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Leak Down Test

black sky

By black sky,
in Engines & Forced Induction

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nfi Community Regular

nfi

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Leak down test involves blowing a lot of air through the spark plug hole and measuring the pressure the cylinder can hold.

This is fiddly as you have to hook the compressor up to a cylinder and then turn the crank until both valves are closed to get a reading.

It is more accurate than a compression test gauge as oil can cover up worn rings where as this doesn't let anything hide.

If the rings are worn badly you will get air up through the dipstick and if the valve stems are worn then you will hear air out the intake or exhaust.

<20% leakdown is considered ok while you really want under 10%.

New engines generally have about 3%.

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black sky Rising Star

black sky

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Leak down test involves blowing a lot of air through the spark plug hole and measuring the pressure the cylinder can hold.

This is fiddly as you have to hook the compressor up to a cylinder and then turn the crank until both valves are closed to get a reading.

It is more accurate than a compression test gauge as oil can cover up worn rings where as this doesn't let anything hide.

If the rings are worn badly you will get air up through the dipstick and if the valve stems are worn then you will hear air out the intake or exhaust.

<20% leakdown is considered ok while you really want under 10%.

New engines generally have about 3%.

and how much does this process cost???

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https://www.sau.com.au/forums/topic/154264-leak-down-test/#findComment-2869279
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