Blowby in Heavy Equipment Engines: Causes, Dangers, and Solutions

Introduction

As a heavy equipment consultant, I often come across the issue of blowby in engines. Blowby can lead to a variety of problems and even cause engine failure if left unaddressed. In this blog post, I will explain what blowby is, the dangers and likely failure modes the engine will experience, the list of causes of blowby, how to know when you have too much blowby, troubleshooting techniques, how to identify a leaking cylinder, how to prevent blowby, and how to fix an engine when you have too much blowby.

What is Blowby?

Blowby is the leakage of combustion gases, fuel, and oil past the piston rings and into the crankcase of an internal combustion engine. This leakage occurs due to the gap between the piston rings and the cylinder wall. Blowby can reduce engine performance, increase oil consumption, and cause harmful emissions.

Dangers and Likely Failure Modes

1. Reduced Engine Performance: Excessive blowby reduces the engine’s power output due to the loss of combustion pressure.
2. Increased Oil Consumption: Blowby can cause oil to become contaminated, leading to increased oil consumption and shorter oil change intervals.
3. Emission Issues: The combustion gases leaking past the piston rings can lead to increased emissions and even cause your equipment to fail emissions tests.
4. Engine Wear and Tear: Excessive blowby can accelerate engine wear, leading to costly repairs or even a complete engine rebuild.

Causes of Blowby

1. Worn or Damaged Piston Rings: This is the most common cause of blowby, as piston rings wear out over time and lose their ability to seal properly.
2. Cylinder Wall Wear: Cylinders can wear unevenly, allowing combustion gases to escape.
3. Piston Ring Gap Misalignment: Incorrectly installed piston rings or misaligned gaps can cause blowby.
4. Overfilled Oil: If the crankcase is overfilled, the rotating crankshaft can cause the oil to froth, which can lead to blowby.
5. High Engine Operating Temperatures: Excessive engine heat can cause piston rings to lose their shape and sealing capabilities.

How to Know When You Have Too Much Blowby

1. Blue or White Exhaust Smoke: Excessive blowby can cause oil to burn in the combustion chamber, leading to blue or white exhaust smoke.
2. Oil Leaks: Blowby can cause oil to leak from various engine components, such as the oil filler cap, dipstick, or breather tubes.
3. High Oil Consumption: If your engine is consuming oil at an alarming rate, it could be due to excessive blowby.
4. Poor Engine Performance: If your engine is not producing the power it should, it may be due to blowby.

Troubleshooting Techniques

1. Perform a Compression Test: This test measures the pressure generated in each cylinder during the compression stroke. Low compression in one or more cylinders could indicate excessive blowby.
2. Conduct a Leak-Down Test: This test measures the rate at which compressed air leaks out of the cylinder. High leak rates could indicate blowby.

How to Identify a Leaking Cylinder

1. Perform a Cylinder Leak Test: This test involves pressurizing each cylinder with compressed air and observing where the air leaks out. A leaking cylinder will show air escaping through the crankcase breather or oil filler cap.

Preventing Blowby

1. Regular Maintenance: Performing routine maintenance, including timely oil changes, can help prevent excessive wear and tear on the engine.
2. Monitor Engine Temperature: Keep an eye on the engine temperature to ensure it doesn’t exceed the recommended operating range.
3. Properly Install and Align Piston Rings: Ensure piston rings are correctly installed and gaps are aligned properly during engine assembly or maintenance to prevent blowby.
4. Use the Correct Oil Grade: Always use the recommended oil grade for your specific engine to ensure optimal performance and protection.
5. Avoid Overfilling the Crankcase: Be careful not to overfill the engine with oil, as this can lead to blowby.

Fixing an Engine with Excessive Blowby

1. 1. Inspect and Replace Piston Rings: If the piston rings are worn or damaged, they will need to be replaced. This involves disassembling the engine to access the pistons and rings.

   2. Address Cylinder Wall Wear: If cylinder wall wear is the cause of blowby, the cylinders may need to be honed or bored to restore the proper clearance between the piston and cylinder wall. In some cases, you may need to replace the entire cylinder.

   3. Repair or Replace Damaged Components: If other components, such as the head gasket or valves, are contributing to blowby, they should be repaired or replaced as needed.

   4. Perform Routine Maintenance: Once the engine has been repaired, be sure to perform regular maintenance to prevent future blowby issues.