, simplified oil control system and improved engine mounts. The offset spigot holes are necessitated by the side-by-side rod configuration. Crankcase cylinder angle is set to 56.25 degrees, versus 45 degrees for earlier V-Twins. The wider cylinder angle, when combined with a higher case deck height, allows larger bore sizes without having to notch the piston skirts for clearance when the pistons are at the bottom of their stroke. A wider 56-degree cylinder angle also results in a more self-balancing engine than a narrower 45-degree angle. X-Wedge crankcases are designed to accept standard primary drive and transmission components. S&S; offers their own six-speed gearbox and heavy-duty clutch components for big, high-torque applications. X-Wedge engine mounts are beefier than stock units and use 7/16-inch bolts instead of traditional 3/8-inch items. To eliminate undesirable performance compromises, X-Wedge case mounts are designed for aftermarket frames and will not fit in a standard frame. Currently, no less than three aftermarket chassis manufacturers are currently offering frames for the X-Wedge engine.

Lubrication is provided by a new dry-sump oiling system utilizing a gerotor pump internally located in the right-side cam case and driven by the crank's pinion shaft. Used oil is eventually collected in a common sump at the bottom of the cam case and returned to the remote tank. Oil is fed under high pressure to the crank's two main bearings and rod journals along with other components through internal oil galleys and controlled by an 80-psi bypass. A horizontal oil scraper chamber is built into the rear of the crankcase. During the pistons' downward stroke, oil collected in the crankshaft cavity is first forced into a scraper chamber, then through a one-way reed valve, and finally into the cam case sump for scavenging by the gerotor pump. A case-mounted reed valve eliminates the need for a traditional rotary breather valve.

The engine's top end is lubricated by oil flowing up through the pushrods and returned to the cam case sump through the large-diameter pushrod tubes. Therefore, the cylinders are not machined with an oil return galley. One large and another small hole in the crankcase near the pushrod tubes provides sufficient space for top-end oil to drain into the cam case and for internal engine air to move freely between the heads and bottom-end areas. To maintain a clean-looking silhouette, no external oil lines are used, and the front-mounted oil filter is fed through internal galleys in the cases.

The heart of the X-Wedge engine is its serpentine belt-driven three-cam design. Three camshafts, two exhausts, and one common intake are actuated by a Gates carbon-fiber cord belt kept in adjustment by an automatic tensioner. The three-cam design offers straighter pushrod angles and shorter pushrods for improved valve timing and higher rpm running. When combined with automotive-styled roller-tipped rockers and roller lifters, the result is an incredibility quiet valvetrain. The three camshafts are supported on the right side by a cam plate and on the left by three needle bearings pressed into the crankcase. When assembled, the cams are enclosed in the cam case along with the gerotor oil pump. The three cams are lubricated by oil while the 30mm-wide toothed timing belt and its three idler gears run dry in an adjacent timing chest.

Hydraulic roller lifters, which are shorter and lighter than earlier V-Twin lifters, are secured by lifter blocks integral to the crankcase. The lifters and lifter blocks are covered by common front and rear lifter covers. The rotating cam lobes actuate the lifters, which in turn actuate four pushrods. S&S; calls this a "free-spin" design in that the valves will not hit each other or the pistons if the belt should break and the cams go out of phase.

The flattop pistons are forged for strength and designed with small slipper-style skirts. Slipper pistons provide minimum skirt area for reduced friction, narrow pin towers for a short and lightweight pin, and judicious lightening where possible. To further reduce friction and scuffing, piston skirts are coated with an anti-friction coating. One benefit of the X-Wedge's 56-degree design is that there is no need for piston-skirt relief to accommodate large bores, resulting in improved piston stabilization, reduced wear, and increased cylinder sealing. For simplicity, a common piston design is used for both the front and rear cylinders.

The common front and rear cylinders are die-cast aluminum and fitted with an aggressively textured cast-iron liner for improved retention and heat transfer. The cylinders are relatively short in length and secured using a five-bolt stud pattern. A five-bolt pattern offers higher and more even clamping forces than a four-bolt pattern, resulting in improved base and head gasket sealing. For improved cooling, the cylinders have about 15 percent greater fin area than an S&S; Evo-124 cylinder and are round in shape with no top-end oil return galleys for reduced distortion. The current cylinder liner accepts bore sizes between 4.125-inch and 4.375-inch.

S&S; engineers topped of the X-Wedge engine with aluminum cylinder heads and a wedge-style combustion chamber. In fact, the X-Wedge was named for the shape of its combustion chamber. Unlike earlier V-Twin engines, the X-Wedge chamber sets the valve stems parallel to one another instead of angled fore and aft. This design allows for a more compact chamber with higher compression ratios using a flattop piston. The wedge chamber also offers reduced surface-to-volume area for better heat retention, a centrally located spark plug for short flame travel, and generous squish area for high turbulence. The result is excellent cylinder filling and efficient, unimpeded combustion for optimized power along with reduced potential for detonation and fuel octane requirements. Using a flattop piston with the wedge chamber on a 117ci engine produces a 9.75:1 mechanical compression ratio.

Large-bore engines provide much room for large valves. As such, S&S; engineers designed the X-Wedge head with a 2-inch intake valve and modern intake port. The exhaust side sports a 1.6-inch exhaust valve along with an efficient, short exhaust port to minimize heat loss and maximize exhaust gas velocity for optimum cylinder scavenging. A single beehive valve spring (progressively wound and tapered from bottom to top) per valve minimizes harmonics and allows for reduced valve-seat pressure.

In the rocker box area, the X-Wedge head offers improved rocker arm design. Rocker arms on earlier V-Twins are heavy, long, and tend to flex. The result is inaccurate valve control and reduced power. In contrast, the X-Wedge rockers are arranged transversely, which keeps valvetrain components in a single plane. The result is a lighter, stiffer valvetrain and more accurate valve action. X-Wedge rockers are automotive-style, stamped out of steel and tipped with rollers for reduced friction and wear. The 1.7:1-ratio rockers are set parallel to the valves and attached to head studs instead of the rocker cover as with earlier V-Twins. S&S; engineers also wanted to eliminate the earlier multi-piece rocker covers, which provide poor rigidity for valvetrain support and often lead to oil leaks. X-Wedge rocker covers are one-piece and non-structural, requiring only one gasket surface to maintain, which offers a wide clamping area for solid gasket sealing.

Since the X-Wedge engine had to be worldwide emissions compliant, S&S; developed a new closed-loop fuel-injection system using a new 52.3mm single-bore throttle body and port-mounted injectors controlled by a new proprietary electronic-management system. The new system includes one oxygen sensor for each cylinder, thereby processing each cylinder as a separate engine.

The X-Wedge engine represents a huge step forward for S&S.; S&S; goals were to design an engine with the look, feel, and smell of a traditional V-Twin, but with simplified engineering, superior durability, increased power, and compliance with worldwide emissions requirements. Clearly, the X-Wedge is elegantly simple while design improvements should eliminate earlier V-Twin durability gremlins. Rated at about one rear-wheel pound-feet of torque per cubic inch in emissions-legal trim, the X-Wedge provides an excellent foundation for even more performance. It seems to us that S&S; is not only keeping it simple, but also maintaining the look, feel, and smell of the traditional V-Twin while meeting '08 and future worldwide emissions standards.

S&S; X-Wedge
First Look Specs

  • 117 cid (4-1/8 bore x 4-4/8 stroke)
  • 56.25 degree V-angle
  • Air cooled
  • Pushrod valvetrain w/hydraulic roller lifters
  • Serpentine belt-driven 3-cam layout
  • 30mm wide carbon-fiber cord belt w/ auto tensioner
  • 1-piece forged Nitrated crank
  • 2-piece, I-beam connecting rods
  • 7.400-inch connecting rod length
  • 2.36-inch main bearing dia.
  • 2.20-inch rod journal dia.
  • Dry sump oiling w/Internal gerotor pump & 80 psi bypass
  • 5-stud cylinder pattern
  • Round die-cast aluminum cylinders w/ cast iron liner
  • Cylinder liner accepts 4.125-4.375-inch bores
  • Forged flattop slipper-style pistons w/.927-inch wrist pin dia.
  • 9.75:1 CR
  • Cross-flow wedge-style combustion chambers
  • 2-inch Int. valves, 1.6-inch Ex valves
  • Automotive-style stamped roller rocker arms
  • 1.7:1 rocker arm ratio
  • One-piece rocker covers
  • Port-mounted fuel injectors
  • Single-bore 52.3mm throttle body
  • Electronic closed-loop fuel injection
  • Accepts standard charging system & primary drive
  • Unique 4-bolt engine-to-chassis mounting system
  • 163 lbs. total engine weight