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Intake/Exhaust Valve Check - Tricks Of The Trade

Helping you wrench.

Scott Tsuneishi
Feb 3, 2012

Cylinder head valves normally will not just bend unless the engine has experienced some sort of trauma. Bent valves can occur as the by-product of a timing belt failure, as the valves strike the pistons. Depending on what bent the valve, there may be damage you can’t see, and won’t until the head is off.

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Visual Valve Inspection:

- Check valves for smooth movement and good seating
- Check guides for wear
- Check lifters/rocker arms
- Check the top of the valve stem for damage/pancaking
- Check camshaft lobes for damage or excessive wear

If you suspect a faulty valve or recently purchased a used cylinder head and are unsure of its condition, but need to get your car running ASAP, we have a quick and easy setup on how to check for bent valves with the cylinder head(s) off.

One test method that can be performed in your own garage is to do a valve leakdown test. To perform the test, you would need an air compressor that delivers at least 90 psi, a wood block with a 9⁄16-inch hole drilled through the center, and water.

Prepare the cylinder head by removing the cams and lifters. Flip the cylinder head(s) upside down and insert any used spark plug to seal the chamber. Pour water into each of the combustion chambers.

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Proceed by taking the wood piece and pressing it up against either the intake or exhaust port to achieve an airtight seal. Using the air hose, insert it into the 9⁄16-inch hole wooden block and release compressed air into the cylinder port.

Impp 1202 05 o+tricks of the trade+wood piece Photo 3/4   |   Intake/Exhaust Valve Check - Tricks Of The Trade

Using the compressed air/water method, you will actually be able to see bubbles forming past a bent valve on the intake or exhaust side—the larger the leak, the bigger the bubbles. If your cylinder head shows symptoms of a bent valve(s), we suggest taking it to a qualified machine shop to fix the problem.

Impp 1202 06 o+tricks of the trade+compressed air Photo 4/4   |   Intake/Exhaust Valve Check - Tricks Of The Trade
By Scott Tsuneishi
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