hello, my 74 continues to burn oil. She smokes a little going down the road and it is time to fix. It has 53,000 original miles. I'm wondering if it is the piston rings letting the oil get past, or the valve guides?? I did a compression check and all were between 130-140. I just replaced the pushroads and lifters, and the valves were out of adjustment so I thought that might have something to do with the oil burning. But it was not. If I pull off the heads, will I be able to tell for sure that it is the guides or the rings?? Also, I'm looking for some more horsepower, is it worthless to think that I can get 400+ with my current 8.25:1 compression ratio? I have a 69 intake, hooker headers, msd ignition, 3 inch dual exhaust. Thank you in advance!!

Just some quick thoughts,make sure the PCV system is working properly and not allowing oil backup into the air cleaner.This is stressing my memory so I'm sure the heavy hitters on the forum will back me up, or correct me if I'm wrong,but I believe valve guide wear or valve seal problems will show up more when you first start the car or when you decelerate after revving (when the vacuum is highest).Oil control rings on the pistons can still be worn and permit smoking even though the compression rings are good enough to give you near normal compression readings.I believe you will see this smoking more when you punch the accelerator.Are you sure your getting oil smoke?
Jules

my 73/350 used to smoke Alot, i thought my rings were shot to. but i just changed the heads to vortec style and new vortec intake and the smoke was gone. the valve guides and seals were bad. thank god, i realy did not want to pull engine in the summer ! good luck

Small block Chevies are known for wearing out valve seals, particularly if they sit a lot. At the relatively low mileage of your car, it's doubtful that your rings are worn outside of poor maintenance over the years. It's simply most likely your motor suffers from valve seals being worn from lack of use, allowing the seals to dry out over time.

A buddy of mine with a '92 LT1 Vette had to replace the seals at about 25K miles due to it sitting so much. Not an uncommon problem.

82collectorshark said: Just some quick thoughts,make sure the PCV system is working properly and not allowing oil backup into the air cleaner.This is stressing my memory so I'm sure the heavy hitters on the forum will back me up, or correct me if I'm wrong,but I believe valve guide wear or valve seal problems will show up more when you first start the car or when you decelerate after revving (when the vacuum is highest).Oil control rings on the pistons can still be worn and permit smoking even though the compression rings are good enough to give you near normal compression readings.I believe you will see this smoking more when you punch the accelerator.Are you sure your getting oil smoke? Jules

I agree on the vavle seals.. unless it is a constant smoke.. if it smokes whether in accel/decel, fast or slow.. its rings..

hello, first off the car is a 454, i don't know whether this makes a difference as far as valve guide wear, since a couple of you said it was not uncommon in small blocks, i'm not sure if it's common in big blocks as well?? The car sat before I bought it for 7 years. While driving down the freeway there is no visible smoke, however, if I check the oil after a tank of fuel, it is noticably lower. Probly a half a quart. As far as pcv, I have a pcv valve coming from each valve cover and into the carb?? I hope this is correct. I don't know how to check whether they are functioning properly though. Any help would be much appreciated, this is something i'd definitely like to take care of. Also you can smell the car idling or if you're following it.

well.. you should not have a pcv running to both valve covers.. one should have a pcv valve and the other a breather.

the pcv system is an airflow mechanism.

the vacuum port on your carb provides the suction, the breather on the other side provides the air intake..

they should always be on opposite ends of the engine (ie one in front, one in back... on opposite sides.

example: I have a breather on the passenger side valve cover at the rear of the engine. The PCV valve is in the drivers side cover at the front.

if you have a pcv vavle in each, you have no fresh air coming in and no airflow and therefore you are pulling the oil into the carb and intake.

think of it like an attic fan. if you open a window five feet away from your attic fan.. you have a great airflow for the five feet necessary for the air to come in the window and into the fan. if you open a window on the opposite end of the house it pulls air through the whole house. if you turn on the attic fan with no window open there is no airflow at all.

in your engine the pcv does this to flush the foul oily engine air out and bring clean air in.

I think you hit on something there Ben,two PCV valves is absolutely not right.Rectify that situation first before anything else.
Jules

Yhank you, I'm going to take care of that first thing tomorrow, I'll let you know what happens. Hopefully that takes care of it. Thanks again.

The PCV is Positive Crankcase Ventilation.
It's purpose is to keep a positive flow of fresh air through out the engine. This vents blow by gasses, and removes moisture and acids from the engine.

One valve is connected through a vacuum hose directly to a manifold vacuum. This attaches to one valve cover. The other valve cover has a inlet air vent. This can either come from the air cleaner, or have it's own intake filter.

The PCV valve is a calibrated vacuum leak that changes it flow rate depending on engine vacuum. At high manifold vacuum (idle and decell) it pulls a smaller amount of air from the crankcase. More air would lean out the engine and cause running problems. But under these conditions there is not as much blowby in the engine, so that's all it needs.

When you open the throttle, there is more blowby due to cylinder pressure. There is also a drop in intake vacuum. Due to PCV design, this causes more flow, which is not needed, and during a point due to throttle opening, the engine can handle more flow.

The valve is a spring loaded tapered pintle. High vacuum pulls the valve against a spring, and the larger taper of the pintle restricts the valve opening. With less vacuum, the spring pushes the pintle back, and unrestricts the opening.

If the PCV does not flow enough, the crankcase and oil become very dirty faster. The engine builds sludge, moisture and acid. All bad. If it flows too much it will suck oil in the intake, and burn it. If it does not flow at all to the manifold, but the vent is open, it blows oil back into the air cleaner or intake vent filter. Makes a heck of a mess when it gets real bad.
Completely blocked will create a lot of crankcase pressure, and cause oil to leak from the seals, gaskets, and anywhere it can.

In a properly working system, you can take the oil fill cap off with the engine running. Place a piece of paper over the opening. You will note the paper tends to puff back and forth. This is from blowby pressures. Hold the paper securely over the hole, and rev the engine to about 2000 rpm and hold it for about 15 or 20 seconds. You should now have slight vacuum which will now hold the paper in place. Unless the cooling fan blows it away. But you can still hold it in place yourself, and check for slight vacuum

If it won't hold you have one of two things. Either there is too much blowby for the system to handle, or the PCV system is not performing properly. Poor performance is caused by restricted passages in the engine, plugged filters, clogged valve or wrong valve, vacuum lines, or vacuum source restrictions.

Although it does not seem like it would work that way, if you have a flow restriction it can cause the engine to smoke out of the tailpipe at low speeds.

Of course the valve seals are a possibility, and common on old cars.