Intake / Valley Pan Leak

[schenker]

M code 351C. It recently started running like crap when hot. Added new Pertronix coil and ignition but no change. I found a bubblin crude coming out at the base of the intake manifold, which I assume is the root of my issues. I ordered FelPro MS96012 valley pan / gasket and will install that this weekend if I have time. Any sage advice on this procedure? I do plan on using the valley pan. TIA

 

[71coop]

What are the symptoms when hot? An oil leak from the manifold base would not necessarily have any effect on running at any temp (I am assuming you don't have a cracked intake and aren't leaking into the runners....?)

 

[schenker]

Symptoms are weak idle and persistent miss not consistent to any cylinder. I'm assuming that the manifold is leaking air somewhere in addition to the oil issue. Plugs look good and I have replaced the coil / ignition already. I'll inspect the manifold, get the valley pan replaced, and replace the carb gasket and see what that gets me.

 

[71ProjectJunk]

Have you checked to see if the carburetor float is not sticking. Sounds like when you have debris on your needle and seat, or you float is sticking open, and your carb gets full of fuel and you start getting a fuel leak through the boosters in the carburetor. Easy to check, just take air cleaner off, turn on the engine and look down the front barrels of the carburetor, if you see fuel leaking slowly through the boosters you have found your problem. Another easy check to see if you have an air leak is to just spray some starting fluid on the manifold gasket surfaces while the engine is running to see if you have air coming in, if air is coming in you will get an increase in RPM as soon as the starting fluid hit the air leak area. Another thing to look for is a vacuum leak on something other than the intake manifold to head surfaces. Check all vacuum hoses, especially the one going to the brake booster, and your PCV valve and hose.

 

[Stanglover]

@schenker;
As you have been a member for many years, may I ask if you've done a 'search' for "manifold" information? I know much has been posted over the years I've been a member and I have posted on my own escapades with my M code.
With no idea as to your own mechanical abilities, swapping a valley pan gasket is not as easy as it may sound. That said, it is doable. However, do all the checks 71ProjectJunk and others suggest first.
I'm no mechanic nor an expert, but I have pulled my intake a couple of time, but for other reasons. First time was when I wanted to block off the heat cross-over passage under the carb because I installed a new Holley 670 and was getting a lot of fuel vaporization or vapor lock and hard starting when hot. The second time was after the engine had to be rebuilt a second time and the manifold was installed with the rubber end gaskets, which were leaking oil. On that issue I will absolutely suggest you use "The Right Stuff" on the ends and up the heads about 1/2". On the pan and paper gasket, I used Permatex gasket sealer #2, which stays soft. When lowering the manifold in place, use a couple of 5/16" long bolts with the heads cut off located one per side around the center. I found that using a couple of 1/4" EYE bolts screwed diagonally into the carb base, and a piece of pipe along with a good helper, make dropping the manifold down square and even, works wonders.
Here's hoping you find the issue without going that far, but if not, good luck, take your time and have fun doing it.

 

[cheezsnake]

Plus one to stanglover install tips! I will say, I’ve had better luck following the FelPro directions for the valley pan. I’ve changed at least 5-6 cleveland intakes over the years, and the only time I had an issue is when I used sealant instead of the rubber seals provided. Developed an oil leak at the back that collected around the sending unit. I’m sure it was something I did wrong with the bead. Just found it’s easier to use the end seals. Last install, went back to them. No leaks. Good luck!

 

[schenker]

Thanks for the advice all

Have you checked to see if the carburetor float is not sticking. Sounds like when you have debris on your needle and seat, or you float is sticking open, and your carb gets full of fuel and you start getting a fuel leak through the boosters in the carburetor. Easy to check, just take air cleaner off, turn on the engine and look down the front barrels of the carburetor, if you see fuel leaking slowly through the boosters you have found your problem.

Dribbly boosters was not even on my radar but was absolutely the problem. I pulled the idle air screw and shot it with carb cleaner / compressed air and she is running nearly perfect. When I replace the valley pan I will need to have at a thorough clean up of the carb while I have it out. I appreciate the hot tip.

 

[Stanglover]

Plus one to stanglover install tips! I will say, I’ve had better luck following the FelPro directions for the valley pan. I’ve changed at least 5-6 cleveland intakes over the years, and the only time I had an issue is when I used sealant instead of the rubber seals provided. Developed an oil leak at the back that collected around the sending unit. I’m sure it was something I did wrong with the bead. Just found it’s easier to use the end seals. Last install, went back to them. No leaks. Good luck!

Both times I had my engine rebuilt, the rubber end seal leaked even though they looked good and in place when the manifold was pulled. And as you say, I too had a big pool of oil around the sender.
A friend who also builds his own engines (cough, Chevy's) suggested using a good 1/4" + bead of "The Right Stuff" and I've had no problem since and that is now 6 years.
I would prefer to just avoid the possibility to start with, but the choice of the poster.

 

[kcmash]

I use the gel pro kit. Use the provided grey RTV, seal the fiber gaskets. Use the black rubber end pieces and the RTV in the corners at the heads. Use brush tack sealant on the top side of the valley pan ports.

Torque in 2 steps per the service manual. Let sit for 24 hours before running.

At least that’s what I have read.

Kcmash

 

[Kenny]

Symptoms are weak idle and persistent miss not consistent to any cylinder. I'm assuming that the manifold is leaking air somewhere in addition to the oil issue. Plugs look good and I have replaced the coil / ignition already. I'll inspect the manifold, get the valley pan replaced, and replace the carb gasket and see what that gets me.

Spray WD-40 all around intake manifold where the gasket seals to the heads and block while the engine is at idle. When you spray the area of the leaking gasket the idle should line out. This will prove you have a leaking gasket and not something else.