After a lot of geometry and some machining I finally had a fixture to make the front intake tube. This tube is long and straight with a simple 90 degree bend. But, it's complicated by the fact that one end needs to be machined to fit into the notch of the angled rear intake tube. The goal is to match the rear tube notch as closely as possible while maintaining parallelism between the right-angled front tube and the three axes of the engine. As the photos show I was lucky and got pretty close. I did, though, have to make a small modification to the rear tube notching fixture and then re-work the run of rear tubes that I had already made to correct for an error I had made in that fixture. Fortunately, I was also able to verify similar fit-ups in the other head positions around the engine. With fit-ups this close, one of the options for joining the tubes becomes a thin (.005") disk of silver solder inserted in the interface between the two tubes. An ideal soldering fixture will exert a small force on the joint to push the tubes together and into final position just after the solder melts so my hands can stay completely out of the process. According to feeler gage measurements, the two faces at the interface seem to be parallel to better than .001". The surface area at the interface is .057 in^2, and the silver solder tensile strength is 16 kpsi. If the soldering goes well I could end up a strong (900 lbs), vibration resistant joint.
For testing, I've ordered minimum quantities of two hard solders that are compatible with 300 series stainless. The first is Silvaloy 355 which is a popular 56% silver (probably with nickel) alloy designed for stainless and sold by Brownell's and others in .005" sheet form. Since it doesn't contain cadmium it's marketed as a good color match to stainless. The second is a similar silver/nickel alloy that does contain cadmium, is also available in .005" sheet, and is sold by McMaster-Carr. This solder may flow more easily than the Silvaloy, but the cadmium will give the joint a yellow tinge if I don't manage to keep the solder wholly within the interface. For flux, I still have a double lifetime supply of Brownells 'Ultra Flux' left over from my H-9 project.
After verifying that random tube pairs fit up similarly in the other head-pair locations around the engine, I went into production mode and made the 40 tubes needed for 20 assemblies even though I really only need 9 completed assemblies. I'm anticipating a steep learning curve with the soldering, and I expect some finished assemblies may fit better than others. So, I want plenty of parts to work with.
I also created a fixture for making, what seemed at the time, the much simpler exhaust pipes. Because I didn't have a plan when I started this one it took me five iterations before I had a final fixture. In order to avoid interference with the heads, the exhaust pipes have to turn upward at a sharper angle than my minimum bend radius will allow. I had to cheat some and move a portion of the curved section pipe into the straight bore of the flange. This required increasing the diameter of the flange bore; and, later, a fixture will be needed to hold the pipe in proper position during soldering. I then made enough exhaust pipes also for 20 assemblies.
The next step, while waiting for the solder to arrive, is to create the last fixture to hold everything in position while the tubes are being soldered into a final assembly. This fixture needs to faithfully replicate the positions and orientations of the tube flanges and plenum compression nut bore that exist in the actual engine.
For now, I've all but given up on tig welding the assemblies even though, with the fit-up I have, I would get away without using filler rod and probably end up with a nice looking result. After my experiences with the fits of these parts during the past few weeks, though, I'm afraid the stainless will move around too much under the heat of welding. And, designing the holding fixture for access around the entire joint will greatly complicate its design. If the sheet solder approach doesn't work, my current plan B is to wrap a ring of solder around the exterior perimeter of the joint and flow the solder into it with an exterior fillet. For that reason, I've also ordered some 1/32" diameter color-matching Silvaloy. -Terry
. Anyway, I'm pretty sure this is one of the goodies we got to try. I recall the solder color being very close to native stainless, but not 100% & obviously its wire not sheet if that was a requirement. I'm sure he'd be happy to provide details.
