Should Alternator Pulley Spin Freely?

Disclosure: This page contains affiliate links, As an Amazon Associate, I earn from qualifying purchases (at no extra cost to you). Learn More

How should an alternator pulley spin? How an alternator pulley spin can be used to make the diagnosis of whether the alternator is good or bad and needs to be replaced.

Knowing how the alternator pulley is expected to spin can therefore help you decide whether it is time to get it replaced or not.

So, should the alternator pulley spin freely? If a standard automotive alternator is off the car, that is, the alternator is not attached to the car engine via the alternator belt, then, when spun by hand, such alternator if in good working condition is expected to spin freely even after the force applied is removed.

It is usually something of a dilemma attempting to decide between two alternators which differ markedly in the manner they spin when whirled with the hand while off the car.

As long as the alternator is off the car and it’s is not attached to any part of the car engine via a belt, the one that can continue to spin after being whirled with the hand signifies a good working state.

Conversely, that which even after applying a considerable amount of force refuses to bulge is indicative of an alternator in a bad working state and requires replacement.

Trending Searches

Table Of Contents

What direction should the alternator pulley spin?

Aside from spinning freely, the direction of spin is also an important factor to be considered and could tell whether or not the alternator pulley is still good. So, what direction should the alternator pulley be expected to spin, or can it spin in both ways?

Ideally, the alternator pulley should be able to spin freely and smoothly without any form of resistance or grinding. This should be in the counter-clockwise direction.

The alternator pulley should be able to spin in this direction even when the cooling fins are still held in place. What does it mean when the alternator pulley fails to rotate in this direction? The alternator pulley whose direction of rotation is locked to that of the alternator shaft and does not rotate in the anti-clockwise direction may have failed and require to be replaced immediately.

The free-spinning of the alternator pulley does not mean a long continuous spin after giving it a single push when off the car, however, the spin should be considered free and not give the impression of any tightness or resistance.

The alternator pulley should only be turned in the anti-clockwise or counterclockwise direction. Spinning in the opposite direction may not cause any serious damage, it may however cause some of the brushes to chip off.

Signs of a bad alternator pulley

When the car’s alternator pulley fails, the presenting signs are usually pretty clear. You will begin to hear disturbing noises usually in the form of a growl or whining noises which can be heard coming from under the car’s hood.

While other engine problems can give off similar sounds, it is best to get a professional to take a look at the car and make a diagnosis of the cause of the noise.

What exactly causes this noise? The growling or whining noise heard when the alternator pulley fails is a result of the alternator belt not aligning properly with the alternator pulley.

The belt, when misaligned, begins to rub against the side of the alternator pulley, producing the characteristics of a growling or whining noise that can be used to make the diagnosis of a failed alternator pulley.

It is unsafe to continue to drive the car while it is obvious that the alternator pulley has failed. It is not a question of how long one can continue to drive the car with a failed alternator pulley, rather, it is a question of how soon can the car be taken to the nearest mechanic who will take a look at It and help fix the alternator pulley problem.

When the car’s alternator pulley begins to fail, the first noticeable sign will be the squeaking or rattling noise that can be heard coming from under the car’s hood. In some cases, even with such noise, the car can run for months without breaking down. In other instances, it takes only a few days after first noticing this sound for the car to break down.

The recommended approach to this problem, therefore, is to tackle it head-on immediately after the noise is first noticed.

You never know when the car is going to break down, this could be in the middle of nowhere, leaving you stranded with few options.

Some of the whining noises may not be a result of a misalignment between the alternator belt and the pulley but rather an issue with the bearing.

When the bearing in the alternator is loose rather than staying tight, this causes the running engine to produce mild rattling noises or some sort of grinding noises.

However, if what is heard is a high-pitched whining noise, this may be that the alternator is failing and power is therefore not being evenly distributed to the various parts of the car that needs it.

A good alternator should therefore spin freely without resistance and without producing any grinding, whining, or rattling noises. The smooth rotation of the alternator signifies it is in good working condition.

As one turns the alternator by hand, it is not expected that it makes any form of noise as it spins. So, even if the alternator spins freely but makes any form of noise especially if it is a squeaking noise, this could mean a problem with the alternator or with its bearing. Either way, find out which it is and have it replaced.

Once the car alternator begins to fail, you will start noticing manifestations such as dead car batteries, and malfunctioning electrical accessories amongst others.

How to identify a good alternator pulley?

If you have two alternators and one spins freely while the other spins with resistance, you don’t need anyone telling you that one of them is defective and needs to be replaced.

A good alternator pulley is identified by how freely it spins, and how smooth and noiseless this process is.

Note that after rebuilding the alternator and fixing new bearings and seals, the alternator may not spin as freely as other older alternators do.

This is primarily because of the new seals. Such an alternator pulley will only make one or two revolutions after tossing it with the hand and stops. However, as the seals begin to wear out, their resistance decreases and it begins to spin more freely.

Whenever you hear incoming noise from under the hood of your car and this to be due to the alternator pulley, run the engine while the accessory belt is off to determine whether the issue is with the accessory belt or with the belt timing system.

Whenever the alternator pulley fails, one of the first manifestations will be a jumping belt. So, if this can be demonstrated, then you can be sure the culprit for the noise is the alternator pulley.

Whenever the belt is taken off and the pulley is spun, it tends to move freely in one direction and resist in the order. The counterclockwise direction is the normal direction of an alternator pulley rotation.

How to fix a bad alternator pulley?

When the signs of a failing alternator pulley are noticed in the car, do not hesitate to take the car to a mechanic for a check-up as soon as possible.

Yes, sometimes, even with those glaring signs, the car may still be able to run and it could be tempting to continue managing it that way. However, this will only cause further damage to other electrical parts of the car.

When the alternator pulley breaks, the first point of call in the sequelae of events to follow is the damage of the alternator belt. the belt is the connection between the pulley and the car engine. It is the belt that ling the pulley with the engine.

When the pulley breaks, therefore, the belt immediately gets turned up. Without the belt, the car engine suffers from stalling and overheating which can create more engine problems.

When this happens, the alternator pulley needs to be replaced. The cost of doing so including payment for the labor is slightly affordable. 

The alternator pulley can be removed in isolation and a new one installed. The new pulley is usually bought together with the plastic protective cap because the old one is not reusable and is rendered useless after its removal.

Replacing an alternator pulley is not a highly complex procedure and can be done without visiting the mechanic shop.

Depending on the person’s background knowledge about car parts and how much they know their way around the car, this could take an average of about 2 hours.

Should Alternator Pulley Spin Freely – Conclusion

As long as the alternator pulley is off the car, that is, the belt is not connecting it to the car engine, it should spin freely, smoothly without any noise or resistance.

Leave a Reply