How To Check for Bad Valves?

Checking for bad or failing engine valves is crucial to ensure optimal engine performance and efficiency. Valves control the air-fuel mixture intake and exhaust gas output of the combustion chambers. Over time, normal wear and tear can cause valves to leak, burn, warp or lose compression. This leads to symptoms like reduced power, high oil consumption, misfires and emission issues.

This article provides a complete guide on how to thoroughly inspect valves and recognize signs of failure. Key steps covered include visual inspection, compression testing, leak-down testing and measuring valve clearances. Common valve problems like burnt exhaust valves, bent intake valves, excessive valve wear and seat damage are highlighted. The article also explains the importance of replacing damaged valves, answers common questions about valve failure and provides valve seal repair tips.

Following the valve inspection steps and techniques outlined here will allow you to identify defective valves early. Replacing bad valves right away restores peak engine performance and efficiency.

How to Check for Bad Valves?

Checking for bad valves and replacing them if needed is an essential part of engine maintenance. This guide will walk you through the steps for inspecting engine valves and signs to look out for.

Visual Inspection

The first step is a visual inspection of the valve train with the cylinder head removed. Look for any visible damage like burnt or bent valves, excessive valve wear, and deposits on the valve stems or seats. Valves that are burnt, cracked or excessively worn need to be replaced. Also inspect the valve springs and retainers – cracked or weakened springs can lead to valve failure.

Compression Test

A compression test gauges how well the valves seal the combustion chamber during the compression stroke. Hook up a compression tester in place of the spark plug. Disable the ignition system and crank the engine for several cycles while monitoring the gauge. Healthy engines should have 150 to 225 psi of compression. Lower compression indicates an issue with the valves or piston rings. Compare readings across all cylinders – uneven compression points to issues in specific cylinders.

Leak-Down Test

The leak-down test is the most accurate way to check valve seals. A leak-down tester pressurizes a cylinder through the spark plug hole and measures leakage. With the piston at top dead center, pressure should hold stable at around 100 psi. A drop in pressure indicates leaks at the valves or rings. Listen for air leaks at the intake, exhaust and crankcase. A well-sealed cylinder will lose under 10% pressure.

Tools and Equipment Needed

• Compression tester
• Leakdown tester
• Feeler gauge
• Spark plug wrench
• Ratchet and socket set
• Flashlight

Steps to Check Valves

1. Remove the cylinder head and inspect the valve components visually.
2. Use a feeler gauge to check valve clearances – tight or excessive clearance indicates issues.
3. Perform a compression test on each cylinder. Compare readings across cylinders.
4. Conduct a leak-down test on cylinders with low compression. Listen for air leaks.
5. Check valve seats for pits, cracks and carbon buildup using a flashlight.
6. Look for burnt or bent valves, damaged valve springs and cracked retainers.
7. Replace any damaged, worn or leaking valves and recheck.

Tips

• Avoid overtightening valve components when reassembling. Torque valve springs and retainers to spec.
• Always measure valve clearance when the engine is cold. Clearances can vary with temperature.
• Make sure the leak-down tester ball valve is fully closed before pressurizing the cylinder.

Signs and Symptoms of Bad Valves

• Visible valve damage like cracks, excessive wear or overheating
• Uneven or reduced engine compression
• Engine misfires, rough idle and loss of power
• Abnormal air/fuel leakage during leak-down test
• High oil consumption due to leaking valve seals
• Excessive valve clearance or tightness
• Odd exhaust noises like tapping or rattling

Why Do Valves Go Bad?

Valves operate in an extremely harsh environment and wear is inevitable over time. The constant opening and closing causes the valve seat and face to deteriorate. High combustion temperatures can also lead to burnt, warped or cracked valves. Excessive clearance allows valves to bounce and strike cylinder walls. Weak valve springs prevent full valve closure allowing hot gases to damage valves. Lack of routine valve adjustments also contributes to premature valve failure.

How Do I Know If I Need New Valves?

If a visual inspection reveals damaged valves or engine compression is below spec, new valves are likely needed. Failures like burnt exhaust valves, bent intake valves, excessive valve wear and seat damage cannot be corrected – new valves will be required. Always conduct a leak-down test to pinpoint leaking valves if compression is uneven or low. Replacing defective valves will restore peak engine performance.

What Are the Symptoms of Bad Valve Seats?

Damaged valve seats prevent valves from fully sealing, causing symptoms like:

• Low, uneven compression
• Rough idle, misfires and power loss
• Increased hydrocarbon emissions
• Engine overheating issues
• Oil burning due to leaking exhaust valves

Leak-down testing and visual inspection will reveal pitted, cracked or worn valve seat surfaces in need of repair.

How to Fix Bad Valve Seals?

Bad valve seals cause oil burning and emissions issues. To fix:

• Remove cylinder head and visually inspect seals for tears and hardness.
• Use a valve spring compressor to replace worn valve seals.
• Apply a light coat of oil to new seals before installing.
• Check valve stem to guide clearance – ream guides if out of spec.
• Perform a leak-down test to confirm no more leakage.

Replacing damaged valve seals restores proper sealing, reducing oil consumption and emissions output.