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       Mike has since acquired a convertible version of the 1970 Torino. Aside from the convertible top, the only difference between the hardtop and convertible NASCAR Pace Cars is the addition of a roll bar to the convertibles. (Photo Courtesy Lee Lundberg)

      You can pinpoint a problem cylinder(s) by checking the power balance between them. Most engine analyzers have the capability of conducting a power balance test, but few of us own this expensive piece of equipment. Luckily there is an alternative means for analyzing power balance. A pad, pencil or pen, and a tachometer (a dwell tachometer will suffice) are the only tools needed for this test.

      First start the engine and set the RPM at 1,000, and then disable the cylinders one at a time by removing the spark plug wire. Be careful not to contact the live ends of the plug wires, as they will continue to carry current even when disconnected. Using a pair of insulated-handle pliers is not a bad idea here. Note the RPM drop and then reconnect the plug wire. Repeat this process until you have disabled each cylinder and noted the RPM on each. The theory here is that the greater the RPM drop when the cylinder is not firing, the more that particular cylinder is contributing to the engine’s power. On the other hand, the lower the drop in RPM, the less that cylinder is contributing to engine power. Thus, any cylinder that is down on power will reveal itself by a smaller decrease in RPM.

      A word of caution here: This method should only be used to disable cylinders on engines that have conventional points-type ignitions, as disconnecting a plug wire in an electronic-ignition-equipped vehicle may cause a power surge that can damage the ignition. There are commercially available test kits that allow you to disable cylinders in an engine equipped with an electronic ignition by shorting out the plug wire without risking a power surge.

       Check Compression

      A compression test is the simplest and least-expensive means of determining how well a cylinder is sealing. Be certain the engine has reached its normal operating temperature prior to checking compression. For this test you will need paper, a pen or pencil, and a compression gauge. Be aware that when you are conducting a compression check, a combustible mixture of air and fuel is blowing out of the cylinders under pressure and any spark or flame could result in an explosion. Make sure the area is well vented and free of any ignition sources. Disable the ignition, remove the spark plugs and block the throttle in the open position, then install the compression gauge in the cylinder to be tested. Using a remote starter, or an assistant, crank the engine over a minimum of three full revolutions and note the highest reading on the gauge. Repeat this process until all the cylinders are checked and the readings recorded.

      The maximum reading in this case is not as important as the percentage of difference between the readings for each cylinder. All cylinders should read above 100 psi, with 180 psi being the norm for a Lima series engine. Each reading should be within 75 percent of the highest, while 90 percent or better is optimum. If you find two adjacent cylinders that read considerably lower than the rest, chances are that a head gasket has blown between the two cylinders. If you experience a single cylinder with a low compression reading, an easy way to determine if the cause is piston-ring or valve related is to squirt approximately a teaspoon of oil into the cylinder via the spark plug hole and repeat the test. If the pressure comes up, the piston rings are not seating. But if there is no change, it is likely that a valve is not seating properly or you have a blown head gasket.

       Perform Leak-Down Test

      A leak-down test is a more sophisticated means of checking how a cylinder is sealing, using external pressure to test the rate at which a cylinder loses pressure. Since a leak-down tester is a more sophisticated tool, you won’t find it in too many home shops, but you can perform this test at home using an air tank and spark plug hole adapter (with the exception of reading percentage of leak down).

      To perform a leak-down test, the piston in the tested cylinder must be at TDC on its compression stroke, so both valves for that cylinder are closed. This test is easiest to perform following the engine’s firing order, so I start by bringing the number-1 cylinder to TDC on the compression stroke.

      Step one is to disable the ignition, remove the spark plugs, and install a compression gauge in the spark plug hole. Then, using a remote starter or a friend, turn the engine over until the compression gauge indicates the cylinder has compression. Don’t be fooled by the weaker exhalation that occurs on the exhaust stroke. Then verify that the timing pointer is at TDC on the damper. Next, take off the radiator cap and engine breather cap and block the throttle in the open position to assist in identifying what is leaking if a leak is present.

      Fill the cylinder with compressed air using an adapter between the hose and the spark plug hole. Caution: Keep hands away from the fan, belts, or pulleys during a leak-down test because if the piston is not at TDC, introducing air under pressure into the cylinder may cause the engine to turn over. The cylinder should hold pressure and not leak down at a rate of more than 5 to 10 percent. More leak down than that indicates a sealing problem in that cylinder.

      If you are using the homemade leak-down tester as previously described and do not have the gauge to determine percentage of leak down, you can still make a fairly accurate determination for the cause for any leakage by performing a few simple checks. Listen for air escaping from the carburetor, breather, oil filler, dipstick tube, exhaust pipe, or radiator. Note that a small amount of air escaping through the breather is common in worn engines. If you hear air escaping through the carburetor, it means that an intake valve is leaking. Air coming from the exhaust pipe means an exhaust valve is at fault. To be doubly certain that either of the valves is leaking, go back and ascertain that the cylinder being checked is still at TDC on the compression stroke.

      If a blown or leaking head gasket is the problem, air will leak from an adjacent cylinder to the one that is pressurized, or through the cooling system via the radiator filler neck if the gasket has blown between the cylinder and the cooling system. Air leaks at the dipstick tube and breather are indications that the piston rings are not sealing properly against the cylinder walls.

      Once you have completed the test on cylinder number-1 and noted the results, you can proceed through the firing order 1-5-4-2-6-3-7-8 (Refer to firing-order charts in the Appendix), testing each cylinder as you go by rotating the engine clockwise to the next 90-degree mark on the damper. Verify the cylinder by removing the distributor cap and confirm that the rotor is facing toward the position on the cap that holds the wire for that cylinder.

       Test Cooling System Pressure

      Head gaskets that have blown or are leaking into adjacent coolant passages in the cylinder block will also show up during a cooling system pressure test. A head gasket problem will reveal itself as air and/or coolant escaping into the affected cylinder. This simple diagnostic test will also identify other leaks in the cooling system.

      The test is performed by obtaining a simple pressure tester designed for this task. Simply install the tester in place of your radiator cap,

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