1970 Intake Manifold

[Lee McGlamery]

Hi - I just purchased a correct intake for my 70 350/350. It was need of much cleaning including the removal of debris under the baffle plate. I removed the 4 rivets that hold the baffle to the bottom of the manifold and the area was full of burnt oil/grease residue. Can I remount the baffle plate with pop rivets or should I try to find aluminum rivets? Also there are three holes drilled in the baffle. Were these holes in the original baffle? What is the purpose of the baffle?

Thanks

Lee

[Joe L.]

Re: 1970 Intake Manifold

Lee------

The gunk that you removed is carbonized oil. The carbonization is caused by the very high temperature of the exhaust crossover passage. The shield is designed to seperate the external portion of the heat crossover passage from oil. It doesn't really prevent oil from contacting the manifold since the oil vapor/mist found in the lifter valley during engine operation will get inside the shield; it's in no way "sealed" and even has the oil drain holes that you described. The main purpose of the shield, in practice, is to keep the carbonized oil from "flaking off" and falling into the engine and to somewhat minimize the contact of oil with the exhaust heat crossover. Not all Chevrolet manifolds were originally equipped with this shield, but the 1970 GM casting #3965577 was originally so-equipped. The baffle was originally GM #3946830, but it's been discontinued for many years. A GM #6271021 can be modified to work, but it's been recently discontinued, too.

As far as attachment of the shield goes, you cannot use pop-rivets or aluminum rivets to attach it. There are 2 options open to you that I am aware of:

1) CAREFULLY drill and tap the manifold stud holes for #8-24 machine screws. Then, install the screws using Loctite locking compound. Use stainless steel machine screws. This is the option that I prefer, BY FAR;

2) replace the studs with new studs and tap them in. NEVER reuse the old studs. They're serrations will be lost and the studs will not fit tightly enough to ENSURE that they don't fall out (and, into the engine). New studs are available from GM under GM #10229247.