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A KNOCKING SOUND IN THE ENGINE IS MOST LIKELY CAUSED BY ONE OF THE FOLLOWING
1. PISTON SLAP: Makes a sharp metallic noise. Idle engine and short out each cylinder plug. The noise will disappear when plug with bad piston is shorted. Noise will also disappear at acceleration. This can be caused by worn or out of round cylinder, or broken piston ring. Correct problem by re-boring cylinder and/or replacing piston.
2. VALVE NOISE: Makes clicking or rattle noise. Caused by excessive wear on valve stem or lifter, out of adjustment, or stuck valve. Correct by adjusting valve clearance, replace worn valve or lifter, regrind cam, replace valve guide and /or valve. A stuck valve can sometimes be loosened by passing oil through the carburetor while engine is running.
3. ROD BEARING KNOCK: Makes sharp metallic noise similar to a piston slap. Detection is opposite of piston slap. Rod knock is not heard at idle. Knock becomes louder as engine speed is increased. Caused by excessive rod bearing clearance. Correct by adjusting rod bearing clearance to .0015 inches by removing shims. May require re-pouring rod bearing.
4. REAR MAIN BEARING KNOCK: Makes dull knocking or thud noise. Detected at speeds between 20 and 50 MPH. Knock will normally decrease or disappear while pulling or decelerating. Noise will be detected the loudest at normal driving speed, when not pulling or decelerating. Correct by adjusting bearing clearance to .001 to .0015 inches. If knock is excessive, crank should be checked for out of roundness. May need to re-pour all main bearings to correct.
5. TIMING GEAR KNOCK: usually the most difficult to diagnose. If gear is loose or badly worn it will knock in all ranges. Run engine slightly above idle speed. Slowly open and close throttle. Knock will continue to be present, but just as engine slows down knock will become a slight rattle. Remove timing pin and reinsert into timing hole on timing gear cover. Press timing pin tightly against timing gear and accelerate slightly above idle. Knock will significantly be reduced or disappear. Correct by replacing both timing gear and crank gear as a matched set. The two gears should have a backlash clearance of .003 to .004. If more than .009 inch backlash, an oversize (.005) timing gear should be installed.
6. WRIST PIN SLAP: This can not be detected by shorting out the cylinder plugs. Rapidly accelerate and decelerate the engine speed. The engine will pass through a certain speed range when the wrist pin will rattle at about the same pitch as a valve tappet noise. This can be corrected by installing a new wrist pin bushing in the rod or new wrist pin f badly worn. Wrist pin should fit the piston and connecting rod with a tight metal to metal fit. The pin can be pushed into the piston and rod with a slight pressure of the hand. Pin to rod clearance is .0003 to .0005 inches.
A couple of ideas for you.
1) When the tires were replaced, in the process of doing that , the car was lifted off the ground somehow, causing the front wheels to "drop".
Please check most carefully the plastic liners ( there are several) that surround the wheels, and see if one or some are rubbing the tires whilst you are driving down the lane.
2) If that is not the problem, jack up one front wheel at a time, and block or "scotch" the other three, and start the engine, and engage the transmission, and see if you might have a bad wheel bearing. ( it should be noisy).
You may choose, ever so carefully, to use a "mechanic's stethoscope", which is a long handled screwdriver, wherein you put the wood handle to your ear, and the metal tip at various places under the car to try to identify the source of the noise.
God bless your efforts.
More information is needed on the type of vehicle. Bank tool is going to be on the side opposite of the number one cylinder on a V-Type engine (v6-v8). Sensor to will be the oxygen sensor that is located after the catalytic converter on that bank.
Check firing order 1,3,5 in the back next to firewall 2,4,6 in front check coil packs. If o.k you could have burnt valves. As for the knocking If its a heavy kock and it happens all the time even at idle it could be the main bearings on the crankshaft.
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