Upgrading your Chevy 350 with a Comp Cams XR270HR camshaft is one of the most effective ways to unlock significant horsepower and torque gains, transforming your small-block into a responsive, street-friendly performer. This hydraulic roller camshaft is engineered to deliver a broad power band, excellent throttle response, and improved efficiency, making it a favorite among builders looking for a reliable upgrade without sacrificing drivability. However, a camshaft swap is a precise mechanical task that demands careful preparation, accurate installation, and correct break-in procedures to ensure long-term reliability. This comprehensive guide walks you through every step—from gathering the right tools to firing up the engine—so you can execute the install with confidence and get the most out of your Comp Cams XR270HR.

Why the Comp Cams XR270HR for Your Chevy 350?

The XR270HR is a hydraulic roller cam designed specifically for small-block Chevy engines (283, 305, 327, 350, 400) and works best with a moderate to high-performance setup. With a duration of 270° intake/exhaust at 0.006" lift and 212° intake/218° exhaust at 0.050", combined with 0.450"/0.460" lift, it delivers a strong idle with some lope, excellent mid-range torque, and top-end pull that shines with a good intake, headers, and a tuned carburetor or EFI system. It pairs well with 9.5:1 to 10.5:1 compression ratios, aftermarket cylinder heads, and performance intake manifolds. Whether you're building a street-driven muscle car or a weekend cruiser, this cam offers a proven blend of power and civility.

Tools and Materials Needed

Having the correct tools and parts on hand before you start prevents frustrating delays and ensures the installation goes smoothly. Below is a comprehensive list. More specialized items, like a camshaft installation tool or degree wheel, are critical for accurate alignment and timing.

  • Comp Cams XR270HR camshaft (part number 08-303-8)
  • New hydraulic roller lifters – always use lifters matched to a new cam (Comp Cams 882-16 recommended)
  • Timing chain set – choose a true roller chain for durability and accuracy
  • Camshaft installation tool – or a long bolt and washer to drive the cam in
  • Torque wrench (ft-lb and in-lb range for precision fasteners)
  • Socket set (metric and SAE; 3/8" and 1/2" drive with extensions)
  • Allen wrenches and screwdrivers
  • Gasket set for timing cover, intake manifold, and valve covers (use quality Fel-Pro or similar)
  • Engine assembly lube (high-pressure moly-based for cam lobes and lifter bottoms)
  • Motor oil (SAE 30 or 10W-30 conventional for initial filling)
  • Priming tool (distributor drive shaft with hex for oil pressure pre-lube)
  • Seal installer for timing cover and front main seal
  • Loctite (medium strength for bolt heads)
  • Shop towels, degreaser, and safety glasses
  • Mechanic's wire ties to label and organize removed parts

Optional but highly recommended: a degree wheel and dial indicator to verify cam timing, especially if installing with aftermarket timing set gears with multiple keyway positions.

Preparation and Safety

Work in a well-ventilated area on a cool engine. Disconnect the negative battery cable to prevent accidental short circuits or component damage inside the electrical system (ECU, gauges, etc.). Drain the cooling system to a level below the intake manifold – removing the radiator is often necessary for access, but at minimum drain coolant to avoid spills. Remove the hood or prop it fully open for better overhead clearance.

Clean the entire engine external area, especially around the front timing cover and valley. Dirt that falls into the lifter valley or oil galleys can score new bearings and cause premature failure. Cover exposed openings (such as intake ports or lifter bores) with clean rags or tape as you work.

If the engine is in the vehicle, you may need to remove the fan, fan shroud, water pump, and radiator hoses for easier access to the front of the engine. For a chassis install, support the engine properly with a jack if you also need to replace the oil pan gasket (though not required for cam swap).

Step 1: Remove the Old Camshaft

Disassemble the Front of the Engine

Begin by removing the valve covers. This exposes the valve train – you'll need to remove the rocker arms and pushrods later, but for now, focus on the front. Remove the intake manifold (if present) to access the lifter valley. This step is mandatory because the lifters must be extracted before the camshaft can slide out. On a Chevy 350, the intake manifold also holds the distributor, which must be removed and its gear indexed for re-installation.

Remove the distributor: Mark the rotor position on the housing and note the orientation to simplify re-installation. Disconnect the spark plug wires and remove the distributor hold-down clamp. Lift the distributor out. If the engine has not been turned after removal, the crank position will remain correlated – but when you rotate the engine later for timing chain installation, you'll need to re-time it anyway.

Timing Chain Cover Removal

Remove the water pump, belt, and harmonic balancer. Use a puller to extract the harmonic balancer – never hammer it off, as this can damage the crank snout or thrust bearing. With the balancer off, remove the timing chain cover bolts. The cover includes the front crankshaft seal; you may replace this seal as part of the rebuild. Gently pry the cover away from the engine block. Remove the gasket material from the block and cover surfaces.

Extract the Timing Chain and Old Cam

With the cover off, you'll see the timing chain and gears. Remove the camshaft gear bolt (this can be tight – brace the crankshaft with a spanner or use a chain wrench). The chain and gears will come off as a set. Now locate the camshaft thrust plate (if equipped) and unscrew its bolts. The camshaft should slide out toward the front of the engine. Use a camshaft removal tool or carefully pull it by hand, supporting the lobes to avoid damaging the bearings. The old cam can be disposed of or saved as a core – but discard it, as used cams are not safe to reinstall after removal.

Important: Remove all lifters from their bores. The XR270HR requires new lifters – never reuse old ones, as they have worn patterns that will not mate correctly with a new cam. Label the pushrods if reusing them, but a cam swap often includes new pushrods if the base circle or lift changes. For this cam, stock length pushrods usually work with stock-style rockers, but measure and confirm later.

Step 2: Inspect and Prepare the New Camshaft

Check Bearings and Clearance

Before installing, visually inspect the new cam lobes and journals. They should be smooth, with no scratches or pitting. Test fit the cam into the engine block to ensure it rotates freely. Apply a light coat of engine oil to the cam bearings inside the block. If the cam is tight or binds, check for debris in the bearing bores or journal burrs – correct before proceeding.

Lube the Lobes and Journals

Apply a copious amount of comp camshaft break-in lubricant (or moly-based assembly lube) to all cam lobes and lifter bottoms. This is not optional – the initial startup relies on this lubricant to prevent galling. Also oil the cam bearing journals. Do not use engine oil alone; it drains off too quickly. Use the supplied tube from Comp Cams or a high-quality equivalent.

Note on lifter pre-lube: Each lifter's base must be coated with the same assembly lube. New hydraulic roller lifters are pre-filled with oil from the factory, but you should install them submerged in a container of engine oil for a few minutes to ensure the plungers are primed. Do not let them run dry.

Step 3: Install the New Camshaft

Insert the Cam

Insert the camshaft slowly into the engine block. Use a camshaft installation tool – a long Allen bolt with a handle or a dedicated driver – to push it in evenly, keeping it parallel to the block. Do not force it; if it binds, stop and rotate slightly. The journals are slightly narrower than the bearing bores; a gentle turning motion helps align them. Slide the cam until the thrust plate or retaining bolt hole is visible.

Secure the Thrust Plate

Install the camshaft thrust plate (if your block has one; most late-model 350s use a plate behind the timing gear). Tighten the bolts to 18-22 ft-lbs (check spec). For earlier blocks, the camshaft retainer plate is part of the timing cover. Follow manufacturer recommendations for your specific block year.

Step 4: Install the Timing Chain and Set Timing

Align Timing Marks

Turn the crankshaft so that the keyway points to 12 o'clock (or whatever is specified for your timing set – typically with the crank gear key at top and cam gear marks aligned). Install the timing chain set: first the crank gear, then the cam gear, with the chain looped. Ensure the timing marks line up exactly: the zero marks on both gears must face each other (crank at 12 o'clock, cam at 6 o'clock when looking at the front, depending on gear design). Double-check with a degree wheel if you want precision – a chain stretched by one tooth can ruin engine performance.

Torque the Cam Gear Bolt

Apply a drop of Loctite to the cam bolt threads. Torque to 50-60 ft-lbs (refer to Comp Cams instructions as exact spec varies). Use a crank holder to prevent rotation. Do not overtighten.

Verify Cam Timing

Using a dial indicator on the inlet lobe (number 1 cylinder) and a degree wheel on the crank, rotate the engine through two full turns. The cam should achieve peak lift at the factory-specified position. If the cam is installed advanced or retarded, adjust the timing set (most aftermarket double-roller sets offer +/- 4 degrees of adjustment). For the XR270HR, installation straight up is typical for most builds, but custom timing can shift the power band.

Step 5: Install Lifters and Pushrods

Install the new hydraulic roller lifters into their respective bores. Use a generous coat of assembly lube on the lifter bases. The lifters should slide in easily – if they stick, clean the bores with a brake cleaner and wipe dry. Push the lifters down until they contact the cam lobes. Rotate the engine a few turns by hand to ensure the lifters move freely and don't bind anywhere.

Install pushrods: for stock rockers, use the factory length or measure with checking pushrods. The XR270HR has a modest lift that typically doesn't require different pushrods with a stock-style valvetrain. However, if you have aftermarket heads or adjustable rockers, set the preload to 0.020-0.060" depending on lifter design (consult the lifter spec sheet). Tighten the rocker arms to the proper torque (usually 20-30 ft-lbs for stamped steel, or to zero-lash plus 1/2 turn for hydraulic roller).

Step 6: Reassemble the Front of the Engine

Timing Cover Installation

Clean the block and cover surfaces. Install a new timing cover gasket (or use RTV sealant as recommended). Install the front crankshaft seal – press it evenly to avoid leaks. Reattach the timing cover bolts, torquing in a crisscross pattern to 18-22 ft-lbs. Do not overtighten the small cover bolts – they can strip or distort the cover.

Water Pump, Harmonic Balancer, and Pulleys

Install the water pump with new gaskets. Apply a thin layer of RTV to the bolts that go into the water jacket to prevent leaks. Torque water pump bolts to 15-20 ft-lbs. Install the harmonic balancer – use a puller tool to press it onto the crank snout until it is flush. Never hammer the balancer on; this can damage the crank and timing gear. Torque the balancer bolt to 150-170 ft-lbs (depending on year – early engines may have less). Reinstall belts and pulleys, noting belt routing.

Intake Manifold and Valve Covers

Install the intake manifold gaskets (locate them properly – many have rubber silicone strips at the front and back). Apply a bead of RTV silicone to the ends where the block meets the manifold. Torque the intake manifold bolts in the correct sequence to 25-30 ft-lbs (three stages: 10, 20, then final). Reinstall the distributor, aligning the rotor with the number one spark plug position. You will need to re-time the engine after startup – for now, just seat the distributor and tighten the clamp lightly.

Install new valve cover gaskets. Use a small amount of RTV in the corners where the cover meets the head. Torque valve cover bolts to 5-8 ft-lbs – these are small, thin bolts that strip easily.

Step 7: Final Checks and Engine Startup

Fluid Fill and Pre-Lube

Fill the crankcase with fresh oil (SAE 30 or 10W-30) plus a bottle of zddp additive or Comp Cams break-in additive. Fill the cooling system with 50/50 antifreeze/water. Before starting, you must prime the oil system. Use a priming tool (a shaft with hex that fits into the distributor drive) and a high-speed drill. Spin the oil pump until you see oil flow to all rocker arms – this ensures the lifters have oil and the bearings are lubricated. Crank the engine (with ignition off) for 15 seconds to build oil pressure after priming. Check for leaks around the timing cover, intake, and valve covers.

Initial Start and Break-In

Start the engine and immediately bring the RPM to 2000-2500 RPM for the first 20 minutes. Do not let it idle! This is the critical break-in period where the cam lobes and lifters mate. Fluctuate the RPM slightly (2000-3000) to splash oil onto the cam lobes. Check for leaks, listen for unusual noises (valvetrain clatter, bottom end knocks). If the oil pressure stays above 20 psi at idle when warm, and no major issues arise, the cam is breaking in successfully.

After the initial 20-minute run, let the engine cool completely. Change the oil and filter (often called "break-in oil" removal). Re-torque the intake manifold bolts and valve covers (if needed). Re-check timing with a timing light and set base timing per your engine setup (typically 10-12 degrees BTDC). Adjust the carburetor or EFI for idle and mixture.

Tuning for Maximum Performance

The XR270HR cam will benefit from a free-flowing exhaust (headers recommended), a matching intake (such as an Edelbrock Performer RPM or Weiand Stealth), and proper jetting or tuning of the fuel mixture. If you have an automatic transmission, consider a higher stall torque converter (2000-2500 RPM stall) to use the cam's power band. For manual transmissions, the cam pulls well from 2000 RPM onward and doesn't require unusual driving techniques.

For more technical data and recommended companion parts, refer to the official Comp Cams website for the XR270HR (part 08-303-8) specification sheet. A detailed Chevy 350 camshaft install guide from Chevy Hardcore can also provide additional insight for your specific engine year. If you are setting up timing, consider a step-by-step guide like this cam degreeing tutorial from OnAllCylinders to ensure optimal performance.

Common Pitfalls and Pro Tips

  • Never reuse hydraulic roller lifters with a new cam – they mate specifically and will score the lobe if swapped.
  • Check lifter preload – too little causes clatter and accelerated wear; too much can hold valves open.
  • Use a high-quality timing set – a true roller chain reduces stretch over time. Budget sets may skimp on metal hardness.
  • Double-check timing marks – one tooth off can cause the engine to run poorly or not start at all.
  • Take notes on bolt torque values – many small block bolts are similar but not identical (e.g., intake bolts vs. cover bolts).
  • Break-in is not complete after 20 minutes – avoid sustained high RPM (over 4000) for the first 500 miles. Change the oil again at 500 miles.

Conclusion

Installing a Comp Cams XR270HR in your Chevy 350 is a rewarding project that unlocks a new level of torque and horsepower without sacrificing everyday drivability when matched with appropriate supporting modifications. By following this detailed step-by-step tutorial, you ensure proper lubrication, timing, and break-in, all of which are vital for cam longevity. The result is a small-block Chevy that pulls hard from off-idle to redline, with a robust exhaust note and crisp throttle response.

Remember that patience and precision during assembly pay off at startup. With the right tools, a clean workspace, and careful attention to the steps above, you'll have your Chevy 350 running stronger than ever. For ongoing maintenance, monitor oil pressure and valve lash at regular intervals, and enjoy the improved performance every time you turn the key.