Why Upgrade to HKS Camshafts on the 4A-GE?

The Toyota 4A-GE engine, particularly the 20-valve versions, is renowned for its high-revving nature and responsiveness. However, the factory camshaft profiles are a compromise between emissions, idle quality, and mid-range torque. Installing a set of HKS custom camshafts allows you to shift that balance toward peak power. By increasing valve lift, duration, and overlap, HKS camshafts enable the engine to breathe more efficiently at high RPMs, unlocking significant horsepower gains—often 15–30 hp depending on the specific profile and supporting modifications.

HKS offers multiple camshaft grinds for the 4A-GE, from street-oriented Stage 1 cams that retain drivability to aggressive Stage 3 or “Racing” cams intended for track use. This guide focuses on a typical HKS Stage 2 or equivalent set, which provides a strong mid-range to top-end power increase while remaining streetable with proper tuning. Before proceeding, verify that your camshaft set includes intake and exhaust cams, shims (if required), and any necessary timing gears.

Tools, Parts, and Preparation

Required Tools

  • Metric socket set (8mm–17mm) and ratchet
  • Torque wrench (capable of 5–25 Nm range)
  • Timing belt tensioner tool or suitable pry bar
  • Camshaft holding tool (or a large adjustable wrench as a backup)
  • Gasket scraper and solvent
  • Feeler gauge set (for valve clearance checking)
  • Dial indicator and magnetic stand (optional but recommended for degreeing cams)
  • Clean lint-free rags, engine oil, assembly lube
  • Safety glasses and mechanic’s gloves

Parts Needed

  • HKS camshaft set (intake and exhaust)
  • New camshaft seals (if not included)
  • Valve cover gasket and spark plug tube seals
  • Timing belt (if due for replacement)
  • Engine oil and filter
  • Coolant (if removing the radiator for access)

Preparation Steps

Begin by parking the vehicle on a level surface and disconnecting the negative battery terminal. Allow the engine to cool completely. Drain the engine oil and remove the oil filter—this prevents contamination when the valve cover and camshafts are exposed. Remove any engine bay covers, the intake air duct, and the radiator fan shroud if clearance is tight. On some 4A-GE variants, you may need to unbolt the engine mount and gently jack the engine to access the timing belt cover bolts.

Clean the exterior of the engine thoroughly to prevent debris from falling into the timing area. Mark the distributor rotor position or note the ignition timing reference for reinstallation. Take photos of the belt routing and timing marks for reference during reassembly.

Removing the Factory Camshafts

Timing Belt Removal

Rotate the crankshaft to bring the No. 1 piston to top dead center (TDC) on the compression stroke. The crankshaft pulley timing mark should align with the 0° mark on the timing cover, and the camshaft sprocket marks should point upward and be level with the cylinder head surface. Use a wrench to loosen the timing belt tensioner and slide the belt off the cam sprockets. If the belt is old, cut it off—you’ll be installing a new one anyway.

Removing the Valvetrain Components

Unbolt the valve cover and set it aside. Remove the spark plugs to make rotating the engine easier later. Loosen and remove the camshaft bearing cap bolts in a staggered sequence (outside-in) to avoid warping the caps. Lift off the caps and keep them in order—they are specific to each position. Gently lift the old camshafts out of the head. Remove the camshaft oil seals with a seal puller, taking care not to scratch the journals.

At this point, inspect the camshaft journals and bearing surfaces for scoring or wear. Check the valve buckets and shims for damage. If you are upgrading to HKS cams with higher lift, you must verify piston-to-valve clearance, especially on the 4A-GE 20-valve engines where valve angles are steep. If clearance is insufficient, thicker head gasket or valve relief machining may be needed. HKS typically provides recommended valve clearance values—record these for later adjustment.

Installing the HKS Camshaft Set

Pre-Lube and Positioning

Apply a generous coat of engine assembly lube or clean engine oil to the camshaft journals and lobes. Place the intake camshaft into the head, aligning the dowel pin with the timing mark on the sprocket (if pre-installed). Repeat for the exhaust cam. Install the bearing caps in their correct order and torque the bolts to factory specification in a three-step pattern: 9 Nm, then 15 Nm, and finally 20 Nm (or as specified by HKS). Ensure the camshaft rotates freely by hand.

Valve Clearance Adjustment

HKS camshafts often require tighter or looser valve clearances than stock. Using a feeler gauge, measure the gap between each cam lobe base circle and the valve bucket shim. Compare against HKS’s recommended intake and exhaust clearances (e.g., 0.20 mm intake / 0.25 mm exhaust for a Stage 2 grind). If adjustment is needed, remove the shims using a shim removal tool and swap them for appropriate sizes. This step is critical for preventing valve float or premature lobe wear.

Installing New Seals and Timing Sprockets

Press new camshaft oil seals into the head using a seal driver or a socket of the correct diameter. Lightly oil the seal lips. Attach the cam sprockets, ensuring the dowel pins align with the slot. Torque the sprocket bolts to 60 Nm (for most 4A-GE applications). Do not fully tighten the bolts until the timing belt is installed and tensioned—this allows you to rotate the cams independently for timing adjustment if you are degreeing the cams.

Reinstalling the Timing Belt and Setting Cam Timing

With the crankshaft still at TDC, install the new timing belt over the crankshaft sprocket, then route it over the water pump pulley, tensioner, and cam sprockets. Align the timing marks on the cam sprockets with the marks on the back timing cover or head surface. The intake cam mark should be at the 12 o’clock position, and the exhaust cam at the 12 o’clock position (or as specified in your service manual). Double-check that the crankshaft hasn’t moved.

Apply tension to the belt using the tensioner and tighten the tensioner bolt. Rotate the engine by hand two full revolutions to verify that the timing marks realign. If they are off, repeat the belt installation. Once confirmed, torque the cam sprocket bolts to final specification (if not already done).

Pro tip: For maximum power gains, consider degreeing the camshafts using a dial indicator and degree wheel. HKS cam cards often provide recommended intake centerline and lobe separation angle. Adjusting the cam timing by a few degrees can significantly shift the powerband. This step is recommended for experienced builders or tuners.

Final Assembly and Initial Start-Up

Install the valve cover with a new gasket, torquing the bolts in a crisscross pattern to 10 Nm. Reconnect all vacuum lines, ignition components, and the air intake system. Refill the engine with fresh oil (use a high-quality 10W-40 or as recommended for warm climates) and a new filter. Reconnect the battery. If you removed the radiator, top up the coolant.

Start the engine and let it idle for 15–20 minutes to allow the camshafts to break in with the lifters. Listen for any unusual tapping (valve noise) or timing chain/belt noise. Shut off the engine and recheck valve clearances after the first heat cycle—they can tighten as the head expands. Adjust if necessary.

Tuning for Optimal Performance

HKS camshafts alter the engine’s volumetric efficiency, which requires recalibrating fuel and ignition timing. A standalone ECU (like a Link, Haltech, or AEM) is strongly recommended. At minimum, you will need a piggyback fuel controller or a reflash of the stock ECU on 20-valve engines. Take the vehicle to a professional dyno tuner. Expect to spend 2–4 hours on the dyno adjusting air-fuel ratios, ignition advance, and VTEC/VVT crossover points (if applicable on 4A-GE 20v models).

During tuning, monitor for knock, high exhaust gas temperatures, and any signs of detonation. Cams with high overlap often produce a lumpy idle and may require a higher idle speed (800–1000 RPM). After tuning, you can expect peak power gains of 15–25 hp at the wheels on a well-optimized 4A-GE with supporting mods such as headers, intake, and exhaust.

Common Pitfalls and Troubleshooting

  • Bent valves: Always check piston-to-valve clearance, especially on high-lift cams. Use modeling clay on the piston dome and rotate the engine by hand.
  • Incorrect cam timing: A skipped tooth or misaligned sprocket will cause poor performance or running issues. Recheck timing marks multiple times.
  • Oil leaks: Failed cam seals or a warped valve cover gasket surface will cause oil leaks. Use a straightedge to check the valve cover mating surface.
  • Idle quality: Expect a rougher idle with Stage 2 cams. It’s normal, but if it stalls, adjust idle speed or check for vacuum leaks.

For further reading on 4A-GE performance builds, refer to Club4AG for community guides, or consult HKS’s official camshaft pages for specific grind specs and clearance charts. If you’re new to camshaft installation, watching a video walkthrough can help visualize the steps.

Conclusion

Installing an HKS custom camshaft set is one of the most effective ways to increase the power output of a 4A-GE engine. The step-by-step process—from removing the old cams, adjusting valve clearances, and correctly timing the belt, to final tuning—requires patience and precision. The result is a more aggressive power curve that rewards high-rpm driving. By following this guide and using quality parts, you’ll be able to enjoy the legendary high-revving character of the 4A-GE with newfound vigor.