Curious about how compression test works

[juntjoo]

Since 1/2 of each engine stroke a valve or two (not quite sure how the valves are set up in either SOHC or DOHC) are open, during a compression test, how do you get any compression. Be nice. Remember I'm in the newbie section. ...oh dang, the other 1/2 of each stroke? Did I just answer my own question? Am I almost out of the newbie section?

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[BoostedBeaver]

If a valve is always open (bent valve) the motor will have a miss or not run at all.

On the compression stroke of an individual cylinder, all its valves will be closed to create the power we crave. Fast foward to 1:30 in this video and learn more than I can explain.

Octane Ratings and the 4 Stroke Engine Cycle - YouTube

Here is another

http://www.youtube.com/watch?v=qXA3tAROnBw&NR=1&feature=fvwp

Robert

 

[rlacasse1]

Watch the video on this page, and read. You will see.

HowStuffWorks "Internal Combustion"

 

[DSM1G90]

Compression testing is simply threading in a tester in the sparkplug hole.

You unplug the MPI fuse so the injectors won't be squirting fuel in the bores when doing this test.

As you crank the motor, compession is is read by the gauge per each compression stroke and is displayed on the gauge in PSI.

Trick in reading is looking at the gause when the motor is cranked where the needle is displaying the compression. There is a button on the side of the gauge which locks the needle when the highest compression reading is reached so that one can stop the motor cranking (only takes a few strokes) and document the reading.

 

[juntjoo]

Ah, the compression stroke, HENCE the COMPRESSION test. Well apparently I have ZERO compression. Okay thanks people.

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[juntjoo]

Awesome vids! Thanks. I like Eric the car guy. Already used a few of his vids.

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[my dreamt dsm]

Awesome vids! Thanks. I like Eric the car guy. Already used a few of his vids.

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Yep, subscribed to him, he is very helpful.