Slant Six Forum :: Manifold Flatness Question

: I just had my intake and exhaust manifolds
: ground. When I got them back, I laid a
: straight edge on the mounting surface, and
: it didn't look all that flat. How flat
: should it be - what is the largest deviation
: that I should accept? I had them ground
: seperately. Should they have been bolted
: together during the grinding?

: Surfacing them as a set saves you some time. I
: have done them seperatly and sometimes find
: that the 3 connecting bolt holes do not
: allow for the movement to get both surfaces
: on the same level. When I see this, I
: drill-out the holes in the intake to get the
: needed movement.
:
: Use the head as a guide, install both manifolds
: to the head with no gasket and with the 3
: connecting bolts and that gasket in place.
: Make contact but leave these 3 connecting
: bolds loose. Install the manifold to head
: washers / nuts and tighten to align
: manifolds to the head surface, then tighten
: the center 3 bolts.
:
: If the exhaust manifold is worped, you will
: need to adjust by grinding / filing flat the
: surface where the intake and exhaust
: manifold make contact. (heat riser area)
: Badly worped exhaust manifolds can never be
: adjusted and ground enough to make a good
: seal so it is better to find a replacement.
: (worped ones work fine when I cut them in
: half and make Duals out of them!)
: Surfacing the manifolds as a set will show you
: how badly they are worped and out of
: alignment.
: DD

: Thanks for the input. I'll try what you said
: and see if it helps. I still have the
: question of how flat the surface that mounts
: to the head needs to be - how much
: out-of-plane displacement can the manifold
: gasket take up?

: If you are still curious, my 1966 shop manual
: says: Test mating surfaces of manifolds for
: parallelism with a straightedge. Surfaces
: should be flat within .008 inch. Hope this
: helps.

Author:	tnsguy [ Fri Dec 07, 2001 7:50 am ]
Post subject:	Manifold Flatness Question
I just had my intake and exhaust manifolds ground. When I got them back, I laid a straight edge on the mounting surface, and it didn't look all that flat. How flat should it be - what is the largest deviation that I should accept? I had them ground seperately. Should they have been bolted together during the grinding? tomc@abac.com

Author:	Dave M [ Sun Dec 09, 2001 8:26 am ]
Post subject:	Re: Manifold Flatness Question
Quote: : I just had my intake and exhaust manifolds : ground. When I got them back, I laid a : straight edge on the mounting surface, and : it didn't look all that flat. How flat : should it be - what is the largest deviation : that I should accept? I had them ground : seperately. Should they have been bolted : together during the grinding? My machine shop told me to bolt them together and than surface both. I did and I haven't had any leaks in 60,000 miles. damuel@kalama.com

Author:	Doctor Dodge (Doug Dutra) [ Sun Dec 09, 2001 10:56 am ]
Post subject:	Re: Manifold Flatness Question
Quote: : I just had my intake and exhaust manifolds : ground. When I got them back, I laid a : straight edge on the mounting surface, and : it didn't look all that flat. How flat : should it be - what is the largest deviation : that I should accept? I had them ground : seperately. Should they have been bolted : together during the grinding? Surfacing them as a set saves you some time. I have done them seperatly and sometimes find that the 3 connecting bolt holes do not allow for the movement to get both surfaces on the same level. When I see this, I drill-out the holes in the intake to get the needed movement. Use the head as a guide, install both manifolds to the head with no gasket and with the 3 connecting bolts and that gasket in place. Make contact but leave these 3 connecting bolds loose. Install the manifold to head washers / nuts and tighten to align manifolds to the head surface, then tighten the center 3 bolts. If the exhaust manifold is worped, you will need to adjust by grinding / filing flat the surface where the intake and exhaust manifold make contact. (heat riser area) Badly worped exhaust manifolds can never be adjusted and ground enough to make a good seal so it is better to find a replacement. (worped ones work fine when I cut them in half and make Duals out of them!) Surfacing the manifolds as a set will show you how badly they are worped and out of alignment. DD

Author:	tnsguy [ Sun Dec 09, 2001 2:09 pm ]
Post subject:	Re: Manifold Flatness Question
Quote: : Surfacing them as a set saves you some time. I : have done them seperatly and sometimes find : that the 3 connecting bolt holes do not : allow for the movement to get both surfaces : on the same level. When I see this, I : drill-out the holes in the intake to get the : needed movement. : : Use the head as a guide, install both manifolds : to the head with no gasket and with the 3 : connecting bolts and that gasket in place. : Make contact but leave these 3 connecting : bolds loose. Install the manifold to head : washers / nuts and tighten to align : manifolds to the head surface, then tighten : the center 3 bolts. : : If the exhaust manifold is worped, you will : need to adjust by grinding / filing flat the : surface where the intake and exhaust : manifold make contact. (heat riser area) : Badly worped exhaust manifolds can never be : adjusted and ground enough to make a good : seal so it is better to find a replacement. : (worped ones work fine when I cut them in : half and make Duals out of them!) : Surfacing the manifolds as a set will show you : how badly they are worped and out of : alignment. : DD Thanks for the input. I'll try what you said and see if it helps. I still have the question of how flat the surface that mounts to the head needs to be - how much out-of-plane displacement can the manifold gasket take up? tomc@abac.com

Author:	Chris [ Mon Dec 10, 2001 7:58 am ]
Post subject:	Re: Manifold Flatness Question
Quote: : Thanks for the input. I'll try what you said : and see if it helps. I still have the : question of how flat the surface that mounts : to the head needs to be - how much : out-of-plane displacement can the manifold : gasket take up? If you are still curious, my 1966 shop manual says: Test mating surfaces of manifolds for parallelism with a straightedge. Surfaces should be flat within .008 inch. Hope this helps. chrisstelling@yahoo.com

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Author:	tnsguy [ Mon Dec 10, 2001 8:22 am ]
Post subject:	Re: Manifold Flatness Question
Quote: : If you are still curious, my 1966 shop manual : says: Test mating surfaces of manifolds for : parallelism with a straightedge. Surfaces : should be flat within .008 inch. Hope this : helps. Thanks, Chris. That's what I was interested in. Mine are no where near that good, so it is back to the machine shop....... tomc@abac.com

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