Dirt bike engine for ultralight?

[Backwoods Smith]

I have a 2001 KTM 125 SX engine just sitting in my shop. They put out hp in the mid 30’s and are super light. Would adapting it using a chain drive or belt drive be recommended for an ultralight application?

[Dana]

I converted a Kawasaki KX100 engine for paramotor use. I kept the gearbox but removed the gearing except for the 3.4:1 first stage which normally drives the clutch, with the prop shaft and support bearings mounting where the clutch cover used to be.

[Backwoods Smith]

Cool. I want it to go in an affordaplane or a minimax. It can be upgraded to a 200cc easily also. I raced KTM’s for years so I know they are tough engines. I’m just brainstorming and trying to get airborn on a budget. I’m a former F-15E mechanic as well so I’m not clueless concerning aircraft.

[Sam Buchanan]

Cool. I want it to go in an affordaplane or a minimax. It can be upgraded to a 200cc easily also. I raced KTM’s for years so I know they are tough engines. I’m just brainstorming and trying to get airborn on a budget. I’m a former F-15E mechanic as well so I’m not clueless concerning aircraft.

Two suggestions:

1) Forget the AffordaPlane, too heavy. The MiniMax is a far superior aircraft and can be built as a legal ultralight.

2) Your inquiry would probably be better served in the Ultralight sub-forum.

Best wishes for a successful project!

[Dana]

One issue with dirt bike engines is the narrow powerband, all the torque is at the top and. On my paramotor it was a fine line between enough prop pitch to hold the rpm down at full throttle vs. too much pitch so it never got "on the pipe".