Because most diesel engines run at low rpms, valvetrain adjustments are usually minor. This implies that massive springs and pushrods aren’t required to keep the valves from floating at high speeds. On the other hand, the effects of turbo boost on the intake valves may be a source of concern.
Many diesel engines have extremely high boost pressures, ranging from 80 to 200 psi on some of the most extreme racing engines. As a result, there’s a risk that extremely high boost levels will overcome the effort exerted by the intake valve springs, forcing the valves open. While some diesel performance experts recommend using springs that are at least 10 psi stiffer than stock (closed seat pressure) for every 10 psi increase in boost, others argue that this isn’t necessary because the pressure developed inside the cylinder will keep the intake valves closed as the piston approaches its compression stroke.
Overly stiff valve springs on Cummins engines have also been linked to increased cam bore wear. There are no cam bearing inserts in Cummins engines; the camshaft journals run directly on the machined bores in the block.
As a result, excessive valve spring pressure forcing the rocker arms, pushrods, and lifters against the camshaft may wear out the bottom of the cam bores. Valve lift and timing are thrown off when the cam sinks lower and lower into the block, resulting in a considerable loss of power. Machine out the cam bores in the block and install aftermarket valve springs in a performance Cummins engine with stiffer than stock valve springs to prevent this.
Camshaft lobe and lifter wear are also an issue when raising valve spring pressure. Except for Duramax and a few late-model Caterpillar and International engines, most diesel engines still use flat tappet camshafts with flat bottom valve lifters rather than roller lifters.
This is for both economic and practical reasons. There isn’t a lot of strain on the cam lobes because most stock diesel engines run at low rpm and have light valve springs. As a result, you can typically get away with using less expensive flat bottom lifters. However, unless a racing oil or crankcase additive with an adequate level of ZDDP (Zinc Dialkyl Dithio Phosphate) is used, when a diesel engine is modified for performance (and stiffer valve springs are installed to allow higher engine speeds), the increased load may cause rapid cam lobe and lifter wear.
To extend the life of the catalytic converter, ZDDP levels in motor oil have been drastically lowered in recent years. ZDDP has traditionally been added to oils at quantities of 0.15 percent phosphorus and 0.18 percent zinc. Phosphorus levels were decreased to 0.08 percent, or nearly half that of the preceding generation of motor oils, when “SM” certified motor oils were introduced in 2005.
Both gasoline and diesel engines with flat tappet camshafts are affected by the same issue. The solution is to use a high-pressure assembly lube on the cam lobes and a crankcase additive or racing oil with suitable quantities of ZDDP. Alternatively, replace the flat tappet valvetrain with a roller cam and lifters (if available).
What are diesel lifters?
What exactly is it? The hydraulic lifter in an automobile engine adjusts a plunger and takes up all of the valve train clearance using oil pressure. If left ignored, a malfunctioning hydraulic lifter will likely cause the rocker arm, valve tip, and push rod to fail as well.
How do you stop a diesel engine from making noise?
How to Make a Diesel Engine Quieter
- Install a sound-dampening hood mat under the hood of the car to absorb engine sounds.
Where are lifters located?
A lifter is a cylinder that sits between the camshaft and the valves of a car’s cylinders. The camshaft actuates as it passes over the top of the lifter, temporarily opening the valve. Due to the fact that the intake and exhaust valves must open at different times, each needs its own lifter.
Depending on the vehicle, lifters can be designed in a variety of ways. Lifters on pushrod engines, for example, trigger a rocker arm rather than directly pressing on the valve.
Lifters are classified as either hydraulic or mechanical. Let’s look at both of them.
Hydraulic lifters are the most prevalent type of lifter on the market, having been designed in the 1930s to reduce noise from earlier mechanical lifters. They didn’t reach the broad market until the 1950s, however, due to their greater price.
Hydraulic lifters are made out of a cylindrical body with a protruding internal piston. This is how it works:
- The lifter body has a hole through which pressurized oil enters and flows into a narrow channel. This oil flows freely out the other side of the internal lifter cylinder.
- The channel is closed when the cam presses down on the lifter piston. Even under high pressure, this locks the valve open temporarily, allowing gas to escape the cylinder.
- The lifter piston can raise when the cam reaches its apex, allowing the oil to flow freely once more. As a result, the valve snaps shut, maintaining proper engine air pressure.
Valve lash, or the distance between the rocker arm and the valve tippet, is reduced with the floating piston design. More lash is more forgiving, but it can create rattling and pounding. The quieter and smoother the ride is, the less lash there is.
Valve lash can be reduced to roughly 0.006 inches with a good pair of hydraulic lifters. That is a minuscule amount of space.
The issue is that in order to execute its job, the lifter must operate within very tight tolerances. The oil will not have enough time to fully re-pressurize the valve if the engine RPMs are too high, resulting in limited airflow and poor performance.
A hydraulic lifter that becomes over-pressurized, on the other hand, may fail to fully close the valves. If the valve is too far open and hinders ignition, this will cause leaks and damage.
From the 1950s until the 1980s, hydraulic lifters were ubiquitous, appearing in practically every vehicle on the road. Some contemporary automobiles, on the other hand, have reintroduced mechanical lifters.
Mechanical lifters have a few significant advantages over their hydraulic equivalents, albeit being noisier. For starters, they’re inexpensive and low-maintenance, making them ideal for economy vehicles. Because they run dependably at higher RPMs, they’re also useful for performance cars.
Mechanical lifters are divided into two categories: solid lifters and roller lifters. A solid lifter is a solid metal cylinder that does exactly what it says on the tin. The cam either presses down on the cylinder or allows it to rise as it revolves.
Roller lifters have a similar design to solid lifters, but they’re designed to be quieter. They have rollers on the back instead of a flat back, which allows the cam to rotate smoothly across the top.
This decreases noise while also improving performance, especially at higher RPMs. The rollers, on the other hand, require more maintenance than a standard solid lifter, resulting in greater long-term mechanic costs.
Why do diesels sound like they knock?
What causes diesel engines to make a clatter that is not audible in gasoline engines? P.S.
The clatter is caused by the engine’s internal burning of diesel fuel. Rather than a spark plug, the fuel in a diesel engine is ignited by high pressure and temperature inside the cylinder.
The clatter is caused by the fuel not burning evenly like it would in a gasoline engine, resulting in a knock. Unlike in a gasoline engine, knock in a diesel engine does not usually pose a threat to the engine. It is simply offensive to the general public.
Because the diesel engine lacks a spark plug and relies solely on the compressive heat inside the cylinder to ignite, the fuel must have excellent ignition characteristics. However, strong ignition quality in any fuel is not always accompanied by good anti-knock capacity. Diesel fuel has a low anti-knock capability since it requires a high igniting capability.
Why do diesels knock when cold?
Many diesel engines, however, create an unpleasantly harsh banging sound during cold starts and warm-up at low outside temperatures. A significantly higher cylinder pressure gradient results in a louder and more unpleasant combustion noise under cold running circumstances.
What is a diesel knock?
Introduction. The characteristic “knocking” noise associated with diesel engines is caused by high pressure-rise rates associated with fuel auto-ignition during the premixed combustion stage. Diesel knock or combustion roughness are terms used to describe this noise.
How many types lifter?
A Flat Bottom Lifter and a Roller Lifter are the two most common lifter designs. The Flat Bottom lifter necessitates the employment of a specially developed material that can withstand the revolving cam lobe’s continual wiping pressure. The Roller Lifter uses a roller bearing to transform the wiping force into a rolling force, resulting in a design with reduced friction and a wider range of camshaft lobe shapes. There are Hydraulic and Mechanical variations of both of these designs. Both types of oiling systems are capable of sending oil to the upper valve train components, depending on the engine’s oiling system design.