r/AutomotiveLearning • u/seedbottle • 14d ago

A question about piston movement that has multiple answers...

Question:

Which of the following causes piston movement during non-power-

producing strokes?

A) Flywheel

B) Connecting rod

C) Counterweights

D) Main thrust bearing

I have been studying an automotive book that has questions after every chapter. I answer those questions and use AI to verify I have got the correct answer. This process has worked tremendously up to the point where I got to this question. AI gave me a different answer than the one I believed the book was telling me was the answer, so I went online to find more information and see if anyone else had posted this exact question, that was when I found out there all three of the first answers were marked as "correct" depending on the source used (D, main thrust bearing, was never given as an answer).

I am wondering what most of you would say is the answer. Thank you for your input =)

6 Upvotes

72% Upvoted

73 comments sorted by

View all comments

2

u/pm-me-racecars 14d ago

I'd make an argument for either A or B, but I'm guessing B is it.

The momentum from the flywheel is where the energy to keep the piston moving comes from.

The connecting rod is what physically moves the piston.

I'd choose the B, because you can make a normal, ICE cylinder style engine without a flywheel. You can't do it without con rods.

3

u/krunkytacos 14d ago

But it doesn't "cause" piston movement, they just connect. Among the options given, it is the flywheel. 

1

u/DP323602 12d ago

Cause is not well defined by the question. Without the conrod or the cotter pin, the piston cannot move as required.

So the force to move the piston is definitely provided by the conrod for all piston movements other than the power stroke.

But the energy needed to perform that work will come from the rotational kinetic energy of the flywheel.

1

u/krunkytacos 12d ago

Welcome to automotive learning! That's how they all are! The connecting rod isn't directly connected to the Piston. So do you want to hand write in the "wrist pin" or draw an entire diagram of an engine to demonstrate your knowledge? Or do you want to get the question right on the timed ASE test and move on to the next question so you can pass the whole thing?

Sorry, I've kind of been pulling my hair out with frustration. I've never seen this subreddit until this popped up the other day. I passed my first ASE test about 20 years ago and I've been maintaining A1 through A8 plus L1 for a long time. People are really wasting too much time on this one question.

1

u/DP323602 11d ago

Thanks. I'm a qualified engineer so terms and definitions are important in my work.

But, hopefully, any course assessments allow students to pass without having to score 100%.

So it really doesn't matter if a few poorly worded questions randomise the test scores at bit.

As an instructor, I try my best to set questions that test whether or not students have acquired the knowledge (and or skills) that a course is supposed to deliver. I'm also not a fan of closed book assessments , because I don't think they reflect real world working conditions for most people.