Cylinder Wall Scoring
Introduction to Cylinder Wall Scoring
Cylinder wall scoring, commonly known as bore scoring, occurs when the cylinder of an engine block sustains damage, precisely due to metal-on-metal contact. This happens when the pistons or piston rings contact the cylinder wall, creating scoring lines and disrupting the cylinder’s spherical perfection. Cylinder wall scoring appears as vertical lines due to the pistons’ up-and-down movement.
Perspective Box: Maintaining the spherical perfection pattern (cross hatch) of an engine block cylinder is crucial for ensuring that the cylinder can retain oil for a healthy engine lifespan. Cylinder wall scoring creates deeper vertical grooves in the cylinder walls that allow oil and gas to mix, a phenomenon known as blow-by. Blow-by triggers a domino effect of engine failures, reducing efficiency and overall lifespan.
Maintaining good oil levels, change intervals and quality increases engine efficiency, and lifespan and slows or deters bore scoring. In this article let’s get into the different ways that cylinder wall scoring is caused and prevented.
What you will learn :
Causes of Cylinder Wall Scoring
Inadequate Lubrication
Engine oil is the lifeblood of an engine. It travels through almost every part of an engine to accomplish one thing, reduce friction. In an engine block, there are a lot of metal engine components that operate essentially touching, with one degree of separating, which is the engine oil. Lack of engine oil allows this component to make full contact resulting in a very high amount of friction to occur causing damage and potential scoring.
Foreign Particles
Alongside the lifeblood of an engine (engine oil), there is the oil filter, which works as the liver. The oil filter acts as a cleaning mechanism for the engine oil, constantly filtering out any foreign particles so it doesn’t cycle through the engine as the oil flows. As an engine operates it wears. It starts on a microscopic scale however, in this modern age engine oils do their best to slow the rate of wear very well. Combined with the oil, the filter is there to catch any tiny particles so they don’t cycle through the oil. If a build-up of particles increases then it could be big enough to cause damage or potential scoring.
Overheating
An engine’s operating temperature ranges from 190-220 F. Engines are kept in this range by a combination of two factors. Coolant and engine oil. Coolant flows through certain areas of an engine block dissipating heat generated by engine combustion. Engine oil dramatically reduces metal-to-metal contact resulting in a reduction of friction and wear. If for some reason an engine was to have inadequate amounts of these two flowing through the system temperatures would rise, particularly in the cylinder walls first. This is where combustion takes place. Once the temperature rises the cylinder wall materials become more susceptible to scoring or damage.
Improper Piston Installation
Improper piston or piston ring alignment is yet another way the bore scoring can happen. Piston rings help keep the pistons aligned and separate from the cylinder walls while keeping the engine oil in the right places. Improper installation of these parts can cause a malfunction of its purposes resulting in blow-by and potential cylinder wall scoring.
Symptoms and Detection
Performance Issues
The combustion chamber in an engine block, which includes the cylinder wall is meant to create a perfect seal for the compression of the combustion cycle. This compression creates the necessary circumstances to create mechanical power which then in turn can be made efficient. Cylinder wall scoring creates tiny pathways for compression to escape resulting in a loss of power, cylinder misfires, and a decrease in fuel efficiency.
Unusual Noises
The nature of bore scoring creates extra unnecessary space that causes all sorts of issues for the movement of the Pistons. The pistons moving unusually may result in knocking or tapping sounds indicative of cylinder wall scoring.
Visual Inspection
Cylinder wall scoring usually starts at the bottom of the cylinder because of the movement of the pistons. There are two ways to look into the cylinder for inspection. You can look either from the top through the spark plug hole or from the bottom through the oil sump area. It’s ideal to look from the bottom first since it usually starts there. If you start by looking from the top through the spark plug hole and you notice cylinder wall scoring, it’s probably gotten bad enough.
Assessment and Measurement
Severity Evaluation
As mentioned in the section above bore scoring happens at the bottom of the cylinder first, so to determine the depth and extent of the scoring, utilizing a bore scope through the oil sump can give you an idea of the extent. Since the scoring happens at the bottom first if you observed the cylinder from the top and you see signs of scoring then that would mean the condition of the scoring is already bad. Oil samples are also another way to determine cylinder wall damage or scoring. From an oil sample, you can spot an increase in wear metals or the material of the cylinder wall to gauge damage or scoring.
Diagnostic Tools
Tools such as a bore scope are specially designed to give you a visual of the inside of a cylinder with precision. Bore scopes allow you to see in real time what the damage is and the extent of it. Other tools like micrometers give the exact size of the cylinder walls and pistons so you have an idea of how much clearance you have in a given cylinder. Micrometers come in handy in cylinder wall repair after honing. In some cases, you need to figure out how much space is left to consider over-boring.
Repair and Prevention Strategies
Honing and Deglazing
Cylinder walls are designed with a specific type of pattern that promotes engine oils to stay on its surfaces during operation. This pattern strikes the balance between constant lubrication and a good seal for combustion. Scoring is when this surface is damaged and can no longer strike that balance. Honing and deglazing is the process of restoring the damaged surface to a state to strike that balance again. Specific tools such as a fixed stone hone or a flex ball hone are used in this process to produce a specific result.
Cylinder Boring
Cylinder over boring is one of the repair strategies where you put larger diameter pistons to fit into a cylinder with enough shaved-out material. This is just to account for the space increase, to keep a proper seal during combustion. You have the benefits of more power with a larger displacement however, you may have to increase the weight points on the crankshaft to account for the larger pistons.
Preventive Measures
Scoring happens when there is Metal to metal contact, and that happens when there is a lack of lubrication. Keeping up with regular engine maintenance and oil change intervals is one of the most significant ways to reduce or prevent issues like cylinder wall scoring. Know the quality of the oils used and the frequency at which you change the oil. These things directly impact your engine’s lifespan. Regular maintenance practices also allow you to catch any oncoming issues before they get much worse.
FAQ
1. What is cylinder wall scoring?
Cylinder wall scoring is the damage to the cylinder walls from metal-to-metal contact between the cylinder wall and the piston/piston rings. The scoring is the grooved vertical lines (scratches) it creates as the piston moves up and down the cylinder.
2. What causes cylinder wall scoring?
Some of the most common causes for cylinder wall scoring are:
- Inadequate lubrication
- presence of foreign materials
- engine overheating
- Improper piston installation
3. What are the symptoms of a scored cylinder wall?
A few symptoms of cylinder wall scoring include:
- Unusual engine noises (knocking or tapping sounds).
- Reduced engine performance.
- Increase in oil consumption.
- Visible smoke from the exhaust pipe.
4. Can a scored cylinder wall be repaired?
Depending on the extent of the damage it can be repaired. Minor scoring can be addressed through methods like honing and deglazing, while more severe cases could require cylinder boring and over-boring pistons.
5. How can cylinder wall scoring be prevented?
As simple as it may sound, keeping up with your regular scheduled maintenance and oil change intervals is one of the most important things you can do to prevent cylinder wall scoring. The maintenance service ensures you have the key components to prevent bore scoring and see any upcoming issues before they get out of hand.
