1968 Dodge Monaco - 383 2bbl - exhaust manifold leak

[EFinMD]

Hello, everyone.

My Monaco has been in the family since new, so I have a complete set of records - and I've been in charge of the car for many decades now. I'm hoping for some additional guidance before I bring this to a new mechanic that specializes in older vehicles like mine and less routine jobs.

This Spring, my car was diagnosed with an exhaust leak. Passenger's side was changed out some 10 or 15 years ago; heat riser was leaking. The sound I'm hearing now on the driver's side is very different. When starting cold and warming to idle, it's very loud, sometimes sounding like ticking, and coming from the front of the manifold as I hear it. It really gets loud when accelerating. No problem with performance, other than I now need to have the carburetor readjusted after running out some old gas.

The engine was last rebuilt 38 years ago, which is when I'm sure the manifold was last off and that gasket was replaced. I'm ready with a new gasket set, a new set of hardware (as I'm sure at least one stud will crack off), and a replacement manifold (2463107 casting, just as on the engine now.). Hardware is the 8065C set from Dante's Mopar Parts. Manifold was purchased from Atlas Obsolete Auto Parts via MoParMall.com; was said to have been cleaned/sandblasted (and looks it) and MagnaFluxed to ensure no cracks.

Based on what I'm writing, it is possible that the manifold itself has actually cracked? Simply a gasket that's had its day? No way to tell?

Many thanks for any thoughts.

 

[Big_John]

The exhaust manifold gaskets just fail after a while.

The factory assembled them with no gasket and that's what I do. No gasket needed.

 

[EFinMD]

The exhaust manifold gaskets just fail after a while.

The factory assembled them with no gasket and that's what I do. No gasket needed.

Here's hoping. I can't quite imagine the manifold cracking. I'm just hoping that it's not major surgery to get any cracked studs out. Except for the end studs, I'm betting the other four are pretty well rusted.

By the way, as I've never had this happen before, I'm assuming it's just noisy and not dangerous to drive. I've been limiting driving to just some exercise around my neighborhood until I can get this sorted out.

 

[413]

Wire brush the exposed ends of the studs, clean the grit off and lubricate before putting a wrench on the manifold nuts.

Many times these will come off without breaking anything.

Sometimes the nut is frozen on the stud and the stud will come out of the head ans you will have antifreeze Avery's here. Best to drain the radiator before starting.

 

[Justin Plant]

I have seen manifolds just crack. Tends to happen on more modern cars, the iron isn't quite as thick as it used to be.
Aero-kroil or Kroil oil is IMO the best for this. Spray it on, next day do it again. When you tackle it, nuts and bolts generally come right off.

 

[CBODY67]

Determine for sure where the leak/tick is coming from. That is important.

OEM, no gaskets between the manifold and head and the manifold to pipe is a ball joint joint, no gaskets there either.

DO check to see that all of the manifold to head bolts are tight when the engine is cold. Don't use a lot of force, just see if they are loose. If loose, just snug them down and see if that diminishes the sound.

When our '66 Newport 383 2bbl was new, it had a slight tick on acceleration when hot. Just a tick, sounded kind of neat, I thought. a bit more than an exhaust pipe tinkle. That turned out to be the rh rr exhaust manifold to head bolt being about 1/4 turn loose. When tightened, all was eerily quiet.

Just some thoughts,
CBODY67

 

[cbarge]

If the studs break, no worries.
Once the manifold is off, determine if there is enough meat/ threads left to double nut it, heat er up with a torch and twist her out.
If broken flush with the head, using a mig welder build up some weld on the broken stud, weld a nut back on, again get her cherry red with a torch abd twist her out.
No gaskets used on exhaust manifold/ head.
But make sure you use a quality donut gasket with a metal o- ring on the exhaust flange to pipe.
El cheapo paper gaskets will burn and guaranteed to leak.

Yes I had a couple manifolds crack on me over the years.
The constant cycle of heating/ cooling, expanding/ contracting leads to metal fatigue or cracking depending on how well the casting was when manufactured.
One big splash going through a puddle and cold water meets manifold..CRACK!
Hope this helps