The first model of the .61 had a bell type rear rotary valve and Schnuerle porting design, both were unheard features of in the 1960's.

These used an odd prop bolt with the spinner nut being part of the stud. The spinner nut was actually cast onto the stud.

The crankshaft was offset to the cylinder bore and the cylinder was flanged in the center, below the fin area.

The offset was in the wrong direction causing greater rod angle on the power stroke.

Soon the .61 evolved into a front intake version which proved to be more suitable for conventional model airplanes.

With crankcase rotated 180° and the exhaust being left side, the cylinder offset is now in the correct position.

The first versions were made from the rear intake case by machining off the front and using a bar stock, screw in back cover with a new cast front intake housing.

A new run of castings were made after modifying the mold for a more conventional back cover.

They also made a blue fin version.

The last version had "MADE IN AUSTRIA" cast under the exhaust port.

Very few parts are available for the first HP .61 (pre 1972)
with four head bolts and rectangular exhaust flange.

A few parts interchange from the Silver Star .61.
The following #’s interchange on some of the 4 bolt engines:
14-2201, 15-2201, 26-2201, and 16-2201.

If you need one of these 4 parts call first.
Tel. 626-359-6972