scott2173

So I seem to have a leak and as far as I can see I don't see a gasket between the head and the exhaust manifold. Did they have gaskets or not? I really hope its not a crack in he manifold.
Sorry forgot to mention its a stock 71 350

Hammerhead Fred

No gasket. Exhaust manifold is easy to replace.

scott2173

so what you are saying is its most likely cracked and I need a new exhaust manifold ?

mikem350

You try snugging up the manifold bolts?

I have seen a loose sparkplug imitate an exhaust leak!

scott2173

they are all tight and the plugs too

Hammerhead Fred

Then time to grab a length of water hose (hose of your choice) put one end up to your ear and move the other end near where you hear the noise until you can pinpoint the source. But, if you've ruled out the bolts and plugs a cracked manifold is next likely source.

Alan 71

Hi Scott,
I don't know just what fasteners you're using but originally in 71 there were 2 different length bolts and also thick washers used on some bolts.
I'm not sure if using these bolt/washer combinations where they were required might have an effect on the manifold to head seal.
Maybe?
Regards,
Alan

Here's one of the washers in place behind the french lock. The AIM indicates where they were to be used.

Calo69

If you still have smog pump check injection lines going into manifold, especially at any bends

7T1vette

Stock heads/exhaust manifolds did not come with gaskets. But, newly machined castings were pretty flat from the factory, so they weren't really needed. If you have stock parts, either they have warped over years of heat/use or the retaining bolts are not really holding the parts tightly together.

There can be cr@p at the bottom of the bolt hole which could limit bolt travel and greatly reduce clamping loads. One of the bolts may be too long for the hole in which it is placed. Or a bolt could have loosened (if not locked in place with french locks or retaining wire), then rusted in place to 'appear' tight...but joint may not be completely sealed.

If you have aftermarket headers, you likely NEED gaskets. Few of them have the face surfaces finish machined AFTER construction. ALL heads and manifolds should be checked for flatness across the entire mating surfaces with a good metal straight-edge...before assembly. Then, gaskets can be installed if needed.

There are several good types of bolt retaining systems for this particular joint. Whatever is used should be able to maintain bolt torque load with the heating and vibration that joint sees every time the engine is run. Just using lockwashers will [usually] NOT get that job done very well.

Rcdizy

interesting thing to learn. I always assumed they had gaskets

scott2173

my car has no smog pump

scott2173

Alan your car is most defiantly the bench mark for a 71

scott2173

Let me explain how this started.
I now live in Key West and if you have ever been here there is no parking here so I keep my car up the keys in Big Pine Key.
I drove it to the airport to get fuel and back to Key West and had no problem "about 65 miles"then later in the evening I went to go wash it and as I was driving all of a sudden it started to make the no doubt exhaust leak noise.
I'm beginning to think its a cracked manifold I have taken it back to the garage where I keep it and I'm going find out what it is for sure this weekend.
Thank you all for your input please keep it coming!!!!!

PAmotorman

have someone stuff a rag up the tail pipe and hold it in there with a hammer handle. with the engine idling listen for a hissing sound around the exhaust manifold

CanadaGrant

Check the seal/gasket where the exhaust manifold joins the exhaust pipe. It might not be at the head.