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Is it Junk or Not?
From the April 2005 issueSo you’re at the junkyard, and you score the perfect turbo that will be just the thing for your new Frankenstein creation. How do you know if it’s any good? Just for you, we put together a short guide to some of the more common parts of a forced induction system, as well as how to test them in the field or on the bench.
Turbochargers
Turbocharger center bearings are the weakest part. With the turbo off the car, where you can reach both wheels, check the bearings by pushing the wheels back and forth radially. If there is more than 0.040 inch (1mm) or so of movement, plan for a rebuild.
Also, look closely at the edges of the exhaust impeller wheel (if you can see it). Any signs of scraping mean that the bearings are so worn that the wheels are rubbing on the housings.
Check the condition of the oil drain opening. If it is clogged or partially clogged with hardened oil, you can bet the oil wasn’t changed often enough and the bearings may be on their last legs.
Look for any signs of oil inside the compressor and exhaust outlet. A little is probably no big deal, but if the inside is wet with oil, then the seals are likely toast. Better budget for a rebuild.
Check the wheels for any signs that foreign material made it into the turbo. Dings, missing fins, scratches and chips are all causes for rejection (or rebuild).
If the turbo passes the mechanical tests, look closely at the exhaust housing; these tend to crack. Look for cracks in areas where the casting is thinnest, such as near the wastegate port, across the exhaust outlet and at the flanges. Check for broken-off bolts, too.
Cracks that don’t extend to the outside of the exhaust housing are probably no big deal, but it might get you a few dollars off the price at a swap meet. Broken-off bolts can be extracted, but not cheaply.
Even if the turbo passes your inspection, it might still turn out to be no good. In the short run, a turbo yanked from a junkyard engine might work fine, but you don’t know how it has been treated, and problems from a lack of maintenance can crop up later.
Rebuild kits are available, but you might want to consider a professional rebuild. It would really stink to have the turbo come apart and destroy your engine. Even small oil leaks into the air stream are a bad sign—oil in the combustion chambers will lower the engine’s knock sensitivity and limit power potential.
Intercoolers
Intercoolers are fairly sturdy, but look closely for signs of accident damage or cracks. Also be on the lookout for corrosion and dirt on the inside of the tanks. Plastic end tanks are notorious for blowing apart, so check them thoroughly, especially the seams between the core and tanks.
Look for signs of oil inside the intercooler, as this can be difficult to remove and insulates the intercooler, making it less efficient. Bent fins are not the end of the world, but make sure the damage is minimal. Check the inlet and outlet for nonstandard connections, as some are flanged and must be welded or otherwise modified before they can be used.
Injectors
Unfortunately, there isn’t a good way to check injectors without specialized equipment. The best method to increase your chance of success is to buy as many injectors as possible and send them off to be flow-checked and leak-tested. Use the best ones in your engine and you will eliminate hours of frustration. The same goes for fuel pumps. There are some good, high-flow pumps out there (look at Bosch CIS-injected cars), but have them checked before use. There is just no way to know if they are good or not.
If you're reading this, you've probably seen these odd links with funny names somewhere on the site and want to know what they're all about. Well, prepare to feel a bit more Net savvy. Those links are what the geeks call "social networks."
Social networking sites allow you to store and share links and pages across the Internet. It's like taking your bookmarks list and being able to see it from any computer.
Even better, social networks allow you to steer friends, relatives, colleagues and pretty much anyone else to the cool stuff you've found, so they have something better to do online than watching the skateboarding squirrel video on YouTube for the thirtieth time. You're making the world a better place.
The only catch is that while all the social networks are free, you do have to register. Each site has a slightly different focus, so take a look through the links and see which service suits you best.
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This story originally appeared in the April 2005 issue of Grassroots Motorsports.
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Reader comments:
Just for you, we put together a short guide to some of the more common parts of a forced induction system, as well as how to test them in the field or on the bench.
This article is fairly accurate. Good Job. One note is is that I have in my experience never seen an compressor end dynamic seal, that has started to leak oil, seal back up. So it must be noted that any amount of oil in the comp outlet will generally grow to a larger amount of oil.
Good point - A good coating of oil is a pretty good sign of bad compressor seals. I’ve also seen turbos (and I’m sure you have too) with a light coating of oil that comes from the PCV valve or engine breather. That’s nothing to get excited about, but it’s hard to tell the difference if there’s just a little oil coating.