Variable valve timing (VVT) components are a fairly new category in the aftermarket, but are becoming more and more common as the new car market embraces fuel-saving technologies, smaller engines and lighter vehicles.
Although many of us have sold the occasional camshaft phaser or oil control valve/solenoid, the technology behind the VVT system is still somewhat unknown or misunderstood. Currently, there are two basic designs for variable valve timing that cover most of the vehicles in today’s aftermarket.
The more popular (and simpler) of the two designs is the camshaft phasing system. Phasing advances or retards the timing event by means of oil pressure and directed flow. The oil control valve routes oil through a series of passages in the camshaft that force the hydraulic phaser to rotate back and forth in relation to the orientation of the camshaft. This rotation determines the amount of advance/retard of the cam, and therefore the valve timing.
The oil control valve contains an electrical solenoid, which opens and closes internal passages in the valve’s body, changing the flow direction and rate as commanded by the PCM. The cam and crank position sensors supply info to the PCM, and VVT failures often present error codes related to these circuits. Oil is the lifeblood of the cam phasing mechanism, and both the viscosity and condition of that oil are key factors for proper operation.
The pressure and rate of oil flow through the system is very important for accurate timing control, so changing oil viscosities from the manufacturer’s specification is not recommended. Additionally, regular oil change intervals are important for the health of the system. Many failures of the VVT components can be traced back to sludging or deposits clogging screens or oil passageways. These blockages can reduce oil flow, and in some cases, particles in dirty oil may limit the full travel of the cam phasers.
As part of their VVT troubleshooting flowcharts, many OEMs also direct the technician to look for the presence of a factory oil filter. Low-quality oil filters may have insufficient or incorrect flow rates for VVT applications, so this is an understandable assumption at the OEM level. I wouldn’t go so far as to insist upon an OEM filter over a quality aftermarket filter, but this is another good reason for parts specialists to upsell the customer from a store brand or white box filter to your preferred premium brand.
Camshaft phasing technology relies on hydraulic pressure, but electronic solenoids are being developed which could possibly eliminate camshafts entirely. Camshaft phaser VVT technology is still limited to the lift and duration provided by the specific lobe design of the camshaft installed. At Concordia University in Montreal, there has been research into direct-acting electronic solenoids which would open each valve independently, without the need for the timing drive, camshafts or valve train components like rocker arms or pushrods. This would open even more new possibilities for variable valve timing, since the duration and lift for each valve would be almost infinitely adjustable as part of the PCM programming. It would also provide another means of cylinder deactivation, as well as engine braking capabilities.
