thunderstick

when my heads were done, they were milled down .008 and i have had an oil consumption issue from day one (through the intake), with no real obvious answer to the problem. i replaced the intake manifold gasket again and used a thin coat of rtv on both sides for added measure. when i disassembled the intake and heads this time, those gaskets separated cleanly and intact, like they were never torqued down properly. in researching all of this, i have come across a machinists chart for milling, based on what was done to the heads. according to that chart, the bottom AND sides both have to be milled down.(?) any machinists out there to confirm or deny this for me? that is the only logical explanation to my problem... am about to take the intake to the shop, but would like to be sure i'm doing the right thing before any metal comes off the intake.

- keith

grumpyvette

if you only had the heads FLAT MILLED .008 I doubt thats your problem, if ANGLE MILLED it could be,

http://forum.grumpysperformance.com/...e+milled#p9055

http://forum.grumpysperformance.com/...464&p=570#p570

read the links and sub links, it will save you hours chasing leaks if you do things correctly

thunderstick

they had a 3-angle valve job done on them...

afremont

That's not what he means, he means changing the angle the head sits with respect to the top of the deck. Technically, any time you mill the deck or heads, you are supposed to mill the intake just to make things aline perfectly. .008 inches isn't likely to be a problem in the real world, in my opinion. Gaskets can make bigger differences than that.

If your real paranoid, you could mill the end rails of the intake a little to make sure it sits down as far as it can. Anytime I mess with any of this, I'm always worried that something is leaking vacuum somewhere.

thunderstick

i figured that's what he meant but i don't know what's all entailed when they do a 3-angled valve job, if the head surface had anything to do with it, so that's why i threw that out there. 008 doesn't seem like alot to me, either. last build i did (when this problem existed) i used a felpro head gasket with a .039 thickness, this time i'm using the gm gasket, .028 thickness, so maybe that combination with work. the machine shop that originally did the head work suspected the (teflon) valve seals, but they seemed to be ok, even tho they replaced them this time. just doesn't make any sense why i'm getting oil in to the upper plenum and consequently down in the cylinders. that is the problem i've not been able to solve... so apparently the heads being milled .008 shouldn't have too much of an effect on the intake fitment...

TTOP350

iTrader: (8)

Do you have a PCV system on the motor?

thunderstick

yes. and at one time when i was trying to figure the oil consumption out, i put a breather in place of the pcv valve, but the pass side was still hooked up to the throttle body. i have an LT4 hotcam in it, which supposedly produces lower vacuum, so on this build i am installing a pcv for lower vacuum. i researched that on here and got the part number so have it standing by. i'm also going to vent the pass side overboard this time to see if that's where it's going. the pcv system is the only way i know of that raw oil can get up in the plenum... and it was well evident, too. seems logical that it would then get in to all 8 holes...

thunderstick

upon some more thought, i probly screwed the pooch in using a .039 head gasket during the original rebuild, meaning that if gm used a .028 gasket originally, i added .011 to that minus .008 that was milled off, but since the heads are at an angle, as that dimension is increased, the heads "move away" from the intake. so i think it never got a good seal (remember i said the gaskets removed cleanly). i'm gonna speculate now that with a .028 gasket that the intake will seat and seal as it should... any other thoughts on this? anybody know what thickness original gaskets were?

1gary

When you get the intake off again,run a straight edge of the sealing surfaces of it and look for it being alittle tweaked too. You want to run the at a angle like 45 degrees to the sealing surfaces. If it's not completely flat,that is your problem.