What Is a Camshaft?
The camshaft is a rotating shaft with precisely machined lobes (or cams) that open the engine's intake and exhaust valves at exactly the right moment in the combustion cycle. It's located either in the cylinder head (overhead camshaft — OHC, the most common modern configuration) or in the engine block (pushrod engines, less common in NZ passenger cars).
The camshaft is driven by the crankshaft via a timing belt, timing chain, or (on older engines) timing gears. On a four-stroke engine, the camshaft rotates at half the speed of the crankshaft — because each valve only needs to open once every two crankshaft revolutions.
SOHC vs DOHC
Two common configurations you'll see on NZ vehicles:
- SOHC (Single Overhead Camshaft): One camshaft per cylinder head, operating both intake and exhaust valves via rocker arms. Simple and reliable. Common on Toyota Corolla and older Honda models.
- DOHC (Dual Overhead Camshaft): Two camshafts per head — one for intake valves, one for exhaust. Allows for more precise valve timing and higher performance. Common on Mazda, Subaru, and modern Honda engines.
Variable Valve Timing (VVT)
Most modern engines use variable valve timing — a system that adjusts the camshaft's phasing relative to the crankshaft depending on engine speed and load. This improves both fuel efficiency at low rpm and power at high rpm. Common systems include Toyota's VVT-i, Honda's VTEC/i-VTEC, and Subaru's AVCS.
What Causes Camshaft Problems?
| Cause | Issue |
|---|---|
| Oil starvation | Cam lobes and bearing journals wear rapidly without adequate lubrication |
| Infrequent oil changes | Sludge deposits block oil galleries supplying the camshaft |
| VVT actuator failure | The oil-pressure-driven actuator that adjusts cam timing seizes or sticks |
| Worn cam lobes | Lobes wear down, reducing valve lift — affecting performance |
| Bent camshaft | Rare — usually caused by a timing belt failure that lets valves strike pistons |
Signs of a Camshaft or Valvetrain Problem
- Ticking or tapping from the top of the engine: The most common symptom. Can be valve clearance (adjustable on some engines), worn cam lobes, or inadequate oil pressure to the head. Note: some ticking on cold start that disappears when warm is normal on VVT-equipped engines.
- Rattling on start-up: Common with VVT actuator issues — the actuator rattles before oil pressure builds. Often accompanied by a check engine light (cam timing fault codes P0010–P0015).
- Rough running or misfires: Worn cam lobes reduce valve lift, causing a cylinder to run poorly.
- Loss of power: Especially at mid to high rpm.
- Increased oil consumption: Worn valve stem seals (associated with the valvetrain) cause oil burning.
- Check engine light: Variable valve timing codes, or misfires related to cam timing.
Valve Clearance
On engines without hydraulic valve adjusters, valve clearances need periodic adjustment. If the clearance becomes too large, the valves tap noisily. Too small, and valves can't close fully — causing overheating and power loss. Clearance adjustment intervals vary by vehicle but are typically every 40,000–80,000 km. Your mechanic can advise if your specific vehicle needs this service.
NZ Cost Estimates
| Service | Estimated Cost (NZD) |
|---|---|
| Valve clearance adjustment (4-cyl) | $200–$450 |
| VVT actuator replacement | $400–$900 |
| VVT solenoid replacement | $150–$400 |
| Camshaft replacement (includes head removal) | $1,500–$3,500 |
| Cam carrier/head rebuild | $1,000–$2,500 |
WoF Implications
Not a direct WoF item, but severe camshaft wear causing misfires can lead to excessive emissions. A vehicle that misfires noticeably during a WoF inspection may be flagged.
When to Book a Mechanic
Book a mechanic if:
- You hear persistent ticking or tapping from the engine top that doesn't clear after warm-up
- The check engine light is on with cam timing fault codes
- You've noticed a loss of power or rough running
- Your oil pressure light is flickering at idle