Engine Noises | Knocking and Ticking | Common Causes


Main Bearing Noise

Damaged or worn main bearing noise is revealed by dull thuds or knocks which happen on every engine revolution. This noise is loudest when the engine is under heavy load. Excessive crankshaft end play is indicated by an intermittent rap or knock sharper than a worn main bearing.

The following are causes of main bearing noise:

 

  • Low oil pump pressure
  • Thin, diluted or dirty oil and/or filter
  • Excessive main bearing clearance
  • Excessive crankshaft end play
  • Out-of-round crankshaft journals
  • Loose crankshaft pulley
  • Loose flywheel or torque converter
  • Loose main bearing cap

Connecting rod Bearings

A damaged or worn connecting rod bearing will produce knock under all speeds. During the early stages of wear, connecting rod noise may be confused with piston slap or loose wrist pins. Connecting rod knock noise increases in volume with engine speed and is at its loudest on deceleration.

The following are causes of connecting rod bearing noise:

  • Excessive bearing clearance
  • Worn crankshaft connecting rod journal
  • Thin, diluted or dirty oil and/or filter
  • Low oil pressure
  • Crankshaft connecting rod journals out-of-round
  • Misaligned connecting rod
  • Connecting rod bolts not properly torqued
  • The wrong bearing inserts or misaligned bearing half

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Timing Chain and Gears

Engines designed with timing gears, or those equipped with a timing chain and sprockets, can produce different noise. The most common noise is a high frequency, light-knocking sound. This sound will generally be the same in intensity whether the engine is idling, operating at high speeds, or under load.

The following are causes of timing gear or chain and sprocket noise:

  • Worn timing chain and/or gears
  • Misaligned gears
  • Excessive backlash
  • A damaged tooth
  • Gear or sprocket loose on the shaft
  • Too much end play in the camshaft or crankshaft

Loose or improperly seated camshaft timing gears are usually loudest when warm. They are speed sensitive only. They are not load sensitive.

Cam gear noise will usually be evident at a warm idle in neutral and sounds much like a loose timing chain noise.

Piston Noise

Piston pin, piston, and connecting rod noise are hard to separate. A loose piston pin, for example, causes a sharp double knock usually heard when the engine is idling, or during sudden acceleration then deceleration of the engine. A piston pin that has been improperly fitted will emit a light ticking noise that is more noticeable with no load on the engine. Excessive piston-to-cylinder bore clearance will cause piston slap noise. The noise is similar to a metallic knock, as if the piston were "slapping" the cylinder wall during its stroke. As with most engine noise, understanding the cause of the noise will help you imagine what the noise sounds like. An indication of piston slap is a decrease in noise as the engine warms up. When the engine is cold, the piston to bore clearance is greater and piston slap will be louder.

Flywheel Noise

A loose or cracked flywheel will produce an irregular thud or click. To test for a loose or cracked flywheel, operate the vehicle at approximately 32 km/h (20 mph) and shut off the engine. If a thud is heard, the flywheel may be loose or damaged. This type of thud is loudest on deceleration. Loose torque converter-to-flywheel or flywheel-to-crankshaft bolts will sound similar to bearing knock. This condition produces several raps during quick acceleration on a free running engine. Depending on the idle smoothness, when the transaxle is in gear, the noise may or may not appear. Check the torque converter-to-flywheel and the flywheel-to-crankshaft bolts before attempting to investigate any bearing-related knock.

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  • Guest - Taylor

    I have a 95 Ford F-150 on way to work I had a popping sound come from front of the engine slight sparks. I went to easy off road but still had power no drop in oil pressure or temperature change. I decide to continue slowly to get out of a high traffic area if possible. I made it no problems about 3-4 miles to the exit. Still no change just the knocking. I went back after work started right up but still knocks. I didn't drive. I'm wondering what may be the issue and if I should drive to the mechanic or just have it towed.

  • Guest - Schwery

    I have a 1994 Suzuki Sidekick 4x4 and hear a clicking sound somewhere in the left front only when driving for a while and the sound increase as I go faster, and decreases when going slower. This ocurrs even when driving straight and not necessarily when turning. What is causing this?

  • Guest - Larry

    In reply to: Guest - Schwery

    It is possible you have a bad front bearing, u joint, CV joint. Try it in 4 wheel drive to see if it goes away or gets louder.

  • Guest - Becca

    I have a 2009 Saab 97x. Was driving perfect no noise. Then it sounded as if something feel off under hood . And started to knock immediately and bogging out . Checked coil packs. Could it be spark knocking? Or is this serious?

  • Guest - Derek (MOBILE MECHANIC)

    i would like to ADD a cause i found in my repair. 2001 olds alero 3.4L engine knock. it was guessed the lifers had colapsed. during dissasembly and reasebly it was found. that when they replaced the intake manifold gasket, they didn't follow torque specs for the ROCKER ARM BOLTS. and one of the rocker arm was pivoting in it's spot, the wear was quite obvios where the knock was from

  • Guest - serina

    i have a 98 chevy blazer i need a water pump for sue but my check gauges light comes on when i stop and the oil pressure drops all the way down now my truck is knocking please help me i dont know what is going on i think i just need pick up tube and oil pressure sensor what do yall think

  • Guest - Ernest p thomas

    Why my 2005jeep laredo4.7liter is taking tha water but comes back up.but I hear a knocking nose.i cut on tha air and then it ran hot on me.this is a new motor in this jeep just put it in two months ago cut on tha air for tha first time and it runs hot.what is it

  • Guest - Krystie

    I was extremely low on oil, I put oil in now my car is making a rattling roaring sound when I go above 20mph. It doesn't do it if I drive under 20mph. My check engine light starts blinking when I go above 20mph. What do you think this is?

  • Guest - jim johnson

    looking at buying a 2003 Chevy S10 4x4. SRLS model .. 155,000 miles, has not been running for 10 months. Just started it and has a knocking sound... Gas is spoiled in tank but did start. What can we put in it to improve gas quality? And one Cylinder has a low pressure output. I'm looking at buying this and getting it to a shop to repair. Most shops dont fix engineds they just replace. What are your thoughts. I'm buying at $1700 trade in value is $1400 to $2400. your thoughts would be appreciated,?Shoud i walk away with these issues or could it be a good opportunity to fix up for $500 and make some money

  • Guest - sabrina

    In reply to: Guest - jim johnson

    I have a GMC 3.0 engine went off the road 2 days ago now it as a knocking sound and when get up speed it starts shaking and if let gas off increase shaking even the stering wheel shakes Help

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