427 BB Chevy problem

[cp1969]

I posted this on a Chevy forum today, but there are some pretty smart people here, too. I apologize if this is not the correct forum.

Hello, first time poster. This post is in relation to a friend's 66 427 Vette. I will try to explain to the best I can because this saga has spanned more than a decade.

Background: Friend bought the Vette in '95 with a newly "overhauled" engine. This engine burned a quart of oil every 200-300 miles, so he complained and was told if he'd furnish parts, they would do it over again. He did; and the result was the same 200-300 miles per quart.

We took the top end apart and found liquid oil everywhere in the intake manifold, so much that when tipped up on end, a big puddle formed around it. It looked like the exhaust crossover had more oil in it than anywhere.

He then had to take a temporary job in California and took the car with him. While out there, he contracted with an engine builder in Livermore to overhaul it "right." Something like $7K later, he gets it back and guess what--same story. That overhaul took place in '99 and he has put roughly 5K miles on it. On the dyno, it made 445 hp and something like 435 ft-lb (which I don't consider to be especially good numbers).

The California overhaul replaced everything on the engine except the block, intake manifold, and valve covers. New .070" oversize hyper eutectic pistons, new rods, new crank, new cam. The block was decked and align bored. The heads that were on it were replaced with the correct ones for that year.

I stopped at his house today and he mentioned he had a problem with his brakes and in the course of diagnosing that, I found out that when the vacuum hose is pulled out of the brake booster, it made absolutely no difference in the way the engine ran. I put my thumb over the hose and it is certainly pulling vacuum, but whether thumb is over the hose or not, makes zero difference in engine idle speed or quality. Out of curiosity, I pulled the PCV hose off the base of the carb and sure enough, that made a difference but the power brake vacuum line doesn't. That's odd. That is what prompted me to ask (again) how the oil consumption was doing and how the spark plugs looked. We pulled #1,2, and 5 plugs. #1 and 2 were a complete mess--black, with oily carbon covering everything. #5 resembled only faintly a normal plug in that the tip of the electrode was brown but the ceramic insulator was black once you got more than 1/4" away from the tip. About 1500 miles on these plugs.

When we had it running to test the vacuum booster, even with doors open at each end of his garage and with a slight breeze blowing through, the exhaust fumes were punishing--it was running so rich you couldn't stand more than a minute or two inside with it. I asked "Do you even have jets in this thing?" and he produced a record which said he has 69's in the primary and 76's in the secondary. I have no idea what size the factory jets were. His record also showed that he and another friend had experimented with changing jet size and had gone down to 65's but then returned to 69's as being "best". I can't imagine that this jetting is correct.

In summary, engine has everything new in it except block, intake, and valve covers. Another bit of info: the drip rails have been removed from the valve covers to clear roller rockers.

I have a hypothesis as to what's wrong but I don't want to pollute anybody's thinking as to what is wrong with this engine.

Any and all help will be greatly appreciated.

Thanks.

 

[rustyjeep]

does the oil smell like it has gas in it? if so it could be that it is running so rich that the gas is actuallly washing down the cylinder walls preventing the rings from seating?? its really hard to diagnose over the internet,let us know how it worksout

 

[Hooked_on_HP]

If there isn"t a baffle inside the valve where the pvc valve goes the oil squirting out of rocker will go through the pvc and into the intake.. One other thing to look at is how the intake mates to the head. If the block has been decked and the heads milled the intake may need to be milled also. if the intake isn't down far enough it will suck oil at the bottom of the gasket

 

[art]

Interesting! I'm playing with a 406 in a ferrari 365 kit car and it seems to be doing about the same with the mileage at the 2500 mark. The short block was built for a stock car all I did was add heads and intake and carb. I don't have power brakes or any other power assists to draw down and I haven't been able to put a handle on it. I hope to do a leak down test on it next week to see what's going on in that department but this thing is baffling me. Many of my friends just tell me to go back to a mopar engine for it but I liked all the aluminum light weight stuff with the chevy at lower prices and the car was originally built around the chevy parts.

 

[KICK]

1, 2 and 5 are fouling. ?

no vacuum signal to speak of?

burning oil?

like HP said, look around the intake manifold. if they've machined it enough the angle of the V between the heads and the intake manifold could be compromised and isn't sealing around the bottom of the joint between manifold and heads.

 

[cp1969]

1, 2 and 5 are fouling. ?

no vacuum signal to speak of?

burning oil?

like HP said, look around the intake manifold. if they've machined it enough the angle of the V between the heads and the intake manifold could be compromised and isn't sealing around the bottom of the joint between manifold and heads.

Bingo. That is my theory, too--that the intake is leaking on the underside, drawing oil mist into the cylinders. The leak is probably worse towards the front of the engine than towards the rear. It makes sense--a big leak would require bigger jets to compensate, plus it runs poorly. Decking the block (which was done) may not change the angle between the heads and intake but it does move the heads down on the intake manifold.

All the plugs foul, with the fouling being worse towards the front of the engine. We only took out 1,2,&5.

It does have manifold vacuum--I didn't have a gauge to tell how much but you can definitely feel and hear it.

 

[joes_427_vette]

Sounds like a " race " motor vs a street version. I think the rings haven't seated ( were the cylinders cross hatched ) and very possibly a gasket leak someplace. Built properly these motors are bullet proof but it depends largely on the application. Did you complete a compression / leak down test and compare results ? Another item to try is the timing could be off 180 degrees. I had this problem years back where it ran hot, had vacuum issues, and ate spark plugs. Be sure to let us know the results. I also have a 425 hp coupe which was a former quarter mile star.

 

[Hooked_on_HP]

The jetting doesn't seem to far off if it is an 850. I looked back in my log books and when I was running a 440 (427+.060) it was jetted 78-79. I would guess you have blown a power valve in the carb and that is what is making it so rich at idle. Is there gaskets on the front and rear of the intake or was silicone used. If they used gaskets that may be holding the intake up to high.We always use RightStuff. If they used silicone, look and see how thick it is.That will tell you if the intake needs milled. Deckin the block and head will not change the angle between the intake and head just the height. Some times you can use a thicker intake gasket to correct the problem. What kind of oil was used during break in. Synthetic will keep the rings from seating. It is great after break in but not before. A BBC will not run 180 deg. out

 

[cp1969]

Thanks for all the help. I had a hunch I might get better response here than at the Chevy forum and so far that has been true.

I don't have ready access to the car so can't answer some questions. I do know there have been a variety of oils tried but no synthetics. Everything from straight 30w to 15w-40 has been tried; currently has Castrol GTX 10w-30 in it. Changing weights, brands, etc. made no difference in oil consumption.

I really do not believe the rings are a factor in this simply because it's had three sets (along with three sets of pistons) and the oil consumption has remained constant. I would bet my last dollar that the short block is fine--the problem is elsewhere.

Only three components (block, intake, and valve covers--four total parts) are common to this sad tale of engine woe.

Block--I can think of no place in the block where a defect could cause oil to get in the cylinders. Correct me if I'm wrong.

Valve covers--Other than the missing drip rails, they are stock. Someone asked about a baffle under the PCV and it has one. I don't know what function the drip rails perform but surely it is not oil consumption.

Intake--I won't even speculate here, but he is really the only suspect left in the room. The question is, how to verify?

Thanks again for the help. Maybe we'll get to the bottom of this before my friend throws in the towel. He is so frustrated with this car he just wants to get rid of it right now. I asked him, "If it used a quart every 1000 miles and the exhaust didn't burn your eyes like mustard gas, would you still want to sell?" and the answer was absolutely not. It is a beautiful car--a black roadster that looks like it came off the showroom floor. He's done some things to it that I think detract from the character of the car, such as put in 4:11 gears which I think limit top end to something like 119mph. He took out and disposed of 3:55's which I think would have been marginally high themselves--I'd think 3.23's would be about right with all the torque that this thing ought to produce, but he has his own ideas about what he wants.

 

[TractorLegend]

I vote for intake not sealing...maybe its not a good fit, milled too much. I'd remove it and look at gasket pattern. It should be easy to see if its not sealing by impressions left behind.
Would be nice to have the benefit of using a "smoke machine" for a diagnosis aid...Id inject smoke into the intake brake vac hose and see if it comes out the oil fill hole with fervor.
If you dont have a smoke machine maybe you and 12 buddies with a box of cigars could blow hits into the hose>>>LOL (take pictures if you do that!!)