C3 smoking .. what am I missing?

[Dale P.]

here is a description of what happens to the 71

it is a 1971 454 LS5 (orginal motor/trans) .. automatic
heads redone with hardened seats, new valve guides and seals
installed a new cam at that same time (the cam is basically a stock replacement), lifters, timing chain, water pump (high flow) and carb (the carb is a QJet replacement ..) and recored the radiator.

The car had not been driven much before I obtained it and it needed a few items replaced/repaired

what I can NOT say for sure is if it did or did NOT smoke before the engine work was done .. as I didn't drive it enough before doing the repairs listed above .. I do know that it was running without a thermostat when I brought it home

since I noticed it smoking I have ..

checked the engine compression .. all 8 cylinders are within 1-3 pounds of the stated pressure in the manual
car can sit for weeks .. start it up no smoke
let idle until up to temp from a "cold" start and you may see some very light smoke it is so light it is hard to see
run it on the highway at operating temperature and stop at the end of the ramp and its smoke immediately ..and I mean noticably! the longer you sit at the ramp the more it smokes ...
I have noticed even an oil film around the rear of the car .. like on the rear bumper
the car has dual exhaust and smokes only out of the one bank .. the passenger side
the car never runs hot .. it might heat up a little in traffic but never over heating to boil over ...
I can run the car around town at operating temp and it will smoke at the lights .. take it home and pull it into the garage smoking .. shut off the engine .. let it cool all the way to room temperature .. start it up and NO SMOKE

what am I missing? Please help!

[Jack H.]

Re: C3 smoking .. what am I missing?

Your symptom list tends to point to an issue with one cylinder bank with the problem being triggered with hot engine operation. There are several possibilities including valve guide leak down, modest failure of full valve closure, gasket leak(s), hairline head fracture and so on. The next step would be to pull the spark plugs on the offending cylinder bank and see how each has been burning. That should tell you mucho on where to look....

[Dale P.]

Re: C3 smoking .. what am I missing?

I agree with the problem being triggered with "hot" engine .. which means thermal expansion ... that is why I did the compression check .. if the valves were not sealing ( for whatever reason) or if the rings were weak etc I would know it .. but the compression check (as done by the book) yielded very consistent results in all eight cylinders ... also as part of the valve job the heads were magged and checked for cracks ... I personally didn't observe this but I need to trust that my machine shop did a good job. As for reading the spark plugs .. I have taken that entire bank out and could not see any difference in them at all ( one from the next) .. I then took a plug from the "good" bank and compared it to the other four and still no difference ........

one thing that I remember now that I didn't include in the original posting was the amount of carbon build up inside the combustion chamber and on the pistons when I pulled the heads for the valve job ... both sides had a tremendous amount of carbon build up .. but of course I remove it from the pistons before reinstalling the heads ....

I even checked all the vacuum lines with a "Qtip" (wiping the inside of the hose looking for oil film) thinking that I might be pulling oil vapor from some where.. IE either the automatic transmission or from the valve cover via the PCV .. and still nothing

[Patrick H.]

Re: C3 smoking .. what am I missing?

Dale,

Based on my own experience, but with my small block, I'd think about leaking intake gasket on the right allowing oil to get sucked into the motor and burned. I had not quite so much smoking at the end of a drive, but had the same carbon buildup as well as oily plugs for the middle two cylinders, i.e. 4 and 6.

Patrick

[Joe L.]

Re: C3 smoking .. what am I missing?

Dale----

I can tell you with virtual certainty what the problem is. It's caused by a leaking intake manifold gasket which is allowing oil to be drawn into the intake ports. Very likely, it's a problem on both sides, but it may be "favoring" one side, so that's where you notice it most. A further confirmation of my diagnosois will be provided by quantification of your oil consumption. If it's in the range of 300, or so, miles per quart, that's further evidence of what I'm suggesting.

Next step: remove the intake manifold. When you do, note very carefully how the manifol bolts come out. Especially note if they are binding against the UPPER surface of the holes. There may even be "thread marks" on the upper surface of the holes. If so, that's a pretty much 100% confirmation.

When the manifold is removed, look carefully at the intake ports in the cylinder heads and also the ends of the intake runners in the manifold. Check to see if there is a film of oil present in all or most. If so, that's more confirmation.

So, how to fix it? The easiest was to deal with it is to slightly elongate the manifold bolt holes so that the "bind" is eliminated. Then, replace the gaskets with stock-type, embossed gaskets. That should do it. Alternatively, you can send the heads and intake manifold out to a specialty machine shop (like Fowler Machine in CA) to have the heads and manifold "angle machined". This won't be cheap and they might not get it right the first go-around. Then, you start all over again.

[Dale P.]

Re: C3 smoking .. what am I missing? More inToofo.

Removed all bolts from intake manifold checking to see if they drag along the hole..appeared to have been centered in hole. All appear to have been tightened to torque specs. Removed intake as carefully as possible so we could observe gaskets. Saw nothing on the gaskets anywhere that would indicate blow-by. Checked intake runners in the heads and manifolds. Found extremely light (potential) oil vapor traces. The only thing that really stands out is the amount of carbon deposits on the stem under the head of the intake valves. The only other confusing thing that we have found is positive signs of oil directly underneath the carb in the intake plenum. We're thinking there is a crack under the oil shield on the underside of the intake......so I guess off to the parts store. What is the absolute best intake gasket to put on?

[Rob Dame]

Re: C3 smoking .. what am I missing? More inToofo.

While the intake is off this time I'd have it pressure tested..Rob

[Joe L.]

Re: C3 smoking .. what am I missing? More inToofo.

Dale-----

Even though you don't seem to have the situation in which the intake manifold bolts are "binding", I still think that you have an intake manifold gasket leakage problem. The light oil in the intake manifold/head runners, the heavy deposits on the intake valves, AND the oil under the carb are all symptomatic of this. I realize that it does not seem like there should be oil under the carb in the manifold plenum, but somehow it gets there. My small block ( a once brand new GM replacement short block that I installed in 1975) has EVERY ONE of the symptoms that you described. Before I gave up on that engine I tried EVERTHING IMAGINABLE to solve that problem, replacing two sets of heads with brand new GM with all new valves, intake manifold changed twice, every sort of valve seal you could imagine, every sort of intake manifold gasket set on the market, numerous sealers including some hi-tech areospace types, re-ringing the lower end, installing several types of liquid/vapor seperators in the PCV system, and on-and-on. NONE of these solved the problem. I did not know about the intake manifold bolt hole elongation trick then, however. I really think that this might have solved my problem, but it's too late for that now. The engine is permanently "retired". I do plan to perform an intensive "autopsy" on it someday, though.

I really don't think that you have an intake manifold crack under the oil shield or otherwise. First of all, as I say, I had the same symptoms that you have and I replaced the intake manifold TWICE (i.e. 3 different intake manifolds on that engine). Every one had the same problem. I really don't think that I had THREE, successive cracked manifolds. Also, if you had a cracked manifold, you would likely also have a vacuum leak that would be notable.

As far as gaskets, I feel that stock-type embossed manifold gaskets are the best. However, I really don't think that you're going to solve this by just replacing the gaskets. If that's all you do, I fully expect that you'll be "going back in" soon for the "next round".

[Mark #28455]

where does your PCV attach?

On my L89 that was converted to L88 style intake, after a rebuild with all new parts including zero gap rings, I had a perplexing problem with oil consumption. As long as I drove the car "normally" there was NO oil consumption, but if I ran it to 6500 RPM and shut the throttle completely to decelerate the car, it would suck about 1/2 quart of oil!

Tried everything - intake gaskets, etc. Talked to my machinist and to make a long story short, under extremely high vacuum, the engine was pulling the oil through the PCV valve. How did I finally prove it? Put a 3/8" fuel filter in the PCV line and it filled up with oil. I put a 1/8" restriction into the PCV line and now it doesn't burn the oil any more. The opposite side breather is connected to the air cleaner and I don't get any blow-by there either due to the low leak down of the zero gap rings.

Makes me ask where your PCV valve goes into the intake. If that's a possibility, temporarily cap the hose and nipple and see how your oil consumption does.
Good luck,
Mark

[Dale P.]

C3 smoking .. Repair plan and follow up question

Thanks to all who have replied... I am amazed at the number of people that have had the same issue.. I was really starting to doubt my abilities to find the solution .. So here is what is planned (and I will keep everyone in the loop)

1 The intake is going to be pressure tested and to verify that the sides are straight.
2 Will purchase replaced embossed intake gasket set
3 Will add a fuel filter into the PCV system JUST to be able to watch if the “paper” turns color
4 Will chase all the threads in the head and on the bolts to be sure that I can get a proper torque when reinstalling
5 Will “elongate” the bolt holes in the intake manifold

I do have one last question ….. I do not ever remember seeing the “rubber” gasket between the heads along the top of the block on either the front and back sides of the motor … the ones that normally seal the intake to the block … I have not done much work on BBs but have always seen them on small blocks .. Is this a hint to that someone has done something “weird” before I bought the car?
AGAIN . THANKS TO ALL FOR HELPING!!!

[Joe L.]

Re: C3 smoking .. Repair plan and follow up questi

Dale-----

Considering what you have found, I'm not so sure that I would elongate the manifold bolt holes just yet. If, indeed, the holes are perfectly centered and there is no bind of the bolts as you run them in or out, then I don't see how elongating the holes in the manifold will do you any good. A good test of this would be this: after you test-install the manifold WITH SIDE GASKETS in place, run the bolts into previously cleaned threads without sealer. If you can turn all of the bolts most of the way down by hand under these circumstances, then bolt hole elongation is not going to do you any good. While I still believe that your problem is intake manifold gasket leakage, this will not be a "route" to a cure.

As far as the end seals go, big blocks use end seals similar to small blocks. One curious thing, though: when I first assembled my replacement 350 engine in 1975, when I installed the original manifold (at that time on the original rebuilt heads bolted to the top of the new GM short block assembly), the end seals were "squished out". In other words, there was too little clearance between the manifold ends and the block ends for the seals. I had the manifold ends machined to "compensate". At that time I had not discovered the merits of replacing the end seals with silicone (I don't even know if silicone RTV was around in 1975; if it was, it was new). Also, I didn't understand that the "squishing out" problem was an "indicator" of other problems. So, the long and the short of it is if your engine "squished out" the end seals, that's another symptom that was identical to my experience. In any event, you can and should replace the end seals with RTV, so there's no need to have the manifold ends machined if you do have reduced clearance between block and manifold. Just make sure that the manifold ends are not right down to and contacting the block surface (with the side gaskets in place). That condition WOULD cause a problem.

As far as adding the PCV system filter, I think that it's a good thing to try. However, let me just say that I fully explored that area. In fact, it was one of my first theories as to what was causing the problem. I installed a "trap" that I custom made to determine if oil was being carried through the system. The "trap" was designed to allow any oil to "condense" in the trap. Some oil was so-captured, but nowhere near as much as the engine was using.

Another thing I tried was to eliminate the PCV system altogether. So, I temprarily changed the right side valve cover to the type with an oil filler hole. Then, I installed breather type caps on the oil filler holes on both valve covers. I did this after the change to a new set of cylinder heads with all new valves and the installation of a new manifold. I drove the car for quite a while this way. It still used a lot of oil and "smoked". When I took the manifold off later, the carb plenum had oil in it, the manifold and head runners had oil in them, and the back side of the intake valves were CAKED with oil deposits. This is with NO PCV system so there was NO WAY that oil could have been carried back into the manifold with the fuel charge.

[Dale P.]

Re: C3 smoking .. Joe was right

as i got more and more into the preparing of the intake to be re-installed I did find an oil track from the lifter valley to 6&8 ,, Joe was right on the money .. I am about 1/2 back to get everything ready for assembly .. so hopefully this weekend .it will be running and that will be the final
test .. once I am sure that the issue is behind ,, I will inform everyone that has followed this thread .. the good news is that I found the problem (thanks again Joe) the bad news is that I have not found the real reason ..