Today I sandblasted the light rust off the exhaust header and gave it a coat of black paint. It will burn off once I start the engine but should stop it from rusting any more in the meantime. I think It looks really good!
I have also been working on a drawing for a spring ball joint for the exhaust. I got stuck on this midwinter and didn't really get it sorted, so it's a good place to start again. I think I have the design mostly sorted now. These are available to purchase on the internet but not in the size I need (41mm ID).
The original CriCri used a flexible coupling but they seem to break all too often. The CriCri at the local airfield has been switched over the the rotax style exhaust ball coupling and has been working really well. the weakness with the rotax style ball joints is the way the springs keep breaking from vibration. Most of the aircraft locally use a slug of red silicon on the spring to limit the fatigue from vibration. I was browsing the internet and came across the style with the springs over the bolts (last picture). I like the look of these as if a spring breaks, everything is held in place. If both springs break the exhaust doesn't fall off completely.
The last pic ball joint would be easy to do: a spherical male mandrel to the size you have, machined, using a hydraulic press to flare the pipe. I would have the mandrel on the top with a wedge sleeve on the tube below to keep the pipe from slipping as it is pressed. The ball would be 'easy' to machine to your size spec 'yourself'. Drill the bolt heads and safety wire them together; I had a SS bracket fracture and go the the prop on the Varieze. Looks like you need a better TIG guy on the pipe junctions. I like the Y-header, but why not on the outboard side?
The video is exactly what I envisioned! Now I see why the header is to the inside..so the tuned pipe is against the fuselage..(brain fart)
I looked at the Kiwi biker site and learned a lot about hydroforming. Seem like the key is edge prebend/butt weld. And pressure control,
rather than all or nothing (ie, handpump); also a pressure gauge? The 4" ring was a good upgrade.
Welds to shoot for:
Purging is a must on SS, 100% penetration not so bad either
These guys are state-of-the-art and worth taking a look at..run through their pics. https://www.goodfabs.com/
Encouraging to see you moving fwd.
The Kiwibiker site has a heap of info on it. Some really interesting rabbit holes to follow down too!
Incidentally I found something on there that I think may be of interest to CriCri owners. In this thread https://www.kiwibiker.co.nz/forums/showthread.php/86554-ESE-s-works-engine-tuner there was some discussion about having four through bolts holding the head on, causing four corner seizures among other things. There was also reference to the flat four air cooled VW engines, in the that later engines used thinner studs to hold the heads on.
Anyhow, it turns out that with the higher heat in the more powerful engines was causing issues with the heads distorting and the gaskets leaking. The thermal expansion of aluminium is close to twice that of the steel head bolts and as the cylinder gets hotter the tension in the cylinder studs increases, distorting the head. By thinning down the studs, they would stretch as the cylinder heated up, maintaining the right tension in the studs holding the head down.
In this youtube video after the 2:55 mark they show a head gasket failure.
This has been a somewhat common issue with the JPX engines in the CriCri. Normally this has been attributed to the four studs holding the head on not clamping the head evenly enough. I suspect that the different rates of thermal expansion of the cylinder and thick steel studs also have something to do with it. Possibly thinned studs would help alleviate the problem?