CMI Header bolt up
 

My new CMI Headers seem to have too much gap between the flange and the head after i tighten all the bolts. there is enough gap that the gasket can move between the flange and the head on the end bolts. What is an acceptable amount of gap between the flange and head after the bolts are tight?

You should have no gap. You need to buy some shorter bolts. If you are trying to use the bolts from the cast manifolds they may be too long.

Most speed shops will have ARP header bolts in oxide finish and stainless in 12 point. If you must buy them at a hardware store they are 3/8" 16 tpi. Dont get anything less than Grade 8.

Ron

i'm using the bolts that came with the headers. they are shorter and should be the correct arp bolts.

the gap is coming from the welded ring that is ground down on the flange around each opening in the flange. it looks as though they did not grind enough off the weld down to keep a tight fit.

Put a straight edge across the flange. You shouldn't see a significant gap across any of the welds. If you do, then there will be a exhaust leak. The flange may have warped, or it may have been a manufacturing defect. The solution will be to grind some more off the weld so it becomes flat. You will not be able to do this by hand. A machine shop will have grinders that are capable of grinding them flat.

Send them back. They should be as flat as possible. For the money CMI's should be perfect.

Ron

i'm going to check with a straight edge tonight. i just hate sending them back because it takes so damn long. i agree they should be perfect for the money. i thought about having a machine shop grind the welds for me. sounds easy, but they are new headers. haven't been run yet. i should hold cmi to their warranty if they are wrong.

Guy. Guys, Guys!
 

Put a straight edge across all of the raised (ground) weld rings and I think you will see that they are all ground flat with respect to each other, and hence, they will put a focused pressure around each port. If you simply bolt them to the head, they will look like the have a large gap from outside, but the ring will be seated tight. my Cmi's and Lightnings are this way...and they have never leaked..

Id follow Brads advice. He has first hand knowledge. Punk originally stated that the gasket could be moved around with the bolts tight. If that is not the case then the raised areas are for sealing purposes.

Ron

I understand the purpose of the raised welds is to add pressure around the port, but it just looks excessive. hell, if they look good with the straight edge i'll just have to run it and see.

thanks guys.

You paid enough, call 'em and ask.