Intake Manifold R&R/Winter Project

[Joe C.]

When I built my L76, in the interest of originality, I used the black, "as-original" lookalike intake manifold gaskets sold by one of our best known parts houses. I am almost certain that an oil consumption issue (uses 1 quart per 500-600 miles) that has been apparent for awhile is due to leakage from the lifter gallery into 3 or 4 of the right bank intake runners. Not sure whether to condemn the gaskets, or not.

Here is some background information. Leak-down test shows no ring sealing problems. On a recent dynamometer test the engine made good torque and power. However, blue smoke was apparent out the right sidepipe on the closed throttle part of the pull (redline back to idle). I have no reason to suspect valve guides, as they were checked and OKAYED before the recent rebuild. Valve seals are o-rings PLUS umbrella type, which look to be oriented and working properly. Under high vacuum, closed throttle operation, I understand that it's not rare for a poorly sealed intake, to suck return oil from the lifter gallery, while displaying LITTLE OR NO symptoms of a vacuum leak. The engine does have a persistent off idle stumble, which has NOT been cured by adjusting the pump timing, and going to a larger pump nozzle. The heads were milled .015". The intake was not machined to match.

I will carefully remove the intake while keeping the gaskets intact, so that I can examine them. Is there anything that I should look for, specifically? I intend to replace with a Fel-Pro gasket set, using RTV instead of the front and rear gallery seals. Any better ideas? Is there an extra-thick gasket set that I can use? What is the limit to a combination of head/deck milling before machining the intake becomes necessary? Any other tips will be appreciated.

Thanks in advance.

Joe

[Joe L.]

Re: Intake Manifold R&R/Winter Project

Joe-----

The reproduction intake gaskets sold by the various suppliers and as originally supplied by Paragon are a stock-type, embossed gasket. These are absolutely the best gaskets for use on street engines. So, I don't think that these gaskets are, at all, related to your problem.

I once chased this exact problem for YEARS. I became absolutely convinced that the oil burning problem was due to oil intrusion past the lower edge of the intake gaskets. Besides a host of other things unrelated to the gaskets, I tried every different type of intake gasket that you could imagine. Thick ones, thin ones, stock type, aftermarket type, Print-O-Seal, you name it, I tried it. GM, Detroit Gasket, Fel-Pro, Victor and McCord; I tried all the brands. No gasket type made a difference.

I tried several different sealers on the gaskets. I even tried an exotic aerospace sealant ($60 per pint 20 years ago). Nothing stopped the intrusion.

As far as intake machining is concerned, I tried that, too (I went through 4 different intake manifolds). 2 different sets of heads, too, including 1 brand new set. Nothing made a difference.

So, how did I finally solve it? Well, I gave up; I never did. Part of the solution, though, will be the installation of the "ZL-1". Some time down the road, I'm going to carefully autopsy the engine (it's not my original engine; it's an exact replacement for the original engine I purchased from GM and installed in 1975). Maybe when I perform the autopsy I'll be able to figure it all out. We'll see.

[William C.]

Re: Intake Manifold R&R/Winter Project

Don't overlook the possibility of a flawed Cyl Head casting when chasing this issue.

[KEN BUTCHER]

Re: Intake Manifold R&R/Winter Project

Hi Joe,
I don't know if this will help, but this is my story. I had rebuilt my L-82 in 2000, and I put 10-30W oil in for the early break-in. Then replaced the oil again with 10-30W for the 500 mile break-in period. After that I put full-synthetic 10-40W in, and after a month noticed I was down 1 litre of oil. So of coarse I topped up the oil and ran the car for 10K miles, and during that time the engine seemed to use a litre (quart) of oil per month. I could not figure it out, why?... Are the piston rings not seating? The engines not leaking oil, It's not burning the blue... Maybe I put synthetic oil in too soon?... I checked an old CAR&DRIVER (I think if memory serves me well) from 63' and it mentioned that the drive testing of the 1963 corvette reveiled that over a period of time the "vette" used a quart every 500 miles, so I thought OK.. that's normal. But it bothered me because I've had other chevrolet's which didn't use oil. So to bring this to a closing, I replaced the synthetic oil with regular 10-40W oil, and after the first month, oil consumption was down by about half, after three months the engine was not using any oil at all. I guess the piston rings just didn't seat as soon as I thought, and before every oil change the oil was always full to the mark. After that I went back to synthetic oil with no problems.

It just might be the piston rings?, in my case it was.
Ken.

[mike cobine]

Re: Intake Manifold R&R/Winter Project

You asked for tips of what to look for.

If possible, run the car down the street, downshift to pull the vacuum and make it smoke, depress the clutch, kill the ignition, and coast back to the garage. It may not be possible, but if you can, it leaves the engine in the best possible condition to examine it. Try to do it without it getting hot, so you can disassemble immediately.

If you are in a place you can do it right in front of the house or garage, consider this. Drain the coolant first. Run the car down the street, pull a big downshift to pull smoke. When you get a bit slow, put it in neutral and shut off the engine. Coast back to the garage.

Don't worry about overheating, it takes an average of 17 minutes for a small block to lock with no coolant. This trip should take you 30 to 60 seconds max.

As soon as you get in, disconnect the fuel line. Pull the distributor, and lift off the intake. Don't bother to waste time on the carb. Then check the head intake runners for wet trails. Shine a light down them and look for oil on the valves.

Pull all of the plugs and look for the oily ones.

On the gaskets, hopefully, they are still on either the heads or the intake and not both. See how they line up. See if they look compressed evenly around each opening. Look for wet trails on them.

Look up the intake runners. See if they have wet trails. You could have an oil leak into the intake.

Now pull the carb. Check for oil under the carb. It could be your PCV valve is passing oil.

I bet you will find the oil is pass the valve guides. Many places knurl them, and they pass oil. New guides usually help. Tops of the valves will have oil but the runners are dry in the upper half.

The other place is pass the rings. Two things are common. Cylinders are not round or the rings have seated under compression only, not under vacuum. Seated under compression won't show in a compression-type leakdown test, as the compression seats and seals the rings. You have to pull a vacuum on the cylinder and see how much vacuum leaks off.

[Joe C.]

Re: Intake Manifold R&R/Winter Project

Mike,

Thanks for the response, and all of the details. First, let me say that Duke is very familiar with this issue, and that's probably why he is conspicuously missing from this thread. He and I have hashed and rehashed this privately over a couple weeks this past month. AFAIAC, the results are still inconclusive, and Duke also had some very valuable input. I wanted to air it out on the FORUM, to see if there were any other good ideas out there. Here is some more background:

1. The car is equipped with GM NOS sidepipes.

2. Dyno tests (with sidepipes connected) show that the engine makes 4% better torque than a similar LT1 cammed 327. The power is substandard because it stops climbing at about 5700 RPM due either to valvetrain harmonics, or ignition deficiencies. One reason to believe that the engine is healthy (under compression).

3. Dyno tests with sidepipes disconnected (open ramshorns) show 10% improvement in power and torque, but the power still stops climbing at 5800 RPM due to the aforementioned issues.

4. During both dyno tests, blue smoke was visible out the right sidepipe, on the COAST, not the PULL.

5. Leak down tests revealed DRAMATIC, across-the-board improvement, when conducted at 100psi versus 17psi. Apparently, the higher pressure seals the rings. (I like your compression versus vacuum reasoning).

6. Number 2 and number 8 cylinders show highest leakdown percentages.

7. AC 44 plugs are also inconclusive. On removing them and studying them on three separate occasions, I have found 2 or 3 black-and wet, but never the same ones. A pattern is not discernable! Engine does not misfire. Runs excellent, except for the occasional stumble when tipping into the throttle during cruising.

Joe