258 header to 4.0 HO head

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

farna wrote: Unfortunately things like this is costing them business!

How much business can they lose in the AMC, 6 cylinder passenger car specific market.

I just unpacked my new Clifford Performance dual outlet header.  Its an unequal length (very unequal) short tube header and has terrible angles to the pipe as they come off the manifold face. I dont like throwing away horsepower so I am going back to my Cliffor Performance (the OLD company) long tube equal length pipe header with great tube angles and good radii that I converted for a 4.0 HO.  Its going to be a lot of work to get it to seal up right but there is no way I am putting this thing on my engine unless I am absolutely backed into a corner.

I did it and have not been happy with the results (exhaust leaks).  See the post on shorty versus long tube headers for fabrication details. Perhaps a better machinist than I could cut a better set of stepped washers and get better results.

Thanks...

I did not have a 4.0 gasket or head  to look at....just in the thought process
at present....

I am not a welder but I have a friend that is...he makes headers for his race engines all the time....


Edited by idrambler - Dec/05/2007 at 12:16pm