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Old 10-12-2012, 07:23 AM
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Intake Leak Into Lifter Valley???

Manifold has been off a few times, and every time, the gasket "crush" appears to be all around. But I'm consistently oil fouling the same three plugs. Clean them and again, the same three!

Engine runs beautifully. Is there a method for checking intake manifold sealing/leakage by pressurizing or ??, so as to accurately eliminate it as a probable cause? I trust my eyeballing the gasket, but it's possible I might be missing something.

This has been going on for a long time now. I'd sure like to have 8 dry plugs so I can begin fine tuning mixture settings.

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Old 10-12-2012, 07:48 AM
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When you have the intake off is there oil in those three ports? Are you sure it's the intake and not valve guides or valve seals?
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Old 10-12-2012, 08:26 AM
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If the gasket is doing its job, look elsewhere. Engine Czar's recommendation is probably the cause of your problem
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Old 10-12-2012, 09:14 AM
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Originally Posted by engineczar View Post
When you have the intake off is there oil in those three ports? Are you sure it's the intake and not valve guides or valve seals?
There's oil in most of the ports, and the valves have oily crud on them. Not sure which, but "most of" best describes the situation. The heads are brand new aluminum and the seals are brand new, gray/white in color with full metal jacket to hold the boss. I installed them, and I'm told that they are "the good ones for street/strip use". Not Teflon, but Viton?
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Old 10-12-2012, 09:17 AM
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Which heads are you using? What intake gasket are you using? Also when you assemble it how much gap do you have between the end rails of the block and the intake?
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Old 10-12-2012, 09:29 AM
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Which heads are you using? What intake gasket are you using? Also when you assemble it how much gap do you have between the end rails of the block and the intake?
Heads are ProFiler 195's ported to 203, 64cc chambers, angle plugs. Intake is LT1/Z28 dual plane, ported. Using FelPro 1205, which is trimmed to port size. This leaves narrow sealing areas in the gasket and the intake, which was not designed for the larger ports in the head. V E R Y careful alignment required, and it's possible that some areas may be "marginally" sealing due to some areas around ports which are as narrow as 3/16". Very hard for me to determine by eye, so that's why the request for a possible pressure test that can be done.

Block was decked so pistons are .004 above decks (ie: about .030" removed). Have about 1/32" thickness RTV on front/rear block walls, I believe. I did have to elongate manifold bolt holes downward towards valley in order to get bolts threaded into heads. Ports in LT1 are slightly smaller than ports in heads, so manifold ports are completely "within" head ports

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Old 10-12-2012, 10:05 AM
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Any reason to not use the FelPro 1206 gasket. It's about 1/32 bigger all the way around so you probably wouldn't have to do any trimming.
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Old 10-12-2012, 02:58 PM
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You could try backing off the adjustment of all of the intake valves so they are closed. Remove the carb and bolt on a plate to seal the manifold. Remove all vacuum hoses from the manifold and plug all fittings except one(say brake booster port) and connect a hose adapter to an air compressor and listen for air leakage?
Sometimes the rocker studs need sealer on the threads to keep oil from being sucked into the ports.
It really sounds like you need to have the sides of the intake milled to drop it down on the mating surface of the heads. By decking the block that much the bottom of the intake ports are probably too high on the head ports, not giving enough area for the gasket to seal well, letting oil get sucked in from the lifter valley. Engineczar asked how big the gap at the ends of the manifold were(front and back). I bet its lower than normal and will probably need milling as well. A good machine shop should be able to tell how much to mill depending on how much was take off the deck of the block. If you do a search, there are recomendations for the correct amounts to be removed from the sides/bottom of the manifold per amount removed from head/block decks.
Happens all the time.
FWIW
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Old 10-12-2012, 04:49 PM
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Any reason to not use the FelPro 1206 gasket. It's about 1/32 bigger all the way around so you probably wouldn't have to do any trimming.
The 1206 is too big for the LT1 intake. Sealing beads around ports are outside LT1 ports.
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Old 10-12-2012, 04:51 PM
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Originally Posted by ssmonty View Post
You could try backing off the adjustment of all of the intake valves so they are closed. Remove the carb and bolt on a plate to seal the manifold. Remove all vacuum hoses from the manifold and plug all fittings except one(say brake booster port) and connect a hose adapter to an air compressor and listen for air leakage?
Sometimes the rocker studs need sealer on the threads to keep oil from being sucked into the ports.
It really sounds like you need to have the sides of the intake milled to drop it down on the mating surface of the heads. By decking the block that much the bottom of the intake ports are probably too high on the head ports, not giving enough area for the gasket to seal well, letting oil get sucked in from the lifter valley. Engineczar asked how big the gap at the ends of the manifold were(front and back). I bet its lower than normal and will probably need milling as well. A good machine shop should be able to tell how much to mill depending on how much was take off the deck of the block. If you do a search, there are recomendations for the correct amounts to be removed from the sides/bottom of the manifold per amount removed from head/block decks.
Happens all the time.
FWIW
ssmonty
Would also have to remove/plug distributor and road draft tube hole in rear of block (small journal 1965 327 block). Wouldn't pressure leak past the stem seals?
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Old 10-13-2012, 10:12 AM
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You wouldn't have to plug the distributor hole or the road draft tube. They should be isolated from the intake ports unless the intake gasket seal to the head is bad, or bad intake valve to seat sealing.
You might want to try removing the distributor and use a piece of hose from the dizzy hole to your ear to listen for leakage after putting compressed air into the carb flange as I described earlier.
There will some leakage past the stem seals. It shouldn't be that much if the clearance between the stems and guides are in spec, and the seals are good.
If you use the same hose or smaller one to get it closer to the seals and hear air you may have found your problem.
I thought the Viton seals were black, but I could be wrong?
ssmonty
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Old 10-13-2012, 11:33 AM
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Originally Posted by ssmonty View Post
You wouldn't have to plug the distributor hole or the road draft tube. They should be isolated from the intake ports unless the intake gasket seal to the head is bad, or bad intake valve to seat sealing.
You might want to try removing the distributor and use a piece of hose from the dizzy hole to your ear to listen for leakage after putting compressed air into the carb flange as I described earlier.
There will some leakage past the stem seals. It shouldn't be that much if the clearance between the stems and guides are in spec, and the seals are good.
If you use the same hose or smaller one to get it closer to the seals and hear air you may have found your problem.
I thought the Viton seals were black, but I could be wrong?
ssmonty
You're right. I thought we were talking about pressurizing the crankcase. I may try it with low pressure to avoid passing air thru the valve seals, which are not designed to seal in this type of situation.

IMPORTANT update..................see next post.
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Old 10-13-2012, 11:45 AM
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Important update

Important update

AS A TEST, I removed and plugged the suction hose containing the PCV valve from the carb base. So now, what I have is:

1. Old road draft tube hole in rear of block STILL connected to air cleaner housing via stock Chevy 1" hose.

2. After removing and plugging 3/8" PCV hose from oil fill tube at front of intake manifold, I installed a temporary piece of filter material from an old breather filter to cover the nipple.

So the crankcase is vented to atmosphere at the oil fill tube, and vented to the air filter housing at the draft tube location.

Took the car for a 130 mile ride where cruising mostly at 50-70 MPH. Took engine at WOT to 7500 RPM three times. Took engine to 6000 RPM in 1st gear a few times and closed throttle. Never saw smoke out the back (not that I had ever seen any before, so no change here).

Got home and removed plugs. All 8 dry. What I did find this time was evidence of oil in the air cleaner, which was completely DRY before.

Now the question: How do I modify my PCV system so it doesn't suck oil? Can I use one at all?
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Old 10-13-2012, 03:33 PM
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Does your rocker cover have a baffle installed?
I run those crappy thin pressed moroso covers and I ripped a breather baffle out of a stock sbc steel pressed rocker cover and rivited it into the moroso cover for mine, mine doesn't suck oil.
You could also try putting an inline fuel filter in the PCV hose, that should trap it. Dont know how long before it would become saturated though. Haven't tried it but I heard that Grumpy Jenkins had.

Duke
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Old 10-13-2012, 04:56 PM
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Does your rocker cover have a baffle installed?
I run those crappy thin pressed moroso covers and I ripped a breather baffle out of a stock sbc steel pressed rocker cover and rivited it into the moroso cover for mine, mine doesn't suck oil.
You could also try putting an inline fuel filter in the PCV hose, that should trap it. Dont know how long before it would become saturated though. Haven't tried it but I heard that Grumpy Jenkins had.

Duke
The taps are not in the valve covers, which are cast aluminum Corvette covers. Was thinking about sticking a separator like used in air compressors into the line, so I could watch it and drain when needed. It would fill up in about 100 miles, based on my consumption, so not practical.

Want to figure a better system, if possible. First need to understand why it's happening, and if it's normal, or not.
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