How do I rebuild a 13B rotary engine in a Mazda RX-7 FB?

Difficulty: Hard

Rebuilding a 13B for your FB is entirely doable in a home garage, but it demands absolute cleanliness and precision. While a rotary only has three major moving parts (the two rotors and the eccentric shaft), the rebuild involves hundreds of small components like springs, apex seals, and coolant seals ³.

Here is the roadmap for tackling a 13B rebuild.

1. Gather Your Resources

Before turning a wrench, get a Mazda Factory Service Manual (FSM) or a Haynes manual for your specific year ³. Additionally, Atkins Rotary sells a highly recommended rebuild video; it focuses on 1986+ engines, but the differences between those and the 1984-1985 GSL-SE 13B are minor ³.

2. Teardown and Support

You don't strictly need a rotary-specific engine stand to do this. Many guys successfully rebuild these blocks by resting the engine on a pair of old steel wheels for support during stacking ³. That said, an engine stand with a rotary adapter will make rotating the block much easier.

3. Inspection and Machining

Once torn down, clean everything meticulously. You will need to inspect the rotor housings for chrome flaking and the irons (side plates) for step wear.

• If your irons are worn, you will likely need a machine shop to true the plates and check tolerances ³.
• Shops like Chips Motorsport specialize in this—they use an in-house surface grinder to deck the irons perfectly flat before sending them out to be nitrided for hardened durability ².

4. Assembly and Clearances

You will be replacing all the apex seals, coolant seals, and their associated springs ³.

I don't have the verified factory clearance specs for your apex and side seals, nor the exact torque specs for the engine tension bolts, so do not take a number from me on those—pull them directly from your FSM. The procedure itself requires using feeler gauges to verify the gap between the apex seal and the rotor groove, and filing the side seals to achieve the correct end-gap clearance. When it comes time to bolt the block together, install the tension bolts by hand, then torque them down in a star/criss-cross pattern in two or three progressively tighter passes to ensure the housings seat evenly against the coolant seals.

5. FB Chassis Specifics

If the 13B you are rebuilding is from a later car (like an S4 1986-1988 model) and you are swapping it into your FB, it is not a direct drop-in without swapping a few exterior parts. To make the mounting points match your FB chassis, you generally need to use the front cover and oil pan from a 1984-1985 GSL-SE 13B ⁴.

Take your time, keep your workspace spotless, and double-check your seal orientations before dropping the next housing on the stack.