Intake Manifold Gasket Leaks??

Marcs66and06 · 02-06-2009, 01:31 AM

I have had this problem for a while now. Let me start with the basics its a 68'302 block with a Edel Performer 302 intake on it. The heads are the procomp alum (vic jr knock offs) and before that they were 66 289 heads (problem occured on both sets).

I keep blowing out the rear intake manifold gasket and pushing the front out ever so slightly. I have checked the vacumm from the carb to the valve cover and it is fine-sucks my finger right into the valve. I thought it might be blowing it out due to high crank case pressure but that does not seem to be the case.

Member on here have said use the cork gasket-dont use the cork gasket. I have done both...use the black RTV and let it sit and dry for 24hrs. Did that and no matter what it seems to be blowing out the rear. I am lost....typically for me I guess.

JayWaite · 02-06-2009, 02:17 AM

It's possible you have excessive blow-by. The only way to get excessive pressure in the crank case is due to rings not seating. If pcv is ok and there is no restriction in the pcv grommet then you have ring problems. A leak down test would be the next step.

Bill73ragtop · 02-06-2009, 08:11 AM

+ Blow-by. Had a similiar problem with a 71 M-code 351c. You may be able to feel the pressure thru the the dipstick tube but the leak-down test should be performed. My 351c problem was only evident above 4500rpm.

I've used cork with good results for years. Typically I install the gasket on the block with an adhesive sealant and let it set for 24 hrs, then a very thin layer of RTV on the top side just before installing the manifold.

joe69 · 02-06-2009, 08:20 AM

The best thing I have found instead of typical RTV is "The Right Stuff". It's awesome, it's thick, and dries faster than RTV. I agree with the others, do a leakdown test to find the condition of your engine.

Joe

68RCodeConv · 02-06-2009, 12:20 PM

Start over. Put the side gaskets one and drop the intake into place dry. Get a mirror and look at the gap at the back of the intake. I'll bet that it is 1/2" or more. Remove the intake. Clean the front and rear rail gasket surfaces clean, clean, clean with lacquer thinner. They need to pass the "white glove" test.

Throw away the cork gaskets.

Get silicone or the Right Stuff. Lay down a bead that is slightly thicker than the gaps front and back. Wait 1 hour. Put a thin layer of silicone on the top of the existing bead and a blob at each end of it. Drop the intake straight down, install the bolts FINGER TIGHT. Wait 24 hours then torque the bolts to spec.

The Edelbrock intake on my 351C had this same problem with the large gaps and just blew out the cork gaskets. When I use the process above I have never had a leak.

Maxum96 · 02-06-2009, 12:43 PM

Don't use the stock intake valley gaskets(the cork or rubber gaskets running between the heads on top of the block). Everytime I've tried to use them (302, 351C, 390) I've had nothing but leaks and problems. Clean up both sides of the valley (block side and intake manifold side) and lay a nice bead of silicon RTV. Don't use too much and have it ooze into the motor when you seat the intake. After you bolt the intake on, let it dry and fire the motor up. If you do it right, you'll have no leaks.

JayWaite · 02-06-2009, 01:38 PM

Just got off the phone with the guy's at Edelbrock. Looking for a common problem with those manifolds for you but nothing was suggested that you havent been told or done. I know you probably don't want to do it again but do as John suggest and the Edelbrock tech recommended the same thing. Just make sure you use The Right Stuff and no gasket as has been suggested. You might get lucky so give it a shot.

shbrandt · 02-06-2009, 02:59 PM

For what it is worth, I've got the same problem in the same location with my custom built 306. Edelbrock heads and intake manifold also. I know my engine builder knows his stuff, and has built many stock and performance engines so I'm sure he used the one of the methods described above. I had not thought about a ring (or two) failing to properly seal and create the pressure needed to blow out the seal. However, I have noticed some smoke on start up. Now I need to know how to do a leak down test.

JayWaite · 02-06-2009, 04:15 PM

Here is how to do a leak down test. However it might be cheaper to take to a mechanic depending on how much a gauge will cost you. Or you can pull the schrader valve out of a compression gauge loosen all the rocker arms hook the air up to the compression gauge hose and start listening. If air comes up thru the oil galleys then the rings are leaking. Another way to test without going to all that trouble is to remove the PCV plug the vent on the other valve cover and put a piece of toilet paper over the PCV hole. You will see the tp blow a little while holding it there but if it wants to fly out of your hand then that’s excessive blow-by. If you put your finger in the hole and remove it after a few seconds and hear air escaping or blowing you finger out the hole then you have to much pressure. That being said the best way is to use a leak down gauge.

Marcs66and06 · 02-06-2009, 04:53 PM

Thanks for the input- pulled the plugs because I am going drag racing tonight and man oh man was the number 4 spark plug had some oil on her. Thats the problem #4 cylinder rings are bad. I appreciate it guys! Now-try to rebore and hone-new piston, possibly? Or just buy a 408 stroker--he he he.

shbrandt · 02-06-2009, 05:02 PM

Will a compression test give me the same information? I already have a gauge with the rubber end on it.

joe69 · 02-06-2009, 09:56 PM

A compression test will tell you some of the story, but not all of it.

Joe

frdnut · 02-07-2009, 12:09 PM

Quote:

Originally Posted by joe69

The best thing I have found instead of typical RTV is "The Right Stuff". It's awesome, it's thick, and dries faster than RTV. I agree with the others, do a leakdown test to find the condition of your engine.

Joe

Throw away the cork gaskets and use this stuff...You don't need to let it sit for 24 hours either..Just let it start to skin over and install the intake..