Question: Oil Past PCV?

[Vette79]

After a complete Top-End rebuild of my 79 L-48, I have oil passing by the PCV. I installed an oil catch can which has resolved the issue of oil making it to the intake manifold. A compression check on all the cylinders revealed no problems before the build. Vette runs strong for an L-48 with 64K original miles. With compression increasing due to the build is this why I am now noticing this issue? If so, what is the fix if any?

 

[6880 Mike]

There should be a baffle in the valve cover to prevent the blow by.

 

[JohnZ]

Have you checked or replaced the PCV valve? They weren't designed to last for 30 years metering hot oil vapors.

 

[Vette79]

Mike and John, how's it going? The aftermarket valve covers I installed have baffles. The PCV is no more then 1 yr old. Could be stuck open but it seems to be functional.

 

[topless82vette]

I installed a small fuel filter in my pcv line and it helped with my oil up the pcv line issue. only problem is when and if it plugs but seems to work and haven't noticed it plugging.

 

[Vette79]

Yep, that was the first idea I had. I still have the filter. I went with a true known resolution with the oil catch can. Much more expensive but effective.

 

[Vette79]

If I decide to replace my PCV, which one do I go with? They are not all the same.

 

[yellow77]

Umm, the pcv valve should have a hose going to manifold vacuum at the base of the carb, either on the rear or front of its base plate where any blow by is drawn into the intake and is thus burnt. The other valve cover should have a filtered breather (mine is attached to the bottom of the open air cleaner).

Cheers

Richard

 

[Vette79]

Umm, the pcv valve should have a hose going to manifold vacuum at the base of the carb, either on the rear or front of its base plate where any blow by is drawn into the intake and is thus burnt. The other valve cover should have a filtered breather (mine is attached to the bottom of the open air cleaner).

Cheers

Richard

Umm, yes, we know that. The question was "Why is there oil passing the PCV after my top-end rebuild?"

I'm going to double check the PCV and baffle for the valve cover again today. Silly question but, Do I have to much compression?

 

[redvett]

Umm, yes, we know that. The question was "Why is there oil passing the PCV after my top-end rebuild?"

I'm going to double check the PCV and baffle for the valve cover again today. Silly question but, Do I have to much compression?

Here are some of the posibilities, oil rings not seated,rings wrong index,wrong PCV valve. Your owners manual should tell you what PCV valve to use.

 

[Hib Halverson]

After a complete Top-End rebuild of my 79 L-48, I have oil passing by the PCV. I installed an oil catch can which has resolved the issue of oil making it to the intake manifold. A compression check on all the cylinders revealed no problems before the build. Vette runs strong for an L-48 with 64K original miles. With compression increasing due to the build is this why I am now noticing this issue? If so, what is the fix if any?

Some oil vapor in the PCV air flow is normal. You will never not have oil vapor in that flow.

The PCV valve itself has nothing to do with the air flow. That valve does two things 1) it provides a way to shut off reverse flow in the event that the engine "backfires" through the intake preventing any flame from entering the crankcase and 2) it meters the airflow through the PCV system.

With a new engine there should only be a small amount of liquid oil in the PCV valve or hose. As the engine ages and the volume of blowby gases increase the amount of oil vapor carried by those gases will increase. A worn engine may have a lot of oil vapor and a fair amount of liquid oil in the PCV system.

If the oil baffle or separator is in place--I should add that the baffles used in 30 year old cars are pitiful compared to the oil seperators on modern engines--and there is a lot of oil vapor and noticeable liquid oil in the PCV the engine is probably worn and ready for overhaul.

 

[mrvette]

Hib is right, I have never seen a SBC valve cover PCV that did not suck oil to a certain extent, baffle or not....

meanwhile for decades the old Pontiac engines with the valve located in the lifter valley cover never sucked oil.....

and when I put my LT1 intake on the L98 engine, I used the stock LT PCV valve position, and no problem, it's analogues to the old Poncho install....

 

[Vette79]

So, what you both are saying is "not to worry". I do have an oil catch can in place to square away the issue. I'm also using newer valve covers with newer baffles. PCV is functional and working. The only thing that I think would be left to the engine to overhaul after my top-end rebuild would be the piston rings?

 

[Hib Halverson]

I did not say "not to worry".

Some oil vapor flow through the PCV on an L48 is to be expected. The amount of liquid oil passed will depend on the design of the oil seperator in the foul side of the PCV system and the condition of the engine.

The reason I mention "condition of the engine" is the first post said this was an L48 with a "top end job". No information about the condition of the engine's lower end was offered. Obviously, a top end job on a high mileage engine with poor ring seal will increase oil vapor flow though the PCV.

The reason oil high amounts of oil vapor in the PCV is a problem is that oil vapor increases the engine's tendency to detonate under high load.

 

[Copdogcorvettes]

Well I guess I'll add 2 cents. I'm a bit old school, and one thing I learned was that if you take an older motor and just rebuild the top end 70% of the time the extra compression will blow by the old ring. Then you have a lot of blow-by . The old ring just can't handle it. The old saying is "You do the heads- You do the ring". I've seen it happen to many times.

Hopefully that's not your problem. Good luck. Also do a leak down test it will tell alot.

Gary

 

[Vette79]

Actually, with all the money and time spent on this project, it would of been best to just buy a crate motor. I'm not dissappointed though. I have learned a lot and spent quality time with my brother and the Vette. Thanks for the input guy's. We plan to take it to a DYNO within a few weeks and I will post some numbers and pics.

 

[Rodney Gold]

I think you need to check your breathing arrangement , one valve cover needs to be vented , ie a breather with no connections to vacuum and NOT a pcv , the other valve cover needs a pcv to intake manifold.
When I rebuilt my top end , I mistakenly installed 2 PCV's on either side and connected both to vacuum , the engine then pushed out oil from the oil filler cap on one of the valve covers and from the dipstick at high rpm.

 

[Vette79]

I think you need to check your breathing arrangement , one valve cover needs to be vented , ie a breather with no connections to vacuum and NOT a pcv , the other valve cover needs a pcv to intake manifold.
When I rebuilt my top end , I mistakenly installed 2 PCV's on either side and connected both to vacuum , the engine then pushed out oil from the oil filler cap on one of the valve covers and from the dipstick at high rpm.

Nope! Breathing arrangement is configured properly. I'm thinking with the increased compression with the top-end rebuild and the old piston rings this is why I have oil blow by.