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Intake manifold vacuum leaks (driving me mad)

Started by Julien Abrahams, July 30, 2014, 02:15:06 PM

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Julien Abrahams

Hey guys, this has been driving me mad for the last half year. I still have a vacuum leak at the intake manifold, between the manifold and the heads. I know it is there because it does not idle as it should (not as smooth) and when I close the choke valve by hand, the RPM's go up. Also, when I spray brake cleaner around the flanges where the heads and the manifold meet, the RPM's go up.
I replaced the intake manifold gaskets more times than I can remember. Now, I made gaskets from rubber-cork gasket material that go around the intake ports (about 2.8 mm thick) and gaskets from a gasket material which is paper/cardboard with a steel core about 1.8 mm thick that I put between the manifold and the heads at the exhaust crossover. 
The rubber-cork material is designed to compress. I don't understand how the hell there can be a vacuum leak when the gaskets around the intake ports are thicker than the ones that are around the exhaust crossover ports.  >:( I was thinking about taking it apart again, and just use Reinzosil gasket maker (fuel and temperature resistant up to F 600 degrees.
1954 Cadillac series 62
1967 Cadillac Sedan De Ville HT
1969 Austin Healey Sprite
1979 Opel Kadett

waterzap

The best gasket stuff I have found was The Right Stuff. It seals very quickly though, so you need to be quick. Could your manifold be warped?
Leesburg, AL

Julien Abrahams

I don't think it is warped as it is cast iron. Cast iron just cracks instead of warping. Just to make sure, I have flattened it with a steel bar and sandpaper. So I doubt it that it is warped.
I also made sure that it is not the PCV valve, brake booster, transmission vacuum or the vacuum for the climate control (checked by disconnecting and plugging). The idle changes when I spray brake cleaner around the intake ports (there were the intake manifold and the heads meet).
1954 Cadillac series 62
1967 Cadillac Sedan De Ville HT
1969 Austin Healey Sprite
1979 Opel Kadett

waterzap

I am wondering. It is possible to make a home made smoke machine.

http://www.thesamba.com/vw/forum/viewtopic.php?p=5282178


Take the carb off, block off some of the ports and blow the smoke into the manifold. If it is leaking, the smoke should come out the sides, right?
Leesburg, AL

Scot Minesinger

I have a 1970 Cadillac and suffered the same problem and cured it.  What year?  Is it a 1967?
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty

Alan Harris CLC#1513

Trust me. Cast iron does warp. The manifold or the head could be warped. They need to be checked.

Roger Zimmermann

I confirm: I had so many problems with my '56 car until somebody else discovered the problem. A flat file, a feeler to check the gap, new gaskets and the problem was solved.
1956 Sedan de Ville (sold)
1956 Eldorado Biarritz
1957 Eldorado Brougham (sold)
1972 Coupe de Ville
2011 DTS
CLCMRC benefactor #101

Julien Abrahams

I will check it (again). It would need to be warped pretty badly if gaskets of about 3/32 inch cannot seal it (as the original steel gaskets are less than 1/16th of an inch.
1954 Cadillac series 62
1967 Cadillac Sedan De Ville HT
1969 Austin Healey Sprite
1979 Opel Kadett

dadscad

Please do not use "Brake Cleaner" around heat or flame. When super heated it can produce a poison gas that even in small doses can kill you or permanently disable you, or an innocent bystander.
Enjoy The Ride,
David Thomas CLC #14765
1963 Coupe deVille

Scot Minesinger

After being positive that the metal surfaces of head, block and intake are all flat and clean, which is sounds like you have and the intake manifold is not cracked or otherwise compromised, it seems like extreme concentration on the right gasket and sealer is essential.  USA Parts sells the correct gasket (or advertise so) and I would use that.  Read the shop manual to install.  Also presuming you have checked all other vacuum leak sources, such as at trans tube connection to vacuum modulator (that 3" vacuum tube often is missed), and etc.

This exact same problem was occurring on my 1970 Cadillac DVC when previous valve job resulted in bad vacuum leak.  The problem was that it was installed wrong in conflict with shop manual, but in concert with gasket installation instructions.  The valley pan area communicates with carb via PCV valve, so the entire gasket must be sealed just as thoroughly as the intake ports.  On my installation before I corrected it one of the end rubber block seals was dislodged during installation (that intake manifold on the 472 is heavy) and sealer was not used except at the intake ports.  In trying to set the timing with this bad of a leak it fluctuated three degrees. 

I sealed it so good when I placed the intake on the heads and block there was no metal to metal sound.  Runs perfect now, a pleasure to drive. 

Unfortunately it sounds like you need to take it apart again, sorry about that.  The right gasket will be worth the price.
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty

"Cadillac Kid" Greg Surfas 15364

Julien,
Your 67 has a 429 cubic inch motor and a separate valley cover below the intake.  Two things, and as scott says it will have to come apart again.  First of all, pull the intake manifold and visually check that the PCV tube and fittings going into the valley cover have not separated. There is a fitting that goes into the valley cover with a gasket that seals it, followed by a metal tube that connects to the "rubber" PCV tube and then the PCV to the carburetor.  This assembly is easily knocked out of place when installing the intake if you are not carefull.   If everything looks to be in order then (if this were mine) I would remove and replace the valley cover gasket, using something like Permatex high temp sealer on the outside edge of the valley cover to ensure sealing.  The valley will be under vacuum, so you need to seal it at the outside edge.
That said, If you engine has been worked on and the heads or the intake have been machined, you are going to have to be sure the contact angle (the angle between the ports on the head and those on the intake manifold) have not been widened to the point of exceeding the gasket's capacity to seal them.  With no gasket installed on the intake, place the manifold on the engine , lightly bolt it in place (just past finger tight), take a feeler guage and see if there is a difference between the clearances (Head to intake manifold) on any place the intake contacts the head, outer and what inner measurements you can make.
If need be have the intake machined to correct any warpage.
I have never had to use any sealer on the intake gaskets for my 429 and I would not thin k you really need to.  That is my experience however and perhaps others have had different "luck".
Greg Surfas
Cadillac Kid-Greg Surfas
Director Modified Chapter CLC
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

Julien Abrahams

hey guys, sorry for the late reply.
The valley pan cover gasket was replaced last year, so that should be good. So after searching on here and on other forums and some videos on youtube, I decided to have a go with a cigarette blowing smoke directly in the intake manifold with a tube on the connection for the whole climate control system (the tube that normally goes to the small vacuum tank. After removing the other vac lines (e.g. from the brake booster, the transmission and the vac advance, I started blowing smoke into the intake. After a while, the smoke started coming out from underneath the choke valve (which is logical). However, no smoke was emerging from the area between the intake manifold and the heads :S. There was a small leak where the intake manifold has a crack, but nothing major. So, this had me puzzled somewhat.
After a tip from a neighbor, I then checked using an unlit propane torch. By running the engine and putting the end of the torch all around the engine (carb,base of carb, intake manifold, flanges etc.) the rpms went up when I put the torch around the place where the manifold has a crack. Nothing happened to the idle speed when I put it someplace else.
Can I conclude from this that there is only a small vac leak were the manifold is cracked? Or is a propane torch not the way to go? I would think that if there is a vacuum leak, and the propane would get sucked in, the RPM's would go up?
And why the difference with using brake cleaner where the RPM's change more radically?
1954 Cadillac series 62
1967 Cadillac Sedan De Ville HT
1969 Austin Healey Sprite
1979 Opel Kadett

Scot Minesinger

If your 1967 Cadillac suffers a cracked intake manifold, it needs to be replaced.  I think Jeff at Willington CAD has one (google).  Follow the shop manual closely when replacing it.  Take note of Greg's post which explains where a mistake can be made in performing the work.  Any rubber hoses that are old and more easily replaced with manifold off, should be changed out with new good ones.
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty

russ austin

Try and weld it first.  Grind a V into the crack, and mig weld away. Heat the area to be welded, to almost a cherry red. Then weld. Wrap in a welders blanket. have heard of folks sticking the piece into the BBQ.  The part needs to cool slowly.
R.Austin

"Cadillac Kid" Greg Surfas 15364

Julien,
First of all, when you used the brake cleaner, or any other aerosol, it would be very difficult to not get some into the air where the carburetor inlet would pick it up, thus speeding up the idle.
If you are taqlking about the external choke stove/bi metalic as the choke valve, that part is not under engine vacuum, but is contiguous with the exhaust. However, if the crack you see extends unseen in the casting you may have discovered the culprit.
depending upon exactly what is cracked and how bad it is it is likely that it can be repaired.  You must, however, (again) remove the intake manifold for a very thorough inspection.
Greg Surfas
Cadillac Kid-Greg Surfas
Director Modified Chapter CLC
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

Julien Abrahams

Thanks for the replies guys!
Well, I have been looking for a replacement, but it seems to be like looking for a needle in a haystack. If you find one, they're pretty expensive (the ones I've seen went for around $400. And that does not include shipping (I'm in the Netherlands). As this thing weighs a ton, its not cheap to get it over here. Last year a guy rang me saying he had one. As it was so hard to find he wanted $650,- for it.
I already have had it welded at that spot, like Russ said: a V was grind (what's the past tense of 'to grind'?) and then it was welded. However, now it has cracked again at the same place.
@ Greg: With the choke valve, I mean the choke valve :). The valve that shuts when the engine is cold and the gas is pressed once. And yes, you could be right that the brake cleaner will get sucked into the air intake of the carb, and consequently raise the idle.
In the attachment is a picture of the intake manifold before it went to the weld shop. Here you can see the crack. I think it extends into the center far enough to cause a leak. So, I think that caused a lot of trouble. It has an LPG system . LPG costs about half of normal gasoline over here), but if you have a minor vacuum leak somewhere, the engine will immediately start to run badly. I wish the PO had not installed the LPG. However, the resale value then increases here in The Netherlands.
As a temporary fix, I put some gasket maker on it. Later this year I will take it to a wel shop to see if they can fix it properly. And I'll run it on gasoline. A bit more expensive, but a lot less of a  hassle.
1954 Cadillac series 62
1967 Cadillac Sedan De Ville HT
1969 Austin Healey Sprite
1979 Opel Kadett


"Cadillac Kid" Greg Surfas 15364

Chris,
Julien has a 67 which is a one year only Quadrajet.  The cylinder heads were unchanged from 66 so the manifold will fit on a 66 (I did mine that way with GREAT success).  The intake has an integral recess for the choke "stove" and the unique small primaries and monster secondaries, and cannot be mistaken for any other.
Greg Surfas
Cadillac Kid-Greg Surfas
Director Modified Chapter CLC
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

Scot Minesinger

I was thinking it was a gasoline powered Cadillac, not LPG.  I am not familiar with LPG and so all of my comments except replace the crack intake manifold may not apply.  Have heard others welding cracked cast iron engine parts (heads and intake manifolds) with limited success (except maybe exhaust manifolds - who has not done that?).  Google Jeff at Willington CAD he is on the East Coast of USA and so shipping may be less than most parts suppliers on west side of USA.  The intake manifold is half the weight it seems of a 472, so be glad it is not a 68 Cadillac with cracked intake manifold.
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty

Scot Minesinger

Greg,

I think a few others converted their 66 to a 67 manifold to use the Quadra-jet carb, making them more rare than 64-66 intake manifold spares.  It is a great idea, and I might have done the same thing.
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty