Cast iron manifold

[Pevehouse]

Most manifolds have a flat spot along one edge of the holes at 90 degrees to the face. You can put it face down first and mill these flat spots. You don't need much, maybe 10 -15 thou. This gives you a perpendicular surface to flip it over and clamp to an angle plate. Way more rigid when milling.
This is a video of the head from a Red Seal continental. I had a video of the manifold but it says it’s too big a file to load. This is on a horizontal but a vertical mill is the same principal
View attachment 481014
Martin W

Didn’t think of that. I used the bolt holes because they had already been milled flat. Seemed to set up just fine like that. Took it slow. Biggest issue was leap frogging my set up to get the entire manifold

 

[Pevehouse]

Thank you to everyone here. There’s been several suggestions that did not cross my mind and would have probably worked better. I did get it done but it was a lot of work and I had to take off what I would consider too much. Worried that I will warp right back up. Upon completion I found that a new manifold is just $99 sooo,lol

 

[pontiac428]

What, no pics?

 

[Pevehouse]

What, no pics?

I will post a couple when I get back to the house

 

[pontiac428]

I will post a couple when I get back to the house

I think you were mostly on the right track... I would have bolted that manny to an angle plate, chucked up a fly cutter, and reinstalled it on the engine without a second thought. Exhaust manifolds need to be flat, but not much more needs to go into it. Fixturing with a fly cutter can be a lot less robust compared to a face mill, the face mill will hammer the crap out of the part with all those interruptions.

 

[RaisedByWolves]

I would try it if it were me. Back when stuff wasn’t throwaway they would true them up with a big belt sander. They set it face down on it and hold by hand to clean it up.

The one we had in tech school was like a belt sander, but it had tracks like a tank tread with stones mounted to them.

You just placed the head directly on the stones and turned it on and ground the head flat.

It was extremely noisy and a pain to dress the stones when needed, but it did a hell of a job.

 

[Pevehouse]

I think you were mostly on the right track... I would have bolted that manny to an angle plate, chucked up a fly cutter, and reinstalled it on the engine without a second thought. Exhaust manifolds need to be flat, but not much more needs to go into it. Fixturing with a fly cutter can be a lot less robust compared to a face mill, the face mill will hammer the crap out of the part with all those interruptions.

That just sounds like it would have been easier. Atleast I wouldn’t have had to leap frog my setup . In the end it turned out flat as can be however it took a lot to get it there. It had a hellacious bow in the center. Normally I would just bolt it back on and give my handy work a shot but this particular manifold is covered with a turbo deep down in a hole. Book time to replace it is 7.3 hours flat. That’s why I’m scared to try it. Scared it will warp too easily now

 

[pontiac428]

I follow your logic. Turbo manifolds see a lot more heat, and the flanges are subject to a lot more pressure. The thing about heat warping on cast iron is, it's now stress-relieved and taken its natural set in its warped shape. It may move during temperature changes, but it won't warp any more than it already has. So you are actually truing the flange to its seasoned state.

 

[Pevehouse]

I follow your logic. Turbo manifolds see a lot more heat, and the flanges are subject to a lot more pressure. The thing about heat warping on cast iron is, it's now stress-relieved and taken its natural set in its warped shape. It may move during temperature changes, but it won't warp any more than it already has. So you are actually truing the flange to its seasoned state.

Hmm, Never thought about that. Makes sense though. Here’s a few pics of my results. Had a little screw up there at one end trying to knock my nib off. Went too deep,lol