What is that knocking or ticking noise
Many assume this knocking or ticking noise is the end of their engine and just move on. There are some ways to narrow down where the noise is actually coming from.
Internal mechanical problems can also cause engine knocking. One such problem stems from excessive clearance inside the bearings in the connecting rods. They can transfer the downward movement of the pistons to crankshaft rotation. Each time the piston changes direction, there is a knock from the metal hitting metal. This is often referred to as a “rod knock.” It is usually very rhythmic and it increases with engine speed and intensifies with engine load.
Diagnose Noises with a timing light.
Valve train noises occur at half of crankshaft speed so even if your ear can’t tell whether the noise is happening at 800 rpm or just 400 rpm, your eyes can. Hook up the timing light to any one cylinder and watch the flash. Look at the light for a while to see if it coincides with the knock, if so it is valve train related. If the noise seems twice as fast, it is probably in the crank, mains, rods, rod bearings, pistons, harmonic balancer, flexplate, etc.
Rod knocking noise are loudest at higher speeds (over 2500 RPM). Feathering the gas pedal may result in a distinctive back rattle between 2500 and 3500 RPMs.
If enough rod bearing material has been worn away it may even double knock. The piston will whack the cylinder head in addition to the big end of the connecting rod banging on the crankshaft rod journal. It will sound like a hard metallic knock (rod) with an alternating and somewhat muffled aluminum (piston) knock sound.
Wrist pin knock in modern engines is very rare today but still possible.
Diagnose Noises with a low voltage test light.
Shorting out the plug wires one by one with a common low voltage test light may determin which cylinder contains the noisy parts. You won’t get the bulb to light up but it is a convenient way to short the cylinders.
Attach the alligator clip to a convenient ground, away from fuel system components, and pierce the wire boots at the coil pack or distributor end of the wire. You can use straight pins stuck in the ankle of the wire boots in the distributor.Then you touch a grounded jumper wire to each one.
If the noise changes when the plug wire is shorted to ground, you can figure that the problem is in the reciprocating bottom end parts. Possibly piston, wrist pin, connecting rod or connecting rod bearing. The reason the sound changes is that when you short the cylinder plug wire you are stopping the combustion chamber explosions that are slamming the piston downward making the inside of the big end of the connecting rod bang against it’s connecting rod journal.
If you get a change in the sound when you short a cylinder out, you have confirmed that the head and or oil pan must be removed to actually find the problem. Replacing a crankshaft is always risky. Whatever made the bottom end fail has also contaminated the rest of the engine with debris.
Valve train noises generally are loudest up to 1500 rpms. Lifter noise is commonly misdiagnosed. In reality lifters are quite trouble free.
Dirt contamination on a sludged engine is the number one cause of true lifter noises, low oil pressure is number two. Whatever you do, don’t put engine flush in a sludged engine! We call it “Instant rod knock” because of the way it overloads the oil filter to the point of opening the filter bypass valve, flooding and destroying the engine bearings with debris. The only safe way to clean a sludged engine is to accelerate the oil changes and let the detergent in the oil do the cleaning at a controlled rate. Like every 500 miles.
Replacing the oil pump only is a common mistake.
Over 95% of replaced oil pumps did not need to be changed and rarely wear out. If you have low oil pressure I would be more concerned about excessive clearances and worn parts.
And now back to the beginning.
A deep rapping noise from the engine is usually rod knock. This is brought on by extreme bearing wear or damage.
If the rod bearings are worn or loose enough to make a dull, hammering noise, you’re driving on borrowed time. Sooner or later one of the bearings will fail, and when it does one of two things will happen. The bearing will seize and lock up the engine, or it will attempt to seize and break a rod.
Bearing noise is not unusual in high mileage engines. It can also be caused by low oil pressure, using too light a viscosity oil, oil breakdown, dirty oil or dirt in the crankcase, excessive blow by from worn rings and/or cylinders (gasoline dilutes and thins the oil). Incorrect engine assembly (bearings too loose), loose or broken connecting rod bolts, or abusive driving.
Bearing wear can be checked by dropping the oil pan and inspecting the rod and main bearings.
If the bearings are badly worn, damaged or loose, replacing the bearings may buy you some time. If the bearings are badly worn or damaged, the crankshaft will probably have to be reground.
Other mechanical problems that lead to engine knocking are:
- Defective main crankshaft bearings
- A cracked or broken flywheel or flex-plate that attaches the engine to the transmission
- A worn water pump bearing
- A failed or loose timing belt tensioner can knock when the timing belt slaps against it
- An air conditioning compressor can knock when it is failing or icing up
- An alternator with worn rotor bearings can knock when the pistons fire