The GT15 journal bearings have improved over the years. They started with Melett part numbers 1102-015-100 (slender shaft) and 1102-015-101 (straight shaft). The differences in these bearings are shown below.
1st Generation slender shaft bearing with smaller lands.
Provides less resistance meaning increased run-up speeds.
2nd Generation straight shaft bearing with large lands,
used predominantly on larger applications.
There are 2 original designs for the GT15 journal bearings with the most important differences being the length of the internal bearing surface.
GT15/17 slender shaft turbos:
Original GT15 bearing (OE No. 433123-0002 / Melett No. 1102-015-100):
- smaller internal bearing surface length at the compressor side;
- larger length at the turbine side.
On new generation turbos, the improved bearing (Melett No. 1102-015-104):
- internal bearing surface has a larger length on both sides;
- the material is different;
- the oil grooves and holes are slightly different.
This bearing is also used with straight shaft turbos in the GT15-17 range and can be used to replace the old style bearing.
GT20/25 straight shaft turbos:
On the larger turbos in the VNT range:
- the bearing (Melett No. 1102-015-101) has a longer internal bearing surface length (than the 1102-015-104), at both sides;
- on 2nd generation turbos, this bearing has not changed dimensionally but the material has been improved.
GT15 Journal Bearings – Improvements:
The GT15 journal bearings were improved to increase the size of the lands and also to improve the brass alloy used for the bearings. As with the thrust bearings this contained silicon for improved lubrication (similar reason for the use of Teflon in non-stick pans).
2nd Generation slender shaft bearing with larger lands than previous version.
Designed for low viscosity oils. Replaces 1102-015-100 bearing.
This information is meant as a general guide. It is important to identify which bearing is in the turbo when stripping and replace this with the same style. The easiest way to identify the bearing is by measuring from the side face to the start of the internal bearing surface.