One of my many projects is a 250 MotoBi (Benelli) horizontal single for AHRMA Premier Lightweight MX. The class requires an original period frame, but period modifications are allowed. It quickly became obvious that one of the period modifications had to be moving the steering head up and forward, as a 21" front wheel on the stock frame bottoms out on the rocker cover before the forks bottom out. I cut off the stock steering head, cleaned it up, and relocated it at the stock head angle. I decided to also extend the stock swing arm (though I may try my hand at making a replacement part out of larger, period tubing). The rear subframe needs to be higher too, so as to avoid making a superstructure to mount the scrambles seat 5-6" above the existing seat location. Look elsewhere in the MotoBi section for pictures of the Maltry scrambles conversion.

• The donor 250 This shows the right side. I bought the bike from Moto Italia (Aermacchi specialists) in Petaluma CA. It had been parked outside next to the ocean and was SEVERELY rusty, so I felt no qualms about ditching lots of the parts. This is a late 250SS (you can tell from the rocker cover). I'll be running a period mid 60s engine (which you'll see in later pictures) 28K jpeg file
• The donor 250 The left side. 30K jpeg file
• The donor 250 - stripped This shows the right side of the donor bike after stripping off the bodywork. Note the MotoBi's box section steel beam frame. 30K jpeg file
• The bare frame I stripped the frame down and blasted the crud off of it. To make the modifications easier I drew a grid on the frame. 29K jpeg file
• On the frame fixture In this picture I've cut the steering head off, cleaned it up, and positioned the frame and steering head in their new positions on my frame fixture. 32K jpeg file
• On the frame fixture A different view 32K jpeg file
• On the frame fixture It turned out that some 2" x 1.5" rectangular tubing I had on hand slipped into the frame, and matched very closely with the outside dimensions when trimmed to fit on the top of the frame. I profiled the tube ends (conveniently a 90 degree angle was required) with my milling machine which is visible in the background. 25K jpeg file
• On the frame fixture Another view - you can see how I trimmed the upper tube to match the stock frame. 29K jpeg file
• The stock swing arm You can see the marks where I'm going to cut the arms apart. I then made some stepped spacers to plug into the gap and welded things back together. This was a not-uncommon method of lengthening swing arms in the 1960s and 1970s. 22K jpeg file
• Up on wheels Here is the bike mocked up with the period engine and a TM250 Suzuki telefork that I'm thinking about using. That fork came on another MotoBi that I bought, and I was able to move the bearing cups with their taper roller bearings from the other frame to this one, saving several hours of work. 29K jpeg file
• Up on wheels A view from lower down. In the background is a crate that contained 6 MotoBi engines I bought from a fellow in Australia. 33K jpeg file
• Up on wheels The rear half of the bike - you can see the extension in the swing arm. 31K jpeg file

Steve Crocker found himself with some time hanging on his hands and he scanned and converted to PDF some Motobi manuals for me to host. Surprisingly, the Cosmopolitan Motors phone number that appears on the documents will still connect you to the former Benelli/Motobi (and many others) importer. You can also reach Cosmo with a newfangled computer at the Vintage Cosmo website.

• Motobi manuals Owners Manual 4.M/byte
• Motobi manuals Parts Manual, first half 1.4M/byte
• Motobi manuals Parts Manual, second half 1.5M/byte
• Motobi manuals Shop Manual 3.6M/byte

© 1996-2009 Michael Moore, last update for this page 2 January 2009