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Can anyone tell me what material is used on the Bevel Twin frames. The right hand tube on my project Darmah has a dent from an accident. I need to replace about 4 inches. OD is 30mm. Wall thickness? Chrome Moly? DOM mild steel. Better yet does anyone have an unrepairable frame that they could sell me a section from?

Cheers
Don

I just found a reference in Ian Falloon's Ducati 750 Bible that says the 750 frame material is AQ45. Nice but I have no idea what that means.

Don

Translation : water pipe

THANKS

Any idea what the wall thickness. I suspect 2mm?

I don't know but it's crap steel and I would highly advise you to not cut out then add in new material. I'd find a new frame. A Darmah frame should not be the end of the world to find and purchase..... Or you can get a superior aftermarket frame.

Thanks Steve. I had considered a replacement frame. Any square case one would work as the bike will not be a restoration. I have a pretty well equipped machine shop in my garage. Making a lot of my own stuff is my thing and in many cases an economic necessity. One of the arguments in favor of repairing the existing frame is that it has a recorded VIN and is registered and legal in my jurisdiction. Registering a vehicle without registration history and a recorded VIN can be a challenge not to speak of expensive here. I also have access to a master automotive fabricator. It's all just planning at this stage. I do respect your expertise. In the end that's what I may have to do.

Cheers
Don

If you do a repair to the frame I would recommend a chamfered joint / diagonal butt weld this involves cutting the tube at 30 deg or so, this way most of the weld is in shear and not in tension if possible insert a snug fitting sleve into the tube drilling a hole through bith sides of the main tube so you can also puddle weld the sleve in position and another 90 deg to the first on the new section . A good book on this and many other chassis repairs is "Prepare to Win" by Carroll Smith a handy bible to have at hand.

Sam

In theory, AQ45 is a CrMo steel. If you have ever picked up a vintage ducati frame you would swear it was cast iron sewer pipe.

You mean You want to replace the back downtube of a Darmah , the one that goes from the rear engineplate to the toprails ?
WITH a dent, a bend AND the "modification" for a bigger battery ?
Why not look for a old, damaged frame and cut out that part, so that You can use the engine (or a template) to keep the parts in line.
I would be concerned that if there is a dent on the outside and You cut out that part, that the frame itself tends to twist/bend and it would be difficult to fit a straight tube in between, meaning two welds and a lot of stress that is difficult to get out.
Isn't it possible to cut out JUST the dent and replace that with a piece ?
For what it's worth : wallthickness is something like 2.5-2.54 mm and in one of the owners-manuals (All bevels had the same diam. tubes, Verlicchi wasn't too fussy about that) is a picture with all dimensions.
I have a frame of a 1974 sport that had a head-on collision, engine still in the frame.
BIG problem trying to get that engine out, due to distortion and even the rear loop was difficult to get out.
Any pics of the damage, it would be easier to give a "correct" comment ?

ciao
Ducadini