The McCulloch BP-1 chainsaw, also known as the World’s only Balanced Piston engine chainsaw, was manufactured by McCulloch Motors Corp. in Los Angeles, California, USA in September 1962. This high-speed engine chainsaw utilized one piston for power and one for balance and as a sliding intake valve. Although it was a remarkable innovation in the chainsaw industry, it was sold for a very short period of time and then withdrawn from the market by McCulloch in September 1963.
It was feared that if the governor failed, the flywheel would disintegrate and injure the operator due to the RPM that the engine was capable of.
Specifications
| Specification | Value |
|---|---|
| Manufactured by | McCulloch Motors Corp. Los Angeles, California, U.S.A. |
| Series or assembly number | N/A |
| Year introduced | September 1962 |
| Year discontinued | September 1963 |
| Engine displacement | 2.7 cu. in. (44cc) |
| Cylinder bore | 1.75 in. (44.4mm) |
| Piston stroke | 1.125 in. (28.5mm) |
| Cylinder type | Aluminum with cast iron sleeve |
| Intake method | Balance piston acts as intake valve |
| Manufacturer advertised HP | 4.2 @ 10,000 RPM |
| Weight | 15 lbs. (powerhead only) |
| Handlebar system | Rigid |
| Chain brake | none |
| Clutch | Centrifugal |
| Drive type | Bevel gear reduction 2.0:1 or 2.9:1 ratios |
| Construction | Die-cast magnesium |
| Magneto type | McCulloch |
| Carburetor | McCulloch |
| Major repair kit | n/a |
| Minor repair kit | N/A |
| Air filter system | Flocked wire screen |
| Starter type | McCulloch automatic rewind |
| Oil pump | Automatic |
| Maximum engine RPM | Governed at 12,000 |
| Idle RPM | N/A |
| Ignition timing | Fixed at 27 degrees before TDC |
| Breaker point setting | 0.018 in. (0.45mm) |
| Flywheel/coil air gap | 0.008 to 0.010 in. (0.2 to 0.25 mm) |
| Spark plug type | AC C45W |
| Spark plug gap | 0.025 in. (0.63mm) |
| Crankshaft main bearings | Ball |
| Fuel tank capacity | N/A |
| Fuel oil ratio | 20:1 |
| Recommended fuel octane | Regular |
| Mix oil specification | McCulloch two-stroke chain saw mix oil |
| Chain pitch | 9/16 in. |
| Chain type | McCulloch Auto-Mac with built-in sharpener |
| Shortest guide bar supplied | 16 in. (40cm) |
| Longest guide bar supplied | 24 in. (61cm) |
| Colour scheme | McCulloch Yellow with Black |
| Illustrated parts list | Yes |
| Service manual | Yes |
Features
- Engine displacement: 2.7 cu. in. (44cc)
- World’s only Balanced Piston engine chain saw, Utilizes one piston for power and one for balance
- Manufacturer advertised horsepower: 4.2 @ 10,000 RPM
- Weight: 15 lbs. (powerhead only)
- Operator configuration: One-man operation
- Chain brake: None
- Construction: Die-cast magnesium
- Magneto type: McCulloch
- Starter type: McCulloch automatic rewind
- Oil pump: Automatic
- Maximum engine RPM: Governed at 12,000
- Chain type: McCulloch Auto-Mac with built-in sharpener
- Shortest guide bar supplied: 16 in. (40cm)
- Longest guide bar supplied: 24 in. (61cm)
- Color scheme: McCulloch yellow with black
Conclusion
To sum up, the McCulloch BP-1 chainsaw was a unique and innovative saw that introduced the world’s only Balanced Piston engine chain saw. Manufactured in September 1962 and discontinued a year later in September 1963, this saw had a short life in the market. Despite its high speed engine utilizing one piston for power and one for balance and as a sliding intake valve, the saw was withdrawn due to safety concerns. If the governor failed, the flywheel was capable of disintegrating and potentially injuring the operator.
Nevertheless, the McCulloch BP-1 chainsaw remains an interesting and important piece of chainsaw history, representing a significant milestone in chainsaw innovation and design.