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Old 9th May 2007, 09:06   #16
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Quote:
if there is something wrong with the compression of 1 specific cylinder (elf elf)
How did elf lose his cylinder anyways?
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Old 9th May 2007, 12:48   #17
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Originally Posted by moralfibre View Post
How can I test compression ratio values? Are there any tools available in the market for this?

@AnandPadhye, what car do you have?
NHC iDSI. August 2004 model. done 43K KM.
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Old 9th May 2007, 14:12   #18
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Originally Posted by Mayavi View Post
Just a FYI, compression test is needed only for old cars with about 100K on the engine or badly driven cars.
Id still say in petrol engines the best thing to do first is check the plugs, all plugs tan color indicates a healthy engine, a drive around car making power, no hesitation accelreating braking and idling perfect is a great engine a compression check can then follow to make sure urself.
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Old 23rd May 2010, 15:54   #19
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I just got the compression checked on my 2001 VTEC.

These were the results (tested at 2,200ft above sea level)

C1 - 185psi
C2 - 185psi
C3 - 190psi
C4 - 175psi

The numbers are within 10% of each other, but i need to find out why the 4th one is lower.

Maybe a wet comp check will give me a better idea of how the rings are holding up.

"A wet compression test should be used when cylinder pressure reads below the manufacturer's specifications. It helps you to determine what engine parts are causing the problem. Pour approximately 1 tablespoon of 30-weight motor oil into the cylinder through the spark plug or injector opening, then retest the compression pressure.

If the compression reading goes up with oil in the cylinder, the piston rings and cylinders may be worn and leaking pressure. The oil will temporarily coat and seal bad compression rings to increase pressure; however, if the compression reading stays about the same, then engine valves or head gaskets may be leaking. The engine oil seals the rings, but does not seal a burned valve or a blown head gasket. In this way, a wet compression test helps diagnose low-compression problems."


Automotive Systems

Shan2nu

Last edited by Shan2nu : 23rd May 2010 at 16:00.
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Old 23rd May 2010, 16:10   #20
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My engine's cylinders are at 215-220 psi @ 80,000 kms.
Dry.
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Old 23rd May 2010, 16:38   #21
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Originally Posted by Shan2nu View Post
Pour approximately 1 tablespoon of 30-weight motor oil into the cylinder through the spark plug or injector opening, then retest the compression pressure.
I've two questions here
1. What is 30-weight motor oil? Is it 4T or engine or some other oil? Pls shed some light here.
2. If I'm not wrong, in a 4stroke engine the oil doesn't cover over the pistons head right? So if this is done, will it not affect the cylinder & the engine?
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Old 23rd May 2010, 16:46   #22
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Quote:
I've two questions here
1. What is 30-weight motor oil? Is it 4T or engine or some other oil? Pls shed some light here.
2. If I'm not wrong, in a 4stroke engine the oil doesn't cover over the pistons head right? So if this is done, will it not affect the cylinder & the engine?
The tuners should be able to answer this, coz it's the first time i've got a comp test done on my car.

Shan2nu

Last edited by Shan2nu : 23rd May 2010 at 16:48.
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Old 23rd May 2010, 17:40   #23
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Quote:
Originally Posted by aargee
1. What is 30-weight motor oil? Is it 4T or engine or some other oil? Pls shed some light here.
SAE 30 (monograde) oil
Quote:
Originally Posted by aargee
2. If I'm not wrong, in a 4stroke engine the oil doesn't cover over the pistons head right? So if this is done, will it not affect the cylinder & the engine?
The quantity would be too low.
Just a dash to seal the worn ring - cylinder wall clearance.
That said, I haven't needed a wet compression test yet. Touchwood.
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Old 23rd May 2010, 20:45   #24
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Hi Shan,

the reason to this could be as simple as your rocker arms/tappet clearences not set in a similar fashion. It could be possible that the first 2 are same and the second 2 are not set with the same clearence.

I have seen differences happening because of this.

Anyway, a wet test should be a good indicator of the health of the rings.

Quote:
Originally Posted by Shan2nu View Post
I just got the compression checked on my 2001 VTEC.

These were the results (tested at 2,200ft above sea level)

C1 - 185psi
C2 - 185psi
C3 - 190psi
C4 - 175psi

The numbers are within 10% of each other, but i need to find out why the 4th one is lower.

Maybe a wet comp check will give me a better idea of how the rings are holding up.

"A wet compression test should be used when cylinder pressure reads below the manufacturer's specifications. It helps you to determine what engine parts are causing the problem. Pour approximately 1 tablespoon of 30-weight motor oil into the cylinder through the spark plug or injector opening, then retest the compression pressure.

If the compression reading goes up with oil in the cylinder, the piston rings and cylinders may be worn and leaking pressure. The oil will temporarily coat and seal bad compression rings to increase pressure; however, if the compression reading stays about the same, then engine valves or head gaskets may be leaking. The engine oil seals the rings, but does not seal a burned valve or a blown head gasket. In this way, a wet compression test helps diagnose low-compression problems."


Automotive Systems

Shan2nu

@Aargee: I would second what nitrous has explained about a 30 weight motor oil.

About your second question, such a small quantity of oil will not do any harm to your engine, when you fire the engine, that oil will get spewed out from the exhaust. So dont worry, it wont affect the cylinder or the engine.

Quote:
Originally Posted by aargee View Post
I've two questions here
1. What is 30-weight motor oil? Is it 4T or engine or some other oil? Pls shed some light here.
2. If I'm not wrong, in a 4stroke engine the oil doesn't cover over the pistons head right? So if this is done, will it not affect the cylinder & the engine?
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Old 24th May 2010, 00:12   #25
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Quote:
Originally Posted by Shan2nu View Post
I just got the compression checked on my 2001 VTEC.

These were the results (tested at 2,200ft above sea level)

C1 - 185psi
C2 - 185psi
C3 - 190psi
C4 - 175psi

The numbers are within 10% of each other, but i need to find out why the 4th one is lower.

Shan2nu
Also do a cylinder leakage test and a power balance test.
A compression test is too blunt an instrument for subtle diagnosis. As are most of these simple tests taken in isolation.

Sutripta
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Old 24th May 2010, 01:43   #26
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Power balance test is easy to perform, either a DIY way or with a scan tool.
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Old 24th May 2010, 18:53   #27
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Quote:
Originally Posted by Shan2nu View Post
I just got the compression checked on my 2001 VTEC.

These were the results (tested at 2,200ft above sea level)

C1 - 185psi
C2 - 185psi
C3 - 190psi
C4 - 175psi

The numbers are within 10% of each other, but i need to find out why the 4th one is lower.
Cylinder 4? How many kms on your odo? If its over 75K, isn't this variance normal?
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Old 24th May 2010, 22:17   #28
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Cylinder 4? How many kms on your odo? If its over 75K, isn't this variance normal?
Im not having any issues with the engine or the performance of the car, it still goes like stink. Honda says the engine is in great shape.

I was just talking on pure technical terms coz ideally, if one cylinder can hold 190psi, it should be possible for the others to do the same. So what is causing this variation?

PS : Another thing i forgot to mention is that this test was done with a dead cold engine. So will there be any diff if i do the test once the engine has reached it's optimum operating temperature?



Shan2nu

Last edited by Shan2nu : 24th May 2010 at 22:21.
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Old 25th May 2010, 13:14   #29
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Its always a good idea to test when its warm, not hot. Don't burn you fingers.
The engine will definitely show better readings when its warm.
The 4th one seems unusually low compare to other. Difference of 5-10 is considered good.
Also try the oil trick. you will know exactly what is wrong with fourth one.
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Old 29th May 2010, 15:02   #30
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Heres a good link, do read through it : What will a compression test tell me? — Yahoo! Autos

Quote:
Originally Posted by aargee View Post
...
2. If I'm not wrong, in a 4stroke engine the oil doesn't cover over the pistons head right? So if this is done, will it not affect the cylinder & the engine?
It won't do any damage. (Just a bit of white smoke when you first start the car, if at all)

On a 4 stroke engine, when running, the oil makes its way onto the conrods, cylinder sleeve, piston skirt, rings etc - the idea of putting some oil in the sparkplug hole is just to simulate that when the engine is not running, even if it means some oil gets on the top of the pistons.

cya
R
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