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Compression Test and Damaged Valves

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Pathway Hyundai Top Tips: Compression Test and Damaged Valves

Today the team at Pat test and what it means if you have damaged valves.

A compression test reveals the condition of your engine’s valves, its valve seats, and piston rings and whether these parts are wearing evenly. Healthy engines should have compression over 100 psi per cylinder, with no more than 10 percent variation between the highest and lowest readings. With a compression tester, a few hand tools, and 20 minutes, you can try this yourself.

STEP 1 Remove the fuel pump and fuel-injection fuses. Disconnect the main wire to the coil and spark plug wires; remove spark plugs.

STEP 2 Start the threaded end of the compression gauge in a spark plug hole by hand.

STEP 3 Turn the ignition on, depress the throttle, and crank the engine four revolutions. This should result in a stable reading; if not, crank up to 10 revolutions, but do the same with all cylinders.

STEP 4 Mark the pressure reading for each cylinder on the valve cover in chalk, then move to the next cylinder.

STEP 5 For a cylinder below 100 psi, pour 1 teaspoon of engine oil into the plug hole and retest. If the reading jumps, the piston rings are worn. If not, think valve problems.

Valve problems are a sign of serious issues with your car or truck’s engine. Properly sealed valves are crucial to your engine’s compression. A problem with the valve seals or guides will mean that you will have to completely rebuild your vehicle’s motor in order to restore it to good working condition. If you believe your vehicle is having valve problems, you should take it to a certified professional mechanic and have it thoroughly evaluated.

Damaged Values can lead to many problems, such as:

Rough Idle – All of the intake and exhaust valves in an engine must open and close at correct intervals to allow the engine to run smoothly. These valves have a small amount of clearance between the valve itself and the mechanism that activates the valve. This clearance is called “lash.” If the valve lash is set incorrectly (too much clearance, or not enough), the engine may respond by running rough at idle, particularly while warming up.

Reduced Power – Intake and exhaust valves that are not adjusted to open and close at the proper times degrade an engine’s ability to make maximum power. Intake valves control when and for how long fuel is allowed into the combustion chamber, and must be synchronized with the speed of the pistons to allow the maximum amount of mixture into the engine. Exhaust valves perform a similar function, except their purpose is to allow burnt gases to leave the engine. If the valves aren’t adjusted correctly, the engine will not burn fuel at maximum efficiency. Power and mileage then dramatically decrease.

Damaged Valves – The most serious result of incorrect valve lash adjustment is damage to the valves and related components. Setting the clearances loosely causes parts of the valve mechanism to hammer together, damaging valves and creating a knocking or rattling sound. Setting the clearances too tight can prevent valves from completely closing (or not closing for enough time), which may cause extreme heat damage and complete valve failure. Always keep your engine valves adjusted according to the manufacturer’s specifications.

Mar 27th, 2017