Machined surfaces on 66 exhaust manifolds

[Gary 66]

Hi,

I just had a manifold sandblasted and I need to know what surfaces are supposed to have a machined finish. Can anyone tell me which surfaces other than the head mating surface are machined on 66 L79 cast iron exhaust manifolds? Is the outlet flange machined? What about the 45 degree chamfer within the outlet that mates with the exhaust donut? What about the bosses around bolt holes?

Thanks in advance,

Gary

[Bill W.]

Re: Machined surfaces on 66 exhaust manifolds

Gary,

I'am not sure why you would be concerned about machined surfaces other than the head mating surface. Installed, none of them are visable and are not judged. Even pitted surfaces on the outlet will seal fine. There is no machining done on the three bolt holes other than the cutting of their threads. If you are doing an NCRS restoration, don't use gaskets between the head and the exhaust manifold. Hope this helps, Bill

[Bill W.]

Re: Machined surfaces on 66 exhaust manifolds

Gary,

I'am not sure why you would be concerned about machined surfaces other than the head mating surface. Installed, none of them are visable and are not judged. Even pitted surfaces on the outlet will seal fine. There is no machining done on the three bolt holes other than the cutting of their threads. If you are doing an NCRS restoration, don't use gaskets between the head and the exhaust manifold. Hope this helps, Bill

[Gary 66]

A machined outlet face wouldn't show?

Bill,

I figured the 45 degree chamfer for the donut wouldn't show, but I thought the bottom surface of the outlet (which is tapped for the 3 connecting studs) might indeed show. Both the chamfer and the outlet face are rusty and if I machine just the chamfer then the face will get thinner and the chamfer will go futher in, which can only solved by machining the outlet face as well. But if that will show and it shouldn't be machined ... Therein lies my concern.

Gary

[Gary 66]

A machined outlet face wouldn't show?

Bill,

I figured the 45 degree chamfer for the donut wouldn't show, but I thought the bottom surface of the outlet (which is tapped for the 3 connecting studs) might indeed show. Both the chamfer and the outlet face are rusty and if I machine just the chamfer then the face will get thinner and the chamfer will go futher in, which can only solved by machining the outlet face as well. But if that will show and it shouldn't be machined ... Therein lies my concern.

Gary

[Jack H.]

Re: A machined outlet face wouldn't show?

Doughnut should absorb minor imperfections in mani-header junction. If you've got 'lunar surface' or a discontinuity in the chamfer (often the result of broken mounting ear and sloppy weld repair), then re-doing the chamfer might be in order. Caution -- this isn't the easiest job for a machinest as it takes a tapered grinding wheel of proper OD....

On the bottom of mani, this surface was typically hidden on one side due to the heat riser interface and it's gasket. On the LH side, you'll wind up with gap, but it would quickly take on minor surface rust. So, again, if it's not a lunar surface item, let 'er be. I don't know judges that get this picky....

On the mani-head surface, since gaskets were NOT used and their presense/absense IS judged, I'd go and have the surface milled flat. You never know what kind of warp has happened over the years, and making the cylinder head interface flat/true doens't cost much and can save a later headache in finding/killing exhaust leaks if you want to be concours correct and go without gaskets....

[Jack H.]

Re: A machined outlet face wouldn't show?

Doughnut should absorb minor imperfections in mani-header junction. If you've got 'lunar surface' or a discontinuity in the chamfer (often the result of broken mounting ear and sloppy weld repair), then re-doing the chamfer might be in order. Caution -- this isn't the easiest job for a machinest as it takes a tapered grinding wheel of proper OD....

On the bottom of mani, this surface was typically hidden on one side due to the heat riser interface and it's gasket. On the LH side, you'll wind up with gap, but it would quickly take on minor surface rust. So, again, if it's not a lunar surface item, let 'er be. I don't know judges that get this picky....

On the mani-head surface, since gaskets were NOT used and their presense/absense IS judged, I'd go and have the surface milled flat. You never know what kind of warp has happened over the years, and making the cylinder head interface flat/true doens't cost much and can save a later headache in finding/killing exhaust leaks if you want to be concours correct and go without gaskets....