McCulloch BP-1 Specifications

McCulloch BP-1 Specifications

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Although it was a remarkable innovation in the chainsaw industry, it was sold for a very short period of time and then withdrawn from the market by McCulloch in September 1963.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.


Manufactured byMcCulloch Motors Corp. Los Angeles, California, U.S.A.
Series or assembly numberN/A
Year introducedSeptember 1962
Year discontinuedSeptember 1963
Engine displacement2.7 cu. in. (44cc)
Cylinder bore1.75 in. (44.4mm)
Piston stroke1.125 in. (28.5mm)
Cylinder typeAluminum with cast iron sleeve
Intake methodBalance piston acts as intake valve
Manufacturer advertised HP4.2 @ 10,000 RPM
Weight15 lbs. (powerhead only)
Handlebar systemRigid
Chain brakenone
Drive typeBevel gear reduction 2.0:1 or 2.9:1 ratios
ConstructionDie-cast magnesium
Magneto typeMcCulloch
Major repair kitn/a
Minor repair kitN/A
Air filter systemFlocked wire screen
Starter typeMcCulloch automatic rewind
Oil pumpAutomatic
Maximum engine RPMGoverned at 12,000
Ignition timingFixed at 27 degrees before TDC
Breaker point setting0.018 in. (0.45mm)
Flywheel/coil air gap0.008 to 0.010 in. (0.2 to 0.25 mm)
Spark plug typeAC C45W
Spark plug gap0.025 in. (0.63mm)
Crankshaft main bearingsBall
Fuel tank capacityN/A
Fuel oil ratio20:1
Recommended fuel octaneRegular
Mix oil specificationMcCulloch two-stroke chain saw mix oil
Chain pitch9/16 in.
Chain typeMcCulloch Auto-Mac with built-in sharpener
Shortest guide bar supplied16 in. (40cm)
Longest guide bar supplied24 in. (61cm)
Colour schemeMcCulloch Yellow with Black
Illustrated parts listYes
Service manualYes
McCulloch BP-1 Chainsaw Specs


  • 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


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.

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