Question time with Melett – Our frequently asked questions section offers a wide variety of questions and answers collated from technical enquiries, customer feedback, internal training seminars and much more. Should you have any questions you would like us to provide the answer to, please do not hesitate to contact our sales team: [email protected]
Core Assembly / Nozzle Ring Questions:
What are the effects of not balancing a CHRA?
Failure to balance the CHRA on specialist equipment can cause excessive vibrations as the turbo speeds up, resulting in noise (whistling) and a breakdown of the oil film in the bearings. This in turn will cause premature failure of the bearing system, often with no obvious signs of lack of lubrication or oil contamination.
Importantly, the life of the turbo will be significantly reduced if the CHRA is not properly balanced – in worst cases the turbo will make unacceptable noise during operation and fail within days.
Why does a balance graph vary between different VSR machines?
The problem the manufacturers have is that the machine vibration will vary slightly as a result of many uncontrollable factors from machine to machine. By understanding this, it makes these machine to machine variations much more understandable.
Two of the more significant variations are as follows:
The Adapter – From manufacturer to manufacturer, the adapter design is different. Also from adapter to adapter of the same turbo part number, each adapter has slightly different properties (casting wall thickness, plate thicknesses, exact material properties). As a result, each adapter will give a slightly different vibration during the run up in comparison to the original vibration, which was cancelled out by the machine manufacturer. The design of the adapter and the resulting vibration level will therefore vary between adapters.
Clamping Force – It is possible to get the same CHRA to produce slightly different graphs by clamping the CHRA tighter into the housing, as this affects the transfer of vibrations from the CHRA to the machine. The clamping forces will vary from machine to machine and operator to operator:
- As adapters generally use a taper-lock style fixing, slight machining variations in the taper components will produce very different clamping forces and will vary from adapter to adapter;
- Different operators will clamp the CHRA with different forces;
- The different taper design between machine manufacturers will produce different clamping forces.
Taking these into account, it would actually be very difficult to get two different balancing machines to give the same balancing graph for the same CHRA.
What is a variable nozzle turbo?
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
Why is a solid vane design nozzle ring better that welded strip metal?
During the design review of the GT15 nozzle assembly, Melett Engineers analysed failure modes of many units. They concluded, the preferred route for the turbo aftermarket was the solid vane design for the 753420-* GT1544V nozzle ring, rather than the original welded strip metal design. This provides a stronger repair solution and allows you to offer your customers an upgraded repair.
Compressor Wheel & Shaft & Wheel Questions:
What does a 'trim' on compressor wheels mean?
Trim is the area ratio used to define the turbine and compressor wheels. To calculate the trim you use the inducer and exducer diameters.
For Example: Inducer²/Exducer² = Trim
What is Compressor Wheel fatigue?
When a compressor wheel has been weakened, it will begin to show signs of fatigue.
In terms of the compressor wheel fatigue, the blades are exposed to a continuous cycle of positive and negative stress caused by the wheel spinning fast and then slow. As the compressor wheel reaches full speed, the blades bend back and then as it slows down they bend back into position, repeat this over many repetitions suction is created which creates negative stress pulling the blades even further in.
Eventually the continuous stress will become too much and the blades will reach their endurance limit and break causing the turbocharger to fail.
What are the different compressor wheel design variations?
Flatback: Earliest design of compressor wheel and still used by some manufacturers. flatback
Superback: This design was introduced due to the increased speeds which the turbochargers rotate, because of the speed increase the force on the compressor wheel increases significantly, in particular the exducer diameter of the compressor wheel suffered the most. This is the point which rotates the fastest and is therefore under the most stress. The Superback reinforces the back face of the compressor wheel preventing the compressor wheel tearing from the bottom up. superback
Deep Superback: An exaggerated design of the Superback, generally used on more recent applications. Again, one theory is due to the increasing rotation speeds of the turbo. deep-superback
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 Superback compressor wheel at higher boost pressures. MFS – Machined from Solid compressor wheels are becoming increasingly popular as these new developments from the OE’s continue to arrive in the aftermarket. The wheels are fully machined and balanced on leading 5-axis machining equipment and precision balanced on fully automated balancing stations with auto-correction.
What is a MFS Compressor Wheel?
Machined from solid compressor wheels are becoming increasingly popular as these new developments from the OE’s continue to arrive in the aftermarket. The wheels are fully machined and balanced on leading 5-axis machining equipment and precision balanced on fully automated balancing stations with auto-correction. Melett BV40 Machined from Solid (MFS) compressor wheels replace the original BV40 compressor wheels and feature the new extended tip design.
What is the difference between the 1102-015-439 & 1102-015-442 Shaft & Wheels?
Traditionally, the GT15 shaft and wheel (1102-015-439) had a slender shaft and open back. The more recent GT15-15 shaft & wheels (1102-015-442), have a straight shaft and and full back, which helps reduce the risk of fatigue on the inducer diameter.
Bearing Housing Questions:
What is the difference between water cooled and air cooled bearing housings?
Air Cooled: Ambient air and oil act as a cooling mechanism.
Water Cooled: High temperature applications need extra cooling to perform efficiently – more commonly used in gasoline applications.
What is the difference between twin feed and single feed bearing housings?
Twin feed bearing housing incorporate two oil feeds to the journal bearing and use a twin grooved journal bearing/ Single feeds bearing housings have just one oil feed and use a single oil hole journal bearing.
Small Turbo Part Questions:
What is the difference between a minor and a major repair kits?
Melett Minor Repair Kits – All repair kit parts excluding thrust flinger/collar/washer/spacer;
Melett Major Repair Kits – All repair kit components including thrust flinger/collar/washer/spacer;
Melett Universal Repair Kits – Similar to the major repair kit, however the universal kit includes each variation to accommodate for where there are several variations of a model i.e. flat or superback compressors wheels, straight or slender shafts etc.
Why is a twin ring flinger better than a single ring flinger?
The original design was prone to oil leaks at the compressor end as the piston ring seal wasn’t good enough. The upgraded twin ring is available on new complete OE turbos for most newer applications, Melett produce the twin ring flat back flinger to upgrade all old designs as well as new ones.
What is the difference between the 1st & 2nd generation GT15 Journal Bearings?
1st Generation slender shaft bearing with smaller lands, provides less resistance meaning increased run-up speeds. 2nd Generation straight shaft bearing with large lands, is used predominantly on larger applications.
How are RHF4 Thrust Washers produced and what are the costs involved?
Melett invests heavily in our own tooling to ensure each part is precision manufactured to the correct tolerances and specification.
• The tool for the RHF4 Bi-metallic thrust washer is a very intricate tool;
• Made in Japan, the multi-stage press tool – starts with a strip of bi-metallic material (copper and steel), which then goes through 9 different stages to create the finish product;
• Producing the correct tooling requires significant investment and usually cost tens of thousands of pounds.
What is unique about the GT15-25 seal plate screw?
If a standard screw is used, it is possible for oil to work its way up the thread and leak into the compressor cover. To prevent this, the screw has a sharp feature under the head which digs into the seal plate creating the necessary oil seal;
Melett accurate replacement screws are made on special tooling produced to ensure our parts contain this critical feature
Why shouldn't you use the 1102-015-240 thrust collar with the 1102-015-324 thrust bearing?
When using the 1102-015-324 large pad thrust bearing, it is important that this is used in conjunction with the 1102-015-220 thrust spacer and the 1102-015-242 thrust washer, rather than the 1102-015-240 thrust collar.
Although these may appear dimensionally the same at first glance, this is not the case as the thrust washer and thrust spacer offer a different clearance to the thrust collar. If the thrust collar is used this can create premature failure of the bearing system.
What are the differences between the 1102-012-100/102 & 103 Z-Bearings?
1102-012-100 – Replaces the original GT12 Z-Bearing used on the Smart Car and Ford GT1544Z turbos and is identified with a single ring on the OD. The full repair kit is 1102-012-755.
1102-012-102 – Geometrically the same as the 1102-012-100, but is now produced using an improved high strength material specification and is identified with two rings around the OD. (OD 11mm)
1102-012-103 – Larger OD than the original GT12 journal and is identified with two rings on the OD. High strength material (OD 12mm)
What are the advantages of a Z-bearing?
The design of the Z-bearing is popular on the smaller turbos because it simplifies the assembly by incorporating the thrust bearing faces onto the ends of the journal bearing. The design means that there are fewer parts, and hence less room for accumulated tolerance and balancing errors. The detail of the oil ramping on the thrust face also includes some complex geometry rather than the standard linear ramping found on standard thrust bearings.
How and why did Melett improve the strength of 1102-015-300 GT15 seal plate?
Seal plates are prone to failing around the compressor wheel diameter, to improve the strength the Melett 1102-015-300 seal plate has been designed to incorporate extra strengthening ribs to help prevent failures.
What can happen when a standard screw is used instead of a proper Seal Plate screw?
If a standard screw is used, it is possible for oil to work its way up the thread and leak into the compressor cover. To prevent this, the screw has a sharp feature under the head which digs into the seal plate creating the necessary oil seal. Melett accurate replacement screws are made on special tooling produced to ensure our parts contain this critical feature
Thrust Bearing Questions:
What are the critical points of a Thrust Bearing?
Critical Points – highlight the areas of the Thrust Bearing where if the material is too thin, material specification is not strong enough, or the incorrect manufacturing process is used, it will crack.
What is Thrust Bearing failure often misdiagnosed as?
Often, the use of poor quality replacement parts, which are produced using the wrong manufacturing processes and incorrect materials, creates turbo failures – but these are misdiagnosed as being a typical oil related turbo failure creating unnecessary warranty issues.
What is thrust bearing oil ramping?
Oil ramping is designed to allow the thrust bearing to resist thrust forces put on it. It is essential to understand the importance of oil ramping and the part this plays in reducing wear and prolonging the turbos life. The ramp sizing is barely visible but is an extremely important feature on the thrust bearing. It creates a wedge of oil as the thrust component rotates and helps to force the parts away from the surface, reducing wear and therefore increasing the turbos life.
What is the difference and reason behind 360 and 180 degree thrust bearing?
The original BV35, BV39, KP35 & KP39 thrust bearing was the 3 pad, 180 degree design, due to the open thrust pad area oil retention was an issue.
In newer OE turbo applications, the 180 degree design has now been phased out and replaced with the 360 degree design, this has resulted in better oil pressure and lubrication.
What are the disadvantages of using stamped strip for Thrust Bearings?
Stamped Strip – Involves stamping the initial blanks out of a strip of brass material and is used for smaller thrust bearings. This method limits the strength of the material as this has to be weighed against the life of the stamping tool, an increase in strength in the material causes a massive reduction in tool life.
What is the difference between a Melett RHF4 Thrust Bearing and a low quality one?
Lower Quality Sample (RHF4)
To the untrained eye, initial impressions are they look ok, however looking at the parts in more detail;
• The surface is very pitted – pitting can score the thrust parts and lead to premature failure
• Badly de-burred
• The edges are not clean and sharp
• Over polished surface (trying too hard to look nice)
• No scratches to create surface tension
Melett Sample (RHF4)
• Clean, sharp edges
• Machined surface
• No de-burring required – when manufactured correctly this is not required
• Performs in the way it is designed to
• Scratches to create surface tension
Why is a KP31/35/39 360° thrust bearing better than a KP31/35/39 180° thrust bearing?
In newer OE turbo applications, the 180 degree design has now been phased out and replaced with the 360 degree design. This has resulted in better oil pressure and lubrication. Melett only use the 360 degree thrust bearing design in all BV35, BV39, KP35 & KP39 CHRA / Core Assemblies, giving the turbo longer life. A breakdown of the oil film will cause premature failure of the bearing system, often with no obvious signs of lack of lubrication or oil contamination.
Semantics: parts referred to with different names? E.g. back plate/seal plate/insert...?
Seal Plate is also known as a back plate or insert
Turbine Wheel – Shaft and Wheel
Compressor Wheel – Impeller
Bearing Housing – Centre Housing
CHRA – Core Assembly – Cartridge
Nozzle Ring Assembly – VNT – VGT – VVT -VTG
Compressor Housing – Compressor Cover
Heat Shield – Heat Shroud
Turbine Housing – Exhaust Housing
BV43 what makes it different?
BV43 is a VNT version of K03. BV50 is a VNT version of K04.
What is homologation?
Due to Homologation, once a design is approved by a vehicle manufacturer, the turbo OEM’s cannot deviate from this original approved design without seeking a revised approval, something the vehicle manufacturer will not test due to associated costs.
Melett is not restricted by homologation and where possible incorporates improvements in the original design and uses upgraded parts.