Hello, looking for help here and opinions on a situation I've never encountered, but from some online reading, it is not an uncommon issue, that is clearances between the intake and heads causing sealing issues, and the need to mill the intake.

Some background to let you what I tried beforehand, if you do not want to read it all, go to **** below. Thanks.

Ok, I recently did an engine bay resto along with a head and cam swap on my '72 L48 350. I was after a period and factory correct look, so I used a pair of refurbished camel humps (492s) that I acquired many years ago. I know, there are way better heads today, but again, I was after the stock look - not max HP. I also converted to a retro roller cam to complete the changes and a reworked and restored numbers correct QJet.

The history behind the heads. Don't know much other than they are date coded, one is 1970 the other 1972. So not a matching set. The faces have definitely been resurfaced (milled) at one time. How much, I don't know. I did CC the chambers - all 8 63-64 CCs. A few years back I had the heads gone over again to verify the components. All good, SS valves, new bronze guides, vacuum pressure tested, and viton seals added. Heads are not ported.

On initial start-up, the car fired up right away. Great sounding lope at idle with new Corvette Central 2 1/2" exhaust and Magnaflows (BTW, much louder than I thought). Overall very happy. After driving the car over several days about a hundred miles to shake it down, I started to notice that I had some black/grey smoke coming from the right tailpipe. Assumed I was running rich. Just needed some tuning. Car also sounded a bit quieter. Exhaust note not as crisp. Assumed mufflers were breaking in. Tried adjusting the carb, advanced the timing a bit to get it to burn more clean. No change. Odd, on cold start up the exhaust was clean, but after getting hot, the smoking would start. Mostly on the right side, and now a bit on the left.

Started looking at the carb more closely when idling, noticed I had developed the dreaded QJet nozzle drip at idle, but only on the right side. Called my carb rebuilder, who restored the carb and enhanced the internals to match my mods. He says, its running lean and wants more fuel, so it pulling fuel from the main circuit. I try to richen up the idle. No help. He's positive I have a vacuum leak, so I check the manifold externally and the carb gasket. Could not find any vacuum leaks or elsewhere My vac gauge is 14" steady. My son an HVAC tech, used a sensitive sniffer for vac leaks. Nothing. Report back to my carb guy. He says you have an internal issue. I am positive there is none. Car runs good. Everything fresh.

I think about it some more. Heat riser valve open. Yes confirmed. I actually have it there but welded open. I check the plugs. No fluffy black carbon, but they have what looks like oil, but not wet, dry more like a baked on brown. Hmmm. Still thinking it must be rich. Do a compression test as well - 195 lbs across all 8. Never had such a consistent reading. Was expecting less with the cam I have and dish pistons.

I still think its the carb. Maybe the float. I then decide to check the fuel pressure. I'm running a new Carter 6955 pump - muscle series. Test it - 9 PSI. Way too high. Should be like 5. So I decide to put a regulator temporarily in line. Adjust to 5 PSI. Start the car up. The nozzle drip stopped, but STILL smoking. So in a way - some improvement with nozzle drip gone.

I finally pull the carb. I see oil on the bottom of the intake (both sides) mixed with gas. Now starting to have concerns. I check my PCV line and power brake booster line, both clean no oil being pulled from there. Car is a 4 speed, so no vac modulator valve to check. I decide to try the Qjet that was on my car before the mods. Still smokes. I then run a Demon that I have that is set up for a more HP motor, still smokes!

OK, now I decide it must not be a carb issue and time to pull the intake which I do. Wow. I see oil in all the intake runners !! Actually some oil was slightly pooled on one intake valve. I look at the intake gaskets. Hard to tell much other than they have some oil. But one thing, when I installed the Felpro Steel core gaskets (the blue ones) I put a light coating of RTV around the ports on both sides, I know its not needed, but I always have with no previous issues. I figure the excess fuel from the nozzle drip eat away at the RTV and caused oil to be pulled from the engine valley. I think about valve seal failure as well, but they're viton, new, and why would there be oil in the intake and head runners.

*****
So I get a set of Felpro 1256 Gasket this time (composite material .060 thick, same thickness as prior blue gasket) and install it per instructions dry except for a thin film of RTV around water jackets. RTV used on china walls as before. One thing I notice as I'm torquing the intake bolts (10, 20, then 30 lbs), I can still get a .010 feeler gauge under the right side of the gasket (at top but not down to the bottom) and intake up to 20lbs torque. Can't get the feeler gauge under on the left side even at 10 lbs. Doesn't seem right, but I end up torquing to 40 lbs on the right and 30 on the left to get a seal. I can still get a .001 feeler gauge now under the right side but just to the printo seal (blue ring) of the gasket. Hope its enough. Cure 24 hours.

Restart. Running good. Again no smoke of any colour on start up. Now hoping. After the engine gets up to operating temperature, the smoking starts again (no blue smoke, black grey again). Less, but still there. Engine note a bit crisper and Vacuum up to 14.5". Engine appears to be not loading up as much as before. I think maybe I need to drive it and blow any oil out. But before I do that, and after the car cooled off, I pulled the carb again. Oil on the bottom of intake again (I cleaned the inside of the intake before reinstall)! So now I figure the problem is still ongoing. No point driving it. Off with the intake again after running for just 40 minutes.

Pictures are what I found upon lifting the intake off:


Intake - Right side


Right side - Cyl 2 & 4. Oil appears to be entering from bottom


Right side - Cyl 6 & 8. Same issue


Left side - not as much oil


Left - Cyl 1 & 3, these are the only ports that appear to be sealing


Left - Cyl 5 & 7, faint light evidence of oil getting through bottom


Underside of the gasket. On the left is Cyl 2&4 that appear leaking. Note heavy crush at bottom and oil film residue. On right Cyl 1&3 that seem to be sealing best.


Underside. On left is Cyl 5&7, that appear to be slightly leaking - faint to no gasket crush. On right 6&8, leaking. Like 2&4 heavy gasket lower crush.


Oil on bottom of Intake after running 40 minutes


Plug 4 on left, plug 2 on right. Looks shiny, not wet. Dry brown residue. Would expect to be oil fouled!

So now after some research, looks like I have an issue with the mating flanges between the intake and heads. I think about going to .120 thick gaskets, but I don't think I can get the bolt holes to line up. I'll be too high. So after more research I try this method to get numbers on clearances using washers to act as a .060 gasket, and solder to act as like a plastigauge. Results:


I bolted and torqued to specs where the washers are located. I used plumbing solder that is .120 thick at locations in pic


Made up this worksheet. Clearances as noted. Definitely some issues that correspond to gasket inspection.

After looking at the results, from what I can tell, a few things are going on. The big one, being the gap on the right side from .0715 at top tapering to .051 at the bottom explains why I could get that feeler gauge underneath the right side while torqueing the manifold, and why the underside of the right side gasket is biting so hard. But why am I not getting a vacuum leak from the top you'd think? Is it because the manifold is digging in hard and while being torqued it still leaving an opening down low? Trying to visualize the physics.

From what I have read the gap at the bottom of an intake should be only be .005 tighter to seal the lifter valley optimally.

The left side, the difference on Cyl 1 & 3 appears textbook at .004 from top to bottom, and by looking at the gasket - it appears to be sealing. Cylinders 5 & 7 on the other hand have no taper. The gasket imprint also showed this; however, the gaps on the left side appear to be the manifold opening up from front to back.

Looks like the right head has a slight angle mill to it. Whether intentional, who knows. But I need to correct it.

Have any of you guys had intake milling done? Is this a complicated task for an engine machine shop? This intake was not leaking with prior heads. Is original.

Right now I'm thinking that an additional .015 needs to be milled from the right side of intake at the bottom tapering to zero at top. Recheck gaps, then consider left side after right side correction.

Any opinions? Words of wisdom from experience? This is a new one for me.

Thanks for reading this long post.

Dino.

 

FYI

https://www.crankshaftcoalition.com/...cylinder_heads

consider how most guys think they must have an aluminum intake; monkey see, monkey do ...so they do. consider how cast aluminum has more "give" than cast iron, So a mismatch which might be overcome with an aluminum intake, may Not work with a stiffer cast iron intake (like your OE iron piece).

Do you know if your block has ever been decked? If so, how much ?Same goes for your heads; angle milled ?
Study the info in above link. Work with your local auto machine shop.

 

Tell all this to the machinist - he'll tell what needs to happen

 

Thanks Ebb and Rat for the responses.

Block not decked. Original block to car. Heads have been milled. How much? I don't know. I think right head was slightly angled milled from gap test - perhaps a screw up when milling.

Thinking of going to a machinist Tuesday. Just want to make sure what he tells me and what I think, corroborates with you guys thoughts.

 

I second the recommendation for a good machinist.

My guy, when I take him heads to be milled more than just a slight skim, IE I'm milling for more compression, he's got a chart or a formula he uses. The head-block surface is milled, and either the head or intake manifold surface is milled where they meet, and the bottom of the intake is also milled. The end result is a perfect match again, with no "step" between the intake manifold runner and the head port, and no issues with gaskets sealing.

And a decent machinist can tell from how many cc's are in the chamber and the casting numbers how much has been milled from the heads before, and how much more they mill, and the total to be take from the other surfaces to keep all the angles and mating surfaces properly oriented.

 

He will know better. Milling it will set it right into place...bet your plugs clean up too.

 

You have done a great job of taking pics and explaining what you have done so far...please take a little more time to answer the questions below and document pics dealing with each question.

You may have already answered this question: Have you cleaned the head-to-intake surfaces of paint also so that the entire area is clean for the following tests?

Have you cleaned the intake manifold surfaces thoroughly also?

After cleaning the above areas have you placed the intake manifold on the head surfaces WITHOUT gaskets or sealer?
Have you THEN moved/slid the intake manifold to the driver's head to see how good or bad the angles match between the intake surface and the head surface?

Have you slid the intake manifold against the passenger's head to see how good or bad the angles match between the two surfaces?

Does the intake manifold EVEN touch the front and rear walls of the block when you place it on the engine?

Does the intake manifold rest on the heads ONLY (remember...no gaskets installed for these tests)

If you can get some good bright pictures of all the items listed above it will help Forum experts give you more advice about what the problem(s) seem to be.

The extra pics and info will definitely help the machine shop...if the problem is that bad to need the intake machined.
The shop may be able to machine the intake ONLY to correct the problem (i have had to do the same)

 

If I am reading this post correctly, you pulled the carb off and looked down inside the Intake.
Lo & behold, there was gas / oil pooling on or in the Intakes plenum. Correct?

So. How did it get there? Even if the Intake was warped. Even if the cyl head was warped. Even if there was no Intake gasket present, how does oil come from the head, to the plenum? That would be reversed air flow, wouldn't it? How is any oily mix going backwards to the plenum?
Each cyl head port is creating a vacuum from the carb to the valve. Any vacuum leaks at the Intake gasket can pull oil from the lifter valley, then onward into the cylinder to be burned. But not pulled back towards the plenum.

You made no mention of a PCV valve or what type of air cleaner is used. Some of the air cleaners suck air / oil / gas from the valve cover via a tube, then to the carb, then into the Intakes plenum.


Also a very slight chance that the Intake manifolds plenum has a crack or pin hole leading to the lifter valley, where, lo & behold, is oil.

 

Thanks again for all the additional responses. Will answer what I know so far to fill in some of your questions:

HeadsU.P.:
Oil under intake? From what I have read and other postings, reversion within the manifold can cause the oil or hot oil vapor to travel backwards. Somebody may know more about this.

PCV valve? No oil in PCV hose. Factory LT1 valve covers with baffles. Factory L48 air cleaner. I did not mention, but I also tried a PCV valve from a 302 Z28 for lower vacuum motors to ensure valve is closed. Also tried running with PCV pulled out of valve cover.

Crack under intake? Possible could have just happened while tightening from odd angles. Current intake being used is same intake used on this motor since I bought the car 30years ago with the original heads. No issues.

doorgunner
Heads and Intake Services Clean? Yes, both cleaned for the test down to bare iron. Any remaining paint is very thin (under washers). Used lacquer thinner, still having a tuff time to remove it.

Have you placed the intake manifold on the head surfaces WITHOUT gaskets or sealer? No I have not. Will try this tomorrow. I find eying would be difficult to measure gaps. Perhaps I could use a drill bit and place a feeler gauge on top to check gaps on each side.

Does the intake manifold EVEN touch the front and rear walls of the block when you place it on the engine? Yes, it sits on the china walls and can be moved side to side without gaskets. Is it suppose to sit on the intake flanges? No movement side to side with .060 gasket on and bolt holes line up when gasket used.

Thanks again. Much appreciated. Been an education so far for sure.

 

You are supplying the members with excellent info!
Do you have an adjustible machinist protractor that you can check the angle of each head while the heads are on the block? That would be good info.

 

I'm kinda wondering if the intake is hitting the china wall as you tighten it preventing it from setting down properly.
Seems pretty close in your washer test and the washers will not crush like the gasket will.
If the bottom of the runner gaskets are tight then the top should be pulling in the oil. However maybe none of it is really tight? What if you put your new gaskets back in minus the sealer and tightened it down, can you now slide a feeler gauge in between the china wall and the bottom of the intake?
On mine I angle milled the heads a lot from 64 cc down to 56 cc's and did not need to resurface the intake. On a non milled block.
The angle could be wrong too. Just spitballin.

 

Use a 1204 Fel Pro intake gasket.....it has significantly more crush and I think it will make up the difference.

Jebby

 

This is what is needed to check the angles to ensure they are correct. Not all machine shops have this tool, but it works great and will tell you right away where the issue is and the next coarse of action needed. GL with your issue.
ANGLE GAUGE

 

You are lucky you pulled the intake.

I have run into that issue and seen the damage
sucking oil and water.

proper head milling and thick gasket, like Jebby said, along with goop and god torguing
are needed.

Best I can come up with is warped mani?

 

You can set the intake on with no gaskets and see if it is out of angle pretty vividly at the ends….if it is out, you’ll see it….if it is only out a little, reseal with the 1204.
I have sealed up some real crap in my life with the 1204…..never a problem….but only RTV the bottom of the water ports to hold it in place…..nice bead on the China rail and four times around pancake pattern til snug….I like 12pt ARP stainless for this….also PTFE on intake bolts….not much!

Jebby

 

I had a similar issue after installing new Edelbrock heads and a used ZZ4 intake.
The angles did not quite match.
After several tries with the 1256? gasket different sealers, Indian head, black silicone, red silicone.
Switching to the thicker 1204 gasket with a thin layer of high temp silver silicone on both sides worked.
Had to keep re tightening the intake bolts several times.
Still check the bolts occasionally but they eventually stayed tight.

 

Yes....on those the pattern needs to be run 4 times til snug.....

Jebby

 

Hi All again. Thanks for the suggestions and advice.

On the 1204 gaskets, aren't those the blue steel core felpros? I went back on my invoices, and that is the first set of gaskets that I used. I did use RTV on the ports. Not gooped on, but a thin layer smeared around each port on both sides of the gasket. I think the gas attacked the RTV, from either the nozzle drip issue, or being pulled through the leak. After several hot and cold cycles the RTV just lost its sealing properties. I have since learned to use HiTack from the can, or as suggested Indian Head Shellac, as gas will not dissolve it. Another thing, I checked and the 1204 (steel core) and 1256 (composite printo seal) gasket, and they are both listed as .060" gasket thickness. I tried the composite 1256 2nd go around thinking it would be more forgiving than the 1204. Seems like you guys have had better luck with steelcore 1204.

Relaav8R. I'm amazed you have had no issues with that kind of milling. Wish I had this kind of luck. I verified that the manifold is not hitting the china wall. I cut off the end bolt hole gasket areas from the old 1256s, used them as a gasket simulation, and bolted the manifold in the four corners to 30 lbs. Still clearance. Not a ton. .040 up front, and .033 out back.

Doorgunner, I used your suggestion of moving the manifold to one side and measuring gap on opposite side. Numbers consistent. I even tried two other intakes I had laying around. An LT1 GM intake and another cast iron GM Qjet manifold. Weird. The aluminum manifold sat the tightest while on the china wall for side to side movement. Spare cast iron manifold a little looser, and the one I'm using is the the loosest. The side to side movement while resting on the valley did not affect taper numbers. Surprised of the variation in side to side movement with these supposed untouched manifolds, but I have heard this is also an issue with aftermarket intakes.

All tests confirm too much bite on bottom of port gaskets - right side. Why this is causing an intake valley oil leak as opposed to an air leak from top. I don't know. Will be seeing machinist tomorrow. I still think plane .014 or .015 off bottom of right side taper up to zero. Maybe a bit off the china walls too. Will update.

Summary of gap tests :

Summary of 4 new gap tests. Results averaged and compared to initial washer solder method


1204 gaskets used with RTV, then I tried 1256s. I removed the heat riser restrictor plates. Cyl 2 & 4

1204 Cyl 6 & 8


Tried GM OTC LT1 manifold

LT1 left side. Easier to see gaps with aluminum manifold. No gap while on China wall

LT1 Right side. Gap at top of runner

Left side front

Right side front

Old spare cast iron intake used.

I don't think this qualifies as a machinists protractor! LOL I tried with it though. Not really accurate. I have a lot f tools, but unfortunately not a good protractor

 

I bet every machine shop owner wished they had documentation from customers, even if only half as good as yours

 

I urge you to keep the heat riser blockoff in place on these gaskets if running the Winters intake......
The heat it creates leaving open will literally destroy the old porous Winters casting.....from the inside out. Not to mention the excess heat it creates at the carb base. There are some who say you need heat here and I am not one of them. If you live in Detroit and drive it in the winter....fine.....but other than that.....no way. The choke will have to be converted to electric as well but even that is a better setup.
I don't see a lot of variance here...I see intakes that are not flat, and that may be the problem.
I install my 1204's dry....with only some holding RTV under the four water ports to hold it in place.

Jebby