I’ve never paid any particular attention to a SparrowHawk rotorhead but would guess the adjustable spacer was to adjust end play by springing the towers in or out by a few thousandths. Nothing wrong with that and allows plastic spacer washers to be punched from standard thickness sheets.
Certainly, the bearing block can be machined to a close enough tolerance to allow a fixed length 3” spacer otherwise.
I don’t know what all the fuss is about.
The Rotordyne rotorhead, designed by Art Weillage, had no teeter bushings, just a plain 3/8” bolt running through plain 3/8” holes in both towers and teeter block. There were .050” plastic washers on the inside between teeter block and towers which worked fine as long as the teeter bolt was kept greased and just finger tight. Worked just like a floating piston pin and never seized or galled. The Rotordyne bearing block was the same as Bensen with 2.6” inside between towers. These things were ubiquitous 30 years ago and no one ever crashed and burned from worn out or broken teeter bolts.
The spacer washers were a bear to install; many people made up plastic washers with handles.
The Bensen rotorhead was the first with hats and bearings. Aluminum hats of all things and the bearings were some sort of heavily graphited matrix of babbit. They worked just fine but the imitators, believing they were making an improvement, substituted Olite bushings and stainless steel hats. Teeter bearing seizure was nearly instantaneous if the teeter bolt was torqued sufficiently to lock the hats against the bearing block. But I never heard of any crashes as a result; you’d get lots of stick shake and the stick would be forced hard left.
In fact, the first rotorhead I made used steel hats running on Delrin bushings and even this combination had a tendency to seize. The wear surface of the Delrin would acquire a steel coating. That’s when I started using Torrington needle bearings.
Certainly, the bearing block can be machined to a close enough tolerance to allow a fixed length 3” spacer otherwise.
I don’t know what all the fuss is about.
The Rotordyne rotorhead, designed by Art Weillage, had no teeter bushings, just a plain 3/8” bolt running through plain 3/8” holes in both towers and teeter block. There were .050” plastic washers on the inside between teeter block and towers which worked fine as long as the teeter bolt was kept greased and just finger tight. Worked just like a floating piston pin and never seized or galled. The Rotordyne bearing block was the same as Bensen with 2.6” inside between towers. These things were ubiquitous 30 years ago and no one ever crashed and burned from worn out or broken teeter bolts.
The spacer washers were a bear to install; many people made up plastic washers with handles.
The Bensen rotorhead was the first with hats and bearings. Aluminum hats of all things and the bearings were some sort of heavily graphited matrix of babbit. They worked just fine but the imitators, believing they were making an improvement, substituted Olite bushings and stainless steel hats. Teeter bearing seizure was nearly instantaneous if the teeter bolt was torqued sufficiently to lock the hats against the bearing block. But I never heard of any crashes as a result; you’d get lots of stick shake and the stick would be forced hard left.
In fact, the first rotorhead I made used steel hats running on Delrin bushings and even this combination had a tendency to seize. The wear surface of the Delrin would acquire a steel coating. That’s when I started using Torrington needle bearings.