Monster Motor | A Look Inside Harley's 120R Engine

1 As we walked into the manufacturing/assembly portion of the building, we came across engine cases that were waiting to be machined and then put on the assembly line.

1 As we walked into the manufacturing/assembly portion of the building, we came across en

For the 2011 model year, Harley wowed performance enthusiasts when it announced the introduction of its new 120ci Screamin’ Eagle (SE) Pro 120R engine. This was the fist time in several decades that the Factory had offered a fully assembled high-performance, race-ready crate engine. Ready to drop into a stock chassis and bolt right in place with no frame modifications or engine mount relocations, the introduction of the 120R was very appealing to those looking for the thrill of high horsepower and torque. What was most appealing however, was the potential of achieving 135-plus horsepower and 137 lb-ft of torque from the 4.06-inch bore x 4-5/8-inch stroke engine for a modest price ranging between $5,700-$6,000.

However, there’s a catch to the 120R, it’s offered for race-only applications meaning it’s not a street-legal engine. But what it does provide is a relatively low-priced powerplant for entry-level race enthusiasts to dip their toes into the fast-paced world of drag strip racing. Even those with a long history of staring down the “Christmas” tree waiting for the green light found the 120R and its power potential an intriguing option for the strip. In fact to help support the introduction of the new race class engine, Harley sponsored an all-new Draggin’ Bagger drag racing class in conjunction with its other race class sponsorships with the All Harley-Drag Racing Association. Designed for ’99-later H-D Touring models (except Road Kings) and with limited allowable performance modifications to the 120R engine, chassis, suspension, bodywork, and other components of the bike, the Draggin’ Bagger class was created to provide new and old race enthusiasts an economical way to have fun on the drag strip.

Some of the highlights of the SE 120R include: 4.060-inch big bore cylinders, 4-5/8-inch stroke SE pro stroker flywheel and rod assembly, high-compression 10.5:1 nickel-plated forged pistons with Teflon-coated skirts, SE 266E high-lift cams, CNC-ported Maximum Velocity Area (MVA) heads with automatic compression releases, factory-machined engine cases, and now for 2012 the 120R comes with a new billet cam plate and high-volume oil pump. What’s not included and needs to be purchased separately is an SE throttle body, high-flow injectors, high-performance clutch, exhaust system, high-flow air cleaner, and a tuning module. The SE 120R is available for Dyna, Softail, and Touring models, you just need to check the » SE P&A catalog to find out which part number to order for your specific year and application.

2 Here is just a tiny fraction of the tooling equipment used throughout the facility. These cutting tools are all preset and ready to be put to use.

2 Here is just a tiny fraction of the tooling equipment used throughout the facility. The

Intrigued by this monster engine, I took a trip out to Harley’s Powertrain Operations Center (POC) at its Pilgrim Road facility in Milwaukee to learn more about this race-ready engine and see how it comes together. Upon arriving at the facility I was met by Tony Nicosia, category manager for SE Performance and Wheels, Mark Dane, senior project designer for SE Performance Products, Brad Bishop, SE project engineer, and Grif Maupin, project engineer for Powertrain Operations. Working as the category manager for the SE line, it was Tony’s job to work with his team to execute the development of the 120R from concept to final product.

Now you might think Tony and the guys had an easy task set before them when it came to making the 120R a reality right? Well, not exactly. There was one major challenge put before them: keep the cost down for the end user. In order to help keep the overall cost of parts, accessories, manufacturing, assembly, and all the other expenses involved in building a complete engine, they had to build the 120R utilizing as many existing parts as possible and make use of H-D’s large capital investments—the machine tools at the POC and the factory assembly line.

“We wanted to use stock cases to keep the cost down,” Tony told us. “And during the development process we learned that we couldn’t go bigger than a 4.060-inch bore because we would run out of room in the stock cases. To get the 120ci displacement it came to the stroke as well. Mark and Brad had to come up with the parameters around the stroke; what was the right rod length from center-to-center hole. Issues popped up, it wasn’t like, OK it’s a 4-5/8-inch stroke and a 4.060-inch bore and we’re done. Piston design was very crucial. We had to figure out how to create the skirt so it had the proper support as it traveled in the cylinder. We had to create all new piston oil jets, which also involved all new tooling to make the jets. It was a huge amount of development work and a lot of testing. As we tested we found issues, then we had to figure out how to address those issues and figure out what we had to change to get it to work the way we wanted it to work. The flywheel was unique, it was a unique stroke for us, the cylinders already existed, the pistons were unique, and the oil jets were unique. But a lot of the other stuff already existed like the SE ported heads, the SE race springs were already in the heads, the automatic compression releases existed, the 266E cams had just come out, and a lot of the other components were very common like the rocker box covers, rocker arms, and rocker arm supports.”