I dont have an early airbox in front of me, but have wondered why, nobody has made the airboxes of metal. Seems to me that even if just cut and welded together (as opposed to stamped) they might be worth doing, especially if you knew they would not crack.. ever..
They would look pretty cool in Polished Aluminum..
Particularly in the case of the K0 type of box, with its smooth sides, sheet metal would be a great idea, if pricey. The originals were made of plastic, I think it was just styrene plastic, and cracking was quite common. When a Vetter fairing with lowers was fitted (which concentrates the heat right back onto the box), they warped and cracked in a single summer of touring, back in the day. The 'fix' back then was to fit the K1 box instead, because it was a better plastic material. For example, my K2 (actually made with a K1 engine and K1 airbox, mid-production stuff) has the OEM airbox on it still, and a Vetter with lowers for most of its life: the forward side of this box is slightly warped forward, and that's all.
But, the K0 boxes are SO handsome, with those smooth sides. Hmmm...I know a good machine shop and welders, and a good sheet metal shop, and have access to a sheet metal brake and punch....anyone have an old K0 airbox to loan, so I could CAD up the parts? Aluminum might be too soft and not crack-resistant, which would also be the original reason for not using metal, BTW (vibration cracks). But, if someone wanted to pay the $$, a nice stainless resto-shaped box could be built, parting in the same fasion, etc. Are the Honda rubber boots to the carbs still available K0 style? That velocity stack inside of them is very important to the bike's performance (on ALL of the 750/500/550 engines).
To avoid cracking, the upper hanger mounts much be grommeted in a soft-durometer rubber. This would prevent the cracks. On a production bike that sold for $1695, this cost would have been prohibitive for Japan back then, who must import every drop of oil and every pound of steel.
