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Old 4th May 2007, 15:02   #1
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Post What is engine compression test ??

Hi Guys

I would like to know what Engine Compression test is ??. I have heard about performing Engine Compression test for diesel engines cars before buying them....How is it done, what does the test help in and where can it be done....

Regards

Jango
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Old 4th May 2007, 15:48   #2
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Hi Guys

I would like to know what Engine Compression test is ??. I have heard about performing Engine Compression test for diesel engines cars before buying them....How is it done, what does the test help in and where can it be done....

Regards

Jango
Hello jango, engine compression test determeines the compression pressure being built up in each cylinder when the piston is at top dead center.

It is done by removing injector & fitting a pressure gauge in place & engine is cranked such that piston in cylinder being tested reaches top dead center position & reading is noted down. If reading falls below the normal level then a compression leakage is suspected, usual reason being worn out piston rings & liner.

It is not limited to diesels, it can be done in a petrol engine to by removing a spark plug & inserting pressure gauage in place of it.

it can be easly done at any competent workshop.
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Old 4th May 2007, 16:36   #3
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My car maual says compression ratio 10.5:1
Is this "understandard condtions" or practical? I mean if I do the test, what reading I should expect to confirm that compression is all OK?
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Old 4th May 2007, 18:15   #4
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My car maual says compression ratio 10.5:1
Is this "understandard condtions" or practical? I mean if I do the test, what reading I should expect to confirm that compression is all OK?
compression ratio 10.5:1 means, your engine's swept volume(volume of air intaken-in your case its mix. of air & fuel as 10.5:1 indicates petrol), will be compressed 10.5 times of original volume during compression stroke.

It should be 10.5:1 for practical purpose too, expected correct reading depend on dimensions of your engine. 10.5:1 is compression ratio, how much pressure it will exert can be found in workshop manual for your car.
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Old 7th May 2007, 12:38   #5
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okie i guess then its a very gud practice to know abt the health of the engine to some extend !!
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Old 7th May 2007, 13:00   #6
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How can I test compression ratio values? Are there any tools available in the market for this?

@AnandPadhye, what car do you have?
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Old 7th May 2007, 13:05   #7
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How can I test compression ratio values? Are there any tools available in the market for this?

@AnandPadhye, what car do you have?
You get a CR gauge .. Remove the spark plug insert the gauge and crank her .. You will normally get the compression in pounds per cylinder .. Calculating overall CR is slightly complicated and you need to know a lot more parameters .. But compression per cylinder is a good indicative regarding the health of an engine ..

Last time i checked with my car it showed a healthy 240 psi per cylinder ..
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Old 7th May 2007, 13:24   #8
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Does this mean that you can decide on whether engine overhaul is required without opening up the cyclinder head?
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Old 7th May 2007, 13:56   #9
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I think this test is a must only on suspect engines. If your car is having enough power & FE is good, there is no need for this test. Yes, it is nice if you can do that before you purchase a used car.
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Old 7th May 2007, 14:09   #10
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Where could one find such a gauge in Bombay?
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Old 8th May 2007, 16:24   #11
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How to do a Compression Test

hope this helps
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Old 8th May 2007, 17:04   #12
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Old 8th May 2007, 17:10   #13
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Also can someone tell me where can i get the engine compression test done in b'lore ?? any specific workshop !!
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Old 8th May 2007, 22:52   #14
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Just a FYI, compression test is needed only for old cars with about 100K on the engine or badly driven cars.
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Old 9th May 2007, 04:49   #15
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A compression test is never a bad idea, especially on older cars.

If you are having problems it helps point out if there is something wrong with the compression of 1 specific cylinder (elf elf) if the reading is significantly lower than the others (more than ~10-15psi? difference)

Pretty much every garage should have a guage (it looks like a compressed air pipe with a dialguage on the end of it). Its pretty low tech stuff.

cya
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Last edited by Rehaan : 9th May 2007 at 04:50.
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