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Username Post: Stock exhaust manifold flange gasket question...        (Topic#239420)
utahpaul 
Frequent Contributor
Posts: 1332
utahpaul
Reg: 09-16-07
04-05-10 04:25 PM - Post#1893423    

Got a exhaust question here guys, no big deal but this just started happining a few days ago: Before going out for a cruise,( and the engine was cold ), when I shut the cab door I heard a slight squeeky, metal to metal sound from underneath the truck, like a bolt might be loose, so I went under the truck, had the wife close the cab door and heard the squeek sound coming from the exhaust pipe. I checked the tail pipe hangers but all was good there, then I checked the head pipe and found the sound coming from there. So I put a socket onto the bolts where the head pipe mates to the stock cast iron exhaust manifold as there's a metal O ring flange gasket in between to seal it together. I found that I could turn two of the bolts pretty easy with the socket and tightened them a bit and the squeek noise went away, and I drove it around for 20 miles and all was fine, then after it cooled off later that day, I went to the cab for something, shut the door & the squeek was there again. I started the engine and after it warmed up the squeek noise was once again gone until the engine cooled off again. So I guessed the metal flange gasket was expanding as it heated up, and shrunk as it cooled off. I then checked the shop manual as to the bolt torque and 17 ft lbs is correct, so I'll go out tomorrow and torque them all to 17 lbs. Just wanted to know if anyone else has had this happen before as it has never happened to this truck in it's 29 years, or anyother GM i've had. The cast iron manifold ears ( where the flange bolts go through ) are not broken or cracked on either side, but both left and right side bolts did need to be tightened a bit. Do these exhaust flange gaskets go bad after so many years or miles? Thanks for any info...

 
Vaughn 
"12th Year" Gold Supporting Member
Posts: 15226

Loc: Colorado Springs, CO
Reg: 08-08-04
04-05-10 04:54 PM - Post#1893449    
    In response to utahpaul

Problem with a squeak in the exhaust is generally at the rubber mounts and straps holding the exhaust pipes up to the truck, not at the exhaust flange. Tightening the exhaust flange will just cause the exhaust donut gasket to start leaking sooner, but won't help the squeaking noise.

 
utahpaul 
Frequent Contributor
Posts: 1332
utahpaul
Reg: 09-16-07
04-06-10 09:28 AM - Post#1893801    
    In response to Vaughn

Yes, that's what I thought at first too Vaughn, and I sprayed Wd-40 into the rubber hanger mounts, then had the wife shut the door again and that's when I heard the squeek coming from the head pipe, so I checked the bolts and sure enough two when not very tight, I gave them a turn with the socket ( not too tight ) and had the wife shut the door again and the noise was gone. I forgot to metion this is on my 1981 C/10 305 and before I tightened anything up I started the truck, let it warm up, shut it off and closed the door again and the noise was gone until it cooled off, then the noise was back until I tightened the head pipe bolts. Then took it for a 20 mile drive and the the next day when the engine was cold the noise was back, so I'll check the bolts and tighten to the correct 17 ibs of torque. Thanks again for the reply Vaughn, and do you know if the O flange gaskets wear out after so many miles or years?, as there still isn't any exhaust leak ( popping or other sound )happening from the head pipe area, just the squeek noise when we shut the door....

 
John 
Chevytalk Moderator & "3rd Year" Gold Supporting Member
Posts: 7196
John
Age: 45
Loc: Montgomery, AL
Reg: 01-15-02
04-06-10 10:31 AM - Post#1893833    
    In response to utahpaul

Sounds like a good candidate for the locking bolts.
1979 2wd K5 Blazer, 350/TH350
1985 4x4 M1009 K5 Blazer, 6.2/TH400


 
Vaughn 
"12th Year" Gold Supporting Member
Posts: 15226

Loc: Colorado Springs, CO
Reg: 08-08-04
04-06-10 07:45 PM - Post#1894114    
    In response to John

The donut gaskets are usually fine for many years, provided that they aren't too loose - which will cause exhaust gases to slip by, which will quickly burn it out (and it will be audible) and that the gasket isn't too tight, which will crush the gasket, also causing it to fail.

You can add an exhaust hanger a few feet back from the flange to stop the twisting of the pipe at the exhaust manifold, or you may be able to bend one of the existing hangers to get it to stop. Either way, you need to stop the pipe from twisting, which is what is causing your squeak.

 
utahpaul 
Frequent Contributor
Posts: 1332
utahpaul
Reg: 09-16-07
04-07-10 12:19 PM - Post#1894440    
    In response to John

  • John Said:
Sounds like a good candidate for the locking bolts.


Locking bolts? or Locking nuts John? I don't have lock washers on the flange / head pipe nuts ( and there never was from the factory when this paticular truck was built anyway ) but they do look like locking nuts. And Vaughn, I do have hangers at the mufflers & tailpipes with rubber insolaters, ther're high end units. It's been a year & a half from the time of install on these duals & the doors have been shut 500 times or more from then and no noise whatsoever. I did torque the flange nuts to 17 ft lbs as the factory manual states to, but this morning the noise is back, not as bad, but back. This just started last week as to the squeek noise and it goes away as soon as the engine warms up, never heard this before in all the years my grandpa had me service it for him from new. But the sound comes from both head pipes when cold and doors are shut. I'm going to the Muffler shop tomorrow as my muffler guy says he's never heard of a problem like this. That's hard to believe, as these flange doughnuts are 29 year old stock units and are probably worn out at least a little bit, enough to make this sound anyway. Is there some sort of asbestos packing material that goes in between the head pipe and cast iron exhaust manifold when the new O flange gasket is installed? Man, this really isn't a big deal, but now with the truck restored and people seeing it at shows and in the garage, I just hate to have anything sound loose or rattle or squeek, yet when going down the road, all is quite inside and out...

 
John 
Chevytalk Moderator & "3rd Year" Gold Supporting Member
Posts: 7196
John
Age: 45
Loc: Montgomery, AL
Reg: 01-15-02
04-07-10 01:04 PM - Post#1894452    
    In response to utahpaul

Stage 8 locking header bolts

That's just one kit, Summit has many of them from different manufacturers.
1979 2wd K5 Blazer, 350/TH350
1985 4x4 M1009 K5 Blazer, 6.2/TH400


 
John 
Chevytalk Moderator & "3rd Year" Gold Supporting Member
Posts: 7196
John
Age: 45
Loc: Montgomery, AL
Reg: 01-15-02
04-07-10 02:36 PM - Post#1894492    
    In response to John

You're talking about nuts on the studs, aren't you. I gave a bad link...
1979 2wd K5 Blazer, 350/TH350
1985 4x4 M1009 K5 Blazer, 6.2/TH400


 
utahpaul 
Frequent Contributor
Posts: 1332
utahpaul
Reg: 09-16-07
04-07-10 09:48 PM - Post#1894746    
    In response to John

Yes Sir, I am.....

 
utahpaul 
Frequent Contributor
Posts: 1332
utahpaul
Reg: 09-16-07
04-09-10 07:48 AM - Post#1895462    
    In response to utahpaul

Ok, so I went to my muffler guy, we went under the truck, then he showed me that on my stock cast iron exhaust manifolds, the Flange gasket is cast iron, cast into the manifold as one piece. And that there isn't any packing material, just the cast iron flange against the head pipe, metal to metal and of course the truck was warm when he checked it out and the exhaust being hot was expanded, so no noise. I came home, truck cooled off, and squeek came back. I tried some WD-40 on the flange area while the truck was cooling off and the squeek went away until the WD burned off. Do you guys know of any spray lube that can withstand 600 degree heat that I could spray on the flange/head pipe connection? Thanks

 
utahpaul 
Frequent Contributor
Posts: 1332
utahpaul
Reg: 09-16-07
04-09-10 08:21 AM - Post#1895483    
    In response to utahpaul

Looks like I may have found an answer, Permatex makes a anti seize spray lube that's good to 1,600 degrees, I think I'll try that...

 
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