INSANE THROTTLE6d ago

Upgrading Your Camshaft: A Step-by-Step Guide for Big Twin Harley-Davidson Engines

Upgrading the camshaft on a Harley-Davidson Big Twin engine is one of the most rewarding modifications a rider can undertake. Big Twin engines—spanning the Evolution (1984–1999), Twin Cam (1999–2017), and Milwaukee-Eight (2017–present)—are the heart of Harley’s touring and cruiser lineup, delivering that iconic rumble and torque.

A cam upgrade boosts low-end torque, mid-range power, and overall throttle response, potentially adding 10–20 horsepower depending on your choice of cams (think Andrews, S&S, or Woods). But this isn’t a backyard tweak; it’s a precision job requiring mechanical savvy, the right tools, and patience. Mishandling it can lead to engine damage, so if you’re new to wrenching, consider a pro shop.This guide focuses on the Twin Cam 2006–2017 models, as they’re among the most popular for upgrades and share similarities with others.

Variations for Evolution and Milwaukee-Eight are noted where relevant. Expect 8–12 hours for a first-timer. Always consult your service manual for torque specs and model-specific quirks.

Tools and Materials: Gear Up Right

Before diving in, assemble your arsenal. Skipping quality tools here invites frustration.

  • Essentials: Socket set (metric and SAE), Allen wrenches (3/16″–1/2″), torque wrench (up to 50 ft-lbs), rubber mallet, flathead screwdriver, snap-ring pliers, zip ties or bags for labeling parts.
  • Specialty Tools: Inner cam bearing puller/installer (Harley #320640/#320652 or equivalent), pushrod clip installer (#340050), lifter holding tool (magnet or binder clip method works in a pinch).
  • Materials: New cams (matched to your build—e.g., bolt-in for stock heads), lifters (replace every time; S&S or Harley OEM), assembly lube, high-temp threadlocker (Loctite 222), O-rings/gaskets (oil pump, timing cover), adjustable pushrods (recommended for non-stock cams).
  • Optional but Smart: Engine hoist or stand, penetrant spray (PB Blaster), shop vac for cleanup, ECM tuner (post-install must for fuel mapping).

Budget $500–$1,500 for parts alone. Source from J&P Cycles or RevZilla for authenticity. Pro Tip: Work in a clean garage—debris in the cam chest is a death sentence for bearings.

Safety First: Precautions That Save Your Ride

Harleys are beasts, but they’re finicky during surgery. Disconnect the battery negative terminal to avoid shorts. Drain oil and coolant (if applicable) to prevent spills. Wear gloves, eye protection, and knee pads—concrete floors are unforgiving. Park on a level surface with the rear wheel elevated for easy cranking. If you’re cutting stock pushrods (Milwaukee-Eight tip), use bolt cutters only—no grinders, as metal shavings contaminate everything.

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Double-check timing marks; a 180-degree reversal grenades valves. And remember: This voids warranties if not done right. If in doubt, stop and call a mechanic.

Step 1: Preparation and Initial Disassembly (1–2 Hours)

Start with the easy wins to build momentum. Remove the seat (two bolts), then the fuel tank: Disconnect the quick-release fuel line (twist the chrome ring), vent/overflow hoses, and electrical plug under the tank. Loosen front tank bolts (under rubber grommets) and slide it back/lift off—store safely to avoid dents.

Next, evict the exhaust: Spray penetrant on header nuts 24 hours ahead. Remove heat shields, mark O2 sensor positions (front cylinder top, rear bottom), and unbolt mufflers/clamps. Bag clamps for reinstall. Ditch the air cleaner (dozen screws—count ’em) and spark plugs/wires.For rocker access: Pop rocker box covers (six 1/4″ hex bolts each; pry gently). Loosen breather bolts (two per cylinder) but don’t remove. Gradually loosen rocker arm bolts (four per side) in a crisscross pattern to bleed tension.

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Lift rockers, remove pushrods (chrome intake inside, black exhaust outside—mark ’em). Unscrew pushrod tubes (retainer clips counterclockwise), then lifter covers (eight Allen bolts; note O-rings).Variation Note: On Evolution models, drain transmission oil if you have a torque arm; remove pushrods via tank-off method or cut them.

nightrider.com Milwaukee-Eight skips full lifter removal for bolt-ins—cut pushrods clean and hold lifters with magnets. university.fuelmotousa.com

Step 2: Accessing the Cam Chest (2–3 Hours)

Shift to neutral, align TDC on the compression stroke (dot on crank gear at 12 o’clock via timing hole). Remove timing cover (four Allen bolts; catch gasket/oil). Inspect for sludge—clean if needed.Lock the bike in first gear, then “pop” cam sprocket bolts loose with a sharp impact (don’t strip ’em). Remove lock plates/spacers.

Loosen cam plate bolts (six around plate, leave oil pump fours). Wedge a screwdriver to slide the plate off the crank—oil pump stays put.Release the chain tensioner (one bolt), slip off the old cams, and transfer the chain to new cams (align dots side-by-side). Soak new lifters in oil; clean cams with brake cleaner—ditch factory grease.

Now, the bearings: Use the puller to extract inners (tap spreading rod, tighten nuts). Inspect for scoring; replace with Torrington-style (not OEM caged for performance cams).

Pack new ones with lube, install writing facing out (light taps only).Evolution Twist: Drill rivets on ignition cover, remove sensor/rotor first. Use a press for gear timing adjustments (0° stock, ±4° for tuning). Thrust washer end-play: .001″–.016″ via feeler gauge.

Step 3: Installing the New Cams (2–3 Hours)

Lube journals/lobes generously. Slide cams into plate holes, align dots (intake/exhaust gears parallel). Reinstall tensioner (thumb-press chain taut), then plate onto crank (rotate to mesh oil pump).

Torque six bolts in star pattern: 120 in-lbs final.Bolt on sprockets (red Loctite, 34 ft-lbs cams, 25 ft-lbs crank). Verify timing: Crank flat horizontal, upper dot at 6 o’clock, lower at 12. Install tensioner (blue Loctite, 120 in-lbs).

Drop in lifters (rollers down, flat spots aligned), secure with retainer bar. Torque lifter covers (90 in-lbs).Milwaukee-Eight Note: Reuse lifters if under 20k miles, but check preload. Advance timing marks for torque gains.

Step 4: Reassembly and Final Checks (1–2 Hours)

Reverse disassembly: Seat pushrods in lifters (exhaust out, intake in), snap clips (ramp method or tool—mind fins). Torque rockers (18–22 ft-lbs), breathers snug.

Re-gasket timing cover (star pattern, 96–120 in-lbs).Reinstall tank (lube bolts), exhaust (anti-seize nuts, 18 ft-lbs), air cleaner/spark plugs (14 ft-lbs). Top off fluids, reconnect battery.

Crank without plugs first (30 seconds) to prime oil—expect smoke. Install plugs, fire up: Idle high initially, monitor for leaks/ticks. If noisy, cycle a few times.

Tips, Traps, and Tuning: Avoid the Pitfalls

Common noobs: Misaligned dots (valve-piston kiss), dry starts (lube everything), ignored O-rings (oil floods). For Evo, shim cams .055″ if unmeasured.

Twin Cam folks: Upgrade oil pump O-rings religiously. Post-swap, dyno-tune the ECM—stock maps choke performance cams. Expect 10% MPG dip initially; break in easy (under 3k RPM, 500 miles). Pair with intake/exhaust for synergy.

Wrapping Up: Ride Harder, Smarter

A fresh cam breathes new life into your Big Twin, transforming a cruiser into a torque monster. Whether chasing highways on a Road King or twisting canyons on a Softail, this upgrade honors Harley’s legacy while pushing boundaries.

You’ve invested time and sweat—now reap the rewards. Safe rides, and remember: The best mechanics listen to their engine. If it whispers wrong, wrench again.

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