258 header to 4.0 HO head

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   I sent back my Clifford dual outlet 4.0 header yesterday since I am certain I have solved all the problems with getting the modified 258 long tube Clifford (made back in Jacks day) header mounted.

I bought a junkyard head and set it up on the milling machine table to hold it down tight spark plug side down.  Then I bolted up the header and shined a light along the mating surface looking for gaps.  Boy did I find them.  Then I cut the flange into three sections so I could adjust the flange mating surface in pairs.  Tightened everything up again, still had some gaps.  Put Prussian blue on the head and bolted it up again.  Took it apart, found the low sections and used a belt sander to carefully and slowly grind them flat.  I repeated the process, marking sanding, marking sanding several times until it was a perfect seal.

Then I bolted up both the intake and the header.  The header has a 4.0 flange on top of a 258 flange so there is a 3/8 step down to the intake flange.  I got some Chevy 60's-70's straight 6 intake/exhaust washers and then welded 3/8ths (ground to fit) under each washer.  Each one was bolted up separately,  ground to fit, checked for gaps and then welded.  These old Chevy washers are really  neat. Forged, about an inch long and deeply cupped with points on each end that bear on the flanges.  They rock quite a bit to take up any misalignment.  You can only find them on OLD Chevy 6's where the intake and exhaust are not cast into the head.  They are still available from Chevrolet but the dealer want $12 each for them.  I got a dozen at the salvage yard for $10.

If you are having any sealing problems these washer are worth the effort to find them or the price to buy them. 

I will post some pics when I get back home in a few days.

John 

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nosigma Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Apprentice Joined: Dec/30/2007 Status: Offline Points: 188	Post Options Post Reply Quote nosigma Report Post Thanks(0) Quote Reply Posted: Jan/22/2008 at 1:08pm
	I sent back my Clifford dual outlet 4.0 header yesterday since I am certain I have solved all the problems with getting the modified 258 long tube Clifford (made back in Jacks day) header mounted. I bought a junkyard head and set it up on the milling machine table to hold it down tight spark plug side down. Then I bolted up the header and shined a light along the mating surface looking for gaps. Boy did I find them. Then I cut the flange into three sections so I could adjust the flange mating surface in pairs. Tightened everything up again, still had some gaps. Put Prussian blue on the head and bolted it up again. Took it apart, found the low sections and used a belt sander to carefully and slowly grind them flat. I repeated the process, marking sanding, marking sanding several times until it was a perfect seal. Then I bolted up both the intake and the header. The header has a 4.0 flange on top of a 258 flange so there is a 3/8 step down to the intake flange. I got some Chevy 60's-70's straight 6 intake/exhaust washers and then welded 3/8ths (ground to fit) under each washer. Each one was bolted up separately, ground to fit, checked for gaps and then welded. These old Chevy washers are really neat. Forged, about an inch long and deeply cupped with points on each end that bear on the flanges. They rock quite a bit to take up any misalignment. You can only find them on OLD Chevy 6's where the intake and exhaust are not cast into the head. They are still available from Chevrolet but the dealer want $12 each for them. I got a dozen at the salvage yard for $10. If you are having any sealing problems these washer are worth the effort to find them or the price to buy them. I will post some pics when I get back home in a few days. John