I now have a ATC250R engine solidly bolted into the Benelli 2C frame.
After shifting the ATC250R cases around in the Benelli frame a bunch, I came to the conclusion that getting the engine to sit where I wanted would require some cutting. I got out the cut-off wheel and went to work. Since the engine needs to be offset to the left by 1/2 inch, I just need to make clearance on the left side of the frame. I cut the outer frame gusset straight and removed the lower bolt hole on the upper engine mount. For comparison, look at the ones on the opposite side. The lower rear engine mounts had already been roughly hacked off soon after the frame’s arrival.
While I had the cut-off tool handy, I chopped off the badly corroded battery tray as well. (I may simply cut off all the side cover mounting hardware eventually, but there’s no reason to commit to that decision now.)
I had to do a bit of additional grinding on the frame, but there is just enough room for the engine.
I cut 1/8″ thick x 1″ wide flat steel bar to length to create simple, point-to-point mounting brackets between the mounting points on the crankcases and existing mounts on the frame. There are a pair underneath the center of the engine, at the lower rear (under the swingarm, attached to the original centerstand tabs), and at the top rear. This type of attachment is theoretically less than ideal, however, because the individual brackets have no inherent triangulation. The whole arrangement could potentially behave like a multi-bar linkage, allowing the engine to shift longitudinally by rotating on the transverse axis. Fortunately, the various lengths and positions of these particular mounting brackets work against each other to “jam the mechanism.” Once I add new front engine mounts, which will be welded to the front downtubes, the engine will be fixed within the frame pretty solidly.
I had previously calculated that the crankcases needed to be offset 1/2 an inch to the left, so I made one of the brackets from doubled-up 1/4″ thick alloy.
I checked the alignment of the front and rear sprockets with a laser, and a half-inch turned out to be correct—or at least within tolerance.
The downside to utilizing the existing Benelli 2C engine mounts wherever feasible is the need for a bunch of different length spacers — nine at last count.
Proper fastening hardware will need to be procured later.
I also used a couple of 1/2″ solid steel bars to nudge the right passenger peg mount out, away from the the swingarm. I’m not sure I’ve shifted it quite as far out as the left side, but it’s close, and there’s plenty of clearance there, which is all that matters at this point.
