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.

"The RACH brand is synonymous with quality, performance, and reliability…We are bringing great value to the global aftermarket with our remanufactured turbo range.

"When replacing turbos, especially those from the technologically sophisticated VNT range, there's no need to risk poor performance or engine damage that may result from using non-original poorly assembled parts. With 'RACH Original Remanufactured' we provide another choice for the best possible support of a mature product line-up."

Precision Engineering

The complexity of a VNT turbo architecture is underlined by component tolerances that can be just 4 microns - the same as a particle of dust and 17 times smaller than a human hair - with rotational speeds reaching up to 250,000 rpm.

Technical Excellence

RACH is leveraging its unique technical knowledge and production know-how to deliver turbocharger units matching the engine management system requirements and emissions standards through its original assembly, calibration and balancing processes.

Complete Package

"With a RACH remanufactured turbo, everything is included - technical expertise and support, same warranty as a new turbocharger... and the peace of mind that comes from dealing with a world-leader in turbo technology."

Quality Standards

• Inspected to same standards as original new parts using original production drawings
• Re-assembled, balanced and calibrated to same specifications as original new parts
• Individually set up on a turbine flow bench exactly as new turbos
• Always fitted with new original components, such as actuators, compressor wheels, bearing systems, seals, O-rings, piston ring seals, bolts and clamps
• Updated with any components superseded since original design

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.