valve train

The valve train in a car engine – everything you should know

The valve train in internal combustion engines is one of their most important components. It is what enables such complicated construction consisting of several dozen key parts to work properly. Without a valve train, a traditional engine is nothing but a collection of individual parts. A set of sprockets, shafts and valves precisely tied together with a belt or a chain controls the inflow of air and outflow of exhaust from the combustion chamber, bringing order and harmony into those elements, which allows the engine to propel the vehicle.

Types of Valve trains

In principle, there are 3 types of valve trains in modern car engines, depending on where the camshaft is placed: OHV (camshaft inside the engine block, with valve tappets), OHC (camshaft in the head) and DOHC (two camshafts in the head).

Classification based on the drive

Valve trains can also be divided based on the type of drive: belt or chain. Most engines of the new generation have Timing belts, but older constructions used to utilize more durable chains. The common belief is that they are maintenance free, but that’s just nonsense repeated over years.

The truth is that chains can withstand longer mileages, but they also wear down and there comes a moment when they need to be Replaced due to being overly stretched. Chains have been nearly completely Replaced by reinforced rubber Timing belts. Their operation is more quiet and they can withstand the pressures increasing in modern engines.

They may need maintenance more often, but they’re Cheaper to replace compared to chains.

valve train

When to replace them?

It is one of those components that absolutely have to be Replaced according to the manufacturer’s recommendations at specified miles intervals. Everything is clear when the car is serviced regularly and has its history documented. In case of buying a used car with unknown history, it’s a good idea to preventively replace the valve train, as neglecting it might lead to serious consequences.

These include the risk of the timing element bouncing or breaking, which leads to internal devastation of the piston system.

After such incident, the engine needs replacement or a complete overhaul. The exceptions are collision-free engines, in which the timing element breaking doesn’t cause the pistons to collide with the valves.

In such case it is easy to fix the damage, but the cost is still quite high. Estimating the condition of a valve train might pose a problem to an average user, because micro-damages to the timing belt tend to be barely noticeable. It is easier to hear the tensioners wearing down, the bearings of which start to audibly squeak.

When it comes to chains, an experienced professional should be able to hear it operate too loudly (clanking) due to the chain being stretched. Valve train replacement is not just the drive, it’s also the equipment, including the tensioners and the commonly neglected water pump.

When the timing belt breaks

The timing element breaking, be it a chain or a belt, usually means nothing good. The problem is less serious when it comes to collision-free engines that are dropping in numbers.

All you have to do here is install a new valve train and the car is fully operational again.

It is much worse when the construction is of the collision type, which means that the timing element breaking causes a collision between a valve and a piston. In most cases it causes the valves to bend, oftentimes the camshaft to distort, and in the extreme cases even the piston to get punctured. It all depends on the engine speed and the force of impact.

Which is why it turns out once again that it’s better to prevent than repair. If the water pump is driven by the same belt, it should also be Replaced so that it doesn’t cause Unpredicted problems.

Even when I was a kid, I damaged my toys just to fix them later. I run a family business with my father - automotive repair shop. I specialize in diagnostics and repair of delivery trucks. DIY is my middle name. My wife often repeats that thanks to me she never spent money on a plumber or electrician. The classic Ford Mustang is my dream car. Someday I will buy one. Maybe when my children go to college.