Have you ever wondered what the green coating is on the skirts of some of our Cosworth pistons? If you have, then you are not alone! The coating is actually a fluoropolymer material that has the tradename Xylan, and Cosworth have been using this coating for a number of years on a wide range of parts, and not just the piston. Oil pump and scavenge pump bodies also received the Xylan treatment to help prevent wear from rotors.

Not all Cosworth pistons have this coating – pistons from earlier engines like the BDA, for example, were designed without any skirt coating. But the increases in piston speed in their race engines meant that some form of coating was necessary to help prevent scuffing of the skirts against the cylinder bore walls.

In the early ’90s Cosworth started to coat the skirts on pistons from several different race engine categories, including those destined for Formula 1 like this one from the race-winning HB engine (the coating also looks great when etched with the driver’s name!). Cosworth soon started Xylan coating nearly all of its race and high performance engine pistons, including  the ones we sell today for the YB engine.

What is Xylan?

Cosworth PA2062 Piston Xylan Coating

Xylan was developed by DuPont in 1969, primarily for kitchenware utensils as an alternative to Teflon. Its excellent wear properties meant that it was soon adopted by the automotive industry, where it found its way into numerous different applications.

Xylan is in effect a composite material comprising of a dry film lubricant contained in a matrix with high-temperature organic polymers. This creates what can be termed as a plastic alloy that has excellent surface characteristics and is easy to apply. Xylan has a very low coefficient of friction, so its perfect for the interface between the skirt and the cylinder bore. It also provides exceptional wear resistance, and quite often Cosworth would strip engines down and see that the Xylan coating was completely unmarked. This is in part due to another benefit of Xylan – it has excellent surface adhesion.

The Cosworth Process

As with any coating, good preparation of the substrate surface is vital. In the case of pistons, the skirts need to be completely clean and free of any oil. Once cleaned, the skirt area is masked off with special tape which can simply be peeled off after coating.

The piston xylan coating is then sprayed on in one of Cosworth’s special custom-made spray booths onto the skirt. Each pass of the spray adds around 5 microns, so the thickness can be carefully built up to the required level. Most piston skirts only need a couple of passes to get the thickness up to the required level of between 6 and 12 microns.

The pistons are then left to dry – normally this can take 24 hours. Once dry, the pistons are good to go, with no other treatment necessary.

Cosworth YB 4WD 8:1 PA2062 Piston

If you’d like to know more about the Xylan coatings that Cosworth use on piston skirts then get in touch.

All of our Cosworth production pistons start life as a piston forging to ensure that they are as strong as possible.

Put simply, the forging process involves pushing a bespoke die under great pressure into the billet. As a result, the billet material flows into the required shape of the piston. The forging process gives us the finished machined shape in the undercrown. This reduces the amount of machining that is required. Further, the orientation and distortion of the grains in the material is optimised to give superior mechanical strength. Aligning the axes of the material grain in a certain way can have a significant impact on the structural properties of the piston.

Temperature Effects

Our pistons begin their life as a billet of extruded aluminium alloy bar. This billet is heated to a pre-determined temperature to ensure that the billet is soft, but not at melting point. When the billet is at the correct temperature, it is placed into the forge and shaped by the die. The forging temperature needs to be carefully controlled. This temperature will have a significant effect on the homogeneity of the microstructure. If there were localised changes in the billet temperature then this could lead to inconsistencies in the material properties of the finished piston. For example, if the die was cold then the outer surfaces of the piston would cool rapidly. This would lead to a varied grain structure in the finished piston.

Hence the die is heated to the same temperature as the billet, creating a process known as isothermal forging. This process  that keeps the billet at its maximum elevated temperature throughout the entire forging operation. During the forging process, any cooling at the interface between the die and billet is eliminated, which can greatly improve the flow characteristics and hence the grain structure of the finished item.

Cosworth YB 4WD 8:1 PA2062 Piston

If you’d like to know more about our genuine Cosworth pistons and how they can provide you with the performance and reliability that you need from your engine then please get in touch via our Contact page.

A number of Cosworth pistons have what Cosworth refer to ‘piston anti-detonation bands’, but what actually are they? The term anti-detonation is perhaps a bit of a misnomer, as these bands don’t actually stop detonation. Instead, these bands mitigates the effects of detonation.

Piston Anti-detonation Bands

Understanding Detonation

Before we take a closer look at these bands, what actually is detonation? It’s a phenomena that is commonly mentioned in the world of high performance engines, but it does sometimes get used incorrectly. Detonation is broadly defined as unwanted or abnormal combustion. It occurs when both the temperature and the pressure in the unburnt mixture of air and fuel exceeds a critical level.

In a normal combustion event the spark plug will ignite the air/fuel mixture inside the combustion chamber. This happens before TDC whilst the piston is travelling upwards. The ignition of the air/fuel mixture creates a flame front that spreads outwards, igniting more of the mixture and leaving behind the burnt gases.

However, in certain circumstances when the temperature is hot enough, the unburnt mixture that is furthest from the spark plug (towards the wall of the cylinder) will ignite before the flame front reaches it. This unwanted and uncontrolled combustion can happen almost instantaneously, setting up strong pressure waves that hit the walls of the cylinder. These shock waves create the distinctive pinging noise that can be heard and indicate the presence of detonation.

Cosworth Anti-detonation Bands

In the early ‘90s, one step that Cosworth took to reduce the effects of detonation was to introduce anti-detonation bands. These grooves are located above on the top land above the top ring groove. They are typically around 0.2 mm deep and 1.25 mm wide. Most pistons will have two, three or four of these grooves, depending on the height of the top land.

But these shock waves can also be extremely destructive – they can inflict damage to the piston crown and in particular to the area around the top land. If detonation is severe then ultimately the piston will be irrevocably damaged, with the potential of engine seizure.

There are a number of Cosworth pistons that have anti-detonation bands, ranging from those for the YB through to some of the more recent Formula 1 engines. Basically, any engine that will experience high cylinder pressures will benefit from the usage of anti-detonation bands.

Cosworth YB Piston

The aim of these bands is to protect the top ring by disrupting any high-pressure pulse waves from detonation. The volume within these grooves, although small, allows a space for additional atomisation of the fuel and air mixture. When detonation occurs, this extra space provides an outlet for the shock waves.

These bands also bring about a couple of additional benefits. Firstly, they can prevent the build-up of carbon above the top ring which would otherwise cause the ring to stick in the ring groove. Secondly, they reduce the amount of contact between the top land the cylinder bore wall. This makes them very beneficial at high engine speeds and piston temperatures. Hence they are also occasionally referred to as “contact reduction grooves”.

The introduction of anti-detonation bands by Cosworth was another example of their experience and understanding of internal combustion engines. Indeed, when owned by Vickers, Cosworth actually patented their anti-detonation band design in the US, take a look here : https://patents.justia.com/patent/5267505

Anti-detonation Band

Want to know more about the range of  Cosworth pistons that we supply? Then get in touch via our Contact Us page.

One of the most important aspects of any IC engine is the correct timing of the rotational movement of the camshafts relative to the reciprocating movement of the pistons. Any errors in this timing will result in detrimental performance, and could in the worst case lead to contact between the valves and pistons, which could prove to be both catastrophic and costly. There are a number of ways that this meticulously choreographed movement of valves can be achieved, such as with gears or chains. But one of the most common methods in a road car is with the use of a timing (or cam drive) belt. The timing belt is normally driven by the crankshaft, and then turns pulleys that drive the camshafts.

Cosworth 20019488 YB Heavy Duty Timing Belt

Timing Belt Construction

The majority of automotive timing belts are constructed from an elastomer body that contains tension cords, with a fabric backing and a tooth jacket.

Looking at these four ingredients one by one, then the first is the elastomer body. This is normally a high temperature spec rubber such as HNBR (hydrogenated nitrile butadiene rubber) or EPD (ethylene propylene diene). HNBR is more suited to engines, as it can handle exposure to lubricating oils. The elastomer body can sometimes be reinforced with aramid fibres, which help strengthen the belt and provide extra protection for the teeth. Aramid is a heat-resistant and strong synthetic fibre that is sometimes referred to by the tradename Kevlar. Our heavy duty belts for the YB engine contain this aramid reinforcement, which helps make them three times stronger than a conventional automotive timing belt.

The tension cords help to give the belt incredible levels of tensile strength without compromising on flexibility. Tension cords are typically manufactured from high-strength glass fibre, and the individual strands of fibre are bundled together and twisted for added strength. It is the presence of glass fibre that means that a timing belt should never be ‘crimped’, which is the action of over-bending or twisting the belt that then shears the glass fibres.

Next up we have the tooth jacket, which is a temperature-resistant polymide fabric that helps to protect the teeth from abrasion as well as shear forces. The last ingredient is the fabric backing, which is usually another type of polymide fabric. This fabric backing is used on the smooth face of the belt that will run against the belt tensioner, so resistance to abrasion and wear is a must for the fabric.

Cosworth 20019488 Heavy Duty Timing Belt

Toothed Belts

In the majority of cases the timing belt is driven by teeth on the belt that engage with matching teeth in the pulleys on the crankshaft and camshafts. It is these teeth that provide the accuracy in timing, and hence toothed belt drives are often terms ‘synchronous belts’, as the keep the movement of the cams in synch with the crankshaft.

Keeping the teeth engaged at all times is vital. If a tooth jumps out of position then this is called ‘ratcheting’ (some people might use stronger language when this happens!). It is normal for the belt teeth to try to escape from the adjacent teeth in the pulley – when this happens the belt tension increases, which pushes the teeth back together, but this can lead to long lasting damage of the tension cords inside the belt. Complete slippage of the belt teeth out of the pulley teeth usually happens because either the tooth engagement is poor, or because of lack of belt tension.

The profile of the teeth is an important factor for the performance of the timing belt, and there are generally three categories for the profile – trapezoidal, curvilinear or modified curvilinear. Curvilinear profiled belts are sometimes called High Torque Drive (HTD), and modified curvilinear profiled belts are often called Super Torque Drive (STD), S-type Tooth Profile Dual-sided (STPD) or GT.

Belt Tooth Profiles

Tooth Profiles

The trapezoidal profile is the oldest of the three, introduced over 80 years ago. The shape of the profile is a trapezium, with straight flanks that are angled inwards towards the tip of the tooth. When the teeth revolve around the pulley, these flanks create an involute curve that matches the involute tooth profile on the pulley.

One disadvantage with the trapezoidal tool profile is that it has sharp corners at the root of the tooth, and this can create high stress concentrations that can weaken the belt. To overcome this, the curvilinear has fully radiused corners, which helps to even out the stresses. Also, the curvilinear tooth profile is taller than the trapezoidal profile, making it more difficult for the teeth to jump out of position and also giving a larger contact area, which in turn helps to reduce both stress and noise.

The last of these three profiles, modified curvilinear, is today the most popular type with timing belt manufacturers. As the name suggests, this profile is based on the curvilinear profile, but has a shallower tooth height along with an increase in flank angle. These changes help to give the modified curvilinear profile the ability to withstand higher amounts of torque.

Cosworth Engine Belts

Want more information on the belts that we stock for Cosworth engines? Then get in touch via our contacts page.

Turn your volume up to 11 and sit back and enjoy 90 seconds of pure, unadulterated noise in this Cosworth Formula 1 engine test as a CA2010 engine is pushed through its paces on Cosworth’s transient dyno at speeds of up to 18,500 rpm.

The Cosworth CA engine represented a pinnacle in the design of high-speed naturally aspirated engines for Formula 1 racing. Calling on over 50 years of experience that dated back to the legendary DFV, Cosworth created their most ground-breaking engine ever.

Sadly, in 2010 the engine speeds were restricted by regulation to 18,500 rpm, but that didn’t stop the cars of that era sounding amazing.

The Need for Speed

In the ear-splitting ‘90s and 2000’s, engine speed was THE metric that Formula 1 engine manufacturers wanted to push to the limit. In a naturally aspirated engine, the goal is to get as much fuel and air into the combustion chamber, and the best way to do this is to run the engine as fast as possible. Unlike power figures, engine speed is something that rival competitors can measure from the side of the track, using audio recording equipment.

It is generally acknowledged that BMW were the first F1 engine manufacturer to break the 19,000 rpm limit in 2002. Toyota soon leapfrogged their fellow German rivals, reaching 19,200 rpm in 2005 despite the introduction of rules to increase engine mileage. These regulations caused a brief respite in the push for speed, but by the end of the V10 era in 2005 the entire grid was running at 19,000 rpm.

Switch to V8 Power

In an attempt to curb engine power, the FIA mandated a switch from 3.0 litre V10s to 2.4 litre V8s in 2006. However, this had little or no effect on the push for speed. Cosworth’s Bruce Wood explained how they did this to Race Engine Technology as part of their exposure on the CA . “To go faster you just have to keep making the bore bigger and the stroke shorter and sort out your valves.

“While developing the TJ we did tests on our single cylinder rig of 96, 97 and 98 mm bores – it was all about higher speed. We were considering a bigger bore and bigger valves and a compound valve angle before the mandatory switch to V8s was brought in. We had thereby established that combustion was OK with the 98 mm bore (the maximum permitted in 2006), so there was no reason not to move to it…”

In 2010 Cosworth returned to Formula 1 with the CA2010. By this time the rules had necessitated a cap in speed of 18,500 rpm. Nevertheless, the cars still sounded incredible, and drop in speed didn’t prevent engines like the CA2010 from reaching power figures of over 775 bhp.

Keeping It Together

Cosworth CA2010 F1 Engine

20,000 rpm is a huge achievement – as this Formula 1 engine test video shows, even 18,500 rpm sounds terrific, but running at these speeds results in a number of engineering headaches. First of all, the inertia loads on the moving components roughly increase with the square of the speed. So a jump from 10,000 rpm to 20,000 rpm might be double the speed but will result in a quadruple increase in inertia loads.

The second problem with increasing engine speed is that there is a corresponding increase in vibration. This was compounded with the switch from V10 to V8 engines in 2006. A V8 engine like the CA equipped with a flat plane crankshaft will naturally have out-of-balance vibration in a horizontal direction.

Bruce Wood gives a further insight into the problems that this horizontal shaking of the engine would cause on the CA. “When we first started running the CA, the scavenge pumps, which are held onto the sump with horizontal bolts, would fall off. Those are 8 mm cap screws, the heads of which snapped off because of the unbalanced force, which is why our scavenge pumps are now secured by Multiphase bolts!”

Torsional Control

One other problem to resolve before unlocking 20,000 rpm is torsional resonance of rotating components like the camshafts and crankshaft. Torsional resonance has always been an issue in Formula 1 engines – Keith Duckworth had to resort to flexible compound gears to keep the gear drive intact in the DFV in 1967. Fast forward 4 decades, and double the engine speed, and the torsional problems become a whole lot worse.

“In terms of the torsional vibration inside the engine, we knew what we were up against, which is why the CA has far more damping devices in it than our previous V10 engines.”, says Wood. “We have a ‘compliant’ gear train that has been in our Formula One engines for years, then in addition (to two dampened compound gears) the CA has compliant quill drives within each of its two auxiliary drives, a big viscous damper on the back of the crankshaft, viscous dampers on the back of each camshaft and friction quill dampers in the front of each camshaft. That means in total it has 13 dampers – 14 when fitted with KERS.”

Fancy Owning a Piece of History?

We have now started to stock parts from Cosworth’s TJ and CA engines that can be displayed for all to see. Just keep an eye on our Memorabilia section of our on-line shop to see what’s currently available. Each part can be bought directly from the website shop and delivered straight to your door. And then just imagine these components being used in a 20,000 rpm Formula 1 engine!

Cosworth PR8121 BD Valve Springs

The valve spring has one simple job to do – it just has to provide a force that will keep the inlet or exhaust valve under control. But as we’ll see in this technical feature, it’s a bit more complicated then that. And when things go wrong with valve springs, things really go wrong. So it pays in the long run to use the best valve spring available. Nested twin valve springs (made up of one spring inside another) are extremely popular on race engines, and in this technical feature, we’ll discover why.

Valve Spring Behaviour

Before we look in more detail at nested twin valve springs, let’s look at how a valve spring behaves when its loaded. When compressed, the spring provides a reactive force which mainly occurs from the twisting motion of the coiled wire. If the load applied is constant, then the load in each coil will be equal. But when the engine is running, the continuous reciprocating movement of the valve compresses the spring and then lets it expand again.

When the valve begins to open, the spring starts to become compressed and the coils will accelerate. The coils nearest the camshaft will see the entire inertia of the spring. As we move along the length of the spring, successive coils have less inertia loads as there is less mass below them. This means that the acceleration of each coil diminishes down the length of the spring. Hence the first coil will close up most and each subsequent coil less, starting off a compressive wave down the spring.

When the valve gets to around its mid-position, its acceleration will drop to zero, and at this point the coils will all be travelling at the same speed. But as the valve starts to decelerate, the opposite now happens – the coil at the other end of the spring closes up more than the ones above it, and the compressive wave reverses direction.


You can see this wave take place on a child’s Slinky toy spring (remember them?). Hold one end fixed, and then quickly move the other end and you’ll see the wave of movement of each coil pass up and down the length of the spring. The continual back and forth movement of the compression wave creates a vibration in the spring that is referred to as “surge”.

Surge becomes a problem if it gets close to an order of the springs natural frequency. This can lead to the compressive wave going out of control, which will cause loss of valve control and will also result in extreme stresses in the spring. Either of these effects can end up with engine failure.

Nested Springs

Cosworth PR8121 Valve Spring

One way to tackle the problem of surge is to use nested twin springs. A nested spring is made up of two or more springs running in parallel. Typically, the nested twin spring will be a small spring contained within a larger spring. The two springs will have different natural frequencies, which can make the nested twin spring less susceptible or even immune to the problem of spring surge.

The outer diameter of the inner spring and the inner diameter of the outer spring are usually chosen so as to create a small amount of interference between the two springs. If this is the case then it is essential that the direction of windings is different between the springs, otherwise they will get caught up in one another. The interference will provide a means of damping, allowing unwanted energy to be converted to heat from the friction between the two springs.

When run for extended periods, this interference will of course wear the surfaces of the springs and reduce the life of the nested spring assembly. Note that titanium nested springs cannot be run with interference. That’s because titanium has an inherent nature to gall (the macroscopic transfer of material between metallic surfaces) when in contact with other titanium surfaces.

Cosworth Valve Springs

We currently supply two types of valve spring, and they are both of the nested twin spring variety. Our PR8121 valve spring is a non-interference spring, whilst our DR4601 valve spring has interference between the inner and outer springs.

You can see more details of these two springs here: PR8121 VALVE SPRING (INNER & OUTER)


Want to know more about our Cosworth valve springs? Then get in touch, our contact details are here: CONTACT US

Have you ever wanted to take a peek inside a Cosworth Formula 1 engine? And did you ever wonder how these engines were capable of reaching speeds of over 19,000 rpm, producing 900 bhp?

Well, if you did, then we hope you’ll like this video that we made showing the inside of one of these high-revving monsters. Codenamed the TJ, this is the engine that was first used by Jaguar Racing in 2003. The team continued to use this engine when they morphed into Red Bull in 2005. It also saw active service powering the Jordan and Minardi teams in 2004 and 2005, respectively. Its final year of racing was in 2006, when Torro Rosso (formally Minardi) ran the engine against the V8’s.

Last of its Era?

The TJ was the epitome of the “anything goes” regulations from that era. Devoid of rules that restricted the number of engines that could be used by each driver, the emphasis was very much of extracting the maximum out of each engine in just one session or race. It wasn’t uncommon back then for teams to get through over six engines in one weekend (and that’s not allowing for unscheduled engine changes!). As a result, engines like the TJ were designed with performance over reliability in mind.

Midway through the life of the TJ, rules aimed at extending engine life started to creep in. In 2004 the FIA introduced the “two race” requirement that each engine had to attain. Engines like the TJ that were designed for outright power and performance had to be re-engineered to last longer. In addition, restrictions in later years on low density materials plus minimum weights and centre-of-gravity heights meant that the lightweight features seen on the TJ became redundant in subsequent engines.

So grab a cup of tea and see inside the last of the “anything goes” Cosworth Formula 1 engine masterpieces!

Modatek are pleased to be able to help keep these engines alive for historic race series and demonstration events. If you need assistance then get in touch.

Our range of Cosworth YB pistons feature an offset gudgeon pin, which helps to reduce piston skirt wear and engine noise. To understand why, we have to consider the loads that the piston will experience.

Cosworth YB Piston Drawing

When the piston moves up and down the bore the small end of the connecting rod will articulate forwards and backwards around the pin. This creates a loading on the piston that pushes the piston sideways. This side load varies with crank angle and is also different for each stage of the four-stroke cycle. The largest side load occurs during the power stroke, when there is a combination of inertia and gas loads that will push the piston sideways towards what is referred to as the major thrust side.

Side Loads

These side loads can have an extremely detrimental effect on the operation of the piston. For example, they can promote tilting or rocking of the piston in the bore, which in turn can increase wear at the top of the lands and at the bottom of the skirt. This type of movement can also create vibrations that are then radiated through the engine and can be heard outside the engine.

One way to reduce the major thrust side load is to offset the pin’s centre away from the cylinder bore centreline and towards the major thrust side. Even just a small offset can have a noticeable effect in reducing wear and noise during running.

If you’d like to know more about the science behind piston offset pin tech, or about the YB pistons that Cosworth makes exclusively for Modatek, then please get in touch via our Contact page.

In this technical feature, we’re going reveal some oil pump design secrets! A perfectly-working oil pump is vital to good engine health. If the oil pump starts to fail, the oil pressure will drop. And when the oil pressure drops too much, the end result can be catastrophic, such as seized mains or rod bearings.

Cosworth YB0852 4WD Oil Pump

Oil pumps are termed as positive-displacement pumps. The rotors within the pump move to create an open void that expands with movement and the expanding void is filled with oil. As the rotors move around, they take the oil with them, and the void then compresses, forcing the oil out of the rotors.

Internal and External Pumps

Broadly speaking, there are two types of positive-displacement rotary pumps – internal rotors and external rotors.

In an internal rotor pump, an inner rotor with external teeth runs inside an outer rotor with internal teeth. The inner rotor will have one less tooth than the outer rotor, and the two rotors run on fixed eccentric axis.  As the two rotors rotate, the volume created between the meshing teeth expands and contracts the oil.

Most internal rotor pumps need to have a crescent shape in the space under the inner rotor. This crescent separates the two rotors, creating a seal that stops leakage from the high pressure volume back to the low pressure volume. However, this crescent is eliminated in a gerotor pump like our popular Cosworth YB 2WD oil pump (gerotor is short for generated rotor). The gerotor design does away with the crescent, creating a compact and simple solution.

External rotor pumps consist of two identical rotors running side by side. As with the internal rotor pump, one gear drives another, and oil is moved through the rotors by the expanding and collapsing void when the teeth mesh. Usually the two rotors have parallel teeth, but in other applications the teeth can be angled in a chevron pattern.

Rotor Teeth Profile

Did you know that the profiles of the inner and outer rotors in an internal rotor pump are anything but simple curves – in fact, the profiles belong to the “trochoid” family of mathematical curves.

If you’re old enough to remember playing with a Spirograph toy, then you’ll remember the curve created by pushing a pen through a hole in a small cog and then rotating it inside or outside a larger toothed disc. These curves are actually called epitrochoids and hypotrochoids, and these curves are the starting points for the design of the rotor profiles. When the oil pump rotors are first designed, the chosen curves for the rotors are carefully adjusted to reduce the build-up of stress concentrations in the roots of the profiles, and to also provide good resistance to debris without compromising volumetric efficiency.

Its not just the profile of the tooth that determines the how the pump will behave. The other important design consideration is the amount of eccentricity between the inner and outer rotors. This eccentricity influences the shape of the rotor profile.

Teeth Numbers

The number of teeth chosen will have a major impact on pump performance. Fewer teeth mean that the overall diameter of the pump can be smaller, which in turn makes it easier to package in the engine. Fewer teeth also result in a reduction in power loss for a given flow rate, but the downside is that they have to run at a higher rotational speed, which can increase wear.

On the other hand, more teeth will give fewer pressure fluctuations and hence a smoother overall oil pressure. The fluctuation is sometimes referred to as pressure or flow ripple, and is an unwanted side-effect of any positive-displacement pump. The effect of pressure ripple is mechanical vibration in the oil circuit in the engine, which can damage components such as oil hoses, seals, and bearings, so any measures that can minimise pressure ripple are likely to be of great benefit.

Rotor Clearance

Cosworth YB0852 4WD Oil Pump

The clearance between the rotors themselves and between the rotors and the end faces will also have a significant effect on pump efficiency.

Reducing these clearances will have a knock-on reduction in leakage of oil across the end faces from the pressure side to the suction side. However, not enough clearance can cause the rotors to bind and jam up, plus debris will become trapped and then damage the pump.

Fit Genuine Parts!

Cosworth YB0265 Oil Pump

The rotor profiles and clearances in our oil pumps have been carefully designed by Cosworth engine designers to match the requirements of the YB engine, and that’s why we believe that its important to fit genuine Cosworth parts like these. If you’d like more information on the Cosworth YB oil pumps that we stock and sell then please get in touch via our Contact page.

A piston accumulator groove is one way that the sealing of the piston rings can be improved. But why is ring sealing so important?

Piston Accumulator Groove

At the centre of any internal combustion engine lies it’s beating heart. Pistons travel up and down the bore at immense speeds, sucking and expelling combustion gases in and out of the combustion chamber. The piston has to withstand the immense loads from inertia and gas pressure. But they also have to provide a stable housing for the sealing rings to function correctly.

The sealing rings have to stop the combustion gases from escaping from the combustion chamber and into the crankcase. They also must prevent oil from travelling in the opposite direction, from the crankcase into the combustion chamber. So its vital that the piston is designed to keep the rings in place at all times.

Good ring groove design is of course important, but there is another design trick that piston manufacturers can employ is with the usage of what is termed an accumulator groove – you’ll see one in our Cosworth YB piston for example.

Accumulator groove

Look closely between the top and second compression ring grooves and you’ll notice a very small groove. This groove is called an accumulator groove, and its job is to help to control the movement of the top ring.

Cosworth PA2062 Piston Design Features

It is inevitable that some combustion gases will escape past the top compression ring. This might be due to oversize ring gaps. Another reason is the unsettling of the top ring when the piston rapidly changes direction at TDC at high engine speeds. To combat this, the small additional volume in the accumulator groove reduces the pressure on the underside of the top ring.

This reduction in pressure is an effective method to reduce or eliminate unwanted ring flutter. This is a phenomenon that can have an adverse effect on engine performance and can potentially lead to high levels of blow-by. (Blow-by is the escape of combustion gases past the ring).

The reduction in pressure in the accumulator groove also has a beneficial reduction in pressure above the second compression ring. Stabilising both compression rings will improve the sealing performance of the rings.

Want to know more about the range of  Cosworth pistons that we supply? Then get in touch via our Contact Us page.

Cosworth YB1429 Head Gasket

Multi layer steel (MLS) head gaskets, like our popular Cosworth YB1429 head gasket pictured here, comprise of a number of layers of thin sheets of spring or carbon steel that sandwich the sealing material.

Cosworth YB1429 Head Gasket

The upper and lower steel sheets contain a pressed beading. This beading runs around the perimeter of the bores and passageways to increase the local sealing capability. When the head fasteners are tightened, the beading deforms to create extra sealing pressure. This pressure ensures that the combustion gases, lubricating oil and coolant that transfer between head and block all stay away from each other and remain inside the engine. Ideally the deformation will be mostly elastic, so that the beading can adapt to changes in temperature and load. Most MLS gaskets including ours also contain an inner layer called a stopper that prevents plastic deformation of the beading.

Further, the top and bottom layers have an elastomer coating to reduce friction. This can help to prevent microscopic movement of the gasket. Without this coating, there could be damage to the gasket and the firefaces on the head and block.

Our YB1429 MLS head gasket was designed by the engineers at Cosworth and Victor Reinz. They wanted to create a superior gasket. They wanted one that would provide excellent sealing between the block and head for all of the high performance applications that the YB engine ends up in.

If you’d like to know more or wish to order one then take a look in our on-line shop.