A Guide to Injection Timing — What It Is and How to Adjust It

January 24, 2020
A Guide to Injection Timing — What It Is and How to Adjust It

You may have heard of injection timing before, but what is it, and how does it relate to your marine engine? Do you even need to bother if your motor runs just fine?

Whether you’re looking for a boost in power or your engine is a bit older than you’d like to admit, adjusting the injection timing can affect the entire system. In this guide, we’ll discuss how the process works, the benefits of making modifications and how to carry out adjustments on your own.


Injection Timing — What You Need to Know

The internal components of a marine engine are complex and rely on precise movements to deliver efficient and reliable power. You may not understand everything that occurs within the system, but if you have an idea of how an internal combustion engine operates, you can make comprehensive timing injection adjustments.

In an internal combustion engine, thermal energy transfers into mechanical energy. The created power moves an engine’s pistons, therefore, moving the crankshaft, then the marine unit itself. Thermal energy comes from the combusted air-fuel mixture inside the cylinder.

The head of a cylinder contains the system’s valves, camshafts, valve return springs, valve buckets and injectors. The engine block, connected below the cylinder, contains the crankshaft, connecting rod and piston. A piston moves inside the cylinder from the bottom dead center to the top dead center during combustion.

There are a few terms you’ll need to know to understand how the piston moves inside the cylinder, including:

– Top Dead Center (TDC): Top dead center is when the piston is at the top of the cylinder, positioning itself farthest from the crankshaft.

– Bottom Dead Center (BDC): Bottom dead center is when the piston is closest to the crankshaft at the cylinder’s lowest point.

– Before Top Dead Center (BTDC): Before top dead center is the point right before the piston reaches the highest area of the cylinder.

The Internal Combustion Process

The internal combustion process is what generates energy for the pistons to move, leading to a chain of events that propel a motor.

In a fuel injection engine, the intake valves release air into the cylinder. The piston moves upward toward TDC, compressing the air, and the intake and exhaust valves close.

Diesel fuel injects, right before the piston reaches the top. The air-fuel mixture reaches its maximum pressure when the piston reaches TDC. The high-pressured air forms intense temperature levels, causing the diesel to combust spontaneously on its own.

The expanded gases force the piston back down to BDC during the power stroke, moving the crankshaft each time. The gases then exit through the exhaust valves to the exhaust pipe.

As the exhaust moves out, more air injects into the cylinder from the intake valves, starting the process over.

What Is Injection Timing?

What Is Injection Timing?

Injection timing, also called spill timing, is the moment when diesel fuel enters the cylinder during the combustion phase. When you adjust the timing, you can alter when the engine injects the fuel, therefore changing when combustion occurs.

An injection pump is often driven indirectly from the crankshaft by chains, gears or a timing belt that also moves the camshaft. The timing of the pump determines when it will inject fuel into the cylinder as the piston reaches the BTDC point.

A manufacturer will recommend a specified timing injecting according to the make and model of the marine engine you have. They set an appropriate timing when the engine is made, so you receive as much possible power without surpassing the legal emission limits.

If you are looking to adjust the injection timing on any diesel marine engine, its age doesn’t matter. However, the way you make adjustments may differ depending on whether it’s an old-timer or fresh off the production line.


Why You May Want to Adjust Your Injection Timing

The primary purpose of a fuel injection system is to provide diesel to an engine’s cylinders — but how and when the fuel is delivered can impact an engine’s performance, sound and emissions.

Advancing or retarding an engine’s timing is possible. Advancing an engine’s timing causes the injection process to occur earlier than the manufacturer’s settings.

In opposition, retarding is when you make changes, so the fuel releases after the recommended time. Although retarding is less common compared to advancing, it can repair a lag or smoking problem within a marine engine. It can also support performance and fuel economy issues.

Reasons to Adjust Injection Timing

You can adjust injection timing if your marine engine is past its prime running days or has had work done. For example, if you’ve installed a new timing belt or injection pump, you will need to adjust the system to ensure it’s at factory standards. Or, you can choose to adjust it to your specific needs. Over time, the injection pump timing retards, resulting in problems, such as:

Difficult starting

Hot engine temperatures

Poor fuel economy

Smoke during startups and acceleration

Making the proper adjustments can get the system back to its original performance levels or better.

Be aware that upping your engine’s power isn’t always the right move. Sometimes, more power can result in excessive smoking from the exhaust and delay boost. It can also increase the engine’s output of vibration and cause more emissions, which may not be up to par with EPA standards.

Make sure you look at your marine engine as a whole and whether it’s a wise decision. Know what your equipment can handle and what it requires. If you’re not sure, your best bet is to work with a mechanic that knows the ins and outs of an engine’s injection timing.

Advantages of Adjusting Diesel Engine Injection Timing Systems

Because a timing component delivers diesel under intense pressures, the parts and materials can withstand high levels of stress and heat. With high tolerances, the injection system can perform well when the engine runs for an extended time. Diesel injection timing also has more in-depth controls.

When you combine all its properties, an injection timing system can make up about 30 percent of a diesel engine’s total costs.

If you’re looking to advance the timing injection of your marine devices, you want to ensure the engine makes full use of the fuel injection process. Make sure the correct amount of diesel releases at the right time to meet your power requirements. You need both the injection timing and metering to be controlled. Several benefits of advancing your engine’s ignition timing control include:

Boosted engine power capabilities

Higher peak cylinder pressure

Lower exhaust temperatures

Higher NOx emissions

Increased fuel efficiency

Although manufacturers set the injection timing in a way that balances both emissions and power, it doesn’t mean the marine engine system is set to its maximum potential. You can advance the timing of your engine to increase your machine’s power when you want to operate at faster speeds or tow more weight.

If you’re looking to adjust the injection after BTDC occurs, you can reap other benefits such as preventing premature combustion, reducing smoke and repairing lag.


What Effect Will It Have on My Marine Engine?

When you modify the injection timing of your marine engine, it affects many components.

Advancing the system will cause diesel to inject into the cylinder sooner than usual, also causing the combustion phase to occur quicker. A timing advance shows the number of degrees before the piston reaches top dead center and ignition takes place.

Injecting diesel BTDC means the air-fuel mixture can burn completely before the piston reaches the top. The process creates maximum pressure in the engine’s cylinders, allowing the exhaust to force the piston down at the most significant force possible.

If the advance is too far ahead, it can cause the mixture to push on the pistons as they are moving upward, making them knock together and damage the engine. This is also known as detonation.

Changes that occur in your machine depend on the type of marine engine and its age. Advancing the timing on a diesel can affect various aspects of your engine, such as:

Engine longevity

Fuel consumption

Ignition timing

Fuel to air ratio

Engine power

Injection delay

Injection delay is the interval of time from when injection begins to the start of combustion — meaning it directly relates to timing. The period of suspension involves both physical and chemical intervals that coincide. The breakdown of atoms, vaporization and air-fuel mixing delays the process, as does the combustion reaction. When you advance the timing, it decreases the injection delay, but when you retard the injection, it increases the interval.

Setting the ideal injection timing is critical to maintain and boost the performance of your engine. Diesel that enters too soon or too late into the cylinder can result in excessive vibrations or severe damage to components.


How to Adjust Injection Timing

How you adjust the injection timing of the injection pump also depends on the type of marine engine you have and its age. Before making any adjustments, make sure the cold start cable is in, and the camshaft drive belt has proper tension.

Some of the most common ways to advance the timing are:

1. Program the ECM

The engine control module is a computer that analyzes information to control your boat’s performance. It’s almost like the brain of the marine engine.

The engine control module is easier to adjust in newer engines compared to older versions. If you know how to program the ECM, you’re one step ahead. But if not, you can rely on a mechanic to make their way to the EMC and plug in a Flash tool which will reprogram the computer system. For older components, there are other parts you can alter to change the timing.

2. Modify the Fuel Injection Pump

One of the more straightforward ways to convert the timing is to adjust the fuel injection pump. All you have to do is rotate the pump with a screwdriver and socket wrench — standard tools you can find in your garage or toolbox. You need to make sure you accurately measure the timing adjustment with a timer meter or probe for reading.

Any small movement of the pump will cause massive timing changes. Avoid drastic adjustments and stick to minor alterations for the right modifications.

If you decide to alter the fuel injection pump, you’ll need to:

1. Use a socket wrench on the front camshaft bolt to hand-turn the engine clockwise until the first cylinder is at TDC.

2. Both the intake and exhaust valves should be closed, and the TDC mark should be aligned.

3. Install a dial indicator by removing the timing-check plug and ensure it reads at about 2.5-millimeter preload.

4. Turn the crankshaft counterclockwise until the indicator stops, then zero the dial.

5. Turn the crankshaft clockwise, stopping at TDC.

6. If the gauge reads within the manufacturer’s given values, you can choose to advance or retard the timing or leave it as is.

7. Loosen the injection pump to allow the diesel to enter the cylinders sooner and vice versa for retarding.

8. Once you have it at an appropriate position, tighten the mounting bolts.

9. Rotate the marine engine through several revolutions and repeat the procedure to ensure you made proper adjustments.

10. Remove the indicator.

11. ut on the timing check plug.

12. Start your engine, checking for leaks.

Because advancing your injection timing system depends on your specific requests and situations, it’s often better to rely on diesel marine engine experts. They will point you in the right direction of how much to alter your timing to fit your machine.

3. Replace the Camshaft

You can swap the engine’s original camshaft for one that has different sized and shaped lobes. This change allows you to make modifications when the valves and injectors trigger. You may need to work with an experienced mechanic or technician because a decent amount of mathematical calculations go into this process.

4. Swap Out the Cam Gaskets and Followers

One of the cheaper options is to get new cam gaskets and followers. Changing either of the gears can result in similar adjustments that you would see from replacing the camshaft. Installing thicker or thinner gaskets will affect the cam lobes and followers when they come in contact. Therefore, the components can affect how the valve train activates.

You can check the injection timing by measuring the injector pump’s stroke at TDC using a dial indicator.


Find Everything You Need in One Location

With 28 years of experience in the industry, Diesel Pro Power works hard to place you at the forefront of our operations. We carry all marine engine parts and keep them in stock 24/7 for convenient worldwide shipping. Our specialists provide complete solutions and strive to simplify the entire buying process through an ergonomic website that’s fast and easy.

Browse our inventory of marine engine components or reach out to our intuitive customer care team by calling us at 1-888-433-4735.

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