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Turbo Balancing for Efficient Diesel Engine Repair - Turbo Rebuild

Turbo Balancing for Efficient Diesel Engine Repair and Maintenance

A lot of diesel engines nowadays have turbochargers. In fact, some even have twin turbos. Turbo gives you that extra oomph that a regular diesel engine just does not. If you are planning on rebuilding or installing a turbocharger in your diesel engine, one of the most frequent issues to arise is balance. In order for the engine and the turbocharger to function properly and efficiently, the rotary components need to be balanced to ensure a satisfactory diesel engine repair.

What is turbo balancing?

First of all, let’s see what balance really means. Just to be clear from the start, no turbocharger can be fully balanced. The unbalance comes from the rotation itself. It is calculated as weight times the radius of rotation. The preferred unit of measurement is usually a gram-inch, which means that one gram of weight is placed at a one inch radius from the balanced part. Naturally, modern turbos do not have such extreme deviations from the ideal. The unit used in modern turbos is actually milligram-inches, which is a thousandth of the original unit.

Component balancing

As you may know or at least guess, a turbo is a complex machine. Luckily, not all parts need to be balanced. Component balancing refers only to the turbine and the compressor wheel, as they are the ones rotating. It is absolutely essential to balance these components pre-assembly, as any imbalance leads to an unbalance, called the “stackup” unbalance. This kind of unbalance is fairly irrelevant to large turbos, as they are built to tolerate such a thing.


CHRA balancing

However, the advent of small turbochargers, primarily in cars, brings this type of unbalance into the foreground, as the relatively small mass and the sheer speed of rotation cause massive forces. These forces very soon manifest as oil leaking from the bearing housing ends or a shrieking sound caused by the vibration. The best course of action is to perform a CHRA (center housing rotating assembly) balancing.

Turbo balancing

High speed balancing

There are two types of CHRA balancing. You can either chose high speed balancing using a vibration sort rig (VSR), or slow speed balancing, using a balancing machine. Both have some upsides that recommend it over the other. What’s important is that either one of these will decrease the unbalance to an acceptable degree.

Slow speed balancing

The slow speed balancing uses a two-plane balancing machine (VSR only does one-plane balancing). The already assembled turbo is placed in the machine which then rotates relatively slowly, powered by either air or a belt. Being a two-plane machine, readings of unbalance are taken on both the turbo compressor and the turbine. With this kind of balancing, you do not need to feed pressurized oil into the system, because the speeds are fairly low, although the shaft of the machine does need to be lubricated beforehand.

High speed vs. slow speed balancing

High speed balancing uses the vibration sort rig, which rotates the components at high speed using compressed air. Due to high speeds, pressurized oil is inserted in the system. High speeds enable the corrections on the compressor nose. The key advantage of high speed over low speed balancing is that it enables the operator to hear any unusual noises coming from the turbo.

Alternatives

What you need to understand is that speed does not equal precision. Higher speeds do not make the result better. If the machine is set to only correct, say 20 milligram-inches, it will do so regardless of the RPMs. The sensitivity of the equipment is the key factor in balancing.

It is possible to have a balanced turbo even without CHRA balancing. The builder of the turbocharger needs to be extremely critical during the selection of components, as well as during the assembly to ensure the tightest fit possible. This is, however reserved for specialists, and most shops and mass-producers do use CHRA. And if you are doing a diesel engine repair and turbocharger rebuild, you absolutely do need to have a CHRA balancing.

The final word

In summation, to get the most out of your turbocharger, you need to select the appropriate components and have them assembled as carefully as possible and then perform a CHRA balancing of your choice. And, naturally, regular maintenance and inspecting for wear and tear are obligatory.

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