puff of blue smoke at higher rpm decel

[MadBill]

What happened ? A lot of replies have suddenly vanished

Similar comments in a number of threads. Here's mine: https://www.speed-talk.com/forum/viewtopic.php?f=12&t=49981

[Belgian1979]

What happened ? A lot of replies have suddenly vanished

Similar comments in a number of threads. Here's mine: https://www.speed-talk.com/forum/viewtopic.php?f=12&t=49981

Thanks Bill, I was suspecting something like that.

[Belgian1979]

I'm not going to repeat what has been posted in between.

Today I went out for a new drive with repeated accels and decels up to about 5500 rpm. There still is some blue smoke but notably less. I also saw some smoke on accel, but I cannot be sure that it's because of being too rich as the Accel enrichment hasn't been properly tuned and to combat a number of issues I put a fair amount of fuel in it on accel. It did not seem to be blue.
Something remarkable, but difficult to actually assess, was that it sometimes seemed to only smoke on the right or left side. I then did a decel in a turn and it seemed to smoke on the outside corner, but these things are sometimes difficult to actually assess properly.
I also noted that when it smokes I also have exhaust popping. However this has always been like that, so I'm not sure if there is any causal relation.

Next test, I will shut off the AE and see what it does on acceleration.

[Newold1]

This is starting to sound more like a case for oil control and associated windage possibly overcoming the rings ability to control oil excesses on the cylinder walls especially with the higher g-forces of cornering?

[BrazilianZ28Camaro]

Yves, how much oil you have in the engine and what is the oilpan plus filter capacity?

[Belgian1979]

This is a Canton RR pan with kickouts (15-240T). The pan is specified as a 7 quart system capacity pan. Windage has been an issue in the past where at one time I took out the pan, and added a screen to the side of the windage tray and actually measured pan content because oil level was too high in the factory setting. The content now is about 4,5 liter filled. Add another quart for the filter and then there is the canton accusump. I think that holds another 1,5 liter. The valve on the accusump is a 35-40 unit so it only releases oil when the oil pressure gets below 35 psi. During driving even high rpm, it never goes below 60 psi and usually is 65 psi. During that last run the logs show oil pressure as being 65 psi at a point where I was decelerating from 5400 rpm and I had some blue smoke.
The turns were not that hard so that the G's would be that high.

[ptuomov]

Isn't a breather system issue by far the most likely reason for this oil smoke? How about disconnecting the breather system from the intake altogether and running it into a large empty Gatorade bottle (or two). Then driving around doing a little high-rpm engine braking in turns to get the residual oil sucked out of the intake cavity. If it the smoking is reduced and later eliminated by doing that, while the Gatorade bottles have some oil in them, then one can probably conclude it was the breather system. Right?

[BrazilianZ28Camaro]

This is a Canton RR pan with kickouts (15-240T). The pan is specified as a 7 quart system capacity pan. Windage has been an issue in the past where at one time I took out the pan, and added a screen to the side of the windage tray and actually measured pan content because oil level was too high in the factory setting. The content now is about 4,5 liter filled. Add another quart for the filter and then there is the canton accusump. I think that holds another 1,5 liter. The valve on the accusump is a 35-40 unit so it only releases oil when the oil pressure gets below 35 psi. During driving even high rpm, it never goes below 60 psi and usually is 65 psi. During that last run the logs show oil pressure as being 65 psi at a point where I was decelerating from 5400 rpm and I had some blue smoke.
The turns were not that hard so that the G's would be that high.

The oil volume seems right for the engine, but just to make sure the accusump is working right and isn't overfilling the engine and heads, can you close it full and do another test?

[Belgian1979]

Isn't a breather system issue by far the most likely reason for this oil smoke? How about disconnecting the breather system from the intake altogether and running it into a large empty Gatorade bottle (or two). Then driving around doing a little high-rpm engine braking in turns to get the residual oil sucked out of the intake cavity. If it the smoking is reduced and later eliminated by doing that, while the Gatorade bottles have some oil in them, then one can probably conclude it was the breather system. Right?

I understand what you mean. However, the breather for fresh air is inside the airbox over the left valve cover (feeding the right cylinder bank). The pcv valve is on the right valve cover and below the airbox. So in the normal situation the air circulated through the engine would come through the left airbox and would go via the pcv to the vacuum chamber.
I can take off the air tube and see right into the airbox and that way I can see the inside and the breather without much disassembly. The air box is completly dry. So no oil comes splashing out (if that would even be possible because there is filtration in the breather). The breather is the Edelbrock unit that normally goes onto the valve covers.

Here is a photo of the air box and breather when the box was under construction.



Photo of the pcv valve with and without air box :




Manifold, in between the X of the runners is where the vacuum chamber is :

[Belgian1979]

This is a Canton RR pan with kickouts (15-240T). The pan is specified as a 7 quart system capacity pan. Windage has been an issue in the past where at one time I took out the pan, and added a screen to the side of the windage tray and actually measured pan content because oil level was too high in the factory setting. The content now is about 4,5 liter filled. Add another quart for the filter and then there is the canton accusump. I think that holds another 1,5 liter. The valve on the accusump is a 35-40 unit so it only releases oil when the oil pressure gets below 35 psi. During driving even high rpm, it never goes below 60 psi and usually is 65 psi. During that last run the logs show oil pressure as being 65 psi at a point where I was decelerating from 5400 rpm and I had some blue smoke.
The turns were not that hard so that the G's would be that high.

The oil volume seems right for the engine, but just to make sure the accusump is working right and isn't overfilling the engine and heads, can you close it full and do another test?

Yes, I can disconnect the electric valve.

[BrazilianZ28Camaro]

I understand what you mean. However, the breather for fresh air is inside the airbox over the left valve cover (feeding the right cylinder bank). The pcv valve is on the right valve cover and below the airbox. So in the normal situation the air circulated through the engine would come through the left airbox and would go via the pcv to the vacuum chamber.
I can take off the air tube and see right into the airbox and that way I can see the inside and the breather without much disassembly. The air box is completly dry. So no oil comes splashing out (if that would even be possible because there is filtration in the breather). The breather is the Edelbrock unit that normally goes onto the valve covers.

Here is a photo of the air box and breather when the box was under construction.

Do a simple test Yves, put your fingers under this valve cover breather above, if its oily, there's your problem.

Is very common the crankcase pressure increase with some mileage and make oil spit through this type of breather, altough its bafled and filtered.

Oil might be entering directly into the throttles off the breather.

[Belgian1979]

I don't see oil being sucked in by the engine and not showing any traces in the air box, but who knows.

[BrazilianZ28Camaro]

I don't see oil being sucked in by the engine and not showing any traces in the air box, but who knows.

You could run the air box open and put a hose in the breather's place with the open end away for the intake tract to test.

Ive seen several SBCs with this short cap style breathers do not spit oil when new, but as soon as they run around 3000 miles old, they start to drop oil there, and the engines are still mechanically sound.

[Belgian1979]

I checked it but it's rather dry. The sponge and filter mat above it also.

While driving it did it again, this time with new plugs .They were loaded a little and the AE was set at off, so this is clearly oil contamination.
Only things I can see are the seals, the bolts from the shaft rockers or the rings.

No smoke on acceleration though. The puff is also associated with a some exhaust backfiring. Not sure if there is a causality between that and blue smoke though.

[BrazilianZ28Camaro]

I checked it but it's rather dry. The sponge and filter mat above it also.

While driving it did it again, this time with new plugs .They were loaded a little and the AE was set at off, so this is clearly oil contamination.
Only things I can see are the seals, the bolts from the shaft rockers or the rings.

No smoke on acceleration though. The puff is also associated with a some exhaust backfiring. Not sure if there is a causality between that and blue smoke though.

So, you can unbolt the headers and have a good look at the exaust valves. Oil burnt will be easily spoted.