[Z06] More engine problems...still burning oil
12-30-2011, 02:06 PM
#1
Le Mans Master
Thread Starter
More engine problems...still burning oil
So, maybe some of you saw my earlier post about an oil burning issue in my LS7.
http://forums.corvetteforum.com/c6-z...ce-please.html
In summary, I was burning oil at high RPM when the car was rev'd in neutral (not under load). My shop did a leak down and compression test which came back fine. After that we then went into the heads, which after inpsection needed new exhaust valves, seals, guides (basically a complete rebuild except for the Ti valves which were able to be saved). The guides and valves were shot, so we figured that was where the oil burning was coming from, and that I had potentially saved myself from an eventual dropped valve...or so I thought.
When I got the car back with the rebuilt heads, the smoke problem went away and the car ran smooth and strong, things were good. But, in the last couple hundred miles I noticed the car had burnt about 1.5 quarts of oil. Being suspicious, I did the rev test in neutral again and the cloud of oil smoke is back. WTF!!!
I gave her a jab on the throttle while driving down the road as well and now I can see a cloud of smoke under load (which never happened before). I have an elite catch can that is working great, no oil in the intake.
Not really happy after all the money I spent, any thoughts on what could be going on at this point?
http://forums.corvetteforum.com/c6-z...ce-please.html
In summary, I was burning oil at high RPM when the car was rev'd in neutral (not under load). My shop did a leak down and compression test which came back fine. After that we then went into the heads, which after inpsection needed new exhaust valves, seals, guides (basically a complete rebuild except for the Ti valves which were able to be saved). The guides and valves were shot, so we figured that was where the oil burning was coming from, and that I had potentially saved myself from an eventual dropped valve...or so I thought.
When I got the car back with the rebuilt heads, the smoke problem went away and the car ran smooth and strong, things were good. But, in the last couple hundred miles I noticed the car had burnt about 1.5 quarts of oil. Being suspicious, I did the rev test in neutral again and the cloud of oil smoke is back. WTF!!!
I gave her a jab on the throttle while driving down the road as well and now I can see a cloud of smoke under load (which never happened before). I have an elite catch can that is working great, no oil in the intake.
Not really happy after all the money I spent, any thoughts on what could be going on at this point?
12-30-2011, 03:52 PM
#2
Race Director
The question is what're you going to do, next. If it were me I'd be inclined to think the engine needed to be torn down, rebuilt. The mere thought of that would keep me awake at night. Really sorry to hear this, what a lousy break. I mean obviously you're burning oil, but from where? You've hit all the logical places, at great expense & aggravation.
Will BTTT your thread.
Hopefully the board's solid engine guys will catch it & chime in with something more substantive than me.
12-30-2011, 04:18 PM
#3
Former Vendor
Time to do a leak down test again and start back from the beginning.
12-30-2011, 05:19 PM
#4
The Consigliere
Member Since: May 2006
Location: 2023 Z06 & 2010 ZR1
Posts: 22,243
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2,268 Posts
I presume we can rule out the heads as a prob now.
I would think that would only leave worn rings as any sort of likely candidate.
At least you don't have to worry about your valvetrain for a good long time.
I would think that would only leave worn rings as any sort of likely candidate.
At least you don't have to worry about your valvetrain for a good long time.
12-30-2011, 07:20 PM
#5
Le Mans Master
Could the value stem seals be cut from install or loose? Just a thought value springs can cut seals also if they are weak.
z51vett
z51vett
12-31-2011, 01:21 AM
#7
Safety Car
Try installing a catch can on your pcv system. Pull your throttle body and look inside your intake with a light. See oil..?? A bunch of oil..??
These motors are great, but the emission recovery system is not doing it much good.
These motors are great, but the emission recovery system is not doing it much good.
12-31-2011, 08:59 AM
#8
Le Mans Master
Thread Starter
We put in new springs and seals in the rebuilt heads, also already have an elite catch can and there is no oil in the intake. Could they be loose, who knows, but 1.5 quarts in 200 miles loose...I doubt it. Leads me to think it needs new rings, but strange that is passes a compression and leakdown test.
12-31-2011, 10:46 AM
#9
Safety Car
We put in new springs and seals in the rebuilt heads, also already have an elite catch can and there is no oil in the intake. Could they be loose, who knows, but 1.5 quarts in 200 miles loose...I doubt it. Leads me to think it needs new rings, but strange that is passes a compression and leakdown test.
Is everything connected properly on your emissions system? Sucking oil somehow? I can see a gradual increase in oil consumption with wear but not like that. With oil burning that bad you should even be able to see which bank it is from by checking your exhaust for residue. Good start would be to pull the plugs.
12-31-2011, 11:18 AM
#10
I'd be interested in just exactly how the leak down test was done. Rarely is it done correctly..... oil into the combustion chamber through the valve seal/guides does not normally become evident under load, but during start.
Leak down testing is a somewhat finicky process that requires patience. Hell, I've had fresh builds that will show excessive leak by until I rock the piston back and forth on some of the low tension, tight ring pack builds.
Leak down testing is a somewhat finicky process that requires patience. Hell, I've had fresh builds that will show excessive leak by until I rock the piston back and forth on some of the low tension, tight ring pack builds.
12-31-2011, 11:34 AM
#11
Safety Car
I'd be interested in just exactly how the leak down test was done. Rarely is it done correctly..... oil into the combustion chamber through the valve seal/guides does not normally become evident under load, but during start.
Leak down testing is a somewhat finicky process that requires patience. Hell, I've had fresh builds that will show excessive leak by until I rock the piston back and forth on some of the low tension, tight ring pack builds.
Leak down testing is a somewhat finicky process that requires patience. Hell, I've had fresh builds that will show excessive leak by until I rock the piston back and forth on some of the low tension, tight ring pack builds.
12-31-2011, 12:19 PM
#12
.......unless the rings are toast. Which is why a leak down test should be done, and done correctly using a little math to determine leak rate (verse using the playschool method of green/red pass/fail) and listen for air to localize where it's going. Fifty bucks in parts to build a tester (or a hundred to buy one), a couple hours of labor - end of speculation.
If wanted, I can outline how to conduct a leak down test. I'm too lazy to do that unless some would like to hear how I do it - which is simply my method and not the only method.
If wanted, I can outline how to conduct a leak down test. I'm too lazy to do that unless some would like to hear how I do it - which is simply my method and not the only method.
12-31-2011, 01:31 PM
#13
Race Director
I've used my leakdown tester many times with accurat results. I bring the cylinder to be tested to tdc and pressurize.
12-31-2011, 06:37 PM
#14
Team Owner
.......unless the rings are toast. Which is why a leak down test should be done, and done correctly using a little math to determine leak rate (verse using the playschool method of green/red pass/fail) and listen for air to localize where it's going. Fifty bucks in parts to build a tester (or a hundred to buy one), a couple hours of labor - end of speculation.
If wanted, I can outline how to conduct a leak down test. I'm too lazy to do that unless some would like to hear how I do it - which is simply my method and not the only method.
If wanted, I can outline how to conduct a leak down test. I'm too lazy to do that unless some would like to hear how I do it - which is simply my method and not the only method.
DH
12-31-2011, 08:58 PM
#15
Safety Car
Generally speaking, smoke during acceleration is rings, smoking when you back out is guides, which you just did.
Did they replace the guides or just knurl them?
Have you actually pulled the TB and looked into the intake?
Just some ideas
Did they replace the guides or just knurl them?
Have you actually pulled the TB and looked into the intake?
Just some ideas
01-01-2012, 12:53 PM
#16
OK - here you go.......
There are three basic types of testers.
1) Single gauge that reads direct leak-down percentage.
2) Dual gauge that reads supply pressure, and also shows leak-down percentage rate.
3) Matched dual gauge that shows supply pressure and leak-down pressure.
#1 supplies air via regulator and you rely on the gauge and faith in the regulator to tell you if leak rate is green/good, yellow/marginal, red/fail. This gauge is what I would consider Playschool and best used by children. It is not accurate and tells you nothing of value. Think of it as a low oil pressure dummy light from the 70’s.
#2 uses two gauges, a regulator and an orifice between the two gauges. Ones gauge displays supply air pressure, the other is just like gauge #1. This is a step up from #1, but still not very informative.
#3 uses two matched gauges, typically 0-100 psig range, a regulator and an orifice between the two gauges. This is the only set up worth owning - in my opinion. I do not want an arbitrary pass/fail leak down rate determined for me.
When using the third type, the air supply gauge shows whatever pressure you have the regulator set to. You can choose to set any pressure you want; with the tester connected to the cylinder (dynamic) or with the tester not connected (static). It really doesn’t matter how you do this, but it is a bit simpler to set pressure to 100 psi with the tester connected. There is no universal standard for supply air pressure or the size of orifice used in the automotive world. The only standard that I am aware of is 80 psi air supply and .040” & .060” orifices sizes. These standards are for aircraft engines set by the FAA. The different orifice sizes are for engine size based on CID (larger orifice for larger CID – and I do not know the threshold). 80 psi works just fine for automotive engines and generally what I use. 100 psi takes the math out of this. I’ve tried it both ways and the results are always the same. 100 psi air pressure is easier to hear at the leak by area, but it does pose a bit of a problem if you want to test leak down with the piston in a position other than TDC (as it will roll the engine). 80 psi static is what I use, and it’ll roll the engine too so make sure you either block or remove your ratchet from the crank. If I wish to test the rings slight before or after TDC, I’ll drop the pressure to about 20 psi.
After the tester is connected and air pressure set (or left static), the orifice restricts flow between the supply air pressure gauge and the gauge connected to the cylinder. The cylinder gauge will show you just how effectively the engine is sealing the supplied air in the cylinder and combustion chamber. If the supply air pressure is set to 100 psi, and the second gauge shows 85 psi, the leak rate is 15% [100 - (85 X 100%) = leak down rate %]. Conversely, if supply air pressure is set to 80 psi and the cylinder gauge shows 72 psi, you just do a little math. 100 - (72 / 0.80) = 10%.
Leak-down testing will give you a good indication of the engine’s condition. As you test each cylinder, leak by air flow can be heard. If you hear it at the radiator or surge tank, you know you have a bad head gasket. Hear it in the header / ex manifold, you know your exhaust seat is leaking, hear it at the carb venturi or throttle body, the intake valve is leaking and if you hear it at the crank case breather vent (or wherever the engine’s crank case vent is), then you know the rings are leaking by.
Seeing how the automotive industry has no standard for acceptable leak down rate, this particular aspect becomes a bit muddy. Opinions vary. The FAA’s standard is 25% at 80 psi for piston type aircraft engines. That’s a good place to start. With gapped ringed builds, I like to see 10% or less on any sort of performance build. Above 15% and the engine needs a tear down and rebuild. For a stock daily driver type engine, 20% or less is preferable, while 30% would be the max. Anything above that would require tear down and overhaul. And that’s cold testing, as I haven’t had much luck testing them hot. I’m just not quick enough and the engine temp will change way too much from the first cylinder to the last (plus I don’t like to get burned). So, I just test them cold.
When I do test an engine, I have learned to roll the piston back and forth a bit at TDC to ‘load’ the rings. Rolling it back and forth a bit will get the rings to rock over and seat more like they would when the engine is actually running. This is especially important when testing engines with pistons will short skirts and tight ring packages.
As far as what tester to buy, I have a preference for Snap On, but they are expensive. Goodson also makes a nice tester I’ve had that’s reasonably priced.
If clarity is needed, please ask. I have not figured out what the appropriate level of information is on this forum to be ‘enough’, but not too much or too little.
Ragards and happy new year.
There are three basic types of testers.
1) Single gauge that reads direct leak-down percentage.
2) Dual gauge that reads supply pressure, and also shows leak-down percentage rate.
3) Matched dual gauge that shows supply pressure and leak-down pressure.
#1 supplies air via regulator and you rely on the gauge and faith in the regulator to tell you if leak rate is green/good, yellow/marginal, red/fail. This gauge is what I would consider Playschool and best used by children. It is not accurate and tells you nothing of value. Think of it as a low oil pressure dummy light from the 70’s.
#2 uses two gauges, a regulator and an orifice between the two gauges. Ones gauge displays supply air pressure, the other is just like gauge #1. This is a step up from #1, but still not very informative.
#3 uses two matched gauges, typically 0-100 psig range, a regulator and an orifice between the two gauges. This is the only set up worth owning - in my opinion. I do not want an arbitrary pass/fail leak down rate determined for me.
When using the third type, the air supply gauge shows whatever pressure you have the regulator set to. You can choose to set any pressure you want; with the tester connected to the cylinder (dynamic) or with the tester not connected (static). It really doesn’t matter how you do this, but it is a bit simpler to set pressure to 100 psi with the tester connected. There is no universal standard for supply air pressure or the size of orifice used in the automotive world. The only standard that I am aware of is 80 psi air supply and .040” & .060” orifices sizes. These standards are for aircraft engines set by the FAA. The different orifice sizes are for engine size based on CID (larger orifice for larger CID – and I do not know the threshold). 80 psi works just fine for automotive engines and generally what I use. 100 psi takes the math out of this. I’ve tried it both ways and the results are always the same. 100 psi air pressure is easier to hear at the leak by area, but it does pose a bit of a problem if you want to test leak down with the piston in a position other than TDC (as it will roll the engine). 80 psi static is what I use, and it’ll roll the engine too so make sure you either block or remove your ratchet from the crank. If I wish to test the rings slight before or after TDC, I’ll drop the pressure to about 20 psi.
After the tester is connected and air pressure set (or left static), the orifice restricts flow between the supply air pressure gauge and the gauge connected to the cylinder. The cylinder gauge will show you just how effectively the engine is sealing the supplied air in the cylinder and combustion chamber. If the supply air pressure is set to 100 psi, and the second gauge shows 85 psi, the leak rate is 15% [100 - (85 X 100%) = leak down rate %]. Conversely, if supply air pressure is set to 80 psi and the cylinder gauge shows 72 psi, you just do a little math. 100 - (72 / 0.80) = 10%.
Leak-down testing will give you a good indication of the engine’s condition. As you test each cylinder, leak by air flow can be heard. If you hear it at the radiator or surge tank, you know you have a bad head gasket. Hear it in the header / ex manifold, you know your exhaust seat is leaking, hear it at the carb venturi or throttle body, the intake valve is leaking and if you hear it at the crank case breather vent (or wherever the engine’s crank case vent is), then you know the rings are leaking by.
Seeing how the automotive industry has no standard for acceptable leak down rate, this particular aspect becomes a bit muddy. Opinions vary. The FAA’s standard is 25% at 80 psi for piston type aircraft engines. That’s a good place to start. With gapped ringed builds, I like to see 10% or less on any sort of performance build. Above 15% and the engine needs a tear down and rebuild. For a stock daily driver type engine, 20% or less is preferable, while 30% would be the max. Anything above that would require tear down and overhaul. And that’s cold testing, as I haven’t had much luck testing them hot. I’m just not quick enough and the engine temp will change way too much from the first cylinder to the last (plus I don’t like to get burned). So, I just test them cold.
When I do test an engine, I have learned to roll the piston back and forth a bit at TDC to ‘load’ the rings. Rolling it back and forth a bit will get the rings to rock over and seat more like they would when the engine is actually running. This is especially important when testing engines with pistons will short skirts and tight ring packages.
As far as what tester to buy, I have a preference for Snap On, but they are expensive. Goodson also makes a nice tester I’ve had that’s reasonably priced.
If clarity is needed, please ask. I have not figured out what the appropriate level of information is on this forum to be ‘enough’, but not too much or too little.
Ragards and happy new year.
01-01-2012, 01:02 PM
#17
Team Owner
OK - here you go.......
There are three basic types of testers.
1) Single gauge that reads direct leak-down percentage.
2) Dual gauge that reads supply pressure, and also shows leak-down percentage rate.
3) Matched dual gauge that shows supply pressure and leak-down pressure.
#1 supplies air via regulator and you rely on the gauge and faith in the regulator to tell you if leak rate is green/good, yellow/marginal, red/fail. This gauge is what I would consider Playschool and best used by children. It is not accurate and tells you nothing of value. Think of it as a low oil pressure dummy light from the 70’s.
#2 uses two gauges, a regulator and an orifice between the two gauges. Ones gauge displays supply air pressure, the other is just like gauge #1. This is a step up from #1, but still not very informative.
#3 uses two matched gauges, typically 0-100 psig range, a regulator and an orifice between the two gauges. This is the only set up worth owning - in my opinion. I do not want an arbitrary pass/fail leak down rate determined for me.
When using the third type, the air supply gauge shows whatever pressure you have the regulator set to. You can choose to set any pressure you want; with the tester connected to the cylinder (dynamic) or with the tester not connected (static). It really doesn’t matter how you do this, but it is a bit simpler to set pressure to 100 psi with the tester connected. There is no universal standard for supply air pressure or the size of orifice used in the automotive world. The only standard that I am aware of is 80 psi air supply and .040” & .060” orifices sizes. These standards are for aircraft engines set by the FAA. The different orifice sizes are for engine size based on CID (larger orifice for larger CID – and I do not know the threshold). 80 psi works just fine for automotive engines and generally what I use. 100 psi takes the math out of this. I’ve tried it both ways and the results are always the same. 100 psi air pressure is easier to hear at the leak by area, but it does pose a bit of a problem if you want to test leak down with the piston in a position other than TDC (as it will roll the engine). 80 psi static is what I use, and it’ll roll the engine too so make sure you either block or remove your ratchet from the crank. If I wish to test the rings slight before or after TDC, I’ll drop the pressure to about 20 psi.
After the tester is connected and air pressure set (or left static), the orifice restricts flow between the supply air pressure gauge and the gauge connected to the cylinder. The cylinder gauge will show you just how effectively the engine is sealing the supplied air in the cylinder and combustion chamber. If the supply air pressure is set to 100 psi, and the second gauge shows 85 psi, the leak rate is 15% [100 - (85 X 100%) = leak down rate %]. Conversely, if supply air pressure is set to 80 psi and the cylinder gauge shows 72 psi, you just do a little math. 100 - (72 / 0.80) = 10%.
Leak-down testing will give you a good indication of the engine’s condition. As you test each cylinder, leak by air flow can be heard. If you hear it at the radiator or surge tank, you know you have a bad head gasket. Hear it in the header / ex manifold, you know your exhaust seat is leaking, hear it at the carb venturi or throttle body, the intake valve is leaking and if you hear it at the crank case breather vent (or wherever the engine’s crank case vent is), then you know the rings are leaking by.
Seeing how the automotive industry has no standard for acceptable leak down rate, this particular aspect becomes a bit muddy. Opinions vary. The FAA’s standard is 25% at 80 psi for piston type aircraft engines. That’s a good place to start. With gapped ringed builds, I like to see 10% or less on any sort of performance build. Above 15% and the engine needs a tear down and rebuild. For a stock daily driver type engine, 20% or less is preferable, while 30% would be the max. Anything above that would require tear down and overhaul. And that’s cold testing, as I haven’t had much luck testing them hot. I’m just not quick enough and the engine temp will change way too much from the first cylinder to the last (plus I don’t like to get burned). So, I just test them cold.
When I do test an engine, I have learned to roll the piston back and forth a bit at TDC to ‘load’ the rings. Rolling it back and forth a bit will get the rings to rock over and seat more like they would when the engine is actually running. This is especially important when testing engines with pistons will short skirts and tight ring packages.
As far as what tester to buy, I have a preference for Snap On, but they are expensive. Goodson also makes a nice tester I’ve had that’s reasonably priced.
If clarity is needed, please ask. I have not figured out what the appropriate level of information is on this forum to be ‘enough’, but not too much or too little.
Ragards and happy new year.
There are three basic types of testers.
1) Single gauge that reads direct leak-down percentage.
2) Dual gauge that reads supply pressure, and also shows leak-down percentage rate.
3) Matched dual gauge that shows supply pressure and leak-down pressure.
#1 supplies air via regulator and you rely on the gauge and faith in the regulator to tell you if leak rate is green/good, yellow/marginal, red/fail. This gauge is what I would consider Playschool and best used by children. It is not accurate and tells you nothing of value. Think of it as a low oil pressure dummy light from the 70’s.
#2 uses two gauges, a regulator and an orifice between the two gauges. Ones gauge displays supply air pressure, the other is just like gauge #1. This is a step up from #1, but still not very informative.
#3 uses two matched gauges, typically 0-100 psig range, a regulator and an orifice between the two gauges. This is the only set up worth owning - in my opinion. I do not want an arbitrary pass/fail leak down rate determined for me.
When using the third type, the air supply gauge shows whatever pressure you have the regulator set to. You can choose to set any pressure you want; with the tester connected to the cylinder (dynamic) or with the tester not connected (static). It really doesn’t matter how you do this, but it is a bit simpler to set pressure to 100 psi with the tester connected. There is no universal standard for supply air pressure or the size of orifice used in the automotive world. The only standard that I am aware of is 80 psi air supply and .040” & .060” orifices sizes. These standards are for aircraft engines set by the FAA. The different orifice sizes are for engine size based on CID (larger orifice for larger CID – and I do not know the threshold). 80 psi works just fine for automotive engines and generally what I use. 100 psi takes the math out of this. I’ve tried it both ways and the results are always the same. 100 psi air pressure is easier to hear at the leak by area, but it does pose a bit of a problem if you want to test leak down with the piston in a position other than TDC (as it will roll the engine). 80 psi static is what I use, and it’ll roll the engine too so make sure you either block or remove your ratchet from the crank. If I wish to test the rings slight before or after TDC, I’ll drop the pressure to about 20 psi.
After the tester is connected and air pressure set (or left static), the orifice restricts flow between the supply air pressure gauge and the gauge connected to the cylinder. The cylinder gauge will show you just how effectively the engine is sealing the supplied air in the cylinder and combustion chamber. If the supply air pressure is set to 100 psi, and the second gauge shows 85 psi, the leak rate is 15% [100 - (85 X 100%) = leak down rate %]. Conversely, if supply air pressure is set to 80 psi and the cylinder gauge shows 72 psi, you just do a little math. 100 - (72 / 0.80) = 10%.
Leak-down testing will give you a good indication of the engine’s condition. As you test each cylinder, leak by air flow can be heard. If you hear it at the radiator or surge tank, you know you have a bad head gasket. Hear it in the header / ex manifold, you know your exhaust seat is leaking, hear it at the carb venturi or throttle body, the intake valve is leaking and if you hear it at the crank case breather vent (or wherever the engine’s crank case vent is), then you know the rings are leaking by.
Seeing how the automotive industry has no standard for acceptable leak down rate, this particular aspect becomes a bit muddy. Opinions vary. The FAA’s standard is 25% at 80 psi for piston type aircraft engines. That’s a good place to start. With gapped ringed builds, I like to see 10% or less on any sort of performance build. Above 15% and the engine needs a tear down and rebuild. For a stock daily driver type engine, 20% or less is preferable, while 30% would be the max. Anything above that would require tear down and overhaul. And that’s cold testing, as I haven’t had much luck testing them hot. I’m just not quick enough and the engine temp will change way too much from the first cylinder to the last (plus I don’t like to get burned). So, I just test them cold.
When I do test an engine, I have learned to roll the piston back and forth a bit at TDC to ‘load’ the rings. Rolling it back and forth a bit will get the rings to rock over and seat more like they would when the engine is actually running. This is especially important when testing engines with pistons will short skirts and tight ring packages.
As far as what tester to buy, I have a preference for Snap On, but they are expensive. Goodson also makes a nice tester I’ve had that’s reasonably priced.
If clarity is needed, please ask. I have not figured out what the appropriate level of information is on this forum to be ‘enough’, but not too much or too little.
Ragards and happy new year.
DH
01-26-2019, 01:45 PM
#20
Drifting
Member Since: Nov 2006
Location: Sierra Mtns. The Great State Of Jefferson
Posts: 1,810
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You could always just ask for the receipts if he does say he rebuilt it. Not everyone wants to rip you off. Like President Reagan said, "Trust but verify".