Thread: SBC 350 Intake Gaskets Not Sealing

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Hi Everyone,

I have a stock 350SBC that I have recently installed the following parts:
AFR195 heads (AFR-1036)
Comp XE284H hydraulic flat tappet camshaft
Edelbrock Performer RPM Air Gap intake (EDL-7501)
Holley 750cfm carburetor (HLY-0-80508S)

The motor is burning a lot of oil. I’ve narrowed down the issue to the intake gaskets not sealing correctly; they have become oil soaked. I’ve tried two different sets of gaskets, the EDL-7201 0.060 gaskets, and FelPro 1266 0.120 gaskets; both have produced the same results (pictures attached). On the second set of gaskets, I even used sealant around the intake ports (picture also below).

I’m starting to think that it’s possible there is an angle mismatch between the head and the intake; has anyone seen this issue before? All parts are brand new. I compressed some wax between the intake and head on both sides, and they appeared to be quite even on both sides. I’m going to try again tonight using solder in three spots on each side and see what the profile looks like.

Does anyone have any suggestions on how to fix this issue? Should I get a set of MLS gaskets to try and seal it? Any of you seen this issue?

At this point I’m not quite sure what to try next, except checking the angle between the intake and the heads, which confuses me because these parts are all brand new.

Appreciate the help anyone has to offer,

-Alex

Pictures: https://imgur.com/a/Ds10gT6

Welcome to CHR. I'm not sure that it's relevant, but the first thing that comes to mind is that you have no gap at the "china wall" block to intake surfaces front and back. If your Edelbrock intake is sitting too low and actually riding on the block surfaces then the intake to head surfaces aren't going to seal, and this would be made worse if you're using rubber gaskets on the china wall seal. Just my thought, and it may be bogus.

Clean all of that mess off the block. Then with a fresh set of the recommended Fel Pro gaskets and modeling clay on the china walls, set the intake manifold back on. No need to bolt it down, you want to see what kind of impression is made at the China walls. That should tell you what you need to know and BTW, was the block decked?

When you installed the heads were the locator pins in the block? Without the pins the heads can slide down slightly on the bolts and cause interference between the heads and intake, not allowing them to seal.

Originally Posted by NTFDAY

Clean all of that mess off the block. Then with a fresh set of the recommended Fel Pro gaskets and modeling clay on the china walls, set the intake manifold back on. No need to bolt it down, you want to see what kind of impression is made at the China walls. That should tell you what you need to know and BTW, was the block decked?

That's a good idea with the modeling clay. I'm going to use a set of FelPro 1206 gaskets this time (as recommended).

The block has not been decked to my knowledge.

Originally Posted by 36 sedan

When you installed the heads were the locator pins in the block? Without the pins the heads can slide down slightly on the bolts and cause interference between the heads and intake, not allowing them to seal.

The locator pins were in the block when the heads were installed.

Originally Posted by rspears

Welcome to CHR. I'm not sure that it's relevant, but the first thing that comes to mind is that you have no gap at the "china wall" block to intake surfaces front and back. If your Edelbrock intake is sitting too low and actually riding on the block surfaces then the intake to head surfaces aren't going to seal, and this would be made worse if you're using rubber gaskets on the china wall seal. Just my thought, and it may be bogus.

There is a small gap both front and rear (maybe 1/4"?) on the china walls.

have you pulled the sparkplugs??? in the pics seems like ONE cylinder sucking oil--------

Originally Posted by amgnvan

That's a good idea with the modeling clay. I'm going to use a set of FelPro 1206 gaskets this time (as recommended).

The block has not been decked to my knowledge.

Ken's advice is solid. The only thing I'd add is to oil the china wall surface on the intake before you set it down on the clay, to compress the clay and then release clean. W/O oil the clay may stick and you won't get a good impression.

Assuming that this block has never been decked, clean everything real god and start with a fresh set of Fel-Pro 1205 gaskets – not 1206. The 1205 has a bit more gasket and will better seal with this head/manifold combination. Place them with the blue facing the manifold. I have used a very light coat of Gasgacinch on the heads of SBC engines for years – it’s optional, but it helps hold everything in place.

Put a nice bead of black silicone on the China walls and let it skin over. Use an extra blob at the corners.

Set the intake down gently on the engine and follow the exact sequence of tightening as recommended by Edelbrock. DO NOT over torque or you will squish the silicone out and have the same problems all over again.

If the block has been decked - may be a different issue.

Glenn

As per my last post, AFR recommends 1205:

https://www.airflowresearch.com/fel-...intake-gasket/

Originally Posted by glennsexton

Assuming that this block has never been decked, clean everything real god and start with a fresh set of Fel-Pro 1205 gaskets – not 1206. The 1205 has a bit more gasket and will better seal with this head/manifold combination. Place them with the blue facing the manifold. I have used a very light coat of Gasgacinch on the heads of SBC engines for years – it’s optional, but it helps hold everything in place.

Put a nice bead of black silicone on the China walls and let it skin over. Use an extra blob at the corners.

Set the intake down gently on the engine and follow the exact sequence of tightening as recommended by Edelbrock. DO NOT over torque or you will squish the silicone out and have the same problems all over again.

If the block has been decked - may be a different issue.

Glenn

Thanks for the informative post. Unfortunately I read this one too late,...! I have done everything as you have indicated, although I used 1206 instead of 1205. Hopefully the 1206's do the trick for me, if not at least I know what to do.

I also did more reading, and noticed that the rocker studs for the intake valves are not installed into blind holes on the AFR heads,...they go straight through into the intake port. I did not use any thread sealant on these, and believe oil was being sucked in through the bolts here; I made sure to remove all of them and apply thread sealant.

At the moment everything is drying, I will fire it up tonight and see what happens.

Thanks again for the information.

Another area for possible consideration is the intake ports being ground thru next to the push rod holes-------unfortunately this is a common occurrance we see quite often not only in hand ported heads but the CNC ported ones also-----

Originally Posted by jerry clayton

Another area for possible consideration is the intake ports being ground thru next to the push rod holes-------unfortunately this is a common occurrance we see quite often not only in hand ported heads but the CNC ported ones also-----

Thanks for the reply. Are you able to clarify a little? I don't think I'm fully understanding what you're mentioning.

The ports have been enlarged to the point that the walls have been pentatrated by the holes the pushrods go thru-this will be about 1 inch into the intake port where the port is narrowest because of the pushrod passage----------there are 2 intake ports between the pushrods--------????????????