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09-10-2017, 06:51 PM | #1 |
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Join Date: Jan 2004
Location: Whitehorse YK Canada
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Exhaust manifold torque procedures
The left cast exhaust manifold on my 396 in my 1968 C20 cracked/broke. I have replaced the manifold but I am wondering about the torque procedure.
I have tightened them all up, using a pattern to equally apply torque. Should they be tightened hot or cold or maybe both?
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Blaine 59 GMC 9314 a.k.a. Whoopee 68 C20 50th Anniversary a.k.a. The Rat http://www.flickr.com/photos/northerngmc/ http://www.members.tripod.com/P-wee/index_032.htm 1.61803 is one H of a lot better than 3.14159, no really it is! |
09-11-2017, 10:05 AM | #2 |
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Join Date: Jul 2007
Location: Centrally located between Houston, Austin and Waco. BCS area.
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Re: Exhaust manifold torque procedures
It's not a critical part. I've always just torqued the bolts down equally and double check them after I've run the engine to operating temperature. Specs say 25 ft lbs.
The important part is to make sure there aren't any high/low areas of the mating surface. The couple of times I've bought a new manifold I've had to have them resurfaced to make sure they were completely flat.
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68 GMC 250/3 speed Saginaw p/b p/s 69 Chevy 350/350 currently in pieces still lookin for a cab 06 Trailblazer I just want a vehicle that I can work on, that won't talk to me, leave error msgs or keep track of how I drive... Last edited by 68gmsee; 09-11-2017 at 01:09 PM. |
09-11-2017, 06:44 PM | #3 |
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Re: Exhaust manifold torque procedures
Thanks. I warmed it up and re-torqued today.
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Blaine 59 GMC 9314 a.k.a. Whoopee 68 C20 50th Anniversary a.k.a. The Rat http://www.flickr.com/photos/northerngmc/ http://www.members.tripod.com/P-wee/index_032.htm 1.61803 is one H of a lot better than 3.14159, no really it is! |
09-11-2017, 07:53 PM | #4 |
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Location: Centrally located between Houston, Austin and Waco. BCS area.
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Re: Exhaust manifold torque procedures
Forgot to mention that I don't use gaskets on the sbc stock cast iron manifolds, however, I do use one on my 250 six cylinder since the intake and exhaust are combined.
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68 GMC 250/3 speed Saginaw p/b p/s 69 Chevy 350/350 currently in pieces still lookin for a cab 06 Trailblazer I just want a vehicle that I can work on, that won't talk to me, leave error msgs or keep track of how I drive... |
09-11-2017, 11:35 PM | #5 |
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Join Date: Jan 2004
Location: Whitehorse YK Canada
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Re: Exhaust manifold torque procedures
I did not use a gasket. I was surprised to learn that GM did not use gaskets.
Now I just need to find a plug that will fit the hole in the back of the manifold where smog equipment would go. 3/8" NPS plugs fit great in the holes on the top, but 3/8" is too small and 1/2" NPS is too large for the hole on the back. On my way to work tonight I picked up a #8 brass flare plug that I hope fits.......
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Blaine 59 GMC 9314 a.k.a. Whoopee 68 C20 50th Anniversary a.k.a. The Rat http://www.flickr.com/photos/northerngmc/ http://www.members.tripod.com/P-wee/index_032.htm 1.61803 is one H of a lot better than 3.14159, no really it is! |
09-12-2017, 06:14 PM | #6 |
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Location: Whitehorse YK Canada
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Re: Exhaust manifold torque procedures
So I think a combination of me not being familiar with pipe measurements and the bin at the parts store having the wrong size in it has caused me great pain over a small issue.
So I found plugs in the 3/8" pipe bin that fit the holes above each cylinder on the exhaust manifold. But these 3/8" plugs were too small for the hole near the exhaust dump and 1/2" was too large....... hummmmmmmm and they had nothing in between. Turns out the plugs in the 3/8" bin were 1/4".......... and then when I went to a different store and bought a 3/8" brass pipe plug it fit the rear hole just fine.
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Blaine 59 GMC 9314 a.k.a. Whoopee 68 C20 50th Anniversary a.k.a. The Rat http://www.flickr.com/photos/northerngmc/ http://www.members.tripod.com/P-wee/index_032.htm 1.61803 is one H of a lot better than 3.14159, no really it is! |
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