We often get asked questions about shaft play. The concern is valid. Before leaving the factory, all Steam STX turbochargers are inspected and validated to not have shaft movement beyond 0.09mm in any direction as part of our QA process. Without precise measuring equipment, it would be hard for a person to detect that tiny amount of deflection.
Here is an example test where the max deviation was 0.027mm.
Typically shaft play implies bearing failure and damage. Side to side movement implies damage to the main bearings. In and out moment implies damage to the thrust bearing. Once the shaft play is too extreme and the turbo’s wheels touch the housings, the whole turbo is ruined.
The most common reason to bearing failure is lack of lubrication, meaning not enough oil getting to the bearings, or the oil is old or contaminated such that it can’t protect the bearings. Also, if a turbo is not primed before staring your car, the bearings will experience a sever lack of lubrication. It will cause bearing damage and premature turbo failure. FYI: The stand procedure is to crank your engine for at least 30 sec without starting it to get the oil throughout the turbo CHRA.
Poor lubrication is the 90%+ failure case. Upon disassemble of the CHRA, it is very easy for us to detect oil related failures.
The other failures are due to customers just pushing their turbos hard. Pushing your engine components hard isn’t a problem; you just need to be aware, it makes them wear out faster. If you push your turbo to very high shaft speeds for long periods of time, it won’t last as long. Turbochargers are normally balanced on a VSR (vibration sort rig) up to 100,000 RPM; however, pushing a turbo to high pressure ratios will exceed 100k shaft speeds. Customers may run at higher pressure ratios, just like they can also have a 12k RPM readline, but it does impact durability.
Warning: engineering content: Also, the rotating assembly will have natural harmonic frequency as elastic systems do. The force on the turbine will also add additional vibrations at different harmonics depending on the design of the aero. Basically the natural harmonics + forced vibrations can also damage the bearings. Most of this is mitigated though, by the design of the turbine aero, and using the VSR to remove extra vibrations due to imbalance. In other words, this type of failure can be avoided before you get your turbo through proper design and manufacturing.
Compressor surge can be destroy bearings as well, but can generally be avoided by designing your turbo system correctly. If you don’t actually want to figure it out, the I would recommend getting some good advice on what you need. Ask your tuner, or give us a call if in doubt.
For journal bearing turbos, damaged bearings are easy to replace assuming the wheels have not touched the housings. It is possible for a normal person to replace them in their home garage if they are careful. We however, resubmit the turbo through our entire QA process including a re-balance on a VSR.
Garrett ball bearing turbos are more resilient to abuse, but when they break, they are very hard to repair, well at least for any one other than Garrett. Essentially they are designed such that the whole bearing assembly has to be replaced. Garret does not sell then to the public. The ones you see on ebay are fakes, FYI.
To recap, you can avoid most turbo failures by: following correct turbo install procedures, providing a sufficient and clean oil supply, and having the car properly tuned. If followed, your turbo will last for years reliably.