Can The Leakdown Test for VG30E Work With Upper Plenum Off?
04-26-2009, 04:28 PM
#1
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Can The Leakdown Test for VG30E Work With Upper Plenum Off?
LVR, I tried the screwdriver method right now, and notice it raises at maximum height slightly after the mark on the distributor. The test doesn't seem to be working though, maybe i'm doing something wrong, but I hear air leaking out those ports to the UIM. Also, as soon as I connect the 90PSI air, I notice the rotor moves back instantly.
Does the lid have to be on to do this test?
Does the lid have to be on to do this test?
04-26-2009, 08:53 PM
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LVR, I tried the screwdriver method right now, and notice it raises at maximum height slightly after the mark on the distributor. The test doesn't seem to be working though, maybe i'm doing something wrong, but I hear air leaking out those ports to the UIM. Also, as soon as I connect the 90PSI air, I notice the rotor moves back instantly.
Does the lid have to be on to do this test?
Does the lid have to be on to do this test?
As I said in the other thread already:
Leak-down tests generally gets done with the rings under the compression stroke mechanically (iow don't go past TDC and then turn it back!), but still on its way to the top so as to prevent (about 15 degrees before TDC for the particular cylinder) the rings sitting in the normally slightly more worn TDC position where the rings generally tend to wear a radial groove in the barrel.
IMO its very close to a waste of time since a well controlled compression test can tell you the same and much more under the actual working conditions of all the mechanical bits involved in creating a chunk of compressed mixture in any given cylinder.
IMO its very close to a waste of time since a well controlled compression test can tell you the same and much more under the actual working conditions of all the mechanical bits involved in creating a chunk of compressed mixture in any given cylinder.
Do a properly controlled compression test and be done with it - you are wasting your time with this leakdown test imo
04-26-2009, 09:05 PM
#3
The plenum has nothing to do with retaining the volume of mixture compressed in the cylinder when the cylinder is on the compression stroke with the piston at the top.
As I said in the other thread already:
Simple fact of life here ................ even a new engine with no wear and every component 100% as per design spec will leak under the conditions you described above because it is simply not designed to work properly at that snail's rotational speed (or indeed static) and low temperature.
Do a properly controlled compression test and be done with it - you are wasting your time with this leakdown test imo
As I said in the other thread already:
Simple fact of life here ................ even a new engine with no wear and every component 100% as per design spec will leak under the conditions you described above because it is simply not designed to work properly at that snail's rotational speed (or indeed static) and low temperature.
Do a properly controlled compression test and be done with it - you are wasting your time with this leakdown test imo
04-26-2009, 09:15 PM
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04-26-2009, 09:22 PM
#5
if you can hear where the air is escaping from (intake, exhaust, crankcase) it can. unless me and you are talkig about different things, this is where pressurized air is forced into the spark plug hole through a hose and it measures how much air escapes?
04-26-2009, 09:34 PM
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Cool thanks guys. I'll try it with the fuel rail and plenum back in - just out of curiosity. But caped, it does feel like having it open is doing something. I can feel air coming out that port - where the injectors were.
LVR, I don't have the compression tester yet - I only bought the leakdown tester in the winter because it was on sale. I could return it still, but i'll think about it. It could be useful one day.
You are the first person actually, i've heard of that said it's useless. From what I've read on the internet, the leakdown test is specific like Caped points out, to pinpoint problems. It is typically used to supplement the compression tester. Plus it has % leakage from LOW - MED- HIGH.
And actually, here's the thing. Let's say you do a compression test and things didn't work out...it's out of range of FSM. Then you'll probably want to do the Leakdown to further investigate right? My question is, what's the point of the compression test if you have to do the Leakdown later anyways. If you do the leakdown and everything is good, then no need for compression right? If you do the leakdown and it turns out bad - then you've got bigger problems. So you could go back and do the compression test to confirm....or start to figure out the problem right?
LVR, I don't have the compression tester yet - I only bought the leakdown tester in the winter because it was on sale. I could return it still, but i'll think about it. It could be useful one day.
You are the first person actually, i've heard of that said it's useless. From what I've read on the internet, the leakdown test is specific like Caped points out, to pinpoint problems. It is typically used to supplement the compression tester. Plus it has % leakage from LOW - MED- HIGH.
And actually, here's the thing. Let's say you do a compression test and things didn't work out...it's out of range of FSM. Then you'll probably want to do the Leakdown to further investigate right? My question is, what's the point of the compression test if you have to do the Leakdown later anyways. If you do the leakdown and everything is good, then no need for compression right? If you do the leakdown and it turns out bad - then you've got bigger problems. So you could go back and do the compression test to confirm....or start to figure out the problem right?
04-26-2009, 09:35 PM
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Let me give you this example:
He has now taken the plenum off. I will bet you a pound to pinch of any manure of your choice that some dirt dropped down into the intake runners in the heads and may/have gotten stuck on the valve seats .................... since you are turning the motor so slow, there is no chunks of air to help move the gunk off the seat on the intake stroke and thus the valve will never close properly - thus even if you were to "detect" the leaking valve you will incorrectly conclude that you have a burnt valve
Come now - this is rediculous - if you have low compression when the motor is working at a speed/temp as intended, that is all you need to know - iow if its bothering you so much its time for an overhaul and dirty hands.
04-26-2009, 09:38 PM
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Caped, your right it says that in the manual - if the meter shows high loss, you next check various spots to hear the tone of the hissing sound - at the muffler, dipstick tube etc.... either stethescope or a piece of heater hose connected to your ear.
Now unless the manual is lying....it's just snake oil, but Milton is a reputable company..
Now unless the manual is lying....it's just snake oil, but Milton is a reputable company..
04-26-2009, 09:48 PM
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Point is LVR - I can't avoid buying the compression tester right? I guess i'll have to buy it. Or now that I have the hose already, could I just buy a cheap gauge and buy the little Milton M Style coupler to connect the gauge to the hose.
Does your gauge have a reset button where it remembers the highest reading?
Does your gauge have a reset button where it remembers the highest reading?
04-26-2009, 09:48 PM
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Caped, your right it says that in the manual - if the meter shows high loss, you next check various spots to hear the tone of the hissing sound - at the muffler, dipstick tube etc.... either stethescope or a piece of heater hose connected to your ear.
Now unless the manual is lying....it's just snake oil, but Milton is a reputable company..
Now unless the manual is lying....it's just snake oil, but Milton is a reputable company..
04-26-2009, 10:08 PM
#13
................... and you will somehow be able to listen at every valve, at the rings, at the gasket edges inside the cylinder, at every metal wall of the block, at the cylinder head surfaces and on top of that be also able to measure the amount of bearing/piston wear as well as state of lubrication distribution so as to correctly identify the "cause" of low compression?
Let me give you this example:
He has now taken the plenum off. I will bet you a pound to pinch of any manure of your choice that some dirt dropped down into the intake runners in the heads and may/have gotten stuck on the valve seats .................... since you are turning the motor so slow, there is no chunks of air to help move the gunk off the seat on the intake stroke and thus the valve will never close properly - thus even if you were to "detect" the leaking valve you will incorrectly conclude that you have a burnt valve
Come now - this is rediculous - if you have low compression when the motor is working at a speed/temp as intended, that is all you need to know - iow if its bothering you so much its time for an overhaul and dirty hands.
Let me give you this example:
He has now taken the plenum off. I will bet you a pound to pinch of any manure of your choice that some dirt dropped down into the intake runners in the heads and may/have gotten stuck on the valve seats .................... since you are turning the motor so slow, there is no chunks of air to help move the gunk off the seat on the intake stroke and thus the valve will never close properly - thus even if you were to "detect" the leaking valve you will incorrectly conclude that you have a burnt valve
Come now - this is rediculous - if you have low compression when the motor is working at a speed/temp as intended, that is all you need to know - iow if its bothering you so much its time for an overhaul and dirty hands.
04-27-2009, 01:08 AM
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ok well how about with everything properly installed, with the test performed immedately after the car was ran and warmed up to proper operating temp?
The amount of variables playing a role in drawing a sensible conclusion from a leakdown test is simply staggering - not least of all being a decent mechanical knowledge of the particular motor you are dealing with and compression mechanics in general .................... and this is simply not in the realm of the avg home mechanic trying to maintain/troubleshoot a 15+ year old motor
Let me give you a few examples of how to incorrectly determine the source of low compression while using leakdown test:
1. Using the recommended fixed pressure the manufacturer of the guage suggest - ie you ignore the real operating combustion pressure of the particular motor. You should be using something like what you see on a guage during a compression test - or if you know the ambient air pressure you can calculate what you should be using by looking at the particular motor's compression ratio (ie - use ambient x CR) ................ and not the typically suggested 600-700kpa most home compressors that are used for the leakdown test are limited to ..................... major league different effect on cracks/gaskets etc!
2. So you do a leakdown test and hear a hissing in the sump/dipstick tube and the manual tells you its worn rings ................... well - it could also be blown headgasket, cracked cylinder wall, scored barrel, broken ring/s, crack in the head, damaged piston, simple carbon buildup in ring lands etc etc etc ...........
3. So you do a leakdown test and hear a hissing in the exhaust and the manual tells you its exhaust valves ..................well - it could also be a cracked head, worn valve guides, funky lifter, etc etc
4. So you do a leakdown test and see lots of pressure leaking away but hear no obvious hissing anywhere, but open the radiator cap and see liquid moving or bubbles escaping and the manual tells you its a blown headgasket ..................... well, it could also be a cracked block, cracked head
5. Any oil film gets broken down when the parts to be lubricated comes to rest and the oil pressure/source disappears - ie - read engine sitting still..................... serious effect on sealing ability of rings when compared to a motor rotating at normal speeds with lube constantly being fed to it.
6. The sealing ability of the compression rings is a huge function of them being located properly in the ring lands ..................... and I have seen very few if any leakdown guage manufacturer telling you to ensure you stop the and keep the motor stationary while the piston is traveling towards TDC on the compression stroke before you do a leakdown test on that cylinder ................... huge effect in motors that have done many 100K miles where the ring lands are no longer tight.
The supposed obvious goal of a leakdown test is to identify the cause of low compression - imo it can do little if anything more than what you eg can do by using logic and with a simple well controlled compression test and by looking at the oil/water/exhaust on the engine.
Yes I know the above are all rather acedemic, but as I said before, you are not going to affect a lasting external repair on a motor with low compression on one or more cylinder - if it already bothers you, then you need an overhaul and oily hands to figure the exact cause.
04-27-2009, 01:42 AM
#16
i see. so basically all it does is make you jump to conclusions because the manual tells you "it IS this" when in reality there's too many possibilities for just that tool to tell you the real answer.
granted some of those options are kindof rare, like a cracked VG block, which i've ever heard of in all my 2 years on this site.. but technically they are possibilities.
granted some of those options are kindof rare, like a cracked VG block, which i've ever heard of in all my 2 years on this site.. but technically they are possibilities.
04-27-2009, 11:16 AM
#18
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Thanks LVR. This does help to explain alot. Now here's my question to you. If you bought the leakage tester on sale, and you could return it but it would be a hassle, is it possible to do at least the diagnosis that the compression tester can do, thus avoiding having to buy the compression tester? I think the leakage tester was on sale for like 64.00 or something.
04-27-2009, 12:57 PM
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The compression tester can quantify :
1. What the maximum pressure is in a given cylinder under close to normal operating conditions
2. What the differences are between the individual cylinders ito max pressure (pressure = power)
3. What acceptable actual values are to determine if any action should be taken as per FSM engineering recommendations.
A leakdown test can do none of those, but it can tell you where you can hear a hiss and thus pressure escaping ............... yet it cannot tell you if that escaping volume of air is "normal"
A leakdown test would be extremely useful if one could compare the results obtained today with results obtained from the same test on the same motor after it was just run-in 15+ years ago. In the absence of identical measurements when your particular motor was young and strong and healthy, then, if you have a compressor able to supply about 10bar you can do the same hiss tracing as with a leakdown tester guages and come to the same conclusions by just pumping up the cylinder and playing doctor doctor on the individual suspect items involved with a stethoscope.
BTW - what exactly is it that you are trying to do here? - are you aware of any problem symptoms with the motor? .................... are you just trying to quantify the condition of the motor?
As for your direct question:
I would return it, buy a compression tester and 2 cases of beer for that money, and live happily ever after.
1. What the maximum pressure is in a given cylinder under close to normal operating conditions
2. What the differences are between the individual cylinders ito max pressure (pressure = power)
3. What acceptable actual values are to determine if any action should be taken as per FSM engineering recommendations.
A leakdown test can do none of those, but it can tell you where you can hear a hiss and thus pressure escaping ............... yet it cannot tell you if that escaping volume of air is "normal"
A leakdown test would be extremely useful if one could compare the results obtained today with results obtained from the same test on the same motor after it was just run-in 15+ years ago. In the absence of identical measurements when your particular motor was young and strong and healthy, then, if you have a compressor able to supply about 10bar you can do the same hiss tracing as with a leakdown tester guages and come to the same conclusions by just pumping up the cylinder and playing doctor doctor on the individual suspect items involved with a stethoscope.
BTW - what exactly is it that you are trying to do here? - are you aware of any problem symptoms with the motor? .................... are you just trying to quantify the condition of the motor?
As for your direct question:
I would return it, buy a compression tester and 2 cases of beer for that money, and live happily ever after.
04-28-2009, 11:43 PM
#20
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LVR when you get a chance can you read my other post and what happened after my injector install. You don't think it's possible that the leakdown test itself screwed something up do you? Is that possible?
04-29-2009, 03:35 AM
#21
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The amount of variables playing a role in drawing a sensible conclusion from a leakdown test is simply staggering - not least of all being a decent mechanical knowledge of the particular motor you are dealing with and compression mechanics in general .................... and this is simply not in the realm of the avg home mechanic trying to maintain/troubleshoot a 15+ year old motor
04-29-2009, 12:56 PM
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