Why preasure testing an engine ?

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waltmil
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Re: Why preasure testing an engine ?

#16 Post by waltmil » Mon Oct 15, 2018 6:13 pm

A pressure leak will cost power, a vacuum leak can cost an engine.
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evan_calgary
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Re: Why preasure testing an engine ?

#17 Post by evan_calgary » Mon Oct 15, 2018 6:17 pm

waltmil wrote:A pressure leak will cost power, a vacuum leak can cost an engine.
Generally they will come together at the same location thus why a pressure test is good to find vaccuum leaks.

waltmil
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Re: Why preasure testing an engine ?

#18 Post by waltmil » Mon Oct 15, 2018 6:32 pm

Still, I've seen pressure tests pass and vacuum fail.
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JanBros
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Re: Why preasure testing an engine ?

#19 Post by JanBros » Mon Oct 15, 2018 7:52 pm

waltmil wrote:Still, I've seen pressure tests pass and vacuum fail.
yep, that's why I do not understand pressure testing (as explained in my first post). Vacuum testing I can understand.
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Re: Why preasure testing an engine ?

#20 Post by silverstrom » Mon Oct 15, 2018 8:30 pm

A crank seal is a Garlock seal that has sealing lips and springs on both sides. If you understand how a 2 stroke works and the role the crank well plays in its function, you'll understand why that seal does seal on both sides; for pressure and vacuum. After all, the piston does go up and down. If you don't believe that a pressure test is needed to test the pressure side of the crank seal, why do you believe a vacuum test is needed to test the vacuum side of that same crank seal?

To say that pressure leaks cost power and vacuum leaks cost engines is misleading. I have tested many engines that have passed the vacuum test and failed the pressure test. Those engines with failed right crank seals on the pressure side were all consuming gear box oil. Using the "pressure leaks cost power" theory described above would suggest that is impossible. In fact, it is possible, and it does occur. At 8000 RPM the piston travels up and down 133 times per second. At those piston speeds, whether a leak is on the pressure or vacuum side becomes irrelevant, what you have is a leak that is always present.

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