Hey guys,

I keep getting this vacuum leak accompanied by oil on some of my plug threads. I am pretty sure that it could be caused by my manifold to head fitment. I had my block decked .020" (9.005 deck height), and from what I had heard should not need to have the manifold milled.

Well since I keep getting this manifold leak (already tried 2 differant manifolds) and i pretty sure that I should get the damn intake milled, but I was wondering what you guys thought.

Any comments?

 

Are you sure that the leak is between the manifold and the heads? As for the oil, are you using thread sealer on the intake bolts?

 

Thats the only place left the for the leak to be, as far as I can tell. I have NEVER had a problem like this on any motor, this is the first motor that I have had decked, 2 + 2 = vacuum leak? lol.


ps...I love your little icon!

 

Do you have oil getting sucked in the cylinders?

You will have to put the manifold on the heads without a gasket and use feeler guages to see what the gap is.

You could try a thicker gasket also.

 

I am getting oil on the plug threads...doesnt look like on the insulator though. I was thinking about thicker gaskets, or doubling them up.

 

I have a freshly built 305 lg4 with those same symptoms. I first noticed the wet threads on the plugs and just ruled it as a little blowby, until the rings seated.No oil on the plugs. I was looking into some valvetrain noise, so i pulled the intake to look at the lifters and rest of valve train, when i noticed an excessive amount of oil coating the intake runners of the head, and about 1.5 inches upward on the manifold runners. My guess too, was that the intake gaskets were leaking. I only used rtv around the water jackes, maybe i should seal the whole gasket on the next install. My block was decked .010 to clean up and square. The intake gasket that my machineist recomended was the felpro #90314-1. It is aprox. .070 thick. Torqued the intake to 30 ft.lbs. on regular pattern, but i never went back to retorqe after intial break in. The engine runs pretty good, but just acts like it had a vac leak some where. And after seeing oil coating the intake runners, i bet it was coming from the lifter valley.All this time it has never shown any signs of burning oil. Hope this helps you guys, and always open for suggestion as well.

 

You know, that is the weird thing that i noticed too: It doesn't seem to burn oil. Huh, did you ever get it fixed? Did those gaskets work?

 

The motor is opened up as we speak. Not sure what gasket i going to use next. Might get more done this weekend. I might try the feeler guage technique for guaging thickness, but the gasket i used seem to fit well on orginal install. I think i failed to keep the intake bolts torqued after the motor was broke in. Also I am going put in new PCV valve too.

 

don't use RTV or silicone on the intake runnes, it disolves in gasoline, and will cause allot of problems later on(I know from experance) just use it on the "china walls" and mabe on the water passage, and as for the origanal question, you are supposted to get the intake milled when you get the heads or block milled or you will get oil leaks/vacume leaks.

 

i had the same prob on my engine rebuild and my machine shop milled both heads and intake .so id think you need both milled. are you useing new gaskets? good luck

 

Well, I always that you should never mill the intake manifold because then it will only mate up to that paticular eng. and what if you wanted to upgrade to a differant intake. Mill the intake side on the cyl. heads. Just my .02

Auggie

 

I used new gaskets, now i am trying a new manifold .

My machinist wants me to have the heads milled instead of the manifold for that same reason. I really don't care if that manifold/head/block combo are stuck together, i dont really plan on changing it again so I would rather just have the intake milled (but I don't think he wants to do that).

Thanks for the info guys.

 

My LG4 heads had a .010 clean up, and the deck surface has .010 clean up and square.The original gasket was metal and .018 thick. My machine shop used the felpro 1003 perma torque head gasket measuring .041 thick. So, the .010, .010 and .018 (original gasket) total is .038. New gasket is .041, so the head is aprox. .003 higher than its original location from stock. We didnt see the need to do any other special milling. The intake gaskets that i used the first go around were #1256 felpro, and plan to use them again. I think there is enough compression in those to absorb the .003 difference.I just need to keep the intake bolts torqued properly.Someone mentioned in here about a .020 cut on the deck,if the heads are uncut, that would be the same situation.Hope this helps. A friend reccomended the K&W copper coat gasket sealer, a light coat around the intake runners. Both sides, to prevent vacuume leaks.At this point, i will try anything.