Skip to the content
Peabody TeachFor teachers and grown-ups

Egg-Shaped Lobes That Time an Engine's Breathing

8th grade nonfiction passage about the engine camshaft: 281 words, six questions, an answer key and vocabulary.

8th grade nonfiction the engine camshaft 281 words

Egg-Shaped Lobes That Time an Engine's Breathing

A gasoline engine has to breathe, which means that air and fuel must flow into each cylinder at precisely the right moment and the burned gases must flow out at another moment. Small metal doors called valves open and close the passages, and if a valve opened a little too early or too late, the engine would run poorly or not at all. The component that sets the timing is a rotating rod known as the camshaft.

A camshaft resembles a long bar with a series of bumps, each shaped a bit like an egg, and each bump is called a lobe. As the camshaft turns, the round part of a lobe slides past a valve without moving it, but when the pointed part arrives, it pushes the valve down and opens the passage. As the lobe turns away, a strong spring pushes the valve closed again. The height of the lobe controls how far the valve opens, while the length of the lobe controls how long it stays open.

The camshaft does not turn by itself. A belt or a chain connects it to the crankshaft, which spins as the pistons move up and down. In a common four-stroke engine, each valve needs to open only once for every two turns of the crankshaft, so the gears or sprockets are sized to make the camshaft rotate at half the speed of the crankshaft.

Engineers can change an engine's personality simply by changing the lobes. Tall, wide lobes admit more air and favor high power at high speed, whereas lower, narrower lobes suit a smooth, economical engine. The shapes may look like ordinary bumps, but each one is carefully calculated.

Questions

  1. What do the valves in an engine do? in the text

  2. What is a lobe? in the text

  3. What closes a valve after the lobe turns away? in the text

  4. How fast does the camshaft turn compared with the crankshaft? in the text

  5. Why would a valve opening too early or too late cause trouble? think about it

  6. Why do engineers change the lobes on a camshaft? think about it

Words to know

cylinder
the tube in an engine where the piston moves
camshaft
a rod with bumps that opens an engine's valves
lobe
a rounded bump that sticks out
crankshaft
the shaft that the pistons turn as they move
economical
using little fuel or money
Share

One passage, three levels

The same topic and facts written three ways, so a mixed class can read and talk about one text. Each group’s sheet shows only a shape; the key says which is which.

● Easier · 269 words · Flesch-Kincaid grade 3.3

A gasoline engine has to breathe. Air and fuel must go into each cylinder at just the right moment. The burned gases must go out at another moment. Small metal doors called valves open and close the paths. If a valve opened a little too early or too late, the engine would run badly or not at all. The part that sets the timing is a turning rod called the camshaft.

A camshaft looks like a long bar with bumps on it. Each bump is shaped a bit like an egg. A bump is called a lobe. As the camshaft turns, the round side of a lobe slides past a valve and does not move it. Then the pointed side comes around. It pushes the valve down and opens the path. When the lobe turns away, a strong spring pushes the valve shut. A taller lobe opens the valve farther. A longer lobe keeps it open longer.

The camshaft does not turn by itself. A belt or a chain links it to the crankshaft. The crankshaft spins as the pistons go up and down. In a common four-stroke engine, each valve needs to open only once for every two turns of the crankshaft. So the gears or sprockets are sized to make the camshaft turn at half the speed of the crankshaft.

Engineers can change how an engine acts by changing the lobes. Tall, wide lobes let in more air and give high power at high speed. Lower, narrower lobes suit a smooth engine that saves fuel. The bumps look plain, but each one is planned with care.

▲ This passage · 281 words · Flesch-Kincaid grade 8.7

A gasoline engine has to breathe, which means that air and fuel must flow into each cylinder at precisely the right moment and the burned gases must flow out at another moment. Small metal doors called valves open and close the passages, and if a valve opened a little too early or too late, the engine would run poorly or not at all. The component that sets the timing is a rotating rod known as the camshaft.

A camshaft resembles a long bar with a series of bumps, each shaped a bit like an egg, and each bump is called a lobe. As the camshaft turns, the round part of a lobe slides past a valve without moving it, but when the pointed part arrives, it pushes the valve down and opens the passage. As the lobe turns away, a strong spring pushes the valve closed again. The height of the lobe controls how far the valve opens, while the length of the lobe controls how long it stays open.

The camshaft does not turn by itself. A belt or a chain connects it to the crankshaft, which spins as the pistons move up and down. In a common four-stroke engine, each valve needs to open only once for every two turns of the crankshaft, so the gears or sprockets are sized to make the camshaft rotate at half the speed of the crankshaft.

Engineers can change an engine's personality simply by changing the lobes. Tall, wide lobes admit more air and favor high power at high speed, whereas lower, narrower lobes suit a smooth, economical engine. The shapes may look like ordinary bumps, but each one is carefully calculated.

■ Harder · 289 words · Flesch-Kincaid grade 9.5

A gasoline engine has to breathe, which means that air and fuel must flow into each cylinder at precisely the right moment, and the burned gases must flow out again at another carefully chosen moment. Small metal doors called valves open and close the passages, and if a valve opened even slightly too early or too late, the engine would run poorly or fail to run at all. The component that sets this timing is a rotating rod known as the camshaft.

A camshaft resembles a long bar studded with a series of bumps, each shaped somewhat like an egg, and each bump is called a lobe. As the camshaft turns, the round part of a lobe slides past a valve without moving it, but when the pointed part arrives, it pushes the valve down and opens the passage. As the lobe rotates away, a strong spring pushes the valve closed again. The height of the lobe controls how far the valve opens, while the length of the lobe controls how long it remains open.

The camshaft does not turn by itself. A belt or a chain connects it to the crankshaft, which spins as the pistons move up and down. In a common four-stroke engine, each valve needs to open only once for every two turns of the crankshaft, so the gears or sprockets are sized to make the camshaft rotate at exactly half the speed of the crankshaft.

Engineers can alter an engine's personality simply by changing the lobes. Tall, wide lobes admit more air and favor high power at high speed, whereas lower, narrower lobes suit a smooth, economical engine. The shapes may resemble ordinary bumps, but each one is the product of careful calculation.

Download as one PDF

How to use it

  1. Press Read it big (or B) to put the text on the projector, or Full screen (F) to fill the whole screen.
  2. Ask the questions one at a time and use Show answer when the class has decided. A shows or hides every answer.
  3. Print student copy for the class, or Print with answers for yourself.

Ideas for class

  • Before reading, put cylinder, camshaft, lobe, crankshaft and economical on the board with their meanings from the Words to know section and have students predict what the text will be about.
  • Read it aloud once while students follow along, then have them reread it alone or with a partner. At a calm 100 words a minute it takes about 3 minutes to read aloud.
  • Use the Read it big button (or B) to put the text on the projector, and Show answer on one question at a time so the class commits to an answer first.
  • Question 5 asks the reader to infer. Ask students to point to the words in the passage that led them to their answer.
  • Ask students to write one question the passage did not answer, then look for the answer in a book or on a classroom screen.
  • Print the student copy for independent work and keep the answer-key copy for yourself.

Related

Questions

What reading level is "Egg-Shaped Lobes That Time an Engine's Breathing"?

It was written for 8th grade. It has 281 words and works out to a Flesch-Kincaid grade level of about 8.7. That is a formula's estimate from sentence length and syllables, and it is not a Lexile or a guided reading level, so check it against your students.

What do the questions ask?

There are six. 4 ask for something the text says directly and 2 ask the reader to work something out from clues. Each has an answer in the key, and the answers are written as a teacher would accept them, not as the only possible wording.

How long does it take to read?

About 3 minutes read aloud at 100 words a minute. For a one-minute fluency check, paste it into the fluency timer and use the word count.

Can I print it?

Yes. Print student copy gives the passage, the questions with lines to write on, and the word meanings. Print with answers gives the same page with the answers filled in. Both are made in your browser.

Is this passage from a published book?

No. It was written for Peabody Teach, so there is no book to buy and no login to read it.

Nothing you do here is sent to us. No sign-in, no ads.