Oil Consumption Issue

[Steve K]

Can cutting a head from 75cc chamber to 65cc chamber cause an angle mismatch between the head and intake manifold mating surfaces. My 427 SBC has a good appetite for oil, 1lt in 150 km (1qt in 90 miles). I've replaced the valve stem seals with no difference. Smokes on start up a bit. When the intake was off for another reason there was oil pooling up on the intake valves (thought it was the valve guide seals). Had the same issue on a 383 with the same heads and intake. Heads are AFR 210's and Edelbrock Tunnel Ram. Engine runs good and has good power. Vacuum is steady.

[miniv8]

If they where straight milled from 75 to 65 there might be an issue with the chinawalls on the block, lifting the intake from mating with the heads. There might only be room for a thin bead of silicone instead of a gasket on the walls.

But regardless, the angles are sometimes an issue, even mostly stock.

[rebelrouser]

If you think you are pulling vacuum from the crankcase, lifter valley, do a simple test. block the valve cover vents, and install a vacuum gauge into one of the cover holes. Fire the engine and read the gauge if it reads any vacuum, it has to be from a vacuum leak. Normal will read zero to a slight pressure from blowby. It takes a minute or so for the leak to pull the crankcase into a vacuum. Chrysler magnum engines used to have a plate on the bottom of the intake and it would leak causing oil consumption and rough idle, that is how we tested them.

[mag2555]

Don’t run the motor hard until you get this issue resolved.
Nothing cuts into a fuels octane level more then oil getting into the chamber!

[rebelyell]

Regarding milling heads & any resulting intake mismatch / corrections ... following link offers rudimentary guidelines ... Not necessarily absolutes.
https://www.crankshaftcoalition.com/wik ... nder_heads

[Steve.k]

If you are pulling oil from valley your intake ports will show signs of oil residue. Especially the amount it’s using.

[F-BIRD'88]

When sbc heads are milled down the material at the bottom of the heads intake port flange gets thinner.
AND the intake get raised up relative to the heads.
(Because the "V" of the heads intake flanges gets smaller)
The sealing surface contact area between the intake and heads ,at the gasket gets thinber. The gasket will have trouble holding a seal at the bottoms of the ports.
The intake may now need corrective cutting.
The intake gasket may need to be bonded to the heads on install. The mating angles of the intake and heass needs to be checked too so that the intake bolts crush the intake gasket evenly top and bottom.

This is why I tell people if you are going to mill down the heads a lot for compression to not lower the intake port floor at the opening.. Keep this area as thick as possible.
(eg: 1205 gasket size VS 1206 size.) It is a easy area to get carried away when porting sbc heads.
Result is intake gasket leaks and oil consumption.

Making the intake port openings at the flange biggy size looks good on a flow bench, but once the intake manifold is bolted on its a different story.

You need to check the intake flange geometry of BOTH HEADS.. While mounted on YOUR BLOCK.
do not assume they are both the same nor the block decks are cut right nor both R+L sides of the intake are cut the same angle and amount.

[Steve K]

Thanks for the responses, guys. So can the intake be cut to match or am I looking at new heads?

[BillK]

Thanks for the responses, guys. So can the intake be cut to match or am I looking at new heads?

You can cut the intake or the intake surface of the heads. Your choice. I prefer doing the heads. That way if you want to switch intakes in the future its not a big deal. A real good indication of how far off you are is to look at how the intake bolt holes line up with the heads.

[rgalajda]

I'm currently working on a 1969 427 / 425 hp Copo Chevelle .

I drilled holes in the intake gasket , one just above and just below the intake port, set a lead shot there and torqued intake down evenly with no end gasket. Removed intake and measured lead shots. The lead shots at the bottom of the ports were not compressed evenly. The right rear lower lead shot at .160" was not compressed at all. Intake gasket is .060".

The owner wants the OEM intake manifold retained.

Next I bolted on an aftermarket aluminum intake ( same process ) , removed and measured lead shots. All lead shots measured same thickness as intake gasket within thousands of an inch.

Heads had been machined before, but we don't know how much. Block has not been. These oem intakes are quite often warped after 50 years.
Machine shop is trying to correct OEM intake now

[Steve K]

Thanks for all the responses guys. I'll probably wind up replacing the heads...and putting off breast implants for my wife.

[FC-Pilot]

Thanks for all the responses guys. I'll probably wind up replacing the heads...and putting off breast implants for my wife.

Wooooh, no need make decisions like that. This is a poor mans fix, but I have fixed a few this way. If you can confirm it is coming from the valley into the intake, you can use sealant around he ports while installing new intake gaskets. I have done it a couple times to fix this issue as well as when I could not afford to have it become a problem. Yes, messy and poor, but sometimes when the combo is solid you just don’t want to tear it down and this is an option. Then you still have the money for the second investment.

Paul

[Steve K]

Well that certainly sounds like a better plan!

[1972ho]

Why not just set the intake on the heads without a gasket with a few bolts not tightened and use feller gauges around the sides of the flanges top and bottom and see how far off it is then make drawings of where it’s off and take it to a machine shop they should be able to get it squared up on the heads with your reading.

[Steve K]

So I nailed in in 2nd gear and got a nice cloud of white smoke out the exhaust. Cleared up by the time I hit 3rd. To me that sounds like oil getting past the intake gaskets under load.