Adjustments used to be a significant part of a mechanic’s job. Adjust the timing. Adjust the idle. Adjust the fan belt. Adjust the wheel bearings. Adjust the valve lash. Adjust the spark plug gap. Ah, the good old days. A mechanic was a mechanic. A mechanic had to have a feel for mechanical adjustments. “Just a smidgen tighter.”
For your mechanic, the 21st century should be called the “no adjustment necessary” century. All fan belts are now automatically tensioned. Ignition timing - non-adjustable. Spark plug gap - do not adjust. Wheel bearing loose? Likely it is time to replace that wheel bearing. Valve lash -non-adjustable. Idle speed - no adjustment necessary. Ignition timing - non adjustable.
So if we are not adjusting anything, what are we doing?
Sometimes we are finding ways to adjust something that was not made to be adjustable. Wheel alignment comes to mind. Many a vehicle has only one adjustable wheel alignment angle and that is the toe. The manufacturer thought they could build the vehicle with such precision that no other adjustments would be necessary. On some vehicles they thought wrong. Maybe one of the suspension angles is causing premature tire wear. Replace a couple of holes with a couple of slots and now the necessary adjustment can be performed.
Sometimes we are replacing worn out automatic tensioning devices. You may have just replaced your alternator belt when you replaced your alternator with the seized bearing. But what you really need is a new automatic belt tensioner. These units tend to over tighten the belts when they fail.
When your vehicle is idling too slowly we are not turning a screw clockwise to raise the idle and when your vehicle is idling too fast we are not turning a screw counterclockwise to lower the idle. Instead we have a scan tool communicating with the engine control computer. We must interpret some data and possibly run some tests. Is there an air leak? Is the temperature reading correctly? Is the throttle plate dirty? Can the electrical throttle motor move the throttle plate open and closed like it should? Idle speed is automatically controlled.
Your engine is pinging(knocking). You ask your mechanic to adjust the timing for you. On most vehicles that is an impossible request. The crankshaft position sensor is fixed. There is no distributor to turn. Your mechanic will again install that scan tool that communicates with the engine control computer. Interpreting the inputs and outputs will lead to a diagnostic decision on your pinging problem. If your vehicle has a knock sensor, is it recognizing the knock (ping)? Is the timing automatically adjusting for it? Does it reach it’s adjustment limit? Is there a software update for the engine control system to rectify this problem? Maybe the engine is carboned up. Maybe the fuel quality is substandard?
As you can see, the adjustments are not what they used to be. Most solutions rarely come in the form of an adjustment. If you are turning screws it is likely you have not found the problem but you are probably creating another.