Rattle noise.

[85silverado]

There is something rattling intermittently in or near my pass side exhaust manifold, I can see some kind of emissions aparatus on the manifold. It looks like it may have a flap inside it that rattles? Any ideas? It rattles at idle and if a rev it up it'll go away and eventually come back.

[123 pugsy]

Did they have heat risers on 1985?

[Lt.Del]

Your exhaust valve may have broken, inside the left exhaust manifold.  There is a diaphram that should be attached above your exhaust manifold, using two of the last three exhaust manifold bolts.  This diaphram pulls a rod when your engine warms up via vacuum. That rod opens the valve.   As a cold engine, it keeps the valve closed to allow exhaust to circulate w/in your intake manifold to heat it up for better emissions burning.  Again, a vacuum hose is attached from the diaphram to the thermastadt TVS.  When warm, it uses vacuum to open that valve.

Try turning on your engine, cold.  After about three minutes or so, you will actually see the rod move to open up that valve--if it is working right.

You free hand activate that too.  Keep your engine off, try to pull the rod up as if vacuum was pulling it.  If it moves, the valve isn't broke.

That valve may be broken.




SgtDel

Edited by: SgtDel at: 2/27/06 2:20 pm

[ChevyGuy]

We always cut that butterfly because those would always freeze up. Chevys are always cold nature. If it gets stuck closed you can burn a valve. What im talking about is in the second pic of sgtdel. You can replace if you feel like everything needs to stay stock. But they were always a pain on any gm car or truck we owned that had that.

[Lt.Del]

Luckily on my 79, it never froze up, but many moons ago, one froze on my dad's 76.  I didn't know what it was, check timing, carb adjustment, etc.  I couldn't figure it out.  Then one day, taking the old motor out, we noticed the frozen valve on the exhaust manifold.  

When i put my new 383 in my 79, i just transferred all the emissions stuff to it.  She runs great and everything works as it should.

As far as the noise, If it is coming from your diaphram, you can replace those very easily.  Go to a wrecking yard and throw another on it.  Test the diaphram however...take the hose off, pull up on the rod, put your finger over the opening where the hose goes and see if the rod hold still.  If it slides back down, your diaphram is shot.  By keeping the suction in the diaphram, your rod should not move back down.

SgtDel

[85silverado]

I have moved the valve before, it is kinda hard to move but it does move. All of my emissions stuff is here but there is not a belt on the air pump, could this make it not work? Good idea about the metal tube, I need to check that out too. Thanks for the advice.

[85silverado]

Well I figured out it is not working and it never opens, but I can open it myself. When it is closed is when it rattles so I think it has a hole it in since it doesn't affect performance.

[85silverado]

My valve looks different than the pictures but it does the same thing. I can see the crossbar that goes through the valve piece rattle as I rev it up. I think I will just wire the thing open so the noise goes away.