hydraulic adjusted valves

[GPdriver1986]

I always keep hearing that GM engines have hydraulic adjusted valves and that they never need adjustment, but the imports need adjustments. How does this work?

[GnatGoSplat]

From some site Google picked up:

 

Hydraulic versus Solid Lifters

Hydraulic lifters are self-adjusting. A plunger inside the lifter body is exposed to engine oil pressure, which is enough to keep the pushrod and rocker arm against the valve stem to eliminate lash, but not enough to overcome the spring pressure and open the valve. As the cam lobe pushes the lifter up, a check-valve between the plunger and lifter body closes, trapping the oil, and as liquids can't be compressed, the lifter body and plunger effectively become solid, rise as one, and open the valve. When the cam lobe rotates and the lifter drops down, the plunger is able to relocate itself to compensate for any heat-related expansion that takes place. The obvious advantage to hydraulic lifters is that they self-adjust, so maintenance is minimal. The disadvantage is they have some limitations in rpm potential; 6,500 is probably a practical maximum.

 

Solid lifters are just that--solid chunks of iron. The advantage to them, other than simplicity, is that they generally allow the engine to achieve higher rpm. The downside is because dimensional changes take place in an engine as it heats and cools, some slack, or lash, is necessary in the valvetrain. Without lash as the engine warms, the valves could be held off their seats, obviously detrimental to performance. Valve lash ensures that valves close completely. Obviously, there will be some maintenance involved with solid lifters, but often not as much as most fear. Properly set, valve lash should stay consistent unless, or until, wear becomes a factor. However, with the proper valve springs and regular oil changes, wear should not be a significant factor, so valve adjustments should not be required any more frequently than routine tune-ups.

 

While the downside of solids is that valve adjustments are often seen as a nuisance, the upside is that they offer some flexibility in cam tuning. Lash changes can alter lift and effective cam timing (more lash results in less duration and vice versa). Particularly valuable in drag racing, lash changes can impact everything from elapsed time to launch characteristics.

 

Although the tuning capacity of solids may not be particularly relevant for street applications, another factor to consider with solids is noise. Because of the necessary valve lash, some mechanical sound will be evident as the rocker arms contact the valve stems. For some it's racket, for others it's music to the ears.

[GPdriver1986]

Thanks, I wanted to know becuase my parents have a 2003 Toyota 3.0L DOHC V6 and it requires an "audible" valvetrain inspection every 90k km. So if they find noise they will have to adjust it.