Crankcase ventilation problem
05-04-2019, 06:42 PM
#41
Le Mans Master
Exactly. And a plenty big enough hole that any combustion gases that get below the pistons or above the valve guides will pass right through that open hole to atmosphere with no restriction - thus no pressure develops.
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05-04-2019, 08:13 PM
#42
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Can't see it from the top with the alternator in the way.
However, I was looking at both carbs and at the base of each of them in the front there is an open nipple that with the engine running draw no air into them. The pcv hose at the back is plumbed to a fitting that is in the same base of the carb as both nipples. Maybe there is no vacuum there? It is screwed in there and the shielding is in the way so I did not remove it to see.
However, I was looking at both carbs and at the base of each of them in the front there is an open nipple that with the engine running draw no air into them. The pcv hose at the back is plumbed to a fitting that is in the same base of the carb as both nipples. Maybe there is no vacuum there? It is screwed in there and the shielding is in the way so I did not remove it to see.
05-05-2019, 07:12 AM
#43
Team Owner
Can't see it from the top with the alternator in the way.
However, I was looking at both carbs and at the base of each of them in the front there is an open nipple that with the engine running draw no air into them. The pcv hose at the back is plumbed to a fitting that is in the same base of the carb as both nipples. Maybe there is no vacuum there? It is screwed in there and the shielding is in the way so I did not remove it to see.
However, I was looking at both carbs and at the base of each of them in the front there is an open nipple that with the engine running draw no air into them. The pcv hose at the back is plumbed to a fitting that is in the same base of the carb as both nipples. Maybe there is no vacuum there? It is screwed in there and the shielding is in the way so I did not remove it to see.
05-05-2019, 08:50 AM
#44
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Hmm, a nipple in a carb base with no vacuum is very unusual. Are you sure it’s not ported vacuum? An open nipple even if not drilled through would bother me and have a vacuum cap just for piece of mind.
This is a very interesting problem as a new engine should not have crankcase pressure issues, particularly significant enough to create oil leaks. I’m sure your mechanic is competent and has diagnosed the issue properly. Again, are you sure the pcv valve is oriented properly to allow manifold vacuum to draw crankcase gases out of the engine?
This is a very interesting problem as a new engine should not have crankcase pressure issues, particularly significant enough to create oil leaks. I’m sure your mechanic is competent and has diagnosed the issue properly. Again, are you sure the pcv valve is oriented properly to allow manifold vacuum to draw crankcase gases out of the engine?
05-05-2019, 02:52 PM
#45
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Hmm, a nipple in a carb base with no vacuum is very unusual. Are you sure it’s not ported vacuum? An open nipple even if not drilled through would bother me and have a vacuum cap just for piece of mind.
This is a very interesting problem as a new engine should not have crankcase pressure issues, particularly significant enough to create oil leaks. I’m sure your mechanic is competent and has diagnosed the issue properly. Again, are you sure the pcv valve is oriented properly to allow manifold vacuum to draw crankcase gases out of the engine?
This is a very interesting problem as a new engine should not have crankcase pressure issues, particularly significant enough to create oil leaks. I’m sure your mechanic is competent and has diagnosed the issue properly. Again, are you sure the pcv valve is oriented properly to allow manifold vacuum to draw crankcase gases out of the engine?
My mistake. After closer inspection with magnifying glass and flashlight they are adjustment screws. Boy my eyes are getting bad. Now you know why I no longer do my own work.
Here is a picture of the rear of the rear carb were it is plumbed to the draft tube hole.
05-05-2019, 03:46 PM
#46
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The photo helps, as that brass elbow is not a 63' style screw in PVC valve. This is important because your crankcase inlet at the oil fill tube (vented cap) and the crankcase outlet at the draft tube tomato can is the same as the 63' PVC system (and the airflow is backwards from later year PVC systems).
The photo provides evidence that you should have an in-line PVC valve somewhere in the hose between the brass elbow and the tomato can port at the back of the block. The PVC valve can be installed backwards, as mentioned in post 19, so verify the PVC valve restricted airflow direction is correct. The PVC valve is a 0.090 restriction with high vacuum, and closes tight with intake manifold pressure (like during a backfire).
The tests mentioned in post 18 can be enhanced by blocking the oil fill and measuring the resulting vacuum at the dip stick tube at idle with a vacuum gauge and hose (wrap electrical tape around the vacuum hose end to make it large enough for a tight seal inside the dipstick tube end). Don't expect a vacuum gauge at the dipstick tube to read much more than an inch or two of vacuum, but it should read something. If it does not move the vacuum gauge needle, you have confirmed a bigger leak somewhere.
A big misconception with a PVC system is that it pulls vacuum at all engine speeds and throttle positions. The intake manifold and PVC vacuum drops as the throttle plates open, and you have less crankcase scavenging as the throttle plates open (less PVC effect). If you are in the throttle a lot, the blow by pressure will quickly exceed the (reduced open throttle) intake manifold vacuum. You can test this with a long hose from a manifold vacuum port (or tee) to a vacuum gauge located in sight of the drivers seat, and driving the car while monitoring the vacuum swings. Idle and low load cruising should show high vacuum, and WOT fun should drop the vacuum reading (and quickly return to high vacuum decelerating). If you move the vacuum hose to read at the dipstick tube, with the breather cap removed and oil fill tube blocked, you can carefully monitor the crankcase vacuum and pressure as you throttle engine (be careful because extended WOT with no breather vent cap can build excessive crankcase pressure and blow gaskets).
Most engines that see a lot of throttle fun tend to spit oil out the crankcase inlet vent (at the breather cap on the oil fill tube in your configuration, or the air filter housing hose in the stock 63' system). The reports that you do not see oil at the breather cap and down the oil fill tube to discolor and collect dirt on the manifold, locations high on the engine, counter the premise of excessive high crankcase pressure.
Look for oil, and do a few vacuum tests, but do not rule out poor gasket and seal sealing.
05-05-2019, 04:16 PM
#47
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The photo helps, as that brass elbow is not a 63' style screw in PVC valve. This is important because your crankcase inlet at the oil fill tube (vented cap) and the crankcase outlet at the draft tube tomato can is the same as the 63' PVC system (and the airflow is backwards from later year PVC systems).
The photo provides evidence that you should have an in-line PVC valve somewhere in the hose between the brass elbow and the tomato can port at the back of the block. The PVC valve can be installed backwards, as mentioned in post 19, so verify the PVC valve restricted airflow direction is correct. The PVC valve is a 0.090 restriction with high vacuum, and closes tight with intake manifold pressure (like during a backfire).
The tests mentioned in post 18 can be enhanced by blocking the oil fill and measuring the resulting vacuum at the dip stick tube at idle with a vacuum gauge and hose (wrap electrical tape around the vacuum hose end to make it large enough for a tight seal inside the dipstick tube end). Don't expect a vacuum gauge at the dipstick tube to read much more than an inch or two of vacuum, but it should read something. If it does not move the vacuum gauge needle, you have confirmed a bigger leak somewhere.
A big misconception with a PVC system is that it pulls vacuum at all engine speeds and throttle positions. The intake manifold and PVC vacuum drops as the throttle plates open, and you have less crankcase scavenging as the throttle plates open (less PVC effect). If you are in the throttle a lot, the blow by pressure will quickly exceed the (reduced open throttle) intake manifold vacuum. You can test this with a long hose from a manifold vacuum port (or tee) to a vacuum gauge located in sight of the drivers seat, and driving the car while monitoring the vacuum swings. Idle and low load cruising should show high vacuum, and WOT fun should drop the vacuum reading (and quickly return to high vacuum decelerating). If you move the vacuum hose to read at the dipstick tube, with the breather cap removed and oil fill tube blocked, you can carefully monitor the crankcase vacuum and pressure as you throttle engine (be careful because extended WOT with no breather vent cap can build excessive crankcase pressure and blow gaskets).
Most engines that see a lot of throttle fun tend to spit oil out the crankcase inlet vent (at the breather cap on the oil fill tube in your configuration, or the air filter housing hose in the stock 63' system). The reports that you do not see oil at the breather cap and down the oil fill tube to discolor and collect dirt on the manifold, locations high on the engine, counter the premise of excessive high crankcase pressure.
Look for oil, and do a few vacuum tests, but do not rule out poor gasket and seal sealing.
The photo provides evidence that you should have an in-line PVC valve somewhere in the hose between the brass elbow and the tomato can port at the back of the block. The PVC valve can be installed backwards, as mentioned in post 19, so verify the PVC valve restricted airflow direction is correct. The PVC valve is a 0.090 restriction with high vacuum, and closes tight with intake manifold pressure (like during a backfire).
The tests mentioned in post 18 can be enhanced by blocking the oil fill and measuring the resulting vacuum at the dip stick tube at idle with a vacuum gauge and hose (wrap electrical tape around the vacuum hose end to make it large enough for a tight seal inside the dipstick tube end). Don't expect a vacuum gauge at the dipstick tube to read much more than an inch or two of vacuum, but it should read something. If it does not move the vacuum gauge needle, you have confirmed a bigger leak somewhere.
A big misconception with a PVC system is that it pulls vacuum at all engine speeds and throttle positions. The intake manifold and PVC vacuum drops as the throttle plates open, and you have less crankcase scavenging as the throttle plates open (less PVC effect). If you are in the throttle a lot, the blow by pressure will quickly exceed the (reduced open throttle) intake manifold vacuum. You can test this with a long hose from a manifold vacuum port (or tee) to a vacuum gauge located in sight of the drivers seat, and driving the car while monitoring the vacuum swings. Idle and low load cruising should show high vacuum, and WOT fun should drop the vacuum reading (and quickly return to high vacuum decelerating). If you move the vacuum hose to read at the dipstick tube, with the breather cap removed and oil fill tube blocked, you can carefully monitor the crankcase vacuum and pressure as you throttle engine (be careful because extended WOT with no breather vent cap can build excessive crankcase pressure and blow gaskets).
Most engines that see a lot of throttle fun tend to spit oil out the crankcase inlet vent (at the breather cap on the oil fill tube in your configuration, or the air filter housing hose in the stock 63' system). The reports that you do not see oil at the breather cap and down the oil fill tube to discolor and collect dirt on the manifold, locations high on the engine, counter the premise of excessive high crankcase pressure.
Look for oil, and do a few vacuum tests, but do not rule out poor gasket and seal sealing.
Thanks for the info. There is a pcv valve between the fitting shown and the draft tube hole. Mechanic has checked the pcv valve for correct direction but I will give him this info.
05-05-2019, 06:29 PM
#48
The photo helps, as that brass elbow is not a 63' style screw in PVC valve. This is important because your crankcase inlet at the oil fill tube (vented cap) and the crankcase outlet at the draft tube tomato can is the same as the 63' PVC system (and the airflow is backwards from later year PVC systems).
The photo provides evidence that you should have an in-line PVC valve somewhere in the hose between the brass elbow and the tomato can port at the back of the block. The PVC valve can be installed backwards, as mentioned in post 19, so verify the PVC valve restricted airflow direction is correct. The PVC valve is a 0.090 restriction with high vacuum, and closes tight with intake manifold pressure (like during a backfire).
The tests mentioned in post 18 can be enhanced by blocking the oil fill and measuring the resulting vacuum at the dip stick tube at idle with a vacuum gauge and hose (wrap electrical tape around the vacuum hose end to make it large enough for a tight seal inside the dipstick tube end). Don't expect a vacuum gauge at the dipstick tube to read much more than an inch or two of vacuum, but it should read something. If it does not move the vacuum gauge needle, you have confirmed a bigger leak somewhere.
A big misconception with a PVC system is that it pulls vacuum at all engine speeds and throttle positions. The intake manifold and PVC vacuum drops as the throttle plates open, and you have less crankcase scavenging as the throttle plates open (less PVC effect). If you are in the throttle a lot, the blow by pressure will quickly exceed the (reduced open throttle) intake manifold vacuum. You can test this with a long hose from a manifold vacuum port (or tee) to a vacuum gauge located in sight of the drivers seat, and driving the car while monitoring the vacuum swings. Idle and low load cruising should show high vacuum, and WOT fun should drop the vacuum reading (and quickly return to high vacuum decelerating). If you move the vacuum hose to read at the dipstick tube, with the breather cap removed and oil fill tube blocked, you can carefully monitor the crankcase vacuum and pressure as you throttle engine (be careful because extended WOT with no breather vent cap can build excessive crankcase pressure and blow gaskets).
Most engines that see a lot of throttle fun tend to spit oil out the crankcase inlet vent (at the breather cap on the oil fill tube in your configuration, or the air filter housing hose in the stock 63' system). The reports that you do not see oil at the breather cap and down the oil fill tube to discolor and collect dirt on the manifold, locations high on the engine, counter the premise of excessive high crankcase pressure.
Look for oil, and do a few vacuum tests, but do not rule out poor gasket and seal sealing.
The photo provides evidence that you should have an in-line PVC valve somewhere in the hose between the brass elbow and the tomato can port at the back of the block. The PVC valve can be installed backwards, as mentioned in post 19, so verify the PVC valve restricted airflow direction is correct. The PVC valve is a 0.090 restriction with high vacuum, and closes tight with intake manifold pressure (like during a backfire).
The tests mentioned in post 18 can be enhanced by blocking the oil fill and measuring the resulting vacuum at the dip stick tube at idle with a vacuum gauge and hose (wrap electrical tape around the vacuum hose end to make it large enough for a tight seal inside the dipstick tube end). Don't expect a vacuum gauge at the dipstick tube to read much more than an inch or two of vacuum, but it should read something. If it does not move the vacuum gauge needle, you have confirmed a bigger leak somewhere.
A big misconception with a PVC system is that it pulls vacuum at all engine speeds and throttle positions. The intake manifold and PVC vacuum drops as the throttle plates open, and you have less crankcase scavenging as the throttle plates open (less PVC effect). If you are in the throttle a lot, the blow by pressure will quickly exceed the (reduced open throttle) intake manifold vacuum. You can test this with a long hose from a manifold vacuum port (or tee) to a vacuum gauge located in sight of the drivers seat, and driving the car while monitoring the vacuum swings. Idle and low load cruising should show high vacuum, and WOT fun should drop the vacuum reading (and quickly return to high vacuum decelerating). If you move the vacuum hose to read at the dipstick tube, with the breather cap removed and oil fill tube blocked, you can carefully monitor the crankcase vacuum and pressure as you throttle engine (be careful because extended WOT with no breather vent cap can build excessive crankcase pressure and blow gaskets).
Most engines that see a lot of throttle fun tend to spit oil out the crankcase inlet vent (at the breather cap on the oil fill tube in your configuration, or the air filter housing hose in the stock 63' system). The reports that you do not see oil at the breather cap and down the oil fill tube to discolor and collect dirt on the manifold, locations high on the engine, counter the premise of excessive high crankcase pressure.
Look for oil, and do a few vacuum tests, but do not rule out poor gasket and seal sealing.
05-05-2019, 07:18 PM
#49
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That's the way it's supposed to work. At some point though, a worn out engine will puff harder than the PVC can suck.