manifold not sealing
 

I have a big block chevy 396, with 401 heads and 359 manifold.I'm geting oil in the intake port, and seeing it on the plugs.useing mr.gasket #110 gaskets. the angles on head and manifoild seem to be ok. any ideas out there thanks.

Re: manifold not sealing
 

Check the front and rear rail, if it contacts the block it will hold your intake up and it will suck oil. In most cases they need to be trimed.

Re: manifold not sealing
 

I use Mr. Gasket 5828 intake gaskets on our 427/425 Stock engine, with 401 heads, and a 359 intake.

As Bob said, I had to radically mill the ends of the intake, and on at least one of the blocks. I'm pretty sure I took 0.080" off the ends of the intake.

If you put the intake on the engine, with the gaskets, when you tighten the intake, there needs to be at least 0.060" between the ends of the intake and the block.

Take a new set of gaskets, with the block and heads clean, and install them, with no sealer anywhere. Tighten the intake down as you would to install it. Let it sit for an hour or so. Check the clearance on the ends. Then remove the intake, and check to see how well the intake gasket is imprinted on both sides. You should see a good solid imprint, on both sides, of the intake flange and the head flange. Pay particular attention to the bottom of the ports.

When used on the closed chamber engines, in Stock and Super Stock, the 401 heads are angle milled a fair amount, and then flat milled. It would be easy to miss getting the right amount of material removed from the intake flange of the head, and/or to miss correcting the angle.

Re: manifold not sealing
 

I have taken the block end rails down a touch so I'm free to change intakes without modifying them.

Re: manifold not sealing
 

I had the same issue, had to completely cut the manifold. Took .100 off each end and then milled the sides to make them flat. Sucking oil causes severe detonation.

Re: manifold not sealing
 

do the intake rockers stud bolt hole in head go thru to intake port? if so use teflon tape and some indian head sealant on the stud threads. just another possible cause.

Re: manifold not sealing
 

Yes, the stud bosses are open to the intake ports.