Turbo - Re-indexing

'HarryMann - Re-indexing a turbo involves rotating/swivelling the turbine and compressor casings in relation to each other
or to the shaft housing. I had to do this to a Garrett T2, off a 1.6TD diesel T25
- so I took a few photos and wrote it up as I couldn't find anything on the web even vaguely describing how its done.

Why and when is this necessary?

The same turbocharger unit is often used on different engines, or the same design but with different comp/turbine size ratios can be used on different engines. This usually means that both the turbine and compressor's inlet and exit manifolding will be arranged differently i.e. they'll be pointing in different directions. This entails twisting, rotating the two sections in relation to each other, as well as ensuring that the oil feed axis of the central bearing housing (CHRA) is also aligned suitably. It might also be that you wish to fit an intercooler, and to suit the compressor pipework, it needs angling differently.

In my case, I had a 1.9TD diesel whose turbo was well past it's useful life (proved to be a shot central bearing, with comcomitant leaky seals, giving a smokey truck amongst other problems (running on oil, etc!). I managed to find a second-hand turbo of the same type and size, but it was indexed up differently. I needed to move the compressor casing Vs the turbine and also twist the bearing housing in relation to both, to match the pattern of the one on the vehicle...

Hint: It's handy to have the original one sitting on the bench before you finalise the configuration... not always possible, so look carefully or take photos.

NB. This describes re-indexing a Garret AirResearch T2 - I imagine others use similar means of retaining the two main sections to the central bearing housing. The T3 is similar. KK K14, the more common fit for the Transporter's JX TD engine, can be re-indexed similarly.

Tools

You'll need at the minimum a good pair of internal circlip pliers that are both strong and large enough (a pair of long-nosed pliers might suffice, but I wouldn't like to bet on it); depending on the state of the thing, some good well fitting 13mm ring and open-ended spanners, maybe even 1/2" (12.5mm), if the exhaust section is like mine was. A rubber mallet is handy, and definitely a large well-mounted vise, with soft jaws. Other tools as well as the odd dose of cunning here and there, may be required, read on...

File:Hilka J12.jpg Hilka J12 circlip pliers (the smallest that will do this job)

The turbo parts and how they fit together

Here is a good link to another Wiki that describes the history and development of turbochargers very well [Turbochargers]

Aluminium Compressor casing (volute); Iron Turbine casing; central housing comprising bearings, gland seals and the main rotor shaft within, with the two wheels protruding at their respective ends; wastegate parts: vacuum solenoid and mounting plate (mounts to compressor casing), push-rod and connecting pipe (actual spill-valve integral to exhaust turbine housing).

The ally compressor casing locates over the compressor wheel and into the centre-section using a dual stepped seal on its rim, the outer carrying a large O-ring and is retained with a mighty internal circlip.

The iron turbine casing is fitted over the turbine wheel and sealed against the centre section with a roll taper-seal, close tolerance and metal-to-metal. It is retained, with six set-screws, M8x12mm, pulling down on two semicircular washer plates, the screws threaded into the turbine housing itself. The plates overlap the seal's center-section boss, pulling it tight and flush up to the housing face.

File:IMG 5736(800x600).jpg Turbine housing, wheel and it's tapered roll seal (C-plates on vise)

Quick Check

The main problem that comes to light are worn bearings and particularly seals. Holding opposite ends of the rotor, with thumb and forefinger of each hand, try to rock or move the shaft axially. Some small movement will probably be perceptible,almost zero axial movemen (up to 8 thou) and maybe 20~30 thou rock, very little! Likewise it should also spin freely through a full rotation. If movement is sticky, or excessive axial or radial (rock) play exists, you might just be wasting your time, particularly if you notice damage to either of the wheel blades or thick sticky deposits in the oil-feed or oil drain pipes - these should always be checked and if fitting a new turbo, it is suggested you throrughly clean or renew the feed pipe !

Doing it

First off, block off all inlets, particularly the oilways, with gaffer tape or similar. Clean things up a bit if that is your style... particularly the hex heads of those exhaust housing retaining bolts and any thick muck. You definitely don't want any muck, swarf, grit or foreign bodies down the oilways. NB. Whenever a casing is removed or being refitted, be very careful not to damage either wheel or knock the rotor assembly - don't drop it, or leave it around to collect swarf, filings etc. Also, it's a good idea to scribe or paint the existing positions of both sections, against a line on the centre section, for future reference.

NB. Read the rest of the article before you make a start, so you don't have to repeat any work i.e. know what you are going to move in relation to what, and the best order of doing so.

Rotating the Central Bearing Housing

This is just a matter of arranging the hot and cold section casings suitably, either one, the other or both to suit your needs. Work it out beforehand pretty well where they should all be, as you don't want to move the turbine section twice! The compressor can be the final adjustment. It's usual that the bearing oilway angle is critical to the turbine exhaust manifolding, so get this right to start with.

Rotating the Compressor casing

It might be possible to just tap this casing around with a rubber or plastic faced hammer without loosening the big circlip (but the potential fro damaging the hidden O-ring seal is there, if it's dried-up or stuck); mount the iron turbine section of the turbo in a vise and choosing your spot (under a thick edge or boss), try tapping the compressor casing around, gently at first. It will only move in very small steps if at all at this stage, but it's worth a try. I had to get a good hold of the circlip with the pliers and loosen its grip whilst spinning the casing and circlip together. Subsequently, having moved the circlip's tangs to a better location, I found I could then pretty well tap it around without loosening or removing the circlip. I later removed the circlip and casing completely, as I needed to drill and tap a new hole for the wastegate vacuum solenoid mounting plate. Note: The circlip has a chamfered face, which faces up towards the fitter, so that the circlip slots in easily and then compresses the O-ring, making a good tight seal.

Rotating the Turbine casing:

If you need to to move this in relation to the centre-section (the oilway positions determine this), then hold tight, it might not be fun getting those six setscrews out. I've seen turbos with almost non-existent heads on these bolts, and even when they are in good condition, due to the closeness of the oilway bosses and cooling fins of the centre-section, severely modified ring spanners or open-endeds are needed to shift them. I ground a shallow offset ring down to get on one head, and used a variety of techniques to loosen others, a couple resorting to using a screw/bolt-head punch to shock them a bit General Screw/bolt punch. Being 13mm, one good trick is to try 1/2" (12.7mm) AF spanners, in fact I'd give little hope of loosening any like mine with a 13mm open-ended - nothing but rounded off heads, as a 13mm will be a sloppy fit to start with on anything but fairly newish screws heads.

File:IMG 5731(800x600).jpg

The hot-section seal, being of a taper variety, and possibly coked or rusted up, will probably not just swivel around easily after removing the screws - but it maybe worth a try, with a soft faced mallet.

NB. Once the screws and plates are removed though, be careful to keep the casing and bearing housing aligned (try not to rock it), the clearances on the turbine wheel and it's housing are very tight, and these things are not damage tolerant.

So to rotate the two relative to each other, either carefully rotate the housing without wobbling it off-axis, or remove it completely and re-insert. Using new screws if you have them (do not use screws any longer or much shorter than the exisiting ones, mine were exactly 12mm from under head to end of thread, M8's 8.8 quality or better), and after cleaning any corrosion or detritus from the mating surfaces, tighten down the clamping plates very gradually, moving alternately across the housing to keep the centre-section boss nicely aligned as it goes into the casing's matching bore.Don't rush it, you'll know when the plates have pulled up fully, the screws will suddenyly tighten, at which point go round them all again, evenly nipping them up to a final tightness. Don't go crazy with them, in other words, and certainly don't get anywhere near rounding the flats off the heads!

Repositioning the wastegate vacuum solenoid

In this case, to ensure the pushrod was well-aligned with the wastegate's lever, I managed to reuse one of the threaded holes in the compressor casing, moving the solenoid mounting plate around and then marking and drilling off the second. This was a std M6 thread, critical on depth, so I bound some masking tape around the drill bit, using a 5mm bit as the tapping drill size after piloting with a 3mm Tapping drill sizes

Finally

Blow-Off-Valve - blocking it up if you are overboosting beyond about 12 psi (using a synthetic wine bottle cork)

Cleanliness If either of the impeller housings have been completely off, ensure they are spotless before re-assembly. A powerful wet/dry vacuum with a range of nozzles is an essential workshop tool here, sometimes better than compressed air, that just blows muck over everything else. Work clean as you can with the turbo disassembled, and if you drill or file, vacuum up immediately.

Acknowlegements: Thanks to Simon Baxter (at the Brickwerks) for first suggesting this and pointing out some of the pitfallls.