compression and leak down testing?
ludeguy1
12-13-2004, 06:45 PM
I know what compression is and how it works, but my question is when you test it (which i have done to my 93 h23a1) is the number that you get...like 170...180.... the pressure(psi) at the compression stroke? I'm pretty sure thats what those numbers stand for.
Second question: ive been looking at h22's on ebay and some of them say they have been compression tested and LEAK DOWN tested or something like that. What is LEAK DOWN testing? what do they do in this process and what do the results stand for? Thanks for the input:)
Second question: ive been looking at h22's on ebay and some of them say they have been compression tested and LEAK DOWN tested or something like that. What is LEAK DOWN testing? what do they do in this process and what do the results stand for? Thanks for the input:)
ludeguy
12-13-2004, 07:37 PM
I know what compression is and how it works, but my question is when you test it (which i have done to my 93 h23a1) is the number that you get...like 170...180.... the pressure(psi) at the compression stroke? I'm pretty sure thats what those numbers stand for.
Second question: ive been looking at h22's on ebay and some of them say they have been compression tested and LEAK DOWN tested or something like that. What is LEAK DOWN testing? what do they do in this process and what do the results stand for? Thanks for the input:)
yeah usually it is on compression stroke - because that is when all the intake and exhaust valves (for that cylinder) are closed at the same time (ie: it wouldn't make sense to do it on the exhaust stroke because the exhaust valves would be open!) how do you find compression stroke? usually by removing the spark plug - and putting your thumb over the hole - while someone manually turns the engine - when air is pushed out past your thumb - you should be on the compression stroke - saying that i imagine it's pretty hard to use your thumb on a prelude - haha, but yea anything to block the hole but so that you can tell when the air stops gushing.
you are correct about the numbers they are in psi - for a 4 cyl - you should get 4 of them.
as for a leak down - not completely sure about this one - so someone correct me if i'm wrong - but imagine they add the pressure to the cylinder and do a differential pressure test between the cylinder and say the exhaust manifold - that way they can tell if their is any "leak" by the difference in pressure. - It's great if a cylinder can reach 200psi - but for how long? how much leak? i think that's what they are getting at.
it's recomended that the engine is run before doing a compression/leakdown (heh impossible with floor sitting jdms) but that is just because a coat of oil could probably "increase" the sealing capability- so if anything the numbers should only get better then if it was dry-tested.
i've also heard that during a compression test you should open the throttle right up (just so you are taking that buttefly valve out of the equation if there is something wrong with one of the intake valves.
that's the way i see it.
hope that helps - and someone please correct me if i'm wrong.
Second question: ive been looking at h22's on ebay and some of them say they have been compression tested and LEAK DOWN tested or something like that. What is LEAK DOWN testing? what do they do in this process and what do the results stand for? Thanks for the input:)
yeah usually it is on compression stroke - because that is when all the intake and exhaust valves (for that cylinder) are closed at the same time (ie: it wouldn't make sense to do it on the exhaust stroke because the exhaust valves would be open!) how do you find compression stroke? usually by removing the spark plug - and putting your thumb over the hole - while someone manually turns the engine - when air is pushed out past your thumb - you should be on the compression stroke - saying that i imagine it's pretty hard to use your thumb on a prelude - haha, but yea anything to block the hole but so that you can tell when the air stops gushing.
you are correct about the numbers they are in psi - for a 4 cyl - you should get 4 of them.
as for a leak down - not completely sure about this one - so someone correct me if i'm wrong - but imagine they add the pressure to the cylinder and do a differential pressure test between the cylinder and say the exhaust manifold - that way they can tell if their is any "leak" by the difference in pressure. - It's great if a cylinder can reach 200psi - but for how long? how much leak? i think that's what they are getting at.
it's recomended that the engine is run before doing a compression/leakdown (heh impossible with floor sitting jdms) but that is just because a coat of oil could probably "increase" the sealing capability- so if anything the numbers should only get better then if it was dry-tested.
i've also heard that during a compression test you should open the throttle right up (just so you are taking that buttefly valve out of the equation if there is something wrong with one of the intake valves.
that's the way i see it.
hope that helps - and someone please correct me if i'm wrong.
AcesHigh
12-15-2004, 01:41 AM
You plop out the spark plug; one at a time. In its place you screw on a little pressure gauge. You have to disconnect the wires, and then start up the engine. Usually you let it crank 4-5 times until the gauge slows way down. As long as its uniformed, it doesnt matter. Record your reading, move on to the next one.
Its really a waste of time unless your car is super old or has been sitting out in the snow for a year or two. Most cars that seemingly run fine have good compression.
Its really a waste of time unless your car is super old or has been sitting out in the snow for a year or two. Most cars that seemingly run fine have good compression.
ludeguy
12-15-2004, 02:40 AM
You plop out the spark plug; one at a time. In its place you screw on a little pressure gauge. You have to disconnect any fuel lines, and then start up the engine. Usually you let it crank 4-5 times until the gauge slows way down. As long as its uniformed, it doesnt matter. Record your reading, move on to the next one.
Its really a waste of time unless your car is super old or has been sitting out in the snow for a year or two. Most cars that seemingly run fine have good compression.
excuse me if i'm wrong - but that doesn't make any sense - how is the cylinder you are "cranking" on going to hold any pressure if the "crank" ends on the exhaust stroke or the intake stroke when the valves are open? how are you possibly testing the compression of the engine (moreover the seal of the valves) by taking an average of the compression thru-out an engine cranked over 4 or 5 times?
we did this at school on a radial aircraft engine... it was always on compression stroke and the engine was never cranked over - way to dangerous for students - in fact students had to hold the prop in the "detent" so that the psi added to the cylinder on compression stroke wouldn't "spin" the prop.
perhaps it's a difference between aviation and automobile but unless you have a gauge that records peak psi, I really can't see the point of taking a cylinders pressure thru the whole range of suck squeeze bang blow.
Its really a waste of time unless your car is super old or has been sitting out in the snow for a year or two. Most cars that seemingly run fine have good compression.
excuse me if i'm wrong - but that doesn't make any sense - how is the cylinder you are "cranking" on going to hold any pressure if the "crank" ends on the exhaust stroke or the intake stroke when the valves are open? how are you possibly testing the compression of the engine (moreover the seal of the valves) by taking an average of the compression thru-out an engine cranked over 4 or 5 times?
we did this at school on a radial aircraft engine... it was always on compression stroke and the engine was never cranked over - way to dangerous for students - in fact students had to hold the prop in the "detent" so that the psi added to the cylinder on compression stroke wouldn't "spin" the prop.
perhaps it's a difference between aviation and automobile but unless you have a gauge that records peak psi, I really can't see the point of taking a cylinders pressure thru the whole range of suck squeeze bang blow.
boytiti
12-15-2004, 03:14 AM
yeah usually it is on compression stroke - because that is when all the intake and exhaust valves (for that cylinder) are closed at the same time (ie: it wouldn't make sense to do it on the exhaust stroke because the exhaust valves would be open!) how do you find compression stroke? usually by removing the spark plug - and putting your thumb over the hole - while someone manually turns the engine - when air is pushed out past your thumb - you should be on the compression stroke - saying that i imagine it's pretty hard to use your thumb on a prelude - haha, but yea anything to block the hole but so that you can tell when the air stops gushing.
you are correct about the numbers they are in psi - for a 4 cyl - you should get 4 of them.
as for a leak down - not completely sure about this one - so someone correct me if i'm wrong - but imagine they add the pressure to the cylinder and do a differential pressure test between the cylinder and say the exhaust manifold - that way they can tell if their is any "leak" by the difference in pressure. - It's great if a cylinder can reach 200psi - but for how long? how much leak? i think that's what they are getting at.
it's recomended that the engine is run before doing a compression/leakdown (heh impossible with floor sitting jdms) but that is just because a coat of oil could probably "increase" the sealing capability- so if anything the numbers should only get better then if it was dry-tested.
i've also heard that during a compression test you should open the throttle right up (just so you are taking that buttefly valve out of the equation if there is something wrong with one of the intake valves.
that's the way i see it.
hope that helps - and someone please correct me if i'm wrong.
Engine in good shape should have no more than 10-15% difference between cylinders on your compression test results. if compression test is more than 20% difference on cylinders, you may want to do a cylinder leak down test on that weak cylinder.
Cylinder Leakage test is best test that can be used for checking cylinder condition. Pressured air is injected into the cylinders one at a time through a cylinder leakage gauge into the spark plug hole. Some cylinder leakage test gauge readings and what they mean: less than 10% leakage = good, less than 20% = acceptable, less than 30% = poor, more than 30% = definite problem.
http://store1.yimg.com/I/autotoolexpress_1823_13363600
see my ride >> http://preludevtec93.tripod.com/pics
you are correct about the numbers they are in psi - for a 4 cyl - you should get 4 of them.
as for a leak down - not completely sure about this one - so someone correct me if i'm wrong - but imagine they add the pressure to the cylinder and do a differential pressure test between the cylinder and say the exhaust manifold - that way they can tell if their is any "leak" by the difference in pressure. - It's great if a cylinder can reach 200psi - but for how long? how much leak? i think that's what they are getting at.
it's recomended that the engine is run before doing a compression/leakdown (heh impossible with floor sitting jdms) but that is just because a coat of oil could probably "increase" the sealing capability- so if anything the numbers should only get better then if it was dry-tested.
i've also heard that during a compression test you should open the throttle right up (just so you are taking that buttefly valve out of the equation if there is something wrong with one of the intake valves.
that's the way i see it.
hope that helps - and someone please correct me if i'm wrong.
Engine in good shape should have no more than 10-15% difference between cylinders on your compression test results. if compression test is more than 20% difference on cylinders, you may want to do a cylinder leak down test on that weak cylinder.
Cylinder Leakage test is best test that can be used for checking cylinder condition. Pressured air is injected into the cylinders one at a time through a cylinder leakage gauge into the spark plug hole. Some cylinder leakage test gauge readings and what they mean: less than 10% leakage = good, less than 20% = acceptable, less than 30% = poor, more than 30% = definite problem.
http://store1.yimg.com/I/autotoolexpress_1823_13363600
see my ride >> http://preludevtec93.tripod.com/pics
AcesHigh
12-15-2004, 04:35 PM
I am not quite sure of the mechanics on it myself, but.. here's maybe what happens. The gauge itself is not a real-time gauge, whenever pressure is applied to it the gauge moves up and it stays there; it does not matter if pressure is lost during the exhaust/intake strokes because the gauge is measuring peak compression, and not temporal compression of any specific stroke.
*shrug* I just know it works. Also, since there is no spark, no combustion is taking place. Its fairly harmless.
*shrug* I just know it works. Also, since there is no spark, no combustion is taking place. Its fairly harmless.
ludeguy
12-15-2004, 08:37 PM
I am not quite sure of the mechanics on it myself, but.. here's maybe what happens. The gauge itself is not a real-time gauge, whenever pressure is applied to it the gauge moves up and it stays there; it does not matter if pressure is lost during the exhaust/intake strokes because the gauge is measuring peak compression, and not temporal compression of any specific stroke.
*shrug* I just know it works. Also, since there is no spark, no combustion is taking place. Its fairly harmless.
yeah I agree - if you have a gauge that can record PEAK psi or something (much like those rpm gauges that can tell you what the highest rpm was that yout hit). But since what you are really interested in is the ability of the cylinder to hold pressure on the combustion stroke - there isn't much point testing it thru the other cycles - I imagine the method you're talking about would prob be a bit faster because you wouldn't have to go into the wheel well to position each cylinder at tdc, you could just hook up the gauge crank it thru and record the peak psi for one cylinder then move on to the next. makes sense.
*shrug* I just know it works. Also, since there is no spark, no combustion is taking place. Its fairly harmless.
yeah I agree - if you have a gauge that can record PEAK psi or something (much like those rpm gauges that can tell you what the highest rpm was that yout hit). But since what you are really interested in is the ability of the cylinder to hold pressure on the combustion stroke - there isn't much point testing it thru the other cycles - I imagine the method you're talking about would prob be a bit faster because you wouldn't have to go into the wheel well to position each cylinder at tdc, you could just hook up the gauge crank it thru and record the peak psi for one cylinder then move on to the next. makes sense.
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