AMSOIL AU BLOG: Why Does My Engine Knock? 3 Possible Explanations
Author: John Baker Date Posted:9 September 2019
There are a few different reasons your engine might make a knocking, ticking or pinging sound. Let’s break each down and talk about what might be happening.
Is it an engine knocking sound, tick or ping?
One driver’s knock is another driver’s tick. Or ping. Still others compare the engine knocking sound they hear to marbles rolling around inside a coffee can.
The spontaneous ignition of air/fuel inside the cylinders is a common source of engine knock.
While the description of the sound may differ, the circumstances under which it occurs are often the same – low-speed, high-torque conditions common when you’re accelerating.
How engine knock occurs
Say the clock has struck 5:00 and you make a bee-line to your truck and take off for home. When you mash the accelerator out of the parking lot, that’s when you hear an engine knocking sound. Or ping. When you let off the gas, it goes away.
This is likely due to either pre-ignition or detonation. They’re effectively the same phenomenon, but they occur at different times.
In a properly running engine, spark-triggered ignition typically occurs a few degrees before the piston reaches top dead centre (TDC). This careful timing ensures the downward force of the exploding fuel/air mixture works in tandem with downward piston momentum, resulting in optimum efficiency and power.
That’s bad timing
Pre-ignition (and its cousin, low-speed pre-ignition [LSPI]) are abnormal combustion events that throw off this precise balance. Under certain conditions, the fuel/air can spontaneously ignite too early in the combustion cycle. Sometimes low-octane fuel is to blame; sometimes it’s deposits on the piston crown.
Fuel with too low an octane rating for your engine can sporadically ignite prior to the piston reaching TDC.
Or, chunks of carbon can heat up and create a hot spot that effectively ignites the fuel/air before the plug fires. Then, when the plug does fire a fraction of a second later, the two flame fronts collide. In certain conditions, they can clash with the upward-moving piston. The resulting shock wave rattles the piston inside the cylinder, creating the knock, ping or can-of-marbles sound you hear.
Detonation has the same effect, except it occurs after the plug fires.
Computers in modern vehicles can detect engine knock and compensate by adjusting engine timing. Though it saves your engine from destroying itself, performance and fuel economy can suffer.
Tick, tick, tick
Say your engine is ticking like a time bomb, especially in the morning when it’s cold. You likely have a valve-train issue.
Your engine uses intake valves to feed clean air into the cylinders and exhaust valves to kick spent combustion gases out. The valves open and close thousands of time per minute in a choreographed whirlwind of activity.
A finely balanced system of parts – rocker arms, valve stems, cam lobes, lifters – control their movements. The clearances between these parts, known as lash, can become loose (or sloppy, in automobile nomenclature). When that happens, all those moving parts clattering against each other can create a ticking sound.
It’s especially noticeable in the morning before the oil has had a chance to circulate throughout the upper end of the engine.
Many engines use hydraulic lifters, which use an oil-pressure-assisted plunger and spring to compensate for lash, helping ensure the system runs smoothly and quietly.
Proper oil pressure plays a big role in valve-train operation and noise. Low oil pressure can reduce the effectiveness of hydraulic lifters, increasing lash. This is most likely to occur with a low-quality conventional oil that thins at high temperatures, preventing the engine from developing good oil pressure.
If the rods are knockin’…
Rod knock is yet another possible explanation for your engine knocking sound.
Your engine is built with a designed clearance between the crankshaft journals and the connecting rods. In a properly running engine using a good oil, the motor oil fills those clearances and prevents metal-to-metal contact.
But, let’s say you’ve been using a poor-quality conventional oil.
At high temperatures, the oil thins and the fluid film weakens. The pressure between the crank journals and connecting rods squeezes the oil from the clearances. Now, metal is riding on metal, wearing the surfaces and widening the clearances. Eventually, the clearances widen so much that you begin to hear the metal surfaces clattering against each other. Eventually, they’ll weld together and destroy the engine.
Quieting a noisy engine
This all sounds dire. But you can sometimes address pre-ignition by using a higher octane gas or by cleaning deposits from your engine with a fuel-system cleaner like AMSOIL P.i. Performance Improver.
The term ‘Amsoil Australia ’ or ‘us’ or ‘we’ refers to the owner of the website whose registered office is Unit 5/159 Arthur St Homebush West NSW 2140. Our ABN is 63619623399. The term ‘you’ refers to the user or viewer of our website.
The content of the pages of this website is for your general information and use only. It is subject to change without notice.
Neither we nor any third parties provide any warranty or guarantee as to the accuracy, timeliness, performance, completeness or suitability of the information and materials found or offered on this website for any particular purpose. You acknowledge that such information and materials may contain inaccuracies or errors and we expressly exclude liability for any such inaccuracies or errors to the fullest extent permitted by law.
Your use of any information or materials on this website is entirely at your own risk, for which we shall not be liable. It shall be your own responsibility to ensure that any products, services or information available through this website meet your specific requirements.
This website contains material which is owned by or licensed to us. This material includes, but is not limited to, the design, layout, look, appearance and graphics. Reproduction is prohibited other than in accordance with the copyright notice, which forms part of these terms and conditions.
All trademarks reproduced in this website, which are not the property of, or licensed to the operator, are acknowledged on the website.
Unauthorised use of this website may give rise to a claim for damages and/or be a criminal offence.
From time to time, this website may also include links to other websites. These links are provided for your convenience to provide further information. They do not signify that we endorse the website(s). We have no responsibility for the content of the linked website(s).
Your use of this website and any dispute arising out of such use of the website is subject to the laws of Australia.
We are committed to ensuring that your privacy is protected. Should we ask you to provide certain information by which you can be identified when using this website, then you can be assured that it will only be used in accordance with this privacy statement.
We may change this policy from time to time by updating this page. You should check this page from time to time to ensure that you are happy with any changes.
What we collect
We may collect the following information:
name and job title
contact information including email address
demographic information such as postcode, preferences and interests
other information relevant to customer surveys and/or offers
What we do with the information we gather
We require this information to understand your needs and provide you with a better service, and in particular for the following reasons:
Internal record keeping.
We may use the information to improve our products and services.
We may periodically send promotional emails about new products, special offers or other information which we think you may find interesting using the email address which you have provided.
From time to time, we may also use your information to contact you for market research purposes. We may contact you by email, phone, fax or mail. We may use the information to customise the website according to your interests.
We are committed to ensuring that your information is secure. In order to prevent unauthorised access or disclosure, we have put in place suitable physical, electronic and managerial procedures to safeguard and secure the information we collect online.
A cookie is a small file which asks permission to be placed on your computer's hard drive. Once you agree, the file is added and the cookie helps analyse web traffic or lets you know when you visit a particular site. Cookies allow web applications to respond to you as an individual. The web application can tailor its operations to your needs, likes and dislikes by gathering and remembering information about your preferences.
We use traffic log cookies to identify which pages are being used. This helps us analyse data about webpage traffic and improve our website in order to tailor it to customer needs. We only use this information for statistical analysis purposes and then the data is removed from the system.
Overall, cookies help us provide you with a better website by enabling us to monitor which pages you find useful and which you do not. A cookie in no way gives us access to your computer or any information about you, other than the data you choose to share with us.
You can choose to accept or decline cookies. Most web browsers automatically accept cookies, but you can usually modify your browser setting to decline cookies if you prefer. This may prevent you from taking full advantage of the website.
Links to other websites
Our website may contain links to other websites of interest. However, once you have used these links to leave our site, you should note that we do not have any control over that other website. Therefore, we cannot be responsible for the protection and privacy of any information which you provide whilst visiting such sites and such sites are not governed by this privacy statement. You should exercise caution and look at the privacy statement applicable to the website in question.
Controlling your personal information
You may choose to restrict the collection or use of your personal information in the following ways:
whenever you are asked to fill in a form on the website, look for the box that you can click to indicate that you do not want the information to be used by anybody for direct marketing purposes
if you have previously agreed to us using your personal information for direct marketing purposes, you may change your mind at any time by writing to or emailing us.
We will not sell, distribute or lease your personal information to third parties unless we have your permission or are required by law to do so. We may use your personal information to send you promotional information about third parties which we think you may find interesting if you tell us that you wish this to happen.
If you believe that any information we are holding on you is incorrect or incomplete, please write to or email us as soon as possible at the above address. We will promptly correct any information found to be incorrect.
Shop Now. Pay Later. Always interest-free.
Add your favourites to cart
Select Afterpay at checkout
Log into or create your Afterpay account, with instant approval decision
Your purchase will be split into 4 payments, payable every 2 weeks
All you need to apply is to have a debit or credit card, to be over 18 years of age, and to be a resident of country offering Afterpay
Late fees and additional eligibility criteria apply. The first payment may be due at the time of purchase
For complete terms visit afterpay.com/terms