Community Forums

dnebout · 10-21-2007, 09:14 AM

Passenger side exhaust manifold cracked and was replaced 3 years ago. They overtightened the end stud and the stud cracked the head. We're going to weld the piece back on. When we took it apart, we noticed that the new exhaust manifold has 3 straight slits that apear to be cracked between the bolt patterns at the thinnest part of the manifold.
Are these cracks or is this something GM integrated into the design to correct cracked manifold problems? Note the driver's side does not appear to be cracked or have any slits.

Thanks.

dnebout · 10-21-2007, 09:14 AM

Passenger side exhaust manifold cracked and was replaced 3 years ago. They overtightened the end stud and the stud cracked the head. We're going to weld the piece back on. When we took it apart, we noticed that the new exhaust manifold has 3 straight slits that apear to be cracked between the bolt patterns at the thinnest part of the manifold.
Are these cracks or is this something GM integrated into the design to correct cracked manifold problems? Note the driver's side does not appear to be cracked or have any slits.

Thanks.

dnebout · 10-21-2007, 09:48 AM

Sorry P-30 Chassis.

milham · 10-21-2007, 03:46 PM

dnebout,
I have a 1996 Vectra with the 7.4 TBI but I have the Banks system installed which solved all of the cracked manifold problems (previous owner installed the Banks). I do have the Chevrolet Motor Home Chassis Service Guide and in Chapter 7 page 7-4 Chevrolet Dealer Service Bulletin No. 86-255 (Nov 1987) mentions that an improved cast iron exhaust manifold using nodular iron instead of grey iron was installed on 1987 vehicles. It also mentions the following NOTE: A recent study by our engineering department has revealed that a substantial increase in exhaust manifold life can be obtained by cutting the manifold attaching support in 3 places between bolts #2 & 3 and 4 & 5 and 6 & 7 with a metal saw which allows each runner to move independently. If you would like me to scan a copy and forward it to you please send me a PM. I also remember reading something about elongating the bolt holes to allow for expansion but I can't find it right now.
Ron

milham · 10-21-2007, 04:08 PM

dnebout,
A quick addition regarding the elongation of the bolt holes. Page 7-3 states "Before installing a new manifold, the dowel pin holes and bolt holes should be increased 1/32 inch in diameter to enable the manifold to expand and contract without buckling." Also goes on to state "Apply a liberal amount of anti-seize compound #1052771 to the manifold face and head face to increase manifold life. The compound appears to create a hard slate-like film with a very low coefficient of friction allowing the manifold to expand and contract...". In addition "torque the center bolts to a full 40 ft. lbs. torque and slightly less torque for each bolt as you proceed towards either end."

Ron