Early Rotary & 1979-85 Mazda RX-7 : Engine Rotors

 : Engine - Rotors : Super Lightweight Rotor Assembly 1974-85 12A

Super Lightweight Rotor Assembly
1974-85 12A

Part Number: 10003

Price: $2,137.00

See below for special ordering options
and instructions.

Super Lightweight Rotor Assembly - 1974-85 12A - Detail 1

Addtional Photos - Select to Enlarge

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Super Lightweight Rotor Assembly
1974-85 12A

Super Lightweight Rotor Assembly
1974-85 12A

Our Super Lightweight Rotor Assemblies are machine-lightened using a CNC (computer numerically controlled) mill. These rotors are based on the stock 1976-82 12A rotors with the initial weight of each front and rear rotor at approximately 10.2 pounds.  Upon completion of the machining processes the weight is reduced by 1.1 lbs to approximately 9.1 pounds.  PLEASE NOTE:  this 12A rotating assembly requires the use of the following 12A Eccentric Shaft--MAZDA PART NUMBER N201-11-400.  The use of any other 12A Eccentric Shaft will adversely impact the balance of the rotating assembly.


Years of experience have allowed our engineers to refine the lightening process to maximize the amount of material that is removed. The lightening process removes material from both the external sides of each rotor and the internal ribbing and bearing support areas. To view a larger photo of a finished rotor, click here.


The Racing Beat machining process also include the installation of a snap ring between the rotor gear and the basic rotor to prevent the rotor gear from working away from the basic rotor at higher RPM. The ring gear is removed using proprietary tools and then an indexing groove is cut into both the rotor and the ring gear. A snap-ring is placed into the groove on the ring gear and the assembly is placed into the rotor. Once the snap-ring expands into the groove on the rotor, the ring gear is permanently seated onto the rotor.


After completion of the machining process, we fully balance each pair of rotors with matching front and rear counterweights to provide an assembly capable of high RPM operation. As seen in the photo below, additional material is removed from the lower portion of each counterweight during these balancing steps .

Each assembly includes two (2) super lightweight rotors, and one (1) front, and one (1) rear counterweight. This rotor assembly has been balanced with a front counterweight that requires the use of the 1992 and later large diameter thrust bearing components. See the following PDF for important component information and specifications.

Replacement rotors are available, also see part numbers: 10037 (front) and 10039 (rear).

Racing Beat Recommended Accessories:

Race Apex Seal Spring - 74-85 12A

Race Apex Seal Spring - 74-85 12A

Our Racing Beat Race Apex Seal Springs, specifically designed to fit the underside of our 1974-85 12A (3mm) Race Apex Seals, provide proper pre-loading for these lighter one-piece seals. Unlike the stock inner and outer dual apex seal spring... Race Apex Seal Spring - 74-85 12A
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