Unkwown Frame, help needed !

We sold these back in the day.

I don't remember anyone fitting one who didn't have a headset loosening problem.

I'm sure some people did it for the look though.
 
Curious and beautiful painting
Welding with fittings was actually a "joint" where the steel tubes were inserted into the fittings and brass (or silver in very thin tubes such as Reynolds 753) was applied. On road bicycles the system worked very well, but on MTBs it proved insufficient and that is why it was basically used until reaching the '90s, then moving on to welding.
There was also the issue of geometry: road bicycles traditionally used the "square" geometry where sizes 54 and generally 55 had the same height as length (54 x 54 or 55 x 55) losing 0.5 in the horizontal tube. by 0.5 cm as they were larger and vice versa for the smallest. Mass consumer bicycles used to range from size 50 to 58, 2 by 2 cm (50, 52, 54...) and you could find brands according to the range that gave sizes 48 and 60 or even 62 cm.
The more "premium" bicycles already offered a greater variety of sizes. But all the geometries were square with seat angles ranging from just over 72º (for example Colnago) to almost 74º. The same for the direction. The fittings allowed some angle flexibility, but not much... so it was difficult to innovate in geometries without having to make special fittings, making the product more expensive.
MTB in the '90s became a crazy idea. Imagination to power. It was impossible to focus on a fitting that forced you to specific angles.
In addition, slooping arrived, which not only benefited mobility on the bicycle, it also allowed the manufacture of fewer sizes and that meant manufacturing bicycles at a better price.
 
Well, having said the above, I think the frame must be before '90.
And here comes something curious: the rear drop outs. They are very vertical and without rack threads, something unusual in those years even in the high range. They look like road bikes from those years
There is another detail that catches my attention: the absence of "dents" or "chafed" (I don't really know how to explain it in English) on the inside of the chain stays. It was very common at that time to be able to give clarity to the wide tires because also when welding with fittings the tubes come out in a predetermined direction, you cannot vary it, so you need that "flat" or make the chain stays very long.
In fact your chain stays seem long, greater than 44 cm center/center. It would be curious if you could measure them.
But there are more curious things: the frame has good quality details, but the cantilever brake supports DO NOT. It is a simple piece even for the 80s
The rear brake cable routing inside the horizontal tube is finished off in its holes with the classic road bicycle decoration.
The geometry is evidently very "square"
The bottom bracket in Italian (36 x 24) was little used in MTB. It is a sport made in the USA and they immediately applied the 1.37 x 24 tpi standard. Furthermore, the system is much more effective by threading the right cup backwards, preventing it from loosening with pedaling (quite the opposite) and therefore worked better with the MTB. It's true that some brands also used it at first, but it didn't last long.
My opinion: It is a handmade bicycle made with road fittings, road tubes and road and cyclocross accessories. Someone had some extra tubes and took advantage of them or a client asked them that way.

It's strange...yeah
It's unique...no. I know of at least one frame made with road tubes. I imagine there will be more
Just because the bottom bracket is Italian does not mean that the craftsman was. We could rule out the English, Americans and French (when the 35 x 1 metric system disappeared, the French "embraced" 1.37 x 24 in a general way) but in the rest of Europe they used English pitch and Italian pitch interchangeably to manufacture.
So it could be Italian, Spanish, Belgian, German...especially if it is someone who uses road equipment (the bottom bracket fitting is very significant)

Nice frame
 
Hi, thank you for this complete analysis.

I've spent a few hours watching "old italian MTB" on Google images and i found some frames with similar lugs, seat stay & chain stays bridge.

Forks were always different but with the same lug between the blades.

You're right, chain stays aren't embossed but the tubes have a kind of oval shape.
I measured 420mm long (center to center).

Globally, tubes are oversized (compared to my steel road bikes - older)

Seat tube : 46cm
Top tube : 55cm
 
Back
Top