Does anybody know what process gm used to bond the runner tubes to the cast plates? It is darker gray in color and seems to be unaffected by heat. I can basically melt the metal without the seam material breaking down. I am asking because I bought 1 3/4 aluminum mandrel bends and machined out the plates to make larger runners and I am know experimenting with the best method to put them together. Haven't had a lot of luck with lower temp aluminum brazing rod bonding well with the cast pieces and heat required for 4043 is melting/distorting the metal.

 

Interesting I always thought they were just cast in one piece... without knowing the first answer, I would say the best way to bond in the current day and age, with what your trying, will always be TIG welding

 

I think on F-bods, the flanges were cast, and the runners are tube...extruded or welded tube. IDK how they're bonded though.

 

I've always wondered that myself, quick seach came up with a few promising things
https://www.google.com/search?q=bond...ile-gws-wiz-hp

 

I think your right, bonded and also slightly flared to make a tight fit.
theres a small lip inside the stock runner that I’ve smoothed out and ran steel ***** through. I think that’s a slight flare.

 

If any of you ever worked in either a fire-tube or water-tube boiler, you probably realize that the tubes are roll-formed into the head plates, and are not welded, brazed, or otherwise connected. They seal on helluva lot more pressure differential than 25" Hg of vacuum, and under a lot of heat/cool cycling. It wouldn't take a lot to do that with four thin steel tubes into the cast flanges and make it work.

That doesn't mean that is how it was done, but it would work pretty well. Without destructive testing, it might be difficult to find out exactly what happened in Rochester.

 

I made some practice pieces out of a pair of old beat up runners and some of the cut offs from the tubing. Tried brazing, tig and mig. Tig did not do well on the cast at all. Mig bonded great but a lot of splatter and not the prettiest stuff in the world. The other problem with welding is accessing all points of the joint with the torch, especially with the bulkiness of the mig spool gun.

 

My first thoughts were epoxy. But after researching several types I learned that most epoxies break down anywhere between 250-500F. The only place i would be concerned about this is directly adjacent to the egr tube. From what I've read the egr passage can reach upwards of 600-700 when the egr is open for any length of time (cruising).

 

Thanks for the replies. I was just curious if anybody knew what the factory did. I think I'm gonna mig everywhere I can reach with the gun and then fill in the hard to reach areas with brazing as I can get the rod just about anywhere. The mig welds should give me th structural element and the brazing while not the best bond should seal it all up.

 

I made a tubular, custom LTR intake at work, and mig welded the runners to the plenum and hand-made flange. I knew it would leak with MIG welding....and it did! I don't know how to weld with a MIG welder and not have some porosity and leaks. After doing it for 30+ years, what I've learned is that a MIG weld? It's gonna leak!







My techs and I discussed options, brazing being one of them. I like your idea of brazing over the MIG weld -that is a great way to solve the leaks, issue, IMO. I'm lazy and didn't want to spend the time required to braze, so I bought this crap called "Red Kote", which is gooey, slow-flowing liquid that is meant to seal the inside of a fuel tank. We poured it into the plenum, runners, etc, then covered the head flange over w/a piece of wood and turned the intake every which way to get the goop evenly distributed through all the walls/floors, runner ID's etc. Stuff worked wicked good and no leaks after that. Easy, fast, effective. I'm not typically a fix-it-in-a-can kind of guy, but that stuff did work. Also used it in a fuel cell that I built for the Kart, in that case, as a redundant back-up.