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Discussion Starter #1
I suspect an intake manifold leak on my 428/Blue Thunder intake manifold. Stock block and Heads and exhaust 69 Mach 1 SCJ. Car seems to runs fine except that #6 plug fouls up at about every 300 miles. I did install the intake about 5 years/7000 miles ago but the plug has been fouling up/missing in the last 1000 miles or so. I borrowed a camera and will go in through the plug hole for a look around. My question; what should I be looking for if the gasket is the problem ? Thanks, Brian
 

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When I pulled the original intake off my 351C I found a crack in the manifold. The crack didn't do any harm because it was not through a runner and the Cleveland had its turkey pan gasket. Upon closer inspection, I could see an imprint of the corner of another manifold on one side of the crack. Looks like it was still hot out the mold and another manifold fell on it.
 

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I borrowed a camera and will go in through the plug hole for a look around.

It seems to me that you should remove the carb and send the camera down the intake runner if you are looking for a gasket failure between the intake and the head. Since you're working on an FE maybe remove the valve cover and snake a light down into the intake valley and then look for light leaking into the intake runner.
 

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Assuming, by "fouling", you mean OIL fouling of the plug, I'd pull the carb, run the camera down the #6 intake runner, and look for oil entering at the parting line between intake manifold and cylinder head. If none, go down further and look for oil entering through the valve guide.

BTW, before you do all this... have you run a cranking compression test on ALL the cylinders?
 

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Discussion Starter #5
Thanks for the thoughts guys. Not much to see going in through the plug hole. In through the top of the intake should be a better look. Yes checked the compression and the numbers were all the same as a test done two years back. #6 is steady at 190 lbs. Oil on the plug threads each time I pull it and enough to need cleaning not just a drop. Brian
 

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Oil isn't going to get on the threads of the spark plug from inside the combustion chamber. Oil on the threads is from a valve cover leak.
 

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Discussion Starter #7
I agree with that. Checked the valve cover all around more than a dozen times, over six months, and the paper towel come up clean every time ? Also would not be fouling only the one plug. Thanks for the thought any other ideas ? I am listening.. Brian
 

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Discussion Starter #9
Replaced and switched wires. #2 into #6 and #6 over to #2
 

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Any chance someone plumbed the EGR valve from the valve cover into a vacuum port on that cylinder, folks do that all the time instead of plumbing it into the carb base...


If not, your probably looking at an intake gasket failure sucking from the lifter valley. In any case, sounds like the manifold needs to be pulled and both the gasket and intake inspected.


Perhaps a failed valve seal also...
 

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how are the heads ?

Brian, how are the cylinderheads ? have they ever been worked on ? On the old FE, there is a big lump in the roof of the port on cylinders 3 and 6. Frequently this lump gets ground away to equalize the ports. This leaves you with a small hole in the roof of those two ports. If your heads have ever had this done, you have to put sealant on the threads so you don't drizzle pressurized oil into the port. We use studs for the rockershafts if we have opened up the ports. LSG
 

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Discussion Starter #12 (Edited)
OK great observations and questions. Attempting to keep it simple I was holding back on some information/modifications. The rest of the story; Yes the heads have been 'worked on'. Shaved/milled and ported also the block surface may have been surfaced. The intake has been milled in order to fit the modified heads. How much material removed from where is hard to know. I have no history on the engine mods/rebuild. Probably not important but the heads have also been switched. No working smog or parts installed PCV and oil filler cap only. Hydraulic lifters are gone and running a flat tappet set-up. Great observation on the oiler bumps at # 3 and 6. A local FE buddy informed me of this possibility and I have explored it a bit. Did not install any studs but did do some measuring and did add a washer to the oiler/rocker arm assembly bolt. While that bolt was not bottomed out is was close. Did not add any sealant. This may be something I should re-visit ? Trying to explore every possibility before actually taking the top end off. Thanks, Brian
 

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oil leaks, machining errors

Brian, it looks from the picture that the oil lumps are untouched. does the lump appear to have a crack or a stain where oil may have been weeping out of it ? What intake gasket have you benn using ? How do your stem seals look ? And who machined the intake and assembled the engine ?! The intake should NOT have been machined, proper procedure is to measure & check fit with an unmolested factory iron intake, then, you need to make room, you mill the intake sides of the cylinderheads. Unfortunately, there are LOTS of folks out there who either didn't go to machine shop school don't understand geometry, or both. Do you still have the original iron intake ? ( for comparison ) How do we know if the intake was cut straight and not screwed up ? A goofy intake, all by itself, is enough to cause the oil problem you are having. Can't stress it enough, the intakes ought to be left alone. Why on earth would you do that ? ! If you have any work done, pick someone else next time. LSG
 

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Discussion Starter #14 (Edited)
OK thanks for the observations and the suggestions. Yes the oil bump appears alright but will get a closer inspection. No staining or oil seepage was observed the last time I was there. Valve stem seals are of the perfect circle type and appear 0K. Will be replaced as I proceed. I had the intake machined. A local shop did as I instructed removing a total of .095 from the sides and .250 off the carb. pad to accommodate the Shaker assembly. The intake gaskets I used are the FelPro MS 90145. Who performed the engine mods and assembly is unknown. The owner before last did the work and his widow knew nothing of the motor or car. The OE 428 intake was not on the car when I got it. Had been replaced with a machined to fit Weiland intake. Machining the heads, after all they already been machined, may have been the correct procedure it was not the route I choose. So it's still looking like the intake gasket is the problem ? Any other suspect areas to inspect before the real job begins ? Brian
 

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well,........

Brian, I think I'd leave the heads on unless you're purchasing a new intake and remachining the sides of the heads. My best guess, is that the intake is way too small ( width ) and you aren't getting a good seal on the intake gaskets. How did you come up with .095 needed to be removed ? The shop I retired from has an unmolested iron intake ( mine ) to use for test fits, once the heads are torqued down. Then, if there is not enough room, the heads come back off, and they get cut on the intake face, then washed and reinstalled. You might ask 'Dr Rabotnik' @ Survival Motorsports if he has a thicker version of a Fel-Pro 1246S-3 gasket. Regular gaskets are .065, I thought he had .090 or .125 thick. He usually has some in stock to help out guys with exactly your problem. Don't feel too bad, 40 yrs ago this stuff was common knowledge, but it would seem almost everyone has forgotten how to do a lot of basic things, intake manifolds being a comon problem. LSG
 
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