Air under valve cover

[Jan_280Z]

Hey Mates

 

Finally got the "new" motor running in my 620 - did an engine swap as old engine was pretty toast. Started and ran it until I got it to operating temp and the thermostat opened. I opened the oil fill plug  on the valve cover to look at the cam lobe while the car ran and was met with a large amount of air coming out as the car ran. Is this normal? With my Z I can open the oil fill plug and watch the cam lobe as it turns - and get oil all over the place - but there is no air.

 

Thanks

Jan

[Atomic]

Is the breather hole clogged with something? If your engine can't breathe, I would assume it can build up some ''air'' and different gasses inside the valve cover

[datzenmike]

The air is 'blow by' .... combustion gasses getting past poorly sealing rings. If a well used engine this would be normal (although not that good) an a new engine perhaps the rings haven't fully seated yet.

 

Expect the oil mileage to be poor also. Does the exhaust smoke?

[Jan_280Z]

The engine does not smoke from the exhaust, or at least I haven't seen it smoke. The motor was used so I can see it being rather used. The breather tube is quite clean and so is the inside of the valve cover. Other then a rebuild is there anything one can do to fix this?

Thanks

Jan

[DanielC]

Is the PCV valve plugged?  Normally, the crankcase should be at a very slight vacuum when idling.  The PCV valve draws air out of the crankcase, and air flows into the valve cover, from the air cleaner.  At part throttle, with a light load, the PCv valve opens more, but this is hard to check in your driveway.  At WOT, there is little vacuum in the intake manifold, and air flow reverses in the breather tube going to the air cleaner.

 

A good PCV valve also reduces oil leaks, because the crankcase is a a vacuum a lot of the time.  hard for oil to leak out, when air is trying to leak in.

[ggzilla]

Daniel is right on. Check that the hose from the valve cover is attached to the air cleaner and the hose is not plugged up.

 

 

The engine does not smoke from the exhaust, or at least I haven't seen it smoke.

Oftentimes the driver will not notice a smoking car. But drivers in the cars behind will see it. To check, do the engine rap test:

 

1. With the engine fully or partially warm, and running, set the parking brake

2. Open the car door and step outside

3. Walk around the back of the car and observe the location of the tail pipe

3. Go back and stand by the front door. While watching in the general direction of the tailpipe, reach in with your foot and rap the accelerator briefly three times. Rev it up each time to about 4000 rpm (heavy throttle, but only for as long as it takes to press the pedal, immediately let up).

 

What are the results?

* Good engine -- no bluish-white smoke should be observed.

* Worn engine -- any amount of bluish-white smoke, even small amounts, indicate the engine is worn

 

Even with severely worn engines rings, an engine may run very well and the car drive perfectly. Looking for the bluish-white smoke will indicate the true condition.

[datzenmike]

The PCV valve operation is a function of intake vacuum, nothing more. It would be highest at idle and deceleration and draw the most fumes then. As the PCV is a vacuum leak it is not very large (maybe 0.020"???) or it would affect the air mixture and thus does not draw much air from the crankcase, except idle and deceleration. At part throttle it is less and at full throttle none. In no way can it absorb huge amounts of blowby when driving normally. It just changes the air inside the crankcase slowly over time to reduce vapors and condensation.

 

I would doubt very much that any vacuum can be measured inside the crankcase with the PCV working. There is a finger sized hole on the valve cover vent that would leak any vacuum. Yes there would be a very slight draw to pull fresh air in but unlikely enough to keep oil in as well.