Noise coming from Hyundai engine pistons can be concerning. Understanding the potential causes of piston noises can help diagnose and address issues. This article explores common reasons for piston noises and how to assess possible damage.

What Causes Piston Noises?

Piston running noises can be caused by a few key factors:

Tilting Due to Excessive Running Clearance

The piston needs to fit closely within the cylinder to stay aligned as it moves up and down during combustion. Over time, this running clearance can increase due to normal wear or improper boring/honing tolerances. Too much space allows the piston to tilt back and forth slightly as it travels. This tilting motion causes the edge of the piston crown to strike the cylinder wall repeatedly, creating noise.

Ignoring Piston Install Direction

Some performance piston and rod assemblies have the piston pin bore offset from the true piston center. This requires orienting the piston correctly during installation to account for the direction of the offset. Turning the piston the wrong way fails to align the pin bore offset with the connecting rod plane. This misalignment leads to a binding and tilting motion as the engine runs, causing the piston to slap against the cylinder bore.

Tilting from Stiff Connecting Rod Bearing

The connecting rod bearing relies on a thin film of oil for smooth rotating and pivoting motion between the rod and crankshaft. Restricted movement from a faulty bearing not receiving proper lubrication can tilt the orientation of the connecting rod. This uneven plane binds the piston differently at the top dead center versus the bottom dead center. Binding forces the piston to a slanted, tilted position inside the cylinder. This prominent tilt causes repeated contact between the piston crown and cylinder wall.

Piston Striking Toward Piston Pin

The piston pin joining the connecting rod to the piston sees tremendous forces during combustion. Side loads on the pin from improper bearing clearance or an out-of-alignment connecting rod can force the piston to shift and sway slightly in the pin direction. This horizontal motion causes the piston to strike the cylinder wall opposite the pinned side. Repeated blows on each up/down cycle lead to noisy, problematic operation.

Piston Pin Striking Circlips

The piston pin fits inside the small end of the connecting rod and installs with a circlip on either end to retain it. If the connecting rod is twisted or distorted within normal tolerances, it can bind against the piston pin ends alternately as it moves up and down. This binding thrusts the pin horizontally back and forth against the circlips. The resulting metal-to-metal strikes create repetitive noise each cycle.

Assessing Piston Noise Damage

Piston noise that is audible externally occurs when the piston head strikes the cylinder wall repeatedly. Depending on the cause, the impact points can be in the piston tilt direction or the piston pin direction. Understanding the nature of the noise and damage patterns can help diagnose the root issue.

Causes of Tilting Impacts

There are a few potential causes of piston tilting and subsequent cylinder wall strikes:

 

• Excessive Clearances: Overly large cylinder boring or honing leads to poor piston guidance and room to tilt.
• Ignored Install Directions: Pistons with offset pins need to be installed facing the right way.
• Tight Piston Pin Fit: Restricted clearances between the pin and connecting rod can tilt the piston head when hot. This can stem from the connecting rod bore, piston pin bore, piston pin shrink fit issues, or piston pin seizing.

Causes of Piston Pin Direction Impacts

Impacts in the piston pin direction occur under the following conditions:

Connecting Rod Misalignment

The connecting rod needs to remain straight and properly aligned between the piston pin and crankshaft journal to function properly. Over time, fatigue can lead to bending or twisting of the connecting rod. This distortion takes the orientation of the small and big ends out of parallel alignment. 

 

The side-to-side pivoting of a misaligned rod leads to a somewhat pendulum motion of the piston. This forces the piston first one way and then the other way on its path of travel, making the edges of the piston strike the cylinder wall with each stroke.

 

Excessive bearing clearance can also impact connecting rod alignment. Too much space in the bearing allows unwanted rocking motion and misalignment. This contributes to pendulum-style piston movement and subsequent piston slap against the cylinders.

Piston Pin Thrust

Even a connecting rod assembled within normal factory specifications can have a small amount of twists or misalignment. As the rod moves up and down, this slight distortion leads to a non-parallel orientation between the piston pin and the connecting rod. The pin wants to move straight as the rod pivots at an angle.

 

This binding and angled orientation causes the piston pin to thrust sideways against the circlips. It strikes first against one circlip then the other. This alternating axial force and impact make the circlips click against their grooves audibly on each stroke. Too much thrusting force over time can lead to embedded circlips into the piston pin or groove damage.

Assessing Damage

Carefully examining any impact marks or scratches on the piston head, pin, connecting rod, and cylinder wall is key to diagnosing the type of issue. The pattern and location reveal important clues. Documenting any abnormal connecting rod motion or bearing clearances will help pinpoint causes like rod distortion.

Potential Solutions

Depending on root cause analysis findings, solutions could include:

 

• Adjusting clearances during maintenance to OEM factory specifications
• Replacing damaged pistons and rings
• Aligning connecting rods if bent
• Replacing damaged connecting rod bearings or bolts
• Addressing engine overheating issues

Preventing Piston Noise Issues

Some best practices in preventing piston noises include:

 

• Maintaining proper clearances and tolerances during repairs
• Always note piston orientation and installation direction
• Keeping the engine cooling system in good working order
• Upgrading engine bearings, oil, and filters based on severity of use

 

The occasional piston tick isn’t always problematic but consistent noises need to be addressed promptly to avoid complete engine failure down the road. Thorough diagnosis and targeted fixes can return an engine to quiet and smooth piston operation. Reaching out to a professional technician is advised for major engine work.