jjhoneck

1. Exhaust Manifold Gasket
I've got an exhaust leak at the manifold -- probably the gasket. (The whole exhaust system was replaced by the previous owner, but I've found some sketchy workmanship items, like U-bolts installed upside down, and today I found an exhaust flange connecting bolt just finger tight!)

So I go to O'Reilly's website, planning to order the stock 1972 Corvette 350 exhaust manifold gasket for in-store pick-up -- and I find a dozen choices. Some round, some square, some different sizes. WTF?

Which one should I order to fit a bone-stock 350 engine? I'd like to have the part in-hand before tearing into it.

2. Vacuum Choke Gizmo
The choke on my car is not working properly, which makes it very cold blooded. The choke on the Quadrajet carb looks to be a vacuum powered gizmo on the passenger side of the carb. Any suggestion on where I can order that part?

3. Spark Plug Wires
My spark plug wires are routed under the engine, beneath the exhaust, which makes them a real bitch to service (or even trace). I've seen pix on this site of some of your engines with the spark plug wires routed on top of the engine, with spacers to keep the wires neat.

Which way is better? Is my set-up original, or is the "on top" original?

If "on top" is better, where can I order those wires? (I've got the stock distributor.)

Thanks in advance!

SB64

Well GM really out did themselves by putting all of the shielding around the plugs,,wires and yes that fancy boomarang channel that the wires run under the sides of the block. That is the original way.
I ran into the same problem with intake gaskets so I went with an aftermarket vendor like Paragon, Zip there are plenty depending where you live.
Not sure on the choke. I had my carb rebuilt by Lar's and the thing is perfect.
Good luck!
RVZIO

Alan 71

Hi JJ,
Originally your 72 350 engine didn't use any gaskets between the heads and exhaust manifolds.
If you're still using the original heads and manifolds you might want to carefully clean the head and manifold mating surfaces and continue to not use any gaskets.

The original choke on your 72 350 engine was a thermostatic 'divorced type' choke.
It consisted of a small bi-metal coil under a small cover that controlled the operation of the engines choke based on the engine's temperature.

The 72 350 spark plug wires were run the way they were to protect them from the heat of the exhaust manifolds and also to allow them to be covered by the radio interference shielding.
Even if you reroute the wires you'll still need to use the 4 spark plug heat shields.
If you're still using the original radio you'll also need to continue use the distributor and spark plug wire shielding.
When run properly the spark plug wires can't be seen.

Regards,
Alan

No exhaust gasket being used. (71)


Choke stove, cover, linkage. (71)


Concealed spark-plug wires. (71)

jjhoneck

Thanks for the advice!

So GM tried to mate the exhaust to the engine without any gasket? Now I've heard everything. That seems like a really bad idea.

IF I could get at them, I would check the torrque on the connecting bolts. I have discovered that much of this engine is best reached from below, but, of course, I have no easy way of accessing the bottom of the car.

Sounds like a trip to the shop is in my future.

TimAT

The vacuum thing you're looking at is called a choke pull off. With the number from the carb, you should be able to walk into about any auto parts and walk out with it. It's adjusted by bending the link that runs from it's arm to the side of the carb. To confirm yours is good or bad, remove the vacuum line, push the arm back into the pot, compressing the diaphragm, then place your finger over the port where the hose was. Let go of the arm. If it stays in, the diaphragm is good. If it comes back out, it's bad.

Alan 71

Hi JJ,

"So GM tried to mate the exhaust to the engine without any gasket? Now I've heard everything. That seems like a really bad idea."

Chevrolet assembled literally millions of engines that were driven for literally hundreds of millions of miles without any gasket between the head and the exhaust manifolds.
Regards,
Alan

jjhoneck

Thanks! I will check that today.

jjhoneck

My 1952 Pontiac has a gasket.

Apparently by 1972, GM thought that mating dissimilar metals, in a wildly variable temperature environment that is subject to vibration and twisting loads was "a good idea"? lol

Oh, well. It took Japanese competition to get them to acknowledge the benefit of drink holders, too.

TimAT

I'm with Alan71 on this. The SBC was introduced in 1955 and the production run on the Gen 1 went until the LS engines were introduced- the BBC hit the market in 1965, and went until 1991 or so. None of them had factory installed head to manifold gaskets, and very few had problems. The manifold surface was flat, the head surface was flat, and they used French locks on the bolts to keep them tight.

BLUE1972

My 72 still does not leak without gaskets....

I used Aluminized gaskets from Rock Auto on my 71 and 1980 truck after the rebuilds - 2 years , 8 years and lots of miles and no leaks..

jjhoneck

Well, it obviously worked for many years. It's crazy, though.

Regardless, I've definitely got an exhaust leak on the right side of the engine. Once I get the car up on a lift, I will put a torque wrench on those bolts.

Any idea what torque they're supposed to be?

TimAT

I'd confirm that the leak is head to manifold and not the more common manifold/heat riser/pipe. The standard torque runs from 15 ft/lbs. for a grade 2 bolt to 37 ft/lbs. for a grade 8. I don't know what GM's specs are, but should be somewhere in the service manual.

jjhoneck

Thanks!

I never got to look at it today (this whole "work" thing is ruining my lifestyle), but I will be checking every part of that exhaust system.
--
Jay

jjhoneck

So I changed the oil today, for the first time.

Apparently my Corvette has an aftermarket "racing" oil pan. Changed the oil and filter, added the requisite 5 quarts of Mobil One -- and it was barely touching the dipstick.

My 350 cubic inch engine takes 7 quarts. Who knew?

JayRay

I had a similar issue and tightened the bolts and fixed it. Glad there were no gaskets or would of had to pull the exhaust manifold completely and heard horror stories of breaking bolts off.

jjhoneck

Interestingly, today I was able to get it up on a lift and we found the right side exhaust pipe very loose up at the manifold. Tightened those bolts, and the car is much quieter.

Unfortunately, we also found what looks like a poorly welded repair on the right side exhaust manifold, which may be cracked. My buddy was closing his shop for the evening, and we couldn't really tell in the bad light we had, so I may be in the market for a new one.

For now, I am happy to have reduced that exhaust sound by 90%.
--
Jay

JayRay

Glad it helped, When tightening the bolts fixed mine, for $0, which is rare on a Corvette. I bought new Flowmaster mufflers just for good Karma.

wb003

Hi JJ. I just have a few short comments to the thread:

1. You will learn names on the Forum, and can identify the old heads that know this stuff inside and out. Alan 71 and Lars are two of them. Listen to them.

2. The racing oil pan that you have is 2 quarts larger, in order to retain more oil in the sump for pickup and constant oil pressure during turns. Also, I do not use synthetic oil in older cars. It may cause them to leak..a LOT. I use Valvoline VR1 racing oil 10w30, with zinc.

3. I have not seen spark plugs routed "under" an engine. As Alan and RVZIO said, route them down the sides in the spark plug shielding, 4 to a side.

I have a '70 yellow vert similar to the one in your profile pic.

Have fun!
Bill

NewbVetteGuy

My brand new Flowtech (Holley) ceramic coated headers also have no gasket (o-rings only). Still sold today.


https://www.summitracing.com/parts/b...LcYaAkc68P8HAQ


Adam

jjhoneck

Since I may have a crack in the exhaust manifold, it might make sense for me to go the headers route.

Are you happy with these? Did they net you any benefit over stock, other than being cool looking?
--
Jay