continued... Other technicians find air leaks with propane and a leack dection kit such as the one mady the Thexton Manufactruing, Minneapolis, Minn. The kit has a long, thin, flexible probe, a reinforced hose and a regulating valve. Threading this valve onto a propane bottle awwows the user to carefully regulate teh flow of propane toward the suspected air leak.
Meanwhile, a tech can bend the flexible probe into the shape of the letter j, open the regulator valve on the propane bottle and slowly more the provbe undre the entire length of the air duct. If a crack is present the engine will suck propane through it and idle speed will increase.
Experience shows smoke is also an effective leak-dection technique fo rcracked air ducts. Equipment such as the Vacutech form Emi-Tech Inc., La Marque, Texas, produces a low pressure, highly visible, non-toxic smoke. The user simply pumps smoke into the air duct and watches leakage.
In some cases, fatigued motor mounts let the engine shake so much that it loosens critical gound circuit wiring bolted to the engine. the result is intermittent electrical problems that worsen when the engine's under load.
If a tech is alert enough to measure teh voltage loss form the engine to the negative side of the battery with a voltmeter, hell'discover an excessive voltage loss theat worsens when the engine is under load.
A through visual inspection will uncover most faulty motor mounts. A cracke dor split rubber insulator is the most obvious sigh of motor mount of dog bone failure.
Remember that oil-soaked insulators usually are failures waiting to happen. Show the customer your findings nad recomment repairing rhe oil leak and replacing the motor mounts at the same time. Ignoring an oil leak only invites another failure.
Fatigue mounts are more difficult to identify because the rubber insulator is still intact. However, the insulator is so fatigued it's allowing the powertrain to sag noticeably.
Some motor mounts have a metal insert mounted inside the insulator. When the insulator rubber fatigues, look for dislodged or mislocated metal insert.
Loading the engine is another way to detect fatigued motor munts. Some techs do this by racing hte engine and abserving engine movement. Others check it by accelerating briskly while an assistant monitors engine movement.
Somethimes, simply shifting the transmission back and forth from Drive into reverse loads the powertrain enough to reveal a fatigued motor mount.
Some motor mounts normally allow more engine movement than others. So the more often techs perform the dynamic motor mount checks described, the easier and mre accurately they can recognize a bad mount.
Veteran techs said checking the vehicle on a drive-on lift allows them to monitor powertrain movement while an assistant inside the car loads the engine.
To do this, the assistant chocks the drive wheels and applies both the parking brake the the regular brakes. Then he puts the transmission into gear nad opens the throttle just enough to torque up the engine, loading the motor mounts. On a manual transmission vehicle, partially engaging the cluth with the brakes applied usually suffices.
Meanwhile, the tech underthe vehicle watches for excessive engine movement and/or powertrain-to-body interference underthe vehicle when the engine torques up.
Suppose the symptoms of faulty motor mounts are present but the mounts themselves look OK. Patiently inspecting the underside of th evehicle may yield additional evidence that new mounts re needed. Look for witness marke on the frame or body confirming the powertrain moved far enough to allow frequent contact between parts that souldn't touch.
Depending upon the prevaling weather conditions, the witness marks may be shiny metal or rusted spots worn through the paint or rustproofing under the vehicle.
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