These photos are of chassis that use the engine as a ( or "the" ) main structural member. Despite various objections to the use of motors that were not originally designed for this purpose, the bikes shown here gave no problems from such use.
Honda 6. ( Built 1977 / 78 )
The Honda originally had a tubular frame over the top and rear of the engine and the engine weight was carried by mountings on the head, and so this engine was more suitable than most as the basis for being the main structural part. If only Honda had gone all the way and incorporated the swingarm pivot into the gearbox casting. The lack of this neccessitated two aluminium plates to support the swing arm.
Side view of complete chassis.
Detail of front structure.
Detail of rear structure.
These machines originally had a full cradle frame and the engine mounting lugs were on the crankcase/gearbox castings, 2 at the rear, 1 underneath and another at the front. As there were no existing mounting points on the head I made two plate mountings which had spigots to locate well in counter bored holes in the head. The four outside head retaining studs were replaced with longer ones which went through and held these plate lugs. ( these rather heavy plates were later replaced with aluminium pieces machined from the solid )
The swingarm was concentric with the gearbox sprocket to maintain constant chain length. Two magnesium castings were made to hold the bearings for the swingarm pivot. One replaced the clutch cover and can be seen in the pics., the other covered the sprocket and incorporated the clutch release actuating lever.
Head mounting brackets.
3/4 Front view.
This engine was of course designed from the beginning as the main structural element.
Rear side view showing intergral S/A mounting.