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.

I missed that important little detail, RJC. :eek: :mad:

the welded bead is about twice as thick on the starboard side as it is on the port side. the welded beads appear to be straight, but it is just too thick on the starboard side for the flange to be flush with the head. the bolts go in fine and seem to line up fine.

WTF?

The flange is not supposed to be flush. The raised weld creates a better squeeze on the gasket surrounding the port. Give CMI a call, 920 722 7084

Make sure you tighten the bolts up even. If you put a bind on one bolt and the header flange it will not tighten properly. Loosen all the bolts and start over.

Geez RV, you don't trust me? I'm crushed. :(

JOHNNY, it's not that i don't trust you, it just looks excessive on the starboard side. the port side looks fine. you know i worry about everything. if i didn't worry about this, then there would be something wrong.

cmi headers
 

Punk Rocket
You seem to be convinced that the manifolds are not correctly made. Call CMI talk to their tech guy see what he says.
They may want to reinspect them.
Go federal express or ups red both ways its only money and your not boating.
I had them weld in a set of rings in the long extension tubes to eliminate water reversion in the tube and they turned them around in a short time frame.
Post your findings.
Tank u

ran the boat today. the header flange seemed to be sealed to the head. did not appear to be any exhaust leaks. i just fits a bit funny, but it appears to be functional.

i did have some water leaking between the header and the tail pipe around the cool collar clamp. i'll try and re-align the tail pipes and tighten it all up again.

The cool collars should be easier than the old rope style. we'll see if i can get the to seal. they both drip water steady.

i have a 29 fountain. sometimes i run up on clear lake, but usually lake travis. haven't been to conroe. is it worth the trip?

I don't think you should have water that close to the collar as the water should dump out further back in the tail pipe.
Where is the water coming from?

cmi header connection
 

Punk rocket,

I agree with Mr Cig you should not be leaking that far up the tail pipe.
I would remove the headers and bench test the header and tail pipe. I just encountered a similiar situation and upon the water test I found a crack in both tail pipes where they connect to the flange. It was a fine crack, had both welded, retested, and we were back running.
Post what you find.
thanks

I thought the water may be coming from reversion. I have heard of some people who have water leaks at the tail pipe connection if the old rope style gasket is worn out. I'll do some testing tonight and see what it looks like.