67-427ci

I am still working on my oil consumption problem (1 qt in 400 miles. Searching the internet I found an article about checking the crankcase for excessive vacuume. I blocked the PCV & the breather and hooked my vacuume gauge on the dipstick tube. At an idle I was shocked to discover the crankcase built pressure to over 5 psi in less than 1 minute. I immediately saw seepage of oil at the valve cover seals (which normally do not leak). When I pulled the plug out of the valve cover grommet there was a HUGE rush of pressurized air . I have a feeling this is not normal. Any ideas what may be casuing it? I did a compression test a few weeks ago and all cylinders were above 170 psi. With the PCV connected and the valve cover breather connected to the air cleaner you don't notice it. Could this be a contributing factor to my oil consumption and is it bad for my engine? Is it possible my intake gasket is leaking exhaust in to the crankcase? I am confused on this one. My engine is a GM performance Parts 454/425hp crate engine with my original L71 Tri-Power.
Roy

wmf62

piston rings are not perfect seals, so you're going to have a bit of pressure get by; that's what is building up crankcase pressure. the PCV valve and breather scavanges all the vapors and pressure out of the engine... granted, there is a point where you can have too much blowby, but as long as you don't have a positive pressure when your PVC in connected, then you'll be OK.

are your plugs oily?

if you don't have any gross external leaks, the oil may be going down the valve stems and being burnt, do you get a bit of blue smoke from the tail pipes when you first start it up?

or, it could just be getting by your oil rings; do you see blue smoke when you accelerate?
Bill

GCD1962

Why were your surprised when you blocked the pvc & breathers and had a big spike in pressure? The only place for the pressure to escape was the dipstick tube and the poorly sealing valve covers. As was suggeted, check the plugs first to see if they are oily. If so, thern it might be the intake gasket, valve seals, or guides

rongold

Roy,

Hook up everything normally, and then take the PCV return hose off of the bottom of the air filter housing. With the engine idling, you "should" have a small amount of vacuum present in that hose. If you have pressure there with the pcv valve hooked up, then you have a blowby problem. Mine has considerable vacuum there--enough to hold your palm to the hose.

My engine (427/435) uses oil also--sometimes a lot, and sometimes a little. My drive to work is about 40 miles round trip. I've seen it use as much as a quarter to a half a quart in that 40 miles. It all depends if I get on it or not. Normal driving--no smoke out the back and no oil loss, but if I hit it, it blows out quite a bit of smoke, and when I check it, it's usually down. It really doesn't bother me, and it shouldn't bother you either, unless it fouls out the plugs, which mine doesn't. All big blocks that I've owned (66 Chevelle, 68 Impala, 68 Nova, and my 67 vert) have used oil.

If my engine used a quart in 400 miles, I'd be as happy as a pig in s%*t. Does anyone here on the forum have a BB that doesn't use oil ????

GCD1962

A quart in 40 miles! If you drove a hard 300 miles without stopping you would run out of oil. That in any engine is not normal

rongold

I know that, but it doesn't really bother me. It's actually 1/4-1/2 Qt. in 40 miles, and as long as the plugs don't get fouled it's OK with me. I haven't changed them for 3 years, and it's still running great.

GCD1962

Ron - Where is it going then.? If it was going into the cylinders it would foul the plug. If it were gaskets it would be leaking out. If it was blow-by going out the breathers it would be an oily mess in that short distance. What is your take on where it is going? Even 1/4 qt in that distance is a lot. I have an old '40 chev that is a leaker when it
s being pushed (50 mph is being pushed for the old splash lube engines) In 50 miles of travel it pushes less than that out of the draft tube or the rear seal.

knight37128

I do.

Got a lobe down on the cam; but no oil use.

67-427ci

With the PCV connected there is a slight vacuume at the valve cover breather. As you raise the RPM's that reverses to a slight pressure.

The plugs do not foul completely, check this thread for pictures of my plugs a few weeks ago. Oil Consumption

I did a compression test at the same time and all cylinders were from 179 to 190 psi. If it is everyones opinion this kind of crankcase pressure is normal, I'll not worry about it. I guess doing a test like this really did not prove anything. I was just surprised how quickly the crankcase pressure builds-up at an idle (without the PCV connected).

I will be pulling the intake manifold very soon. I should be able to check the back side of the valves for oil deposit build-up and the intake gasket for oil seepage.
Roy

Ironcross

[QUOTE=rongold] Does anyone here on the forum have a BB that doesn't use oil ????
[QUOTE]

I do, in fact 6 0f them and all but one is over 425HP. Similar to another false statement that all BB`s overheat.

rongold

I have a humorous story about using oil that I figure everyone here will get a chuckle out of. Back in my high school days (1960-64), I had a friend with a 56 Chevy Bel-Air 4 door sedan stick six. I never saw an engine that burned oil like that one. I lived in Westchester County, NY about 20 miles north of NYC in Elmsford. My friend lived in Yonkers, about 10 miles south of me. After his High School prom in 65 (he was 1 year younger than me) he decided to go to Jones Beach, which was on Long Island--about a 40 mile trip for him.

His preparation for the trip was to fill the engine right to the top of the valve cover with straight 40 weight reprocessed oil that we used to get for $1.99 for a 5 gallon can back then. He told me that by the time he got to Jones Beach, his oil light was flashing. He pulled the dipstick, and guess what---DRY---That's how much oil that engine burned. Same thing on the trip back--Now, that's an oil burner !!!

wmf62

interesting story, but i doubt the engine would run with "fill the engine right to the top of the valve cover with straight 40 weight reprocessed oil". the crank/rods/pistons couldn't displace all that oil....
Bill

rongold

Hi Bill,

You're right. I just talked to him, and he used to fill it up until it came out the dipstick tube--not to the top of the valve cover. My mistake. You couldn't miss him going down the road though---billowing clouds of smoke, but it never fouled the plugs.

RON

Don SSDD

When I bought the 59 the 283 burned oil at 50 to 1- I told everybody it was a 2 stroke.

Don

knight37128

Fill up the oil and check the gas.

L78racer

Have you done a leak down test on the engine yet?

devildog

The PBJ (B-25) to the right in picture nominally burns 3 gal/hr/eng in the airshow routine. Cross country cruise I get it down to 1-2 gal/hr/eng. 2600 ci/1700 hp each side.

Real fun is when I go to small town airshows and they give me oil but do not advance order a barrel or even gallons of oil...line boys dumping 1 qt. at a time is a hoot.

67-427ci

I have not done a leak down test yet. I'll have to get my hands on the gauge and get it done.
Roy

67beast

My solution was to run breather hose down to the header collector (drag racing trick) from each valve cover. See pictures.