LT1 Based Engine Tech 1993-1997 LT1/LT4 Engine Related

Intake sealing problems

Old May 7, 2006 | 10:47 PM
  #1  
brokeTA's Avatar
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Intake sealing problems

We just finished a rebuild on an engine. Get the engine back in the car to only find it smokes alot. So after spending countless hours on the heads trying to find a problem, and getting close to pulling the engine back out (we thought it might be a ring problem) we decide to pull the intake off to find that every single port had an excessive amount of oil. It was puddled up on top of the valve. While driving it would use about 1 to 1 1/2 quarts about every 20 miles. Put new seals on and still the same problem. Pull the intake back off and find oil in every port again. So this time we decide to load up the gasket with silicone around each port and let it sit over night to see if maybe it would take a little longer to start leaking. Fired it up the next morning and instantly started smoking. Pull it back off and used a micrometer to measure the compressed thickness of the gasket top and bottom to find about 11 thousandths difference from top of port to the bottom. The only thing we had done to the heads is cleaned up, valve job, and had all the surfaces cleaned and checked. We are at a loss as to why it would leak. Unless something was done at the machine shop to alter the gasket surfaces (ie angle milling the heads) there was only .004 taken off the head to assure proper head trueness, and it appears the intake side of the head was cleaned. If anybody has had this problem or might have any suggestions as to why this would be happening we would greatly appreciate all insights. We also used clay to see a pattern around the ports. We found that the bottom looks to be compressing good, but the top has barely any indication.
Old May 7, 2006 | 11:03 PM
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Re: Intake sealing problems

are you using the gaskets that seal the manifold the block? They are the two small cork gaskets. If you are thorw them away and use RTV instead.

http://shbox.com/ci/ci295.jpg
Old May 7, 2006 | 11:12 PM
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Re: Intake sealing problems

its not leaking from the front or rear, but actually leaking into the cylinder heads themselves causing the combustion chamber to fill with oil causing it to smoke.
Old May 7, 2006 | 11:16 PM
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Re: Intake sealing problems

But, if you have these gasket in place. It may not be allowing the manifold to be sit all the way down. they may be pushing the manifold up. Then, when you torque it down it doesn't seat correctly. Causing the internal oil leak and low manifold vacuum.
Old May 7, 2006 | 11:24 PM
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Re: Intake sealing problems

Yes we are using silicone for the front and rear gasket surface. I see what ur saying though, and the first time around I thought that I may have waited to long and let the silicone dry too much causing the same effect but I was wrong.
Old May 8, 2006 | 12:23 AM
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Re: Intake sealing problems

The oil in the ports could be caused by reversion due to the overlap of the cam. .011 is not that much and on top sees no oil.
Ya might have a ring problem and the oil on the piston is being sucked into the intake during the cam overlap cycle.
Old May 8, 2006 | 12:39 AM
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Re: Intake sealing problems

I thought about that with the rings, but wouldn't there be some other types of symptons. I would think if the rings were weak enough to let oil by, then a compression test would have shown the opposite. Compression in each cylinder was 205-210 psi. I will perform a leakdown test in the morning that should give a final answer to a ring problem. Plus it is doing it on every single port. Also you can see the compressed gasket and tell where it is and isn't seating well. What would cause a problem like this with rings?
Old May 8, 2006 | 01:03 AM
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Re: Intake sealing problems

Wrong rings,collapsed rings,incorrect end gap,rings not seated,to much oil on rings during assy,incorrect install,and a bunch more things. Rings like to be installed dry with just a little oil on the walls. Moly rings are bad about not seating with to much oil.
All the oil in the cyls will show ya a good compression reading so a leak down should tell ya more.
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