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Turbocharger Maintenance and Rebuilding Guide

Maintenance

For the most part, the turbocharger is a very durable device that despite its precision internal tolerances and incredible operating speeds (turbine shaft speed can be in excess of 120,000 rpm) is very capable of a long life. However, just like the engine itself, this presumes that certain care and precautions are taken.

If you do nothing else for your turbocharged engine, practice “turbo awareness.” This involves three basic behaviors that stem from understanding the environment where the turbocharger lives and operates.

 


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TURBO: REAL WORLD HIGH-PERFORMANCE TURBOCHARGER SYSTEMS

 

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Turbo Awareness Behaviors

1) At engine startup, keep engine RPM low for approximately one minute.

The reason is that the turbocharger is a supplemental device regardless of whether it’s factory installed or an aftermarket retrofit. This means that it’s likely to be the last subassembly in the engine system to receive lubricating oil, yet it’s rotating very quickly, even at idle. There’s no cause for alarm here, the turbo is designed to withstand startup. Just don’t let it go above idle. While many experts will say that 30 seconds is sufficient, the one minute allows for variations in cold weather operation where oil flow takes more time to reach its destination, as well as the oil lag created when the oil is changed or after extended periods of time between engine starts.

Also, it’s always a good idea not to juice the throttle very hard until the engine has reached full operating temperature. Oil lubricity is at its best at operating temperature. This isn’t just a good idea for the turbocharger’s sake, but your engine will love you for it too!

2) Idle your engine for a while before shutdown to cool it down.

What you’re trying to avoid here is the typical interstate deceleration and stop for refueling, or similar behavior where the engine has been producing a decent amount of power, and the engine is then rather quickly shut down. The turbo is not only lubricated with engine oil, but the oil is a principal cooling medium, just as it is for the engine. Engine exhaust at idle is much cooler, so idling the engine means cooler exhaust and oil flowing through the turbocharger bearing housing helps remove the heat build-up.

When this is not done it causes a hot shutdown, where the turbine housing acts as a heat sink that gives up its heat to all the surrounding components. The exhaust heat that travels from the turbine housing to the turbocharger bearing housing literally cooks the engine oil, which is now trapped since the engine is shut off. The cooked oil forms a hard coke deposit that, over time, builds up like cholesterol in arteries. This can have a very detrimental effect, plugging up internal oil passages and reducing the oil supply to critical areas of the turbocharger.

Allowing the engine to idle for two minutes may seem like an eternity once you are where you’re going. But if you’ve been running the engine hard, and you know you plan to stop shortly, you can anticipate this and intentionally go easy on it for three to five minutes prior to shutting it down. Then you can rationalize more like a one minute idle before engine shutdown. All it takes is some common sense and turbo awareness.

3) Change your oil when you’re supposed to.

The number one cause of premature turbocharger failure is oil related; either contaminated lube oil, or oil starvation. Unless your engine is a diesel, the turbocharger will contain the most precision machining tolerances of any engine component. The bearing surfaces on the turbine shaft are typically held to between two and three ten-thousandths of an inch; that’s the fourth decimal point! (Typically only a diesel fuel injection pump and/or injectors will have more precise tolerances.)

There are abrasives in your oil that will pass through the filter. There are two enemies here. One is the very small particle that will pass through the oil filter even when it’s new. Most engine oil filters will filter engine oil down to particle sizes of about 30 microns. A micron is one-millionth of a meter. As these particles build up, they begin to wear on precision surfaces and cause trouble. Changing the oil at the manufacturers recommended interval, such as every 3,000 miles, is a very good idea, but it’s an even better idea if your engine is turbocharged because the turbo is more sensitive to these very small contaminants.

The other factor is build-up in the oil filter. Many people know that, in general, a slightly dirty filter will filter better than a perfectly clean one. This is due to the roadblock that the dirt build-up causes in the filter medium, which helps to catch more dirt. However, the fallacy to this wisdom is that when the build-up is great enough, the oiling system goes into bypass. As a general system protection, most all engines have a bypass valve so that if the filter does plug, it doesn’t cause catastrophic engine failure by restricting oil flow to all parts of the engine. If an engine goes into bypass mode, it means you’re recirculating completely unfiltered oil! This places a whole new awareness upon the importance of changing your oil and filter doesn’t it?

When it does come time for the oil change, there is one step that’s commonly overlooked by almost everyone priming your oil filter. Prior to installing the engine oil filter, if possible given its position, it’s wise to fill the oil filter with clean fresh oil before installation. The filter will otherwise act like an accumulator and drink up the oil when the engine is restarted, which can cause excessive oil lag to all moving parts, such as the turbo!

Professional commercial fleet operators have learned that the secret to getting a million miles out of their commercial diesel engines is oil filtration down to one micron. While there are specialized ways to achieve this, those how-to facts are beyond the scope of this discussion. However, the point is still valid for any engine, gasoline or diesel; a clean engine is a happy engine.

When running a turbo, you should step-up to the highest grade or API (American Petroleum Institute) rating available in your manufacturer’s recommended oil viscosity. If you’ve rebuilt your engine and incorporated different internal clearances, you should also shift to a higher viscosity oil. Synthetic oil is fine if you don’t mind the cost, but it’s not necessary.

 

Intake Filtration

Another common mistake is to expect too much life from your air filtration system. There are some very basic considerations here that can logically be divided into whether your turbo has been retrofitted or was factory installed.

If your turbo was factory installed, your air filter flow capacity design has taken the turbo’s presence into consideration. Most of us tend to squeeze all we can out of every serviceable component on our cars. But pushing the same change intervals on a turbo engine as we would on a naturally aspirated engine can cause some real problems.

If your filter begins to plug, the turbo will form a vacuum in the compressor underneath the compressor wheel. This vacuum can cause engine oil to be literally sucked right out of the bearing housing area and cause smoking problems, fouled plugs, and generally poor performance. Further, if the filter has gotten bad enough, when you stomp on the gas, you may develop enough suction to distort the air filter’s seal to its housing, causing unfiltered air to enter the turbo and engine.

Foreign object damage is a major cause of turbo failure. There are many forms of foreign objects that have failed turbos besides wrenches, shop rags, and low-flying birds. Dirt and debris entering the turbocharger compressor will erode the inducer blade tips and literally blast the inside of the compressor wheel and housing with small particles entering the compressor at slightly sub-sonic speed. Keep your filter in place and changed often and you will avoid these sorts of problems.

If you have retrofitted your engine with a turbocharger, it’s essential that you also change your air filter size. See Chapter 6 to calculate what size you need. The retrofitted turbocharger is subject to all of the same issues mentioned above, but if you’re using a filter that’s too small, your likelihood for these problems increases.

 

Introduction to Rebuilding

If you suspect your turbocharger does need to be rebuilt, there are a couple of relatively simple things you can do to verify this fact. First, you must have some reason to suspect turbo failure. The most common indicators will be an unusual noise that comes from wheel to housing contact. This will typically be a high-pitched whine that comes on suddenly. Another is extreme power loss from the lack of boost, which can also be seen on the boost gauge. This can also be accompanied with a noticeable increase in black smoke from unburned fuel due to the lack of sufficient air present.

If such conditions exist, inspect the turbo for signs of failure. The easiest way to do this is to remove the intake air connection leading to the compressor section of the turbo.

Caution: Never work around a turbocharger with the air ducting removed and the engine operating. A turbo’s rotational speed, even at idle, contains sufficient force to cause severe bodily injury!

Once the air intake ducting is removed, reach in and grasp the nose of the compressor wheel. It should spin freely. If the wheel will not rotate freely, it has locked up for some reason and needs to be serviced. Also try to move it back and forth. If the turbine shaft has broken, the wheel will move freely back and forth. It’s also possible that an early failure has occurred such that only slight wheel-to-housing contact has occurred. You can determine this by lightly forcing the wheel to one side and determining if you can feel it contact the housing.

One note here: In many turbos, the compressor wheel to compressor cover clearance is so close for turbo compressor efficiency, that the wheel will just slightly contact the compressor contour. Typically, this won’t be felt in a turbocharger where engine oil is present in the bearings because the oil takes up most of the clearance. However, a new turbo may have slight contact because most new turbos are built dry to verify operational clearances during assembly.

 

 

Turbocharger end housings can be removed and the CHRA can be completely replaced. (Courtesy Honeywell Turbo Technologies)

  

If you determine your turbo has failed and it seems like a catastrophic failure such as severe wheel-to-housing contact or turbine shaft breakage has occurred, it is not recommended that you attempt to rebuild the turbo yourself. In such a case, there are potentially two choices. The first and easiest is to simply remove the entire turbocharger and contact a local turbo distributor for an exchanged unit. The distributor will expect your failed turbocharger as a trade-in core. Further, there should be a nameplate on the turbocharger with a part number and a serial number on it. This is more valuable than simply knowing the year, make, and model of your vehicle. It also ensures you getting the correct replacement turbocharger.

If the turbine shaft has not broken, and there appears to be mild wheel-to-housing contact, another option is to replace the center section, also known as the CHRA (Center Housing & Rotating Assembly) or cartridge. Turbo distributors use both terms and will understand either. In some cases, the cartridge has been referred to as a core. This term is an outgrowth of turbocharger production people on the manufacturing floor using the slang reference as the core of the turbo. However, in the service industry, a core is the failed trade-in unit for a replacement assembly.

 

Servicing Your Turbocharger

To determine the best course of action, you’ll need to remove the turbo. If you’re unfamiliar with this process, it’s a relatively simply procedure. All that’s required is a basic mechanical aptitude and an average set of mechanic’s tools. If you plan to get into turbocharger disassembly, a large and small set of inside micrometers will also come in handy, but this can be worked around as will be discussed.

You’ve already removed the intake system, and now you need to remove the exhaust side connection. This can likely be the most difficult part of the entire process. If you have the time, use some penetrating oil on the V-band connection or the bolts that connect the down-pipe leading from the turbine housing to the exhaust. If you need to remove bolts, it may be beneficial to use a blunt chisel and lightly tap the head of each bolt several times to set up vibration to ease the removal. These bolts can be quite difficult to remove because of the high heat environment. With the exhaust removed, the oil inlet and drain connections should be located and removed. The oil inlet will be the easiest and is typically either a threaded pipe-type connection or an inlet pad using two bolts.

 

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If possible, remove the connection in the oil drainpipe leading away from the turbo. This will facilitate an easier removal of the actual drain connection on the bearing housing once the turbo is removed from the engine and the job can be done on the workbench. Next, remove the compressor discharge connection to the boost tube leading to the intake manifold or charge-air cooler.

Finally, remove the turbine housing foot-mount bolts. As with the turbine housing downpipe, turbine housing mount bolts can be difficult to remove, but penetrating oil and several light taps can aid in the process. In many cases, there won’t be sufficient room for setting up vibration and you will only be able to apply elbow grease.

 

 

Prior to turbo disassembly, be sure to use some sort of stamping to index the position of each end housing relative to the oil inlet. Turbochargers will have many different orientations depending upon what engine they’re set up for. (Courtesy Diesel Injection Service Company, Inc.)

 

 

Mount the turbo assembly securely in a vice by the turbine foot. Brass lined vice jaw covers may give too much and the turbo can land on your foot. Clamping the turbo directly in the vice jaws as shown will hold it securely and not harm the mounting surface where the turbo seals against the exhaust manifold. (Courtesy Diesel Injection Service Company, Inc.)

 

If your turbine housing looks like this one, spray a liberal amount of penetrating oil onto the turbine housing bolts. Be cautious, as well-used turbos will commonly break-off bolts in the turbine housing, especially in agricultural and construction applications. (Courtesy Diesel Injection Service Company, Inc.)

 

Once these bolts are removed, the turbocharger can be lifted out. Set the assembly on the bench and be sure to remove the actual oil drain pad if there is one on the underneath side of the bearing housing. The next step is to index the relative positions of the turbine housing and compressor cover relative to the bearing housing. This can be done with a simple punch or small chisel to mark the locations. Next, mount the turbo in a heavy vice by the turbine foot. The housings will be connected to the bearing housing by either bolts or a V-band connection. If it is a V-band connection, you’re lucky. Simply place a bit of penetrating oil on the V-band threads and you should be easily able to remove the V-band on the turbine side first. If there are bolts, remember the penetrating oil and setting-up vibration trick to help loosen the bolts more easily. Once the bolts and/or V-band connection is released, there may be some difficulty in freeing the turbine housing from its centering pilot on the bearing housing. More penetrating oil and some gentle persuasion with the aid of a brass hammer may be helpful.

Caution: Loosen the turbine connection first because the compressor cover will help protect the compressor wheel from damage in case it’s reusable. Also, be sure not to use sufficient force with the hammer as to cock the CHRA inside of the turbine housing such that turbine wheel damage is made by contact with the turbine housing upon removal. Getting these parts into a bind can cause this to occur. Once the turbine side has been freed from the bearing housing, keep the V-band or a couple of bolts in place to hold the bearing housing fixed to the turbine housing, which should still be secured in the vice. Otherwise the assembly could land on your foot and/or cause further damage to the assembly. Broken pieces are typically not accepted as a good core when replacement units are purchased. Loss of a good core credit can cost hundreds of dollars! Remove the compressor cover bolts or V-band and carefully lift the compressor cover from its bearing housing pilot. A soft mallet may be useful depending upon the model and design as to whether there is a tight O-ring seal or not. Also be careful of removing the compressor cover so it doesn’t bind with the wheel.

Now that both housings have been removed you can inspect the wheels and housings for contact damage. If the wheels have severely rubbed their respective housings, the wheels are probably not useable. If this is the case, it isn’t recommended that you attempt to rebuild the turbocharger yourself.

Next, inspect the housings for damage. It’s extremely possible for there to be a turbo failure where the wheels are not reusable, but the housings are. If only slight markings are evident, they can be simply polished out and you can save some expense by purchasing just the correct cartridge or CHRA assembly. Be sure to inspect the turbine housing for heat damage before you attempt to reuse it. If severe heat cracks or erosion is evident along with severe damage to the wheels, you should simply reassemble the turbocharger and find a complete replacement unit. It will not be cost effective to purchase a replacement cartridge and turbine housing, with the intent of saving only the compressor cover. The expense of both of those units will likely exceed the cost of a complete exchanged assembly already built for you.

The last method of turbine housing evaluation before you decide that a cartridge assembly is the way to go is to clean up the bearing housing pilot using a very light emery cloth to remove any scale build up. This can be easily done by hand and won’t take more than five minutes. After carefully cleaning the scale from the bearing housing pilot in the turbine housing, wipe it clean and prepare it for some precision measurements.

Using a set of inside micrometers, measure the bearing housing pilot in the turbine housing taking two readings 90 degrees from each other. This dimension was perfectly round at the time of original manufacture. However, the turbine housing can warp and shift after extended use. What you’re looking for is how egg shaped the pilot has become. If a set of inside micrometers is not available, this can also be done using a large set of calipers. Simply find the smallest diameter point in the pilot, then use a wire-type feeler gauge to measure the gap found where the diameter is the greatest. As a general rule, you should not reuse the turbine housing if it’s egg shaped by more than approximately 0.005 inch. This is a critical measurement for two reasons. First, that area is a seal area where hot exhaust gasses under pressure are sealed to stay inside the turbine housing. Any leakages in this area will not only cause very hot and dangerous exhaust gas from leaking into the engine bay, but also it will cause a loss of turbine energy to efficiently drive the turbo. The other issue at stake here is that an extreme shift seen at this point can indicate you have a very high heat application. Further casting shift can occur and cause turbocharger failure if the turbine housing moves enough to cause housing-to-wheel contact on your new replacement cartridge.

The amount of reusable out-ofroundness in a turbine housing is a debatable issue among turbo rebuilders. However there is a difference in quality among rebuilders and this is a conservative recommendation intended to emphasize the importance of this commonly overlooked step. Completing this process can help you avoid the situation where owners feel that their engine just doesn’t run as well since they serviced the turbo. Exhaust gas leakage can be an elusive issue since you can’t stick your head under the hood while the engine builds boost. It’s better to measure and know for sure. This is also another reason why a turbine pressure gauge is valuable in addition to a boost gauge for any turbo setup.

If the turbine housing and compressor cover are both in reasonable shape, you can proceed with obtaining a replacement cartridge assembly. Be sure to glass bead the housings to clean up all the mounting surfaces, and then wash them thoroughly prior to reassembly and reinstallation.

 

Rebuilding Your CHRA Assembly

If you’ve determined that there has not been wheel contact with either housing, you can potentially rebuild the turbocharger yourself, but extreme caution is recommended. Even slight wheel contact means that wheel rebalancing must be done after wheel prep due to the small amount of material that is removed when dressing the slight wear seen on the compressor and turbine wheels. In this case, it’s vital that you have the wheels rebalanced by a professional with the highly specialized equipment designed to do this job.

Turbocharger wheels are precision balanced in measurements of ounce-inches. Further, each wheel is typically two-plane balanced. This means that the imbalance is measured and corrected on two planes of rotation. Each turbocharger model contains balance specifications for that particular model and size of turbo. This is not something that can be done in the typical garage. If your wheels show evidence of housing contact, it would be wise to ask your local turbo rebuilders to dress and rebalance the wheels for you. This is typically not an extremely expensive process and can usually be done for around $50.

 

Specialized Tools

To proceed with CHRA disassembly you will need some specialized tools that may not be included in an average tool chest. You’ll need both a medium and small set of internal snap ring pliers, an inch-pound torque wrench, a V-block, a dial indicator, a precision bore gauge, and a 1-inch micrometer with ten-thousandths readings on the barrel. If you don’t know what these tools are, you should simply purchase an exchanged CHRA assembly and reassemble the turbo.

 

CHRA Disassembly

Prior to CHRA disassembly, take note of the balance marks, which should be obvious on the nose of the compressor wheel. In some cases, the entire rotating assembly is automatically balanced as a whole rotating group and you’re advised to mark the specific orientation of the wheels relative to each other so that during reassembly they can be positioned back in exactly the same orientation relative to each other. A simple dry marker can be used for this step. If balance material has been removed from the assembly nut, this means that the whole assembly was balanced together and the indexing is critical. If the only balance material removed was from the compressor wheel nose, then the wheels were probably balanced separately and indexing of the wheels before disassembly isn’t so critical.

Position the CHRA in the turbine housing that is clamped in the vise. Secure the bearing housing in the turbine housing so that it will not rock. Find the proper size 12-point (or six point depending upon how the turbine wheel nose is cast) socket to hold the turbine wheel, and the proper size socket that fits the compressor wheel nut. It’s most desirable to loosen the compressor nut with a T-handle-type breaker bar to make sure that equal pressure is applied in both directions. This shaft can easily be bent so great care must be taken in this step.

Once the shaft nut is loosened, you should be able to remove the compressor wheel by hand and set it aside. Next, remove the bolts or V-band anchoring the bearing housing to the turbine housing. Grasp the turbine shaft where the compressor was positioned and lift the entire assembly and invert it on the turbine housing rest. The turbine wheel and shaft assembly should simply lift right out. If it doesn’t, you may have to use a small, soft mallet to help it by lightly tapping on the compressor end of the shaft. If this level of force is required, you may have other internal damage that must be assessed.

 

  

 If the wheels look good, and your turbo is a 3-inch diameter or larger turbine on a diesel, you should use a triangular shaped file and mark the position of the compressor wheel relative to the turbine shaft so you can reposition it in the same position upon reassembly. Smaller diameter turbine and compressor wheels used on automotive type applications will typically require complete core balancing which means the entire center section (CHRA or cartridge) is balanced as an assembly due to the high rotor speeds. This is why it is most advisable to simply service small automotive turbos with using a cartridge/CHRA or complete exchange turbo assembly. Very subtle changes in rotor group components positioning in extremely high-speed turbos can induce a turbo failure due to improper balance. (Courtesy Diesel Injection Service Company, Inc.)

 

 

 With the compressor cover removed and the CHRA secured in the turbine housing, use a T-handled wrench to loosen the compressor nut so as not to bend the turbine shaft. (Courtesy Diesel Injection Service Company, Inc.)

 

 

Once the compressor wheel has been removed, a soft aluminum or brass mandrel may be used to tap the turbine wheel out if necessary. (Courtesy Diesel Injection Service Company, Inc.)

 

Once the turbine wheel has been removed, clamp the bearing housing in a vice and remove the bolts that attach the seal plate if your model uses one, or snap ring pliers that remove the insert located below the compressor wheel pocket. (Courtesy Diesel Injection Service Company, Inc.)

 

Once the seal plate or insert has been removed the thrust bearing and thrust collar may be removed. This will reveal the journal bearings. (Courtesy Diesel Injection Service Company, Inc.)

 

After the thrust components have been removed, the compressor end and turbine end bearings can be removed using a small pair of internal snap ring pliers. (Courtesy Diesel Injection Service Company, Inc.)

 

The small snap rings used in smallframe turbochargers can be virtually impossible to properly remove unless you have the right tool. Armstrong internal snap ring pliers, No. 67-965, work perfectly. (Courtesy Diesel Injection Service Company, Inc.)

 

Depending upon the model of turbocharger, there may be either a flinger sleeve and or thrust collar that will come out with the insert. This will simply push out with hand force, revealing the piston ring seal. This ring is not an oil seal, but a boost pressure gas seal to prevent boost pressure from entering the bearing housing and pressurizing the engine’s crankcase. There is a similar ring on the end of the turbine shaft that you removed.

There are typically two journal bearings inside the bearing housing. Use the small snap ring pliers to remove the outer snap-rings and the bearings should be able to be removed using only your fingers. If these bearings come out easily that is a good sign. If they are locked into the bearing housing and force must be used to remove them, you probably have other internal damage that may be cause for you to reconsider tackling the rebuilding process yourself.

Once the bearings have been removed, the bearing housing can be cleaned using a good clean degreaser so that inspection and measurements can be made. If possible, a good soaking in something like carburetor cleaner is a great idea to soften internal deposits that may be clogging oil passages. At this point, it’s also a good idea to make sure you have made contact with a local turbo shop to obtain the cost of the correct bearing and seal kit for your model and make of turbocharger. Simply providing them with the turbocharger’s part number should allow them to look up the correct part number of the major overhaul kit, which will include new bearings, seal rings, O-rings, and in some cases new snap rings, bolts, and thrust components. The turbo distributor can also provide you with the specifications you’ll need to make sure your turbocharger’s dimensional measurements for wear are correct and will allow reuse of critical components. Once you have the specs you can compare them to your turbocharger to ensure you have a live player. Following are the wear dimensions and specs you will want to obtain:

  • Turbine shaft diameter
  • Bearing housing bore inside diameter
  • Turbine stub shaft run out
  • Compressor wheel nut torque spec for reassembly
  • End thrust measurement
  • Tilt at compressor nut

 

Inspecting the Turbine Wheel & Shaft Assembly

This is the most vital and costly component in the entire turbocharger. It’s critical that this part be well evaluated for a successful rebuild. Use the 1-inch micrometer and measure both portions of the turbine shaft where the bearings have been riding. Measure and write down the compressor and turbine end shaft diameters to the fourth decimal. Be sure to rotate the shaft slightly to ensure that it measures round.

Next mount the turbine shaft into a V-block as shown. Place the dial indicator on the end of the stub shaft just before the threads. While holding down tightly on the V-block, slowly rotate the wheel and watch for dial indicator reading variance. Ideally you will not see any measurable run out.

 

 Measure the turbine-shaft bearing surface using a tenths-reading micrometer and be sure that it’s within rebuild specs for your model. (Courtesy Diesel Injection Service Company, Inc.)

 

Measure the stub-shaft run out to make sure your shaft is not bent. If it is, don’t attempt to straighten it out. Your best bet is to reassemble the turbo and purchase a complete exchange unit. (Courtesy Diesel Injection Service Company, Inc.)

 

Compare these measurements back against the specs obtained from your local turbo shop for your specific model turbo. If you have a wheel and shaft that is out of spec, the best recommendation would be to carefully reassemble the turbocharger CHRA so that your failed unit becomes a valid trade-in core and purchase an exchange unit. If your wheel and shaft assembly measures within specs congratulations, you probably have a turbo that can be successfully rebuilt.

 

Inspecting the Bearing Housing

The next step is to inspect the bearing housing bore diameters exactly where the turbine end and compressor end bearings ride. This will require the small bore telescoping gauges. Carefully rock the bore gauges back and forth to make sure you have an accurate reading, then use your tenths-reading micrometer to obtain the bearing housing bore size on both the compressor and turbine ends. Don’t be surprised if you find them to be slightly different. The turbine end runs quite a bit hotter and accelerated wear can be seen here. Compare these dimensions to your rebuild specs. If they’re in tolerance, you can proceed with final cleaning and prepare for reassembly.

 

 

 Use a small telescope bore gauge to measure the bearing housing bore. However, if your readings are greater than the spec calls for, all is not lost. Many turbo shops can hone the bearing housings oversize and there are oversized bearings available. This is quite a common thing to do. Make sure you can obtain the oversized bearings before you have your bearing housing honed oversize. The typical over sized bearings are 0.010 inch larger than standard.(Courtesy Diesel Injection Service Company, Inc.)

 

Cleaning and Prep

To get started, clean some of your turbo parts in a hot water jet blast that uses a detergent. This should be done with the turbine housing, compressor cover, bearing housing, turbine back plate, and the compressor seal plate if your turbo model is made with one.

The turbine wheel and shaft and the compressor wheel can be hand cleaned carefully. Be sure not to lose your wheel indexing marks. The rest of the small parts can also be hand cleaned in a typical solvent type cleaner, and then dried with shop air.

Once all the parts have been thoroughly degreased, the end housings can be safely placed in the glass bead cabinet and cleaned. The bearing housing can be cleaned this way also, but care should be taken not to blast directly into the bearing bore areas. The turbine wheel can also be cleaned and especially the turbine end seal ring groove. Be sure to tape off the shaft surface to make sure that the glass bead does not come in contact with the shaft surface. This will make the shaft surface too rough and premature bearing failure will rapidly occur.

 

 

 Once the wheel and shaft have been cleaned and checked, the turbine wheel shaft should be placed between centers and the shaft polished with polishing cloth only. (Courtesy Diesel Injection Service Company, Inc.) 

 

Be sure to lay out all of the parts from your rebuild kit to make sure they’re all there and that you’ve gotten the correct kit. Save your old parts to match-up with the kit to compare required contents. There will sometimes be more parts than needed thanks to universal kits that will service more than one turbo model. (Courtesy Diesel Injection Service Company, Inc.)

 

The compressor wheel can also be glass bead cleaned, but be sure to hold the nozzle of the blaster far away so that the aluminum in the compressor wheel is not eroded away. This is a particularly critical step where great care must be taken. After all parts have been through the blast cabinet, be sure to once again run them through the parts washer where hot water and detergent are used to remove all traces of abrasives.

At this point, inspect the bearing housing oil passages with a small inspection light. Sometimes it’s a good idea to use a small wire to probe from every direction to ensure that all oil passages are free of obstructions such as coke build-up or caked glass bead. This will also ensure that all of the dirt and foreign matter has been completely cleaned from the oil passages.

 

Reassembly

You should now be ready to assemble your turbocharger. Place the turbine housing in the vice by clamping the turbine foot just as you did prior to disassembly. This will form a rest for the build. Next, install the internal snap rings that limit the bearings inner movement. Place the bearings in the bore and install each snap ring to keep them in place. Make special note to reinstall any oil control sleeves if they are a part of the design in your turbo model. The oil control sleeve is typically located on the outboard side of the turbine end journal bearing. Its function is to limit the amount of oil flow from the bearing that would flow outwardly close to the turbine seal ring. The oil control sleeve forces the majority of oil to drain toward the middle drain cavity and away from the area of potential leakage near the turbine end. Do not use oil to prelube the internal parts. This will affect your ability to take critical measurements of the oil clearances of the final assembly.

Find, the turbine end seal ring in your rebuild kit. Gently place it into the bearing housing seal ring bore. Square the ring in the bore and measure its end gap. It should show an end gap of at least 0.001 inch, but not more than 0.007 inch. Check this with a feeler gauge. Next, install the turbine end seal ring gently onto the turbine shaft and into its groove. Take care not to over expand this ring; it’s just like installing piston rings onto a piston.

 

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Once this is complete, you can then install the turbine wheel into the bearing housing. Push the gap of the ring into the groove and lightly press the wheel and shaft into the bearing housing bore. There will be a taper to aid in the installation. This is a step where caution must be taken not to force it too hard. The seal ring will walk into place if you gently press down while slowly rolling the wheel around to seat the ring into its groove as it enters the seal ring bore. This may take a couple of tries to get it in without causing damage to the ring.

 

 

 Look closely at the journal bearing snap rings. Most turbo technicians prefer to install the snap ring’s smooth side toward the bearing surface. (Courtesy Diesel Injection Service Company, Inc.)

 

 

Use a small amount of oil to lubricate the seal plate O-ring and carefully seat it in its groove by hand. (Courtesy Diesel Injection Service Company, Inc.)

 

 Carefully expand the seal ring by pressing it over the end of the turbine wheel hub-shaft union and into the seal ring groove. (Courtesy Diesel Injection Service Company, Inc.)

 

Place the wheel and shaft assembly into the bearing housing and carefully walk the wheel around while lightly pressing down, and the shaft and wheel should slip right into the bearing housing. (Courtesy Diesel Injection Service Company, Inc.)

 

Most 3-inch turbos will consume their backplate by wear or the spring washer will lose its tension which holds the thrust bearing securely in place. It’s far cheaper to replace it than try to reuse it. (Courtesy Diesel Injection Service Company, Inc.)

 

Install the compressor end seal ring onto the thrust collar and lubricate it using a good quality grease that will stay in place. (Courtesy Diesel Injection Service Company, Inc.)

 

A popular high-temp assembly lube for compressor end seal rings is the 111 Valve Lubricant & Sealant from Dow Corning. (Courtesy Diesel Injection Service Company, Inc.)

 

Install the thrust collar into the thrust bearing prior to installing the thrust bearing into the bearing housing. (Courtesy Diesel Injection Service Company, Inc.).

 

Once it’s seated carefully, lift the bearing housing and grasp the turbine shaft sticking out of the bottom of the bearing housing. By holding the threaded end of the turbine shaft, invert the bearing housing and gently drop the bearing housing into the pilot bore of the turbine housing. Once it’s seated, you can release the shaft and the wheel will rest on the turbine housing contour.

Now you can begin to assemble the thrust components. Depending upon your turbo model, there are separate thrust rings that must be installed one before the thrust bearing and the other after the thrust bearing, so that you have a thrust ring on either side of the thrust bearing. Many models use a one-piece thrust collar that must be installed into the thrust bearing, and then the thrust collar and thrust bearing must be installed onto the turbine shaft as a unit and come to rest on the thrust pocket floor.

If there is an oil deflector in your turbocharger model, that goes on next and then the insert. Use high quality grease on the O-ring for the insert. This should be placed with hand pressure only. It may take some significant pressure but it is advisable not to use a mallet. Once seated carefully install the snap ring that holds the insert in place.

Install your balance checked compressor wheel onto the shaft and then place the compressor wheel nut on the shaft. If your compressor wheel nut has a self-locking thread that does not allow you to run the nut down by hand, use your wrench to bring the nut down to just barely touch the nose of the compressor wheel to hold all the components together, but not too tight yet. Raise the CHRA assembly out of the turbine housing and be sure to position the wheels one to the other from your marks to ensure proper balance positioning. Once in place, put the bearing housing back into the turbine housing.

Now position the bearing housing in the turbine housing according to your indexing marks and secure it with either its bolts or V-band clamp. Once this is secure you can torque the compressor wheel nut, taking care that the wheels don’t lose their positioning relative to each other. With your socket in place on the turbine end, use the inch pound torque wrench and carefully torque the compressor nut. The proper way to torque the nut is to use one hand to pull the wrench in a direction exactly perpendicular to the shaft while using the other hand to support the socket and turbine shaft from uneven pressure that could bend the shaft. Torque the shaft to the specs for your model of turbo. Note that some specs will specify a torque amount that is to be followed by an additional turn of so many degrees or parts of a turn.

 

 

 Have a turbo shop check the balance of your compressor and turbine wheels. Just because they were running when you disassembled the unit doesn’t mean they’re still in balance for reassembly and another life cycle. These wheels are precision balanced and typically only turbocharger repair shops will have the correct equipment. (Courtesy Diesel Injection Service Company, Inc.)

 

 When finally applying the correct torque to the compressor wheel nut, it’s a good idea to get a third hand to help you secure the turbine wheel in place so that the torque wrench can be properly supported by both hands. It’s very easy to bend turbine shafts if torque is misapplied. Be sure to grasp the pivot point of the wrench to keep from pulling down on the wrench. This is how shaft bends occur. (Courtesy Diesel Injection Service Company, Inc.)

 

Before you install your compressor cover, there are two final measurements you should make to ensure all parts have the proper clearance. The first is the end thrust. Place a small flat piece of metal, such as a turbo nameplate or flat washer, on the end of the turbine shaft. Place the magnetic base of the dial indicator on the bearing housing flange or some other close point of anchor and position the dial indicator on top of the plate. Using your hands, thrust the turbine wheel up and then down to check the thrust movement of the rotating group. Compare this to your specs. Typically you should see approximately 0.003 inch. If this is in spec, you’re almost home.

Next position the dial indicator perpendicular to the shaft nut. Tilt the shaft all the way one direction then force the shaft back the opposite direction to measure the total tilt of the shaft at the compressor nut. This measurement will double-check all of the internal running clearances in the journal bearings. Compare this against the specs you obtained for your model, but as a general rule, a 4-inch turbo will have about 0.025 inch of tilt, while a 3-inch model will see about half as much.

If these measurements check out okay, you’re ready to install the compressor cover. Make note of the cover orientation and reinstall the cover. The last step is to position the turbo on the bench and fill the oil inlet cavity with clean fresh oil. Allow this oil time to flow into the bearings. As you gently rotate the turbine shaft by hand, you’ll feel the clearances tighten up. This way you’ll know that there is lubricating oil in the oil passages.

Now you’re ready to reinstall your turbocharger. The last precaution is to make sure to use new oil inlet and drain gaskets. If your oil inlet uses a tapered pipe-type fitting DO NOT use Teflon tape. This has failed more turbos than an engineering burst cell! Teflon tape can cut off internally and plug the small hole in the thrust bearing and turbocharger failure will soon follow. If several days pass before you start the engine, it’s a good idea to make the oil inlet connection your last step of reassembly. Just before starting the engine, place more clean oil into the oil inlet cavity then connect the oil supply line. This will help avoid oil lag to the turbo at startup.

 

Written by Jay K. Miller and Posted with Permission of CarTechBooks

 

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