Turbo Charger Repair and Rebuilding
Many people rather than incur the high cost of purchasing a new turbo charger for their engine, are opting to repair or rebuild their current turbocharger.
If you would like to see a detailed turbo diagnotsic chart then please fill out this short Turbo Repair form.
Preventing common turbocharger problems
Turbochargers are designed to last as long as the engine itself and they don't require any special maintenance other than a few periodic checks.
To ensure that your turbo charger's lifespan has its maximum potential, you'll want to:
- Maintain proper oil levels due to the tremendous heat created
- Maintain a cuurent oil filter
- Maintain correct and optimal oil pressure for your engine
- Maintain air filters and system maintenance
- Use an aftemarket turbo timer for modified turbocharger systems
Reasons why you might be currently having turbocharger trouble
- Objects like dirt, small stones, or other items got into the turbine or compressor. Many times intake part will get sucked into the inlet.
- The motor oil is very dirty or low. Turbos need plenty of fresh oil after being turned off so it will not coke the oil.
- The oil pressure is too low or the oil filtration system is inadequate.
- The exhaust gas temperatures from the ignition/injection system are too high. You burn the oil up.
- Other mechanical issuess, breakage of parts or a manufacturers defect.
There comes a time in the life of any turbocharger when it no longer performs like it once did. The puzzle, of course, is figuring out when it's the turbo truley failing and when it's something else in the engine.
A turbo's primary purpose is to boost horsepower, so when an otherwise healthy engine suddenly becomes week, it often (but not always) means turbocharger troubles. Some of the symptoms that may indicate a failing turbo includes a loss of horsepower, failure to build boost pressure, turbo noise, increased oil consumption and oil fouled spark plugs, or excessive exhaust smoking on diesel engines.
The place to start in diagnosing a weak turbo is to observe the vacuum/boost gauge. If it doesn't show normal boost pressure at full throttle, typically 9 to 14 PSI for most factory turbo systems, better get the tool out. Be forwarned, however, that excessive backpressure, often due to a clogged catalytic converter, can also keep the turbocharger from building its normal boost levels.
TURBOCHARGER WASTEGATE INSPECTION
Try to observe the operation of the wastegate. If the wastegate does not move at all, overboost and or detonation is the usual result. But if it is binding up and does not fully close, it will bleed off exhaust pressure from the turbine wheel and prevent the turbo from buidling full boost. You can try disconnecting the wastegate and actuating the linkage by hand to check for binding and proper closure.
On vehicles that do not have turbo instrumentation, you can get an indication of boost pressure by attaching a vacuum/pressure gauge to the intake manifold. Most such gauges read vacuum in inches of mercury (Hg) and show pressure in psi. The gauge must be T'd into a manifold vacuum line, not a ported vacuum connection on the throttle body or carburetor.
Make sure the the transmission is in neutral or park and the emergency brake is on, then rev the engine up several times by snapping the throttle wide open. Your gauge should read a change from vacuum to boost as rpms increase. OEM boost setting normaly range from as little as 9 lbs to as much as 14 lbs, so compare your readings to whatever specifications matched your engine when it was new.
If the turbo fails to create any boost pressure, or the boost level is more than a couple of pounds below what it should normally be, take note the vacuum reading at idle. A late model engine with no vacuum leaks or exhaust restrictions should flow about 16 to 22 inches of vacuum at idle. A lower vacuum reading means you either have excessive backpressure in the exhaust system, an air leak somewhere in the intake system below the throttle, check the turbo charger hoses for leaks or loose connections, or its a vacuum leak in one of the many hoses or accessories that tap off the intake manifold.
TURBO CHARGER INSPECTION
Lets assume the engine shows normal vacuum readings but the turbocharger shows low or no boost pressure, the next challenge is to discover what is wrong with the turbocharger. One of the most frequent causes of weak turbocharger performance is failing shaft bearings which often results in binding or rubbing between the compressor and or turbine wheels and their resective housings. Turbochargers spin at speeds often exeeding 100,000 rpm. If there is even moderate play in the shaft bearings, the shaft will wobble permitting the wheels to rub against their housings. The added friction prevents the turbocharger from spooling up normally, reducing the turbo's speed and effective boost delivery.
The best way to check for bearing problems or contact between the housing and turbo wheels is to remove the intake or exhaust plumbing from the turbo, which ever is easier, for a peek inside. Any sign of scraping on either the turbo blades or the housing means the bearings are shot and the turbocharger needs to be replaced or rebuilt. You should also spin the turbo wheel by hand to feel for any roughness or binding. If it doesn't turn freely, repairs are in order.
Other problematic symptoms to watch for are chips, nicks, or cracks in the turbo wheel blades, and or worn down wheel blades. A turbo is a very delicately balanced assembly. Most auto turbo wheel assemblies are balanced to within .001 ounce. A broken blade, worn blades or even nicked blades can be enough to throw the assembly out of balance. The turbocharger may still spin freely, but the imbalance will prevent it from reaching maximum rpm and eventually pound the shaft bearings out-of-round. If this is the case there's no way you can rebalance the rotating assembly, so if there is any of these indications of damage, the damaged parts must be replaced, or you run the risk of catastrofic faliure.
Its quite easy to check bearing clearances, there is usually no need to disassemble or even remove the turbo. A dial indicator can be positioned against the shaft hub to check for bearing free play. Up and down shaft movement should be no more than 0.003 to 0.006 inches. End play should be 0.001 to 0.003 inches. This test may not reveal excessive clearances, however, if the turbocharger has varnished or coked bearings.
An alternate technique for checking bearing clearances is to use a dial indicator with an offset probe that can be inserted into the turbo center housing through the oil supply or return port. Positioning the tip of the indicator against the shaft will allow you to measure free play while the shaft is turned. This technique will also allow you to peek inside the housing to check for fried oil on the shaft or housing.
You will also want to check for the presence of oil in either the compressor or exhaust housing. There are shaft seals at both ends of the wheel shaft normally keep the oil inside where it belongs. But if either seal fails, oil can be pulled out of the bearing housing. Oil leaks are more common on the compressor side because that side of the turbo is exposed to intake vacuum.
Oil leaks can also be caused by residue clogging up the oil return line. If oil is present in both housings, but the turbo shows no signs of binding, wobble, or rubbing, remove the oil return line and check it for obstructions by passing a stiff wire through it.
TURBO FAILURE: THE POST MORTEM
If your turbocharger is bad, you should always tear it down regardless of whether you're going to replace or rebuild it. You need to determine the cause of death so the problem doesn't repeat itself. The first thing to check is the condition of the shaft bearings. The bearings are usually destroyed by either oil contamination, oil starvation or oil coking.
Heavy grooving or pitting of the bearing surface usually indicates dirty oil, possibly due to inadequate oil filtration. Check for a plugged oil filter. Once an oil filter becomes clogged and it's bypass valve opens, unfiltered oil flows to the turbo and the rest of the engine.
If the inside of the bearing housing resembles the bottom of a frying pan and is coated with black crusty deposits, oil coking was the cause of failure. The bearings are oil cooled, and during normal operation temperatures don't get hot enough to cause oil coking. But when the engine is shut off, temperatures can rise to 600 to 700 degrees F. inside the housing as the turbo undergoes a period of heat soak. The oil oxidizes and forms coke deposits in the housing that then act like an abrasive to wear the bearings. Using a high temperature "turbo" oil or synthetic oil, installing an auxiliary oil cooler, and changing the oil every 3,000 miles can avoid oil breakdown and coking problems. In water-cooled turbos, coking is less of a problem provided the oil is changed regularly and you use a quality motor oil. So if you find an accumulation of black crud inside the housing, better check the coolant hoses for a kink or restriction.
Melted or glazed bearings with metal transfer onto the shaft point to oil starvation. Check for a low oil level, oil leaks or a restriction between the turbo and engine, or low oil pressure (30 psi is the recommended minimum for most turbos). Oil starvation when the engine is shut off can be avoided one of two ways: by letting the engine idle for a minute or so after a hard run so the turbo has time to spool back down, or by installing an aftermarket pressure reservoir that automatically maintains oil pressure for up to a minute after the engine is turned off. The oil reservoir will also pre-pressurize the turbo oil line to prevent dry starts.
A bearing that's been pounded out-of-round, cracked or broken is usually the result of an out-of-balance shaft and wheel assembly, or excessive bearing clearances.
The next thing to note is the condition of the compressor and turbine wheels. Cracks can be the result of metal fatigue, but nicked bent or damaged blades can only be caused by foreign objects. If the compressor blades are badly eroded, unfiltered air has been entering the intake system. Check for a missing, torn or poor fitting air filter.
Lastly check the condition of the housings. If cracked, badly corroded, warped or scored, replacement will be necessary. Beware of cheap replacement housings made of ordinary cast iron. The exhaust housing should be of nickel alloy to resist high temperature operation.
TURBOCHARGER OVERHAUL
Installing a new or remanufactured unit is probably the safest way to repair a sick turbo. Not only do you avoid the pitfalls of do-it-yourself rebuilding but you also get a warranty.
If you do decide to overhaul the turbo yourself, one of the most difficult aspects of the job is getting the inside of the center housing spotless clean. Ordinary engine degreaser won't remove the baked on oil deposits but spray-on gasket remover will. Taking the housing to a machine shop to have it "boiled out" in a hot solvent or caustic tank is probably the best way to clean it.
One thing the experts recommend NOT doing is having the center housing sand blasted. Besides the possibility of leaving sand residue inside the housing where it could later damage the bearings, sand blasting changes the surface texture which can lead to lubrication problems. The bearing surfaces must be highly polished, not rough, so sand blasting is out. Glass beading is okay provided a fine bead is used and the housing is thoroughly cleaned afterwards.
The shaft itself can be cleaned in solvent. If the shaft bearing surfaces are not perfectly smooth, round and blemish free, plan on replacing the shaft and turbine wheel.
Dirty turbo wheels can be cleaned with solvent and a wire brush. Avoid using abrasives and don't sand blast. Do not attempt to straighten a bent wheel blade. Doing so will only weaken it further, causing the wheel to explode when the turbo hits high rpm. A bent blade upsets the aerodynamics of the wheel, reducing pumping efficiency, so always replace any wheel that doesn't have perfect blades.
If the compressor or turbine wheels are damaged, they must be replaced. There are a few experts who claim they can successfully repair damaged wheels by welding but for the do-it-yourselfer welding is out of the question -- especially when you consider the "downside" risks of what might happen if a patched compressor wheel were to fail and spew shrapnel into your engine. There's also the problem of rebalancing a repaired turbo wheel. A new compressor wheel may set you back $80 to $100 while a turbine wheel and shaft may run $180 to $200 or more.
Worn turbine shafts can sometimes be repaired by grinding the shaft journal down and installing an oversized shaft bearing, or by building up the worn shaft journal with hard chrome and remachining it back to its original dimensions. Regrinding and using an oversized bearing is cheaper than hard chroming, which if not done correctly, will flake off and cause a repeat failure.
If the lip of either turbo wheel has been rubbing against the seal area on the center housing, you may find a groove worn into the housing. If this is the case, plan on buying a new center housing. In many instances, it is cheaper to buy a new "turbo cartridge" (the center housing with both wheels and shaft preassembled) than it is to try to rebuild a damaged unit.
When reassembling the turbo, cleanliness is absolutely essential. Any dirt, grit or unremoved crud can become the cause of a future relapse. The shaft bearings must be lubricated with assembly lube, and checked for proper fit and alignment. New seals are another must as is torquing the compressor wheel to specs. Once the unit is together, spin the wheels to make sure the shaft turns freely and nothing rubs. A final check of clearances with the dial indicator is advised before reinstalling the unit on the vehicle.
Cranking the engine for 10 to 15 seconds with the ignition coil disabled will pump oil to the turbo charger. Some of the things that should always be done after rebuilding or replacing a turbo include changing the oil and oil filter, checking the air filtration system for leaks or obstructions, and priming the turbo oil supply before starting the engine.
by LCarley
If you would like to see a detailed turbo diagnotsic chart then please fill out this short Turbocharger Repair form.
