Wheels: For a healthy engine, it’s all in the timing

By Eric Meltzer

Engine timing is the relationship between all the things that allow your engine to run. Valves have to be closed when the piston is up, and at that split-second, the ignition has to set off the fuel-air mixture that was fed to that cylinder and compressed, to explosively force the piston down, turning the crankshaft through the connecting rod, creating power.

Timing all that action is critical, and keeping everything spinning, opening and closing, injecting and igniting fuel is the job of the timing chain or belt or gears. That’s a very simple illustration of a very complex operation. As the overhead camshaft controlling the valves got farther away from the crankshaft attached to the pistons, timing belts became a more attractive design element. Older engine designs could make do with gears or very short chains to connect the two closely spaced shafts in a flat head or V-configured engine.

Engines have become more efficient, putting out more horsepower than ever before, but all that is partially the result of very tight tolerances. Tolerance is how much variation is put into a part when it’s manufactured, and the less tolerance designed into a part, the tighter the overall engine is, allowing maximum performance. The same tighter tolerances allow an engine to run much longer than in years past, with several hundred thousand miles is not unheard of. All this is affordable, thanks to technology in the manufacturing end of the business, with computer controlled machines producing accuracy beyond the previously imaginable.

As engine components wear, a certain amount of performance is robbed as the parts approach the limits of their serviceable life, which is why older engines failed sooner. Tell-tale signs of an older, tired engine might be excessive oil getting past piston rings or valve guides into the combustion chamber, producing a cloud of blue haze, or coolant escaping into the combustion chamber, that’s evident by a white cloud of vapor exiting the tailpipe.

These wider tolerances are the reason that older engines had clearance if a timing belt or chain broke. The engine won’t run since the timing is no longer controlled, but the individual components won’t be damaged. Most modern engines, however, do not have the same clearance. These are known as interference engines, and a broken timing belt will usually result in at least bent valves and maybe chipped pistons resulting from their collision. This is why a timing belt replacement, before it breaks, is so important. It is possible to repair an interference engine with a broken timing belt but it’s usually not worth the cost.

 

Timing belts became popular among designers because of several benefits including: They are a low-friction device, don’t need lubrication, are relatively inexpensive and are easily replaced.

Timing chains, however, are seeing more widespread use in engines that were formerly the domain of the timing belt. Timing chains do require lubrication, and most use a hydraulic tensioner that’s maintained by oil pressure. Timing chains are more expensive than belts, and a bit more complicated to engineer, but they are relatively maintenance free and don’t require an expensive replacement. A side benefit for the manufacturers is they can market them as “lifetime” or “maintenance-free.”

A timing chain tensioner is the component that keeps the timing chain taut. Incorrect tension could over stress the chain, causing failure, while lack of tension could cause the chain to jump or skip.

The tensioner is a hydraulic component, meaning that it uses fluid to maintain the correct tension, and engine oil is that fluid. We always advocate correct oil change intervals for a number of reasons, and the components in a timing chain engine is a good example of why that’s important. Clean oil of the appropriate viscosity and quantity will help ensure the timing chain tensioner and chain are maintained correctly.

If there is a future for the gasoline combustion engine then perhaps Swedish Supercar designer Christian von Koenigsegg has seen that future, and is working to make the FreeValve or CamFree engine a reality. This revolutionary design would eliminate timing belts and chains. In fact, it would eliminate the camshaft all together. The very heart of this design is the Pneumatic-Hydraulic-Electric-Actuator which would allow the engine management system to have full control over each individual valve. FreeValve allows independent control over every valve’s precise opening and closing and timing throughout the entire combustion cycle. The amount of control allowed by such a design is unprecedented and could dramatically change an individual engine from a high performance powerhouse to an economic fuel-sipper simply through software programming.

For now, our choices are more moderate. Whether your engine has a timing chain or a timing belt, proper maintenance is the key to longevity.

 

Eric and Michelle Meltzer own and operate Fryeburg Motors, a licensed, full-service automotive sales and service facility at 299 Main St. in Fryeburg, Maine. More than a business, cars are a passion, and they appreciate anything that drives, rides, floats or flies.