Mechanics

Scraping

AD
A scrape or scraping sound is typically created when metal is contacting metal during linear movement. This condition can be created by a bearing that has failed or a brake heat-dust shield that is out of place. Scraping sounds generally do not occur from the engine, transmission or differential. Rotating objects are generally prone to scraping noises because many components have close tolerances and are positioned near objects that are not moving. The first step is locating the region in which the scraping sound is be generated. Some scrapping noises are easily fixed by repositioning a particular brace or shield while bearing failures need to be replaced. Other scraping sounds are activated when the key is brought to the crank position such as the starter motor. We have list common problems below:

Scraping Noise
Scraping Noise

Engine Running, Car Not Moving: This section includes symptoms that present themselves when the engine is running only.

Check Engine Accessory Mounting-Condition - When your engine starts it provides power to various accessories such as the water pump, power steering, air conditioner, alternator, and air pump (if equipped) These accessories are held in place by mounting brackets while being the inner working are supported by a roller bearing. If these roller bearings fail they can allow the impeller or armature to contact their respective housing. To check for this condition start with the engine off, then remove the serpentine belt and rotate all accessories by hand and check for resistance and lateral play. If either of these conditions is present replace the component in question and recheck system. Removing your engine's serpentine belt is a relatively simple repair that can be done in a few minutes with minor tools in most cases. Always wear protective gloves and eyewear before you begin.

Starter Motor Scraping Sound: The starter motor is designed to crank the engine over by engaging onto the engine flywheel. This starter motor has bearings that can fail allowing the armature to contact the starter motor housing which contain cylindrical magnets. These magnets are dense and can make a very generous scrapping noise when the starter is activated. If this noise exits when the engine is cranked over the starter motor has failed and replacement is required.

Checking a Throw Out Bearing (standard transmission vehicles only): A throw out bearing is designed to press against the clutch pressure plate. This bearing is what rides near the pressure plate and is activated when the clutch pedal is depressed. If a scraping noise is heard when the clutch pedal is depressed this bearing has failed and replacement is required.


Clutch Pressure Plate, Disc and Throw-out Bearing
Typical Clutch Pressure Plate, Disc and Throw-out Bearing

Inspecting an Ignition Distributor: The ignition distributor in your car is designed to distribute the ignition spark to each cylinder at the correct time. This distributor is constructed with bearing that can fail allowing the main distributor shaft and stator to contact the stationary housing and pick up coil(s). When this condition occurs it can cause the engine to stall, and then start again once the engine has cooled down. To check for this condition remove the distributor cap and check for lateral movement in the main shaft. Also this condition is sometimes accompanied by rust colored powder in and around the interior of the distributor housing. If this condition has occurred distributor replacement is required in most cases. This problem is especially inherent in Honda motor cars.

Scraping Noise When Air Conditioner is On - The air conditioner is designed to operate using a electromagnetic clutch assembly that receives a command signal from the activation switch. This command controls when electricity is supplied to the compressor clutch that engages and disengages the air conditioner system. If the air conditioner compressor has failed it can cause a scrapping sound when the air conditioner is switched on. Once the system has been switched off the noise will stop, if this is the case with your cars the air conditioner compressor replacement is required.

Inspect Harmonic Balancer: The harmonic balancer on your engine is used to help silence engine vibration by utilizing a rubber mounting metal ring attached to a hub that is connected to the front of the engine. If this ring becomes dislodged because the rubber insulator has failed it will allow the outer ring to bounce and scrape on the rotating hub. This condition will produce a scraping noise that will change with engine speed. To check for this condition remove the multi rib belt and check the harmonic balancer condition. If the outer ring is lose replacement is required.

Failed Harmonic Balancer
Failed Harmonic Balancer

AD

AUTHOR


Written by
Co-Founder and CEO of 2CarPros.com
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


COMMENTS TO THIS ARTICLE


Please use our question form if you have a specific question about your car as we are not able to give you a full answer on this page.



Article first published (Updated 2013-08-16)