AGK valve question During the COMPRESSION and POWER strokes

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CyclicH145
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AGK valve question During the COMPRESSION and POWER strokes

Postby CyclicH145 » Sun Oct 18 2020, 06:11

Hi all.

Wondering if some theory people maybe to shed some light on the question below.

During the COMPRESSION and POWER strokes on the 4 stoke horizontally opposed cycle;

a. The exhaust valve remains closed.
b. both inlet valves remain open.
c. the inlet valve closes.
d. both valves remain open.

So my thinking here is;
a is correct IF we're talking about compression but as it opens on the power stroke, not correct.
b is what the answer keys indicates as correct (videos show during the compression stroke the inlet valve closing as the piston leaves BDC and is closed on the power stroke) :shock:
c. the inlet valve is ALREADY closed as the compression stroke starts
d. inlet is closed and exhaust is opening

Looks like C should be the right answer.

I picked (c) then changed it to (a) as in my mind (b) and (d) aren't correct
Icefather
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Re: AGK valve question During the COMPRESSION and POWER strokes

Postby Icefather » Sun Oct 18 2020, 06:41

The inlet valve shouldn’t open on the power stroke as you’d loose the performance of the explosion from ignition.

The inlet valve closes as the position reaches BDC as the compression stroke starts. And remains closed until the top of the exhaust stroke, the exhaust valve opens at the bottom of the power stroke to expel the waste gases as the piston comes back up.

To answer the question the most correct answer would be A as the exhaust valves remains closed until the bottom/start of the exhaust stroke.

Unless they stuffed up with the answer and meant both inlet valves remain closed then I’d say it would be an error? Unless I’m completely off the mark.
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CyclicH145
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Re: AGK valve question During the COMPRESSION and POWER strokes

Postby CyclicH145 » Sun Oct 18 2020, 06:50

Icefather wrote:The inlet valve shouldn’t open on the power stroke as you’d loose the performance of the explosion from ignition.

The inlet valve closes as the position reaches BDC as the compression stroke starts. And remains closed until the top of the exhaust stroke, the exhaust valve opens at the bottom of the power stroke to expel the waste gases as the piston comes back up.

To answer the question the most correct answer would be A as the exhaust valves remains closed until the bottom/start of the exhaust stroke.

Unless they stuffed up with the answer and meant both inlet valves remain closed then I’d say it would be an error? Unless I’m completely off the mark.


I went with A but its only half right....thanks for confirming I am not going insane!
Icefather
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Re: AGK valve question During the COMPRESSION and POWER strokes

Postby Icefather » Sun Oct 18 2020, 07:01

CyclicH145 wrote:
I went with A but its only half right....thanks for confirming I am not going insane!


No worries... but B is completely wrong lol the inlet valve does not remain open....

C is right for the compression stroke but doesn’t close again on the power stroke.

Bottom line. Poorly worded question for the answers provided.
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CyclicH145
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Re: AGK valve question During the COMPRESSION and POWER strokes

Postby CyclicH145 » Sun Oct 18 2020, 07:20

Icefather wrote:
CyclicH145 wrote:
I went with A but its only half right....thanks for confirming I am not going insane!


No worries... but B is completely wrong lol the inlet valve does not remain open....

C is right for the compression stroke but doesn’t close again on the power stroke.

Bottom line. Poorly worded question for the answers provided.



Just found the exact question in AFT. answer is A. We're sane! No further action
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CyclicH145
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Re: AGK valve question During the COMPRESSION and POWER strokes

Postby CyclicH145 » Sun Oct 18 2020, 07:20

Just found the exact question in AFT. No further action
Wannabe60Driver
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Re: AGK valve question During the COMPRESSION and POWER strokes

Postby Wannabe60Driver » Sun Oct 18 2020, 07:32

Perfect example of Gavin getting the sh*ts with PPE-style websites and examining whether someone understands the ‘why’ behind a question in order to lose the rote learners. Overlap is a fact regardless of whether you learned about piston engines in an air, land, or sea context. Some answers are possible, while the others are not. Welcome to the CASA modus operandi. Enjoy.
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skypig
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Re: AGK valve question During the COMPRESSION and POWER strokes

Postby skypig » Sun Oct 18 2020, 12:34

Pretty relevant question.
Especially if you are considering fitting a self designed custom ground camshaft during your daily inspection.

Don’t look for logic, correctness or relevance in CASA exams.
This is an example of a question written by someone who probably isn’t a pilot, and almost certainly doesn’t understand a reciprocating internal combustion engine.
Rather, he has read a paragraph, in isolation, and based the question on that.

Find the correct answer, according to CASA, move on, and never think about it again.

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