Tool Q&A: Make engine diagnosis easier with the right tools

Technical Editor Dave Cappert answers your questions about borescopes and more.


WHICH IS BETTER FOR DETERMINING PROBLEMS WITH ENGINE COMPRESSION PROBLEMS, A COMPRESSION TESTER OR CYLINDER-LEAKAGE TESTER?

Both have their place. To best pinpoint compression problems, these testers work hand-in-hand. Generally speaking, a compression tester is your best bet to determine which cylinder has compression loss. A cylinder-leakage tester helps you determine the source of leakage from a cylinder with low compression readings.

WHEN TESTING CYLINDER LEAKAGE, HOW MUCH IS TOO MUCH?

Manufacturers don’t provide specifications for cylinder leakage, but most engines in good mechanical condition reveal less than 20-percent leakage (some engines can reveal cylinder leakage readings as high 30 percent and still perform OK). As a general rule, leakage of more than 20 percent indicates a problem with the cylinder.

When there is excessive leakage, remember these potential sources:

Air escaping into the crankcase indicates blow-by due to worn rings, a worn or damaged cylinder, or a cracked or burned piston.
Air escaping into the radiator indicates a compression leak into the cooling system through a bad head gasket or a crack in the head or cylinder.
Air escaping into the intake manifold tells you there’s a leaky intake valve.
Air escaping out the tailpipe indicates a leaky exhaust valve.

SINCE I DON’T DO THAT MUCH ENGINE WORK, IS A BORESCOPE A WORTHY INVESTMENT?

Borescopes are often perceived only as tools for inspecting engine wear and damage, but they can do so much more. For instance, you can look inside hidden areas for fluid leaks, check for gear wear inside differentials, inspect HVAC system airflow control doors, find serial numbers and production dates/codes in concealed areas, and inspect mechanisms in tight spaces like window tracks and regulators. Since you can make these inspections without disassembly, it can make your diagnosis more efficient using a lot less labor. To put this into context, just think of the times where you disassembled something for inspection reasons only to find nothing wrong.

WHAT FEATURES SHOULD I CONSIDER WHEN SHOPPING FOR A BORESCOPE?

Features directly relate to the applications where you plan to use the borescope. Traditionally, rigid borescopes use a straight inspection tube using lenses to create and transmit the image. Flexible borescopes, on the other hand, often use fiber-optic technology to carry the image for viewing. The latest models now feature electronic imaging technology where you can view inspections on an LED/LCD video screen. In some cases you can also project the image on a larger computer screen and even save videos of your borescope inspections. This can come in handy for building diagnostic files or even to show to your customers.

You will also want to consider the thickness of the inspection tube that the borescope uses to make sure it’s both small enough and flexible enough for small openings. Some borescope models also offer articulation control so you can control your point of view when making an inspection. Also consider special attachments such as mirrors and other implements that may help with inspecting certain components, such as engine valves.

To see if a given borescope is the right one for you, see if your equipment rep will let you try one out for a short period before making a purchase commitment. If possible, try several different models out first to make sure you’re purchasing with confidence. If you can, also get the opinions of other techs on their experiences with a borescope.

IS A VACUUM GAUGE STILL USEFUL FOR DIAGNOSING PROBLEMS WITH TODAY’S ENGINES?

Although it’s been around for many years, a simple vacuum gauge connected to the intake manifold provides valuable diagnostic information about an engine’s ability to move air in and out of its cylinders. After all, an engine is really an air pump of sorts and without being able to both take in and exhaust air consistently, it’s impossible to achieve good engine performance. You can also use a vacuum gauge to check for vacuum at vacuum-operated accessories like HVAC controls and solenoid valves.

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