Thunder Mustan PSRU PSRU for Thunder Mustang

HD Precision Machinery LLC manufactures the PSRU used on the magnificent Thunder Mustang kit plane.


  • Stock configuration will bolt to big and small Chevrolet V-8’s.
  • 2.8:1 gear reduction
  • Gear quality exceeds AGMA 12
  • Engine horsepower up to 1200
  • Weight is 95 pounds


External oil source is required.


Custom setups possible at additional cost.




Upgraded Inner Gear Door Cylinders Thunder Mustang Upgraded Inner Gear Door Cylinders Kit Plane Lifter Lockers For Sale

Lifter Lockers: $1800 per set

These were designed to allow control of the clearance between the T bar and the lifter flats.

The center eccentric bushing is rotated until the desired clearance is obtained between the T bar and the lifter pair. This requires a few tries to dial it in as it must come off the block to disengage the bushing from the T bar index ring. I used .0015 total clearance T bar to lifter flat. The bushing is indexed in a fashion that allows very small adjustments in a range from .020 to 0 between the T bar and the lifter flat. The Lifter Locker is fastened to the block using the existing 10-24 hole with a 5/8″ SHCS at 77 inch pounds. The viton O ring is installed around the perimeter of the concentric portion of the bushing that resides in the existing counterbore in the block to provide cushion/stabilization between the block and the T bar.


Gear Door Cylinder
Gear Door Cylinders: $450 – $750 per pair

We have an improved design for the inner gear door actuators. The cylinder bore is increased to .75 inches from the original .625 inches. These cylinders provide 645 lbs for extension and 532 lbs for retraction versus the original 453 lbs and 340 lbs. The original cylinders were working really hard at higher speeds and power settings. Direct replacement, no geometry changes.

These can be purchased in one of two configurations. Option one contains the new cylinders, pistons, and O rings. Move the two glands, piston rod, and rod ends from your stock TM units to the new cylinders. $450 per pair plus shipping. The second option is complete and all new assemblies. $750 per pair plus shipping.



PSRU Thunder Mustang  PSRU Kit Plane Shaft

My revisions to the TM PSRU are complete. Shown in the photo is the new locking mechanism for the prop shaft. This locking device features left hand threads, screws into the the interior of the prop shaft, and has a different thread pitch than the nut threaded to the perimeter surface of the prop shaft. Tests indicate that the holding power is nearly doubled and provides a truly foolproof locking device.


The parting side of the gear mesh is cooled by an oil stream introduced through a port machined through the front cover and into the oil “skimmer”. A pin is inserted for the purpose of illustrating the path of the oil into the mesh.


These two modifications are available to existing TM PSRU’s (billet front covers only) for $1650.00 plus shipping.


Inspection and overhaul of the PSRU is also available.


Contact Dean Holt at