Engineered Accessory Drive Serpentine Belt Replacement

Engineered Accessory Drive Serpentine Belt Replacement

You might not be able to see it, but an accessory drive belt is always both speeding up and slowing down. When a piston accelerates downward after the ignition of the fuel and air, the crankshaft speeds up and then slows down as it reaches the bottom of the stroke. These changes in speed are minimal, but big enough to cause problems.

You might not be able to see it, but an accessory drive belt is always both speeding up and slowing down. When a piston accelerates downward after the ignition of the fuel and air, the crankshaft speeds up and then slows down as it reaches the bottom of the stroke. These changes in speed are minimal, but big enough to cause problems.

If the pulses are not minimized, they can hammer the belt and the attached rotating components. On a four-cylinder engine, the degrees of rotation between power pulses are greater than on a V8. This means the amount of change in speed on the four-cylinder pulley is greater than on a V6 or V8. This has a direct effect on how the belt system is designed.

The belt drive system is working hardest when the engine is at idle. When the engine is below 1,000 RPM, the alternator, A/C compressor and power steering pump are putting the greatest strain on the belt.

MOTORSCH

Some of the forces can be taken up by the belt slipping on the pulleys. But, slipping causes friction and wear on the belt, as well as flutter. Over time, the slipping can get worse as removal of material from the ribs causes the belt to bottom out.

There are three components that help to keep the belt on the pulleys without slipping. The tensioner, harmonic balancer and decoupler pulley work together to keep the accessory belt system quiet and the belt lasting until the replacement interval.

Tensioner

The tensioner applies force on the belt. Some tensioners have devices that dampen the movement of the spring and arm. The tensioner helps to keep constant force on the belt even under a wide variety of conditions.

Harmonic Balancer

The harmonic dampener puts a layer of soft material between the crankshaft and outer ring of the pulley. The material helps to dissipate the power pulses and resonant frequencies. While the dampener may only flex one or two degrees of movement, this takes a lot of strain off attached components.

img_0956Decoupler Pulley

Some alternators have a decoupler pulley. This device serves two purposes. First, it helps to decouple the pulley from the alternator with a one-way clutch. The decoupler reduces parasitic losses by not having to fight against the momentum armature alternator while the engine is decelerating and accelerating. Some decoupler pulleys have a spring and friction dampener to reduce vibration. When an alternator decoupler pulley is compromised, it can no longer absorb the same level of abuse, which has a trickle-down effect throughout the system.

Alternator decouplers and pulleys should be inspected every 10,000 miles for wear. Early design versions have a service life of 40,000 to 60,000 miles, with more recent versions lasting more than 100,000 miles.

When inspecting a decoupler or pulley, there are two signs that replacement is needed. First, after shutting down the engine, if there is an audible buzzing, the bearings in the pulley have likely failed. The second sign depends on whether the vehicle has a one-way clutch (OWC), overrunning alternator pulley (OAP) or decoupler (OAD).

With the inspection cap/cover removed and the center locked, turn the pulley or decoupler with the appropriate tool. If it is an OAP or OWC, the pulley can only be turned in the clockwise direction. If it is an OAD, a counterclockwise turn will reveal a noticeable increase in spring force; a clockwise turn will only have slight resistance.

The tensioner, harmonic balancer and decoupler pulley work together to keep the belt in contact with grooves in the pulleys. The three components are engineered together to match the engine. If one part is compromised, all are compromised, including the belt. 

You May Also Like

The Impact of Fuel Type on Engine Performance

When recommending fuel options for customers, consider engine design, manufacturer recommendations and usage.

You're already aware that the type of fuel your customers put into their vehicles can (and will) have a significant impact on their performance. But do you know why? By understanding the details of how fuel interacts with an engine, you will be better equipped to make informed decisions about which fuel to recommend for any vehicle.

Battery Management Means Knowing How It Ages

The battery may be fully charged, but you also need to measure how low the voltages go while the engine is cranking.

AC Service – R1234yf

With a few simple steps, you can ensure that your A/C machine is properly maintained and ready for the upcoming A/C season!

Ignition Coil Output

To see inductance inside the primary windings, use an amp probe placed around the positive wire for the ignition coil.

Compressor Oil for R1234yf

Working on R-1234yf systems is not that different from the R-134a variety.

Other Posts

Turbochargers on Minis

No matter if it is a BMW or MINI, when the engine stops turning, the oil flowing to the turbocharger stops.

How Extended Interval Oil Filters Have Been Improved

Over time, the oil filter can collect enough contaminants to become restricted. Here’s why new filters are better.

AC Condensers

The characteristics that make the parallel-flow condenser so efficient are among its major drawbacks as well.

Lifter Deactivation

The area of contact between the lifters and cam lobes is the highest loaded surface inside an engine.