70 intake crossover shield

[Dennis D.]

Not sure what its called. Its the metal shield "pinned" on the underside of my L-46 intake. If this part is available, does anyone know the part number?

In my quest to determine the cause the oily intake runner/ valve problem, I noticed that the edge of this shield may have been pinched between the head and intake. This may have caused a sealing problem with the mating surfaces.

Otherwise I'm still thinking the intake and head surfaces are not aligned. I found a site, "fowler automotive.com",that addresses this problem. They also have fixtures and literature for determining proper alignment. They will also do the machining. I believe they are in California. Has anyone had any experience with them?

[Joe L.]

Re: 70 intake crossover shield

dennis-----

The shield that you require was GM #3946830, but it was discontinued in May, 1985. I doubt that the shield has anything to do with your problem, but if you think that there might be some interference, you can grind or otherwise modify the shield to eliminate said interference. It is not critical that the shield be exactly as originally configured, except, of course, from the standpoint of interference considerations.

One thing you might check is to see if the intake manifold bolts bind on the upper surface of the manifold holes as they are being removed or installed. If so, you may see evidence of "thread marks" or galling on the upper surface of the holes. If you do find this condition, you can slightly elongate the holes and I think that it will solve the "wet port"/oil burning problem.

[Dennis D.]

Re: 70 intake crossover shield

Joe

The shield has a slight burr very close to one of the attaching hole. I intended to massage it a little, but I thought having a replacement would be easier. The problem may also be interference with the intake gasket. This can be remedied easy enough.

I'm going to check the bolt interference you suggest. I'm assuming the logic here is that If the block,(I know wasn't decked), or head surfaces have been machined, the intake will want to settle down to the lower position created by the machined surfaces.

Do you think if this is the problem, I should elogate the lower side of the intake bolt hole, or it doesn't matter.

Another observation was when I removed the intake gasket, there seemed to be more of a impression on the upper port openings, with very little imprint on the bottoms.

[Joe L.]

Re: 70 intake crossover shield

Dennis-----

It DEFINITELY matters which side of the bolt holes are elongated. If you elongate them on the wrong side it won't solve any problems, at all. They need to be elongated on the side that the "binding" occurs. I believe that in most cases this will be the UPPER side of the hole.

There are all sorts of reasons that misalignment between intake manifolds and cylinder heads occur. Once-upon-a-time I went through HUGE grief over this problem. Even using BRAND NEW cylinder block, cylinder heads, and intake manifold, I had the problem. I believe that the genesis of the problem had to do with the improper machining of the new cylinder block by GM. I was never able to solve it. However, when I was in the "trying-to-find-a-solution" situation, I never discovered the bolt elongation solution. I don't know how that escaped my intuition, but it did.

I now believe that the bolt hole elongation method will solve most cases involving minor misalignment and the resultant "wet port"/high oil consumption syndrome. Major misalignments will probably need to be solved via angle milling or otherwise milling of the intake manifold and/or cylinder heads as is, apparently, performed as a specialty by Fowler Machine.

I've never personally "tested" the bolt elongation method, but I do think that it will work in many cases. In fact, for the last several years, there has been a tool available from Powerhouse Tools (a division of Comp Cams) which allows the elongation of the holes by using a drill instead of a die grinder. This makes for a much quicker and neater operation. The point is, they don't make and sell the tool because the basic principle of hole elongation doesn't work to cure this problem.

[Clem Z.]

Re: 70 intake crossover shield

set the intake on the block without the end seals,just the side gaskets and see if all the bolts go in with just using your fingers and if not you need to elongate the holes

[Dennis D.]

Re: 70 intake crossover shield

clem and joe

good advice. I noticed the set I removed had a lot of extra material on the lower edge. Not sure who's they were. Do either of you have a preference for intake gaskets?(GM or aftermarket). I found a gasket set, GM # 3931606. Not sure if it's right for my application.

[Joe L.]

Re: 70 intake crossover shield

dennis-----

I prefer the OEM embossed-type intake gaskets. For your application the GM gasket set is GM #10147994.

GM #3931606 was a gasket kit for 1968 small block applications which included head gaskets, other gaskets, and , possibly, intake manifold gaskets. If so, it included intake manifold gasket set GM #3931600. For this set, the side gaskets are the same as your application. The end seals are different. Yours use the "post" type end seals and pre-69 uses the "flap" type end seals. If you use RTV instead of end seals (as I always recommend), the side gaskets in the 3931606 kit will be the embossed type you need and I recommend.