Useful tips for understanding your airplane’s turbocharger.
We get calls every week from someone across the country regarding bearing play. During pre-buy, annual inspections and routine maintenance, the common practice is to reach into the compressor housing inlet, grab the turbine wheel shaft and give it a wiggle. You might be surprised to know that you can expect to find some play when you do this.
A little explanation is in order. As you can see by the photos (directional info here), the main bearings in these turbochargers look more like a bushing.
There are two items to consider when understanding proper bearing clearance: (1) the clearance between the outside diameter (OD) of the bearing and the inside diameter (ID) of the bearing housing; and (2) the clearance between the ID of the bearing and the OD of the turbine wheel shaft.
If you measured the bearing housing ID (.9832) and the main bearing OD (-.9780), the difference—that is, the clearance—of these turbo main bearing components would come to .0052. Similarly, a measurement of the main bearing ID (.6272) and the turbine wheel OD (-.6251) shows a clearance of .0021.
To find out the total clearance in main bearing components, add .0052 and .0021 and you’ll find your total clearance is .0073. So you see, it’s not surprising to find some obvious play in the turbo shaft.
But how much is too much?