There has been an ongoing debate for many years between the original turbocharger manufacturers and the turbocharger repair industry, over whether a turbo can be repaired.

This debate has been raging for over 10 years. Some OEM turbo manufacturers pulled out of the repair market around 2004 – at this time their argument was that most repairers did not have the correct specialist balancing equipment for the new higher speed turbos.

Over the last decade, vehicle technology has continued to improve to reduce emission levels in order to meet the Euro 4, 5 then 6 regulations. As a result of these changes, engine and turbo technology has increased in complexity, and the settings and control of advancements, such as the Variable Nozzles, have become more critical to the correct operation of the turbo.his is now presenting new challenge turbo repairers as the correct setting of the turbo on later models, now requires further specialist equipment in the form of an Air Flow Rig.

What is a Variable Nozzle Turbo?

When a turbocharger is matched to an engine, the Engineers have to balance the low speed response with high speed efficiency. The variable nozzle (also referred to as a variable geometry), is designed to change the exhaust gas inlet area with the engine speed to closely match the desired boost requirements of the engine. For low speed response, the nozzle vanes move to the 'closed vane' position to reduce the nozzle area – this increases gas speed through the turbo giving improved response at low engine speeds – similar to squeezing the end of a hose pipe to make the jet of water more powerful. As the engine speed increases, the actuator moves the nozzle vanes to the fully open position to maximize the exhaust gas flow.

Vane Setting Accuracy

When the first variable nozzle turbos were launched, it was a step change in turbocharging technology. Air mass sensors and ECU's were programmed to manage the whole engine system, however relative to the current engines, tolerances for acceptable air flow were set quite high. When setting up a new turbo, vane setting positions are set using accurate air flow equipment, which ensures that the 'minimum vane opening' position is set to allow a specific mass of air flow through the vanes. If the vanes are too closed, this can cause choking of the engine and overspeeding of the turbine. If it is set too large, the turbo will have too much 'lag' and not respond as well as it should.

Traditionally, turbo repair workshops did not use an air flow rigs to correctly set the flow. The actuator position was set based upon an accurate measured position of the actuator arm. This produced acceptable results and allowed the repairers to keep on repairing.

In reality, this method of setting the vanes can produce quite large inaccuracies in the flow of air. The actuator arm measurement is set against a cast finish on the bearing housing, the position of which is not accurately controlled during manufacture. However, as the engine would accept quite a large tolerance of air flow, the repaired turbo still performed well compared to the broken turbo which it replaced, so the vehicle owner was still happy with the results. On older turbo repairs, the variable nozzle position had to be a long way out before the performance was unacceptably affected or for the ECU to flag a problem. From an OEM perspective, this is not acceptable and is the reason for their lack of support of repairing.

The need for accurate air flow setting of turbos was well understood by reputable repairers, and hence some quality repairers developed their own air flow equipment to accurately set their turbos, resulting in a reduction in warranties and the ability to build on their reputation as a quality repairer.

Today's Turbos

In more recent years, as engines have improved to meet tighter Euro emission regulations, the control over the whole air / fuel system has improved dramatically. Many premium brand vehicles have moved to electronic actuation which gives positional feedback to the ECU. Some more advanced turbo controllers now sit within the CANbus talking directly to the injection system and air mass sensors, to respond more quickly to engine demands. For these turbos, the settings are either correct and accepted by the ECU – or not which results in warning lights, limp home mode or refusal to start.

As more of the Euro 5 compliant vehicles enter the aftermarket, problems will arise and for some turbo models, we have already reached the point where flowing the turbo is a necessity and only possible by workshops who have the correct equipment. However, this will naturally mean that older turbos also become more widely repaired using air flow equipment, which will bring further improvements to the market.

Making the Right Choice

Traditionally, in the turbocharger aftermarket the customer had a choice between a new OE turbo and a remanufactured turbo. Over the past 10 years the turbo repair market has changed significantly with the number of new repairers entering the market and the number of suppliers of parts. What we now have is three tiers, a new OE turbo, a high quality remanufactured turbo repaired using quality parts and the correct equipment, and a poor quality repaired turbo, using inferior quality low cost parts. There will always be a market for all three options depending upon the vehicle owner's requirements.

It is important that garages understand that there are different levels of quality for repaired turbos and therefore a different level of associated cost. When outsourcing turbo repairs it is crucial to consider the real cost of replacing a turbo and to educate your customer about the different options and associated risks for going lowest cost vs paying a little more for quality, so they can make informed decisions. Who pays for the time to fit the second replacement? What if it damages other parts of the engine?

Many turbo specialists already have a flow rig and are repairing turbos to an excellent standard. It is a fact that warranties are reduced when turbos are repaired using quality parts as well as the correct repair equipment.

Today's automotive repair industry is faced with an overwhelming range of repair parts. Amid claims of exceptional quality at extraordinarily cheap prices, here Martyn Howorth, Sales Director, Melett Ltd., explores the reasons why some turbocharger components are offered at such low prices, and what the real cost of these low quality parts means to the repair industry.

Raw Material Costs & Global Pricing

As global demand for turbochargers increases, the raw materials used in the manufacture of the components are becoming more expensive. Raw material prices have conventionally been determined by the Global Price Index (GPI), with stockists adding their margin before selling to the mass market.

Using a turbocharger turbine wheel as an example, a major part of the cost of the turbine wheel is based upon the current market cost of Nickel – the main component of the Inconel material, plus the manufacturers mark-up. The price of an Inconel wheel will be agreed on a monthly basis, if the GPI increases by 3% for example, stockists reserve the right to charge more for the raw materials, therefore increasing the global cost for manufacturers. Nickel is a popular element used during the manufacture of many automotive components, and in particular turbine wheels, as it is able to withstand the tough operating conditions and extreme temperatures of a modern turbocharger.

The Quality Compromise

In countries where the market is saturated with many new parts suppliers, under cutting margins is now common practice resulting in companies selling low quality products at rock bottom prices. In China, for example, there is a limited supply of nickel, and therefore stockists in that marketplace can sell it at a premium, as a result this should be reflected in the market price of a turbine wheel. However, the way many manufacturers are producing turbine wheels at a lower cost is to simply use a lower grade of Inconel with less nickel. This will significantly reduce the wheels overall performance and durability, leading to unreliable repairs and premature failure. Historically, low cost manufacturers were only concerned with undercutting each other's margins, however in today's environment they are now forced to reduce the quality of the cast materials in order to compete with each other. As a result we are seeing a reduction in quality.

Understanding True Value

High quality repair parts will always hold a premium in comparison to the lower quality alternatives. It is important to understand the point at which cutting margins turns into reducing quality. Every component has a minimal price point and anything lower than that point can only be achieved by using lower grade raw materials in the manufacturing process.

Machined from Solid' compressor wheels are the latest in a long line of developments from the OEMs to enter the aftermarket. Here we explore the evolution of the compressor wheel to determine if there are any benefits to using MFS wheels on standard cast wheel applications.

Cast compressor wheels are crucial turbocharger components. With over 15 million turbos produced globally each year they have provided the durability and dimensional precision that, up until now, the majority of turbocharger applications have required. If a cast wheel is used by an OEM there is no particular advantage to using an MFS wheel, unless there are known application issues that could affect the integrity of the compressor wheel.

Traditional Cast Aluminium Wheels

Traditionally, compressor wheels are produced from aluminium because of its low density weighing only one third of the weight of steel. It is also a relatively simple and inexpensive process to cast compressor wheels, but a major disadvantage is that cast aluminium is inherently not as strong as other manufacturing techniques. To create a stronger wheel post production processes are required, which include heat and solution treatments.

A high proportion of new turbochargers are spinning faster than ever before, with higher pressures, and as a result are subjected too much higher stresses which are beyond the limits of cast aluminium. Consequently, alternative materials and manufacturing processes are used.

If the compressor wheel material is not as strong as it should be it will eventually show signs of fatigue, because the blades are exposed to a continuous cycle of positive and negative stress caused by the wheel spinning fast and then slow.

Variations in Design

In response to the ever changing operating conditions there have been significant developments in compressor wheel design over the years.

Flatback:

Is the earliest design of compressor wheel and is still used by some manufacturers.

Superback:

This design was introduced due to the increased speeds that turbochargers rotate, which increases the force on the compressor wheel significantly. In particular the exducer diameter of the compressor wheel suffered the most. The Superback adds more material to the highest stressed area, therefore coping with higher loads.

Deep Superback:

An exaggerated design of the Superback which strengthens the wheel further by adding more material around the highly stressed hub.

Deep Superback – extended tip:

This design promotes greater airflow providing a faster boost response at lower engine speeds. The extended tip design increases the efficiency of the compressor wheel at higher boost pressures.

'Machined From Solid'

Taking the design process one step further, the OEMs introduced a new method of manufacturing compressor wheels known as 'Machined from Solid' (MFS), primarily due to cast aluminium not being strong enough for higher operating conditions.

By using a forged aluminium bar, it is possible to use a much stronger aluminium alloy than can be used in the casting process. By using a stronger material, the wheel has a much longer life in comparison to cast wheels as it can carry much higher loads.

In addition, MFS wheels are ideal for low production runs, enabling manufacturers to respond quicker to new blade design technology as there is no delay due to casting tooling. The wheels are produced using sophisticated 5-Axis technology to carve out the blades from a solid bar of high strength aluminium alloy, providing superior durability.

Each wheel is precision balanced on fully automated balancing stations with autocorrection – although the precision of the machining operation often means that the wheel doesn't need any balance correction. To create an even stronger wheel on specific high stress applications, titanium can be used, which prevents failure in applications susceptible to high cycle fatigue.

MFS and the Aftermarket

To conclude, if the OEM turbo is designed with a cast compressor wheel then there will be little or no advantage to using an MFS wheel other than if the application often suffers failure through fatigue – in which case an aftermarket upgrade would be appropriate.

Overview

We will describe the causes of turbocharger failures on the 1.6 110hp PSA engine widely used throughout the automotive industry. Failure of successful operation of the turbocharger can be caused by external influences and not faulty turbocharger components. In particular residual engine carbon/sludge penetrating the turbocharger and damaging it. This risk can be reduced by, ideally, removing all engine carbon/sludge, but often this is very difficult to do. However, risk can be reduced by following all the procedures set out below

Required Procedures

• Turbocharger oil feed pipe & banjo bolts must be changed
• Oil pump should be removed and checked
• Sump must be removed and cleaned.
• Check that engine has latest specification sump and dipstick.
• Oil strainer (pick up) must be removed and replaced due to residual carbon/sludge build up
• Oil cooler and filter assembly should be removed and cleaned
• Charge air cooler to be removed, cleaned thoroughly and any oil inside drained off
• Inlet and outlet hoses to be checked for damage and cleaned
• Exhaust system to be checked for contamination/blockage (Catalyst, DPF etc.)
• Vehicles with DPF: carry out static regeneration according to manufacturer's guidelines
• Brake vacuum pump to be removed and checked for debris/carbon - clean as necessary
• New oil filter and oil to be fitted
• Fuel injector gaskets to be checked as not burnt or compromised - replace as necessary
• Oil drain pipe checked for blockage/restrictions and cleaned as necessary

Oil Flow Check Procedure

Oil flow must be checked:

• Fit turbocharger to engine leaving oil return pipe off
• Install a longer oil return line and feed into suitable container
• Start engine and idle for 60 seconds, then switch off engine
• Measure volume of oil in container
• 60 seconds of idle should produce at least 0.3 Litres of oil
• Repeat test two or three times to confirm oil flow is correct
• During this test. do not allow engine to run below minimum oil level!!
• Vehicle should be driven 20 to 30 miles then the oil/filter and banjo bolt/filter must be changed
• Advise oil/filter and banjo bolt/filter are changed at 3000 mile intervals

WARNING

To reduce the risk of premature turbocharger failure by residual carbon/sludge, you must ensure you follow the above procedure. You should NOT fit the turbocharger where you know, or have reason to believe, that the risk cannot be overcome due to the possible age of the application and/or lack of service history etc. In these circumstances you must decide how best to prepare the application in order to avoid damage to the turbocharger once fitted.

About the PSA 1.6HDi, DV6TED4 Engine

The PSA 1.6HDi, DV6TED4 engine is a highly sophisticated low emission, high power diesel unit. It is used in many different applications; Citroen, Ford, Mazda, Mini, Peugeot and Volvo.

Due to the engine being clean and powerful, it is designed to operate at high temperatures, which demands the very best lubricants. These lubricants must be maintained in peak condition and PSA have fitted an in-line oil filter to the turbo and an integral oil cooler / oil filter to this engine to ensure this. However there is a drawback to this; reports in the field indicate that if the engine has been operated with the oil level below normal limits, this may potentially cause a high concentration of carbon in the oil. This may then lead to blockage of the in-line filter, oil cooler and main oil filter, which will eventually bring on premature turbo failure. The vacuum pump may also suffer from this same type of contamination.

However, due to its high operating speeds (230,000 revs per minute) the turbo will usually be the first to show signs of damage. This can happen from 30,000 miles onwards if the oil level and correct oil change intervals / procedure have not been adhered to.

Important Note: Experience to date suggests that the carbon build up in this application is particularly difficult to remove.