Breakdown and guts of a GT-R turbocharger.....

Boxersix · #1 02-22-2008, 10:08 PM

In light of some stuff here, I decided that every now and then I'll post some weird off camber technical stuff here for those who just always wondered.....

Todays topic....the breakdown(and subsequent rebuild) of a GT-R Garrett turbocharger. More specifically, a GT2554R. I've been a Garrett dealer in the area for near six years now, but have been rebuilding turbochargers of all makes and models since early 1999. The vast array of manufacturers and assorted CHRA's(center housing rotating assembly) makes it a bit difficult to keep up with the pace of progress and technology if you're not into it full time.

Over the past couple years I hear more and more people speak up/talk about the inability to rebuild the Garrett line of ball bearing center sections. This is completely false, and only spoken by someone who has they head completely up their ass and talking about something they haven't got a clue about. Dynamic piston rings are available and of common nature to the standard journal series of Garrett turbochargers. New bearing cartridges are also available to wholesale dealer direct or large scale rebuilders.

When a GTR blows due to lack of oil, unlike the standard journal bearing turbos, the turbine shaft is reuseable pending it has not been bent or had housing contact on the major. I will explain more on this later in a minute. The pictures below will show you the internals of a GTR CHRA, and speak some basic steps to putting it back together.

Note this people....while I am explaining this here in detail I do not expect anyone here to attempt this themselves on a GTR turbocharger unless the have the proper equipment to do so. **Warned**

The turbocharger is dismantled. Housings are hot tanks and cold tanked(pending material) and then jet washed, followed by either a glass bead blast of 600 grit or a blast run through the soda machine. I'll post pictures of the housings at a later date. When disassembling the CHRA you must be VERY careful. First, the compressor nut is left hand thread. Torque the wrong way to break it free and you break the turbine shaft. Second the turbine shaft does not just tap out easy like journal setups. It requires a special brace and must be pressed out. Doing so releases the BB race on the turbine side, leaving the inner race on the turbine shaft and the comp side bearing intact. This also leaves 8 to 15 balls to roll loose all over the place. these turbos have anywhere from 8-15 balls per race, x 2 that's anywhere from 16 to 30 balls per cartridge so lookout. In the case of the GT2554R it's 8 per race(16 total). The turbine race must then be pressed off the turbine shaft by means of a special holder and brace. I machine mine for each specific series of turbo.

Now some pictures here: First picture shows the turbine/shaft(note the turbine bearing race still on the shaft), compressor nut, compressor seal housing and o-ring, and off to the far right is the turbine bearing retainer. Centered is the bearing cartridge outer shell and the cartridge drift dowel. Note I said compressor seal housing and not thrust bearing/housing.....there are no thrust bearings in these BB turbochargers. Angular contact bearings take that load on their own.....

Close up view of the turbine bearing retainer and 8 balls.

Compressor wheel, compressor inner bearing race with integral compressor dynamic seal(piston ring), compressor bearing retainer and 8 balls, and turbine flame shield.

After everything is sonic cleaned in solvent, the first step is to assemble the complete bearing cartridge. This takes patience and finesse. It also requires special alignment jigs to complete or damage will result. You start with the turbine side, positioning the retainer over the race and installing the balls. It is then aligned and pressed into the rear of the cartridge housing. Doing the same with the compressor side, while keeping the half-cartridge in the jig, you end up with an assembly that looks like this:

The bore of the center housing is not like that of a journal bearing setup. It has a complete smooth bore from compressor to turbine with appropriate drain and feed holes milled in to feed the bearings though the cartridge outer shell:

The complete cartridge is slid into the bore and secured via the drift dowel....

Next up comes the compressor seal housing and o-ring. This only fits one way. O-ring installed loosely and housing pressed down in. Three to nine fasteners secure the housing into the center section. Minute amount of red thread locker secures the fasteners:

Next step is to press the turbine shaft into the CHRA. This must be done with extreme care and precision, and as always, requires yet another special jig and brace to do so properly. The cartridge inner races must be supported and aligned before pressing in the shaft otherwise you'll pop the races and have to start all over. We're talking .0005" type of tolerance here. My jigs/braces are sort of proprietary and are not shown for such reasons, sorry. Once the shaft is pressed inplace, the compressor wheel is heated on a hot plate to expand the inner bore a few thousandths and then slipped over the end of the turbine shaft. Compressor but goes on and is torqued. AS the compressor wheel cools is tightens up around the shaft and maintains a zero clearance press fit....necessary to keep the wheel from backspinning under high boost. In the end you have this, a complete CHRA ready for VSR balancing(vibration sort read balancing) and of course those pretty new housings.

This particular turbocharger came in for a rebuild and light porting....thinking it was a standard GT25 journal setup. Once I popped it open it was apparent that it was in fact a GTR cartridge and in great shape. This particular unit was broken down already, so I thoroughly clean it and installed a new compressor seal piston ring. I'll VSR balance it on Monday and assemble the newly cleaned and ported housings to it, ready for use on a Nissan swap soon.

Sorry for the ****ty pictures, my current camera doesn't focus well anymore.